Rules for Building and Classing

Offshore Units

Part 4
Machinery and Systems

January 2025
RULES FOR BUILDING AND CLASSING

OFFSHORE UNITS
JANUARY 2025

PART 4
MACHINERY AND SYSTEMS

American Bureau of Shipping

Incorporated by Act of Legislature of
the State of New York 1862

© 2025 American Bureau of Shipping. All rights reserved.

ABS Plaza
1701 City Plaza Drive
Spring, TX 77389 USA
 PART 4
Machinery and Systems

CONTENTS
CHAPTER 1 Machinery, Equipment and Systems..................................................1
Section 1 General.............................................................................. 3
Section 2 Machinery and Equipment............................................... 10

CHAPTER 2 Pumps and Piping Systems..............................................................12

Section 1 General............................................................................ 20
Section 2 Pumps, Pipes, Valves, and Fittings................................. 34
Section 3 Tank Vents, Overflows and Sounding.............................. 74
Section 4 Bilge and Ballast Systems and Tanks..............................86
Section 5 Fuel Oil Systems and Tanks............................................ 97
Section 6 Other Piping Systems and Tanks...................................109

CHAPTER 3 Electrical Installations..................................................................... 123

Section 1 General.......................................................................... 130
Section 2 Electrical Systems......................................................... 138
Section 3 Onboard Installation.......................................................172
Section 4 Machinery and Equipment............................................. 201
Section 5 Specialized Installations................................................ 210
Section 6 Hazardous Areas........................................................... 233

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 ii

 PART 4
CHAPTER 1
Machinery, Equipment and Systems

CONTENTS
SECTION 1 General..................................................................................................3
1 Objective.........................................................................................3
1.1 Goals................................................................................. 3
1.2 Functional Requirements...................................................3
1.3 Compliance........................................................................4
2 Requirements for Classification ..................................................... 4
3 Definitions ...................................................................................... 4
3.1 Control Station................................................................... 4
3.3 Machinery Space............................................................... 4
3.5 Essential Services............................................................. 5
3.7 Hazardous Areas............................................................... 5
3.9 Dead Ship Condition..........................................................5
3.11 Blackout............................................................................. 5
3.13 Piping Systems.................................................................. 5
3.15 Electrical Installations........................................................ 6
3.17 Fail Safe.............................................................................6
5 Machinery Plans............................................................................. 6
5.1 Submission of Plans.......................................................... 6
5.3 Plans..................................................................................6
5.5 Additional Notations...........................................................6
5.7 Repair and Modification of Machinery............................... 6
7 Miscellaneous Requirements for Machinery...................................6
7.1 Inclinations.........................................................................6
7.3 Dead Ship Start................................................................. 7
7.5 Unattended Machinery Spaces..........................................7
7.7 Ambient Temperature........................................................ 7
7.9 Materials Containing Asbestos.......................................... 8
7.11 Materials and Welding for Machinery Components........... 8

TABLE 1 Angle of Inclination ................................................................7

TABLE 2 Ambient Temperatures for Machinery, Equipment and
Appliances in Units of Unrestricted Service .......................... 7

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 1

 TABLE 3 Primary Essential Services.................................................... 8
TABLE 4 Secondary Essential Services................................................9

SECTION 2 Machinery and Equipment................................................................ 10

1 Prime Movers................................................................................10
1.1 Application....................................................................... 10
3 Propulsion, Maneuvering and Dynamic Positioning Systems ......10
5 Moving Cantilevers, Skid Beams and Moveable Structures ........ 11
7 Electrical Machinery and Equipment ............................................11
9 Certification of Machinery and Equipment ................................... 11
11 Unattended Machinery Spaces.....................................................11
13 Propulsion Redundancy................................................................11

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 2

 PART 4
CHAPTER 1
Machinery, Equipment and Systems

SECTION 1
General

1 Objective

1.1 Goals
The machinery, equipment and systems covered in this Chapter are to be designed, constructed, operated,
and maintained to:

Goal No. Goal

POW 1 provide safe and reliable storage and supply of fuel/energy/power.

PROP 2 provide redundancy and/or reliability to maintain propulsion.

SAFE 1 promote the occupational health and safety of personnel onboard.

The goals in the cross-referenced Rules/Regulations are also to be met.

1.2 Functional Requirements

In order to achieve the above stated goals, the design, construction, installation and maintenance of the
machinery equipment and systems are to be in accordance with the following functional requirements:

Functional Functional Requirement

Requirement

Propulsion, Maneuvering, Station Keeping (PROP)

PROP-FR1 (POW) Machinery and systems are to operate under all anticipated environmental and operating conditions,
including weather, vibration, inclination, and low and high temperature.

Safety of Personnel (SAFE)

SAFE-FR1 Materials that harm human health are not to be used in machinery.

The Functional Requirements in the cross-referenced Rules/Regulations are also to be met.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 3

Part 4 Machinery and Systems
Chapter 1 Machinery, Equipment and Systems
Section 1 General 4-1-1

1.3 Compliance
A unit is considered to comply with the Goals and Functional Requirements within the scope of
classification when the applicable prescriptive requirements are complied with or when an alternative
arrangement has been approved. Refer to Part 1D, Chapter 2.

Part 4 contains requirements for marine systems. Requirements associated with the unit function (i.e.,
hydrocarbon production) are contained in Part 8.

2 Requirements for Classification

Part 4 contains general requirements for machinery, equipment and systems (Chapter 1) and the design
requirements for piping systems (Chapter 2) and electrical systems (Chapter 3).

Part 5 contains the design requirements for safety systems, including fire extinguishing systems.

Part 6 contains the design, testing and survey requirements for the certification of equipment, machinery
and system components at vendor’s shop.

Part 7A, 7B or 7C contains the survey requirements during construction of units at builder’s yard (Chapter
1) and the requirements for periodical surveys after construction (Chapter 2).

Part 8 contains specific classification requirements for each type of offshore units as well as for specific
machinery, equipment and system installed onboard for the intended offshore services.

3 Definitions

3.1 Control Station

A location where controllers or actuators are fitted,along with monitoring devices, as appropriate, for
purposes of effecting desired operation of specific machinery.

Control Station is defined solely for purposes of passive fire protection as intended by the IMO MODU
Code, in 5-1-1/3.9.2.1.

Centralized Control Station is defined in Part 4, Chapter 9 "Remote Propulsion Control and Automation"
of the ABS Rules for Building and Classing Marine Vessels (Marine Vessel Rules) to refer to the space or
the location where the following functions are centralized:

● Controlling propulsion and auxiliary machinery,

● Monitoring propulsion and auxiliary machinery, and
● Monitoring the propulsion machinery space.

3.3 Machinery Space

Machinery Spaces are machinery spaces of category A and other spaces containing propulsion machinery,
boilers, oil fuel units, steam and internal combustion engines, generators and major electrical machinery,
oil filling stations, refrigerating, stabilizing, ventilation, and air-conditioning machinery and similar spaces,
and trunks to such spaces.

Machinery spaces of Category A are spaces and trunks to such spaces which contain:

i) Internal combustion machinery used for main propulsion; or

ii) Internal combustion machinery used for purposes other than main propulsion where such
machinery has in the aggregate a total power output of not less than 375 KW (500 hp); or
iii) Any oil-fired boiler or oil fuel unit; or

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 4

Part 4 Machinery and Systems
Chapter 1 Machinery, Equipment and Systems
Section 1 General 4-1-1

iv) Any oil-fired equipment other than boiler, such as inert gas generator, incinerator, or waste
disposal units, etc.
Commentary:

Item iv applies only to fire safety requirements similar to SOLAS Chapter II-2. See IMO MSC/Circ.847.

End of Commentary

3.5 Essential Services

Essential services are:

i) Those services considered necessary for:

● Continuous operation to maintain propulsion and steering in self-propelled units (primary

essential services);
● Systems of the unit whose loss or failure would create an immediate danger to the unit
(primary essential services);
● Non-continuous operation to maintain propulsion and steering in self-propelled units and a
minimum level of safety for the unit’s navigation and systems (secondary essential services)
ii) Emergency services as described in 4-3-2/5.3 (each service is either primary essential or
secondary essential depending upon its nature, as described above); and
iii) Other special characteristics (e.g., special services) of the unit whose loss or failure would create a
potential danger to the unit (secondary essential services).

Examples of primary essential services and secondary essential services are as listed in 4-1-1/TABLE 3
and 4-1-1/ TABLE 4, respectively.

3.7 Hazardous Areas

See 4-3-6/2.1 for definition. For hazardous area classification of specific areas, refer to:

● Helicopter refueling facilities, see 4-3-6/6.5.

● Paint stores, see 4-3-6/6.1.
● Battery Rooms, see 4-3-6/6.3.
● Oxygen-acetylene Storage Rooms, see 4-3-6/6.7.
● Areas related to Drilling Activities, see 8-2-1/13.

3.9 Dead Ship Condition

Dead ship condition means a condition under which:

i) The main propulsion plant, boilers and auxiliary machinery are not in operation due to the loss of
the main source of electrical power, and
ii) In restoring propulsion, no stored energy for starting the propulsion plant, the main source of
electrical power and other essential auxiliary machinery is assumed to be available.

3.11 Blackout
Blackout situation means the loss of the main source of electrical power resulting in the main and auxiliary
machinery being out of operation.

3.13 Piping Systems

For definitions related to piping systems, refer to 4-2-1/3.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 5

Part 4 Machinery and Systems
Chapter 1 Machinery, Equipment and Systems
Section 1 General 4-1-1

3.15 Electrical Installations

For definitions related to electrical installations, refer to 4-3-1/3.

3.17 Fail Safe

Fail Safe means that the component or system is designed to return to a predetermined position upon
failure. The predetermined position is to maintain the system in a safe condition.

5 Machinery Plans

5.1 Submission of Plans

Machinery and systems plans required by the Rules are to be submitted electronically by the manufacturer,
designer or shipyard to ABS. Where so stated in the shipbuilding contract, the Owner may require the
shipyard to provide copies of approved plans and related correspondence. A fee will be charged for the
review of plans which are not covered by a contract of classification with the shipyard.

All plans are to be submitted and approved before proceeding with the work.

5.3 Plans
Machinery and systems plans required to be submitted for review and approval by ABS are listed in each
of the sections in Part 4. Equipment plans are to contain performance data and operational particulars;
standard of compliance where standards are used in addition to, or in lieu of, the Rules; construction details
such as dimensions, tolerances, welding details, welding procedures, material specifications, etc.; and
engineering calculations or analyses in support of the design. System plans are to contain a bill of material
with material specifications or particulars, a legend of symbols used, system design parameters, and are to
be in a schematic format. Booklets containing standard shipyard practices of piping and electrical
installations are required to supplement schematic system plans.

5.5 Additional Notations

In the case of units for which additional class notations covered by other ABS Rules and Guides have been
requested, machinery and systems plans related to the services covered by the additional class notations are
required to be submitted for review and approval by ABS as indicated in the corresponding Rules and
Guides.

5.7 Repair and Modification of Machinery

When repairs or modifications are made to ABS approved systems and equipment, documentation
identifying the changes, as well as any documentation that supersedes or replaces previously approved
documentation is required to be submitted for ABS review and approval by the equipment designer or
responsible party. Repairs and modifications are to be carried out to the satisfaction of the Surveyor. If the
service or product bulletin indicates modification or alterations to the component that would impact the
Class approval, these details are to be submitted to ABS Engineering for review and approval.

7 Miscellaneous Requirements for Machinery

7.1 Inclinations
All machinery, components and systems for essential services, as defined in 4-1-1/3.5, are to be designed
to operate under the inclinations as indicated for each of the conditions listed in 4-1-1/TABLE 1.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 6

Part 4 Machinery and Systems
Chapter 1 Machinery, Equipment and Systems
Section 1 General 4-1-1

TABLE 1
Angle of Inclination

Condition Static Dynamic

Column-Stabilized Units 15° in any direction 22.5° in any direction

Self-Elevating Units 10° in any direction 15° in any direction

Surface Units 15° list and 5° trim simultaneously 22.5° rolling and 7.5° pitching
simultaneously

7.3 Dead Ship Start

Means are to be provided to bring the machinery into operation from a "dead ship" condition, as defined in
4-1-1/3.9. See 4-3-2/3.1.4 and 4-3-3/3.27 for the required starting arrangements.

7.5 Unattended Machinery Spaces

Controls necessary for safe operation are to be provided for machinery in spaces which are not normally
manned. Relevant data is to be submitted to permit the assessment of the effect of such controls on the
safety of the unit. See 4-2-4/3.7 for bilge alarm systems and 5-3-1/11 for fire precautions for such spaces.

7.7 Ambient Temperature

For units of unrestricted service, ambient temperature, as indicated in 4-1-1/TABLE 2, is to be considered
in the selection and installation of machinery, equipment and components. For drilling units of restricted or
specific service, the ambient temperature appropriate for the specific nature is to be considered. See
3A-1-4/2.9.

Systems and equipment used solely for specific operations associated with class notations are to follow
temperature requirements as outlined within the applicable recognized standards to which they are
designed and constructed in accordance with 8-1-1/3.

Machinery, equipment and components related to marine equipment on the open deck for units with
unrestricted service are to be rated for a minimum air temperature equal to the Design Service Temperature
(DST) for the unit.

Control, monitoring and safety devices/systems of equipment for essential services (item (l) of 4-1-1/
TABLE 3 and 4-1-1/TABLE 4), when located on the open deck are to be rated for a Minimum Air
Temperature (MAT) of 15°C below the DST. If operation of the equipment is not anticipated at
temperatures below the DST, these devices/systems need not be operable below DST but physical
components are not to be damaged if exposed to temperatures down to the MAT.

TABLE 2
Ambient Temperatures for Machinery, Equipment and Appliances
in Units of Unrestricted Service

Air

Installations, Location, Arrangement (1, 2) Temperature Range (°C)

Components

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 7

Part 4 Machinery and Systems
Chapter 1 Machinery, Equipment and Systems
Section 1 General 4-1-1

Machinery and Enclosed Spaces – General 0 to +45°C

electrical installations
Components mounted on machinery associated According to specific machinery and
with high temperature installation

In spaces subject to higher temperature (details According to the actual maximum ambient
to be submitted) temperature

In spaces with temperature lower than +45°C According to the actual ambient temperature
(details to be submitted) subject to minimum +40

Open Deck (3) –25 to +45°C

Water

Coolant Temperature (°C)

Seawater +32°C

Notes:

1 Electronic equipment is to be suitable for operations up to 55°C. See also 4-3-1/17.3.

2 For environmentally controlled spaces, see 4-3-1/17.3.

3 The minimum air temperature need not be less than the service temperature identified for the unit (see
3A-1-4/1.9 and 3A-1-2/1) and documented in the unit's Operating Manual as per 1B-2-3/1 of the ABS Rules
for Conditions of Classification – Offshore Units (Part 1B), except for control, monitoring, and safety devices/
systems of equipment associated with essential services which are to be based on Minimum Atmospheric
Temperature (MAT) as indicated in 4-1-1/7.7.

7.9 Materials Containing Asbestos

Installation of materials which contain asbestos is prohibited.

7.11 Materials and Welding for Machinery Components

Materials used in the construction of the machinery of units are to be in accordance with the ABS Rules for
Materials and Welding (Part 2).

For welding procedures and details for machinery components, see Section 2-4-2.

TABLE 3
Primary Essential Services

(a) Steering gears

(b) Pumps for controllable pitch propellers

(c) Scavenging air blower, fuel oil supply pumps, fuel valve cooling pumps, lubricating oil pumps and cooling water
pumps for main and auxiliary engines, turbines and shafting necessary for propulsion

(d) Ventilation necessary to maintain propulsion

(e) Forced draft fans, feed water pumps, water circulating pumps, vacuum pumps and condensate pumps for steam
plants on steam turbine units, and also for auxiliary boilers where steam is used for equipment supplying primary
essential services

(f) Oil burning installations for steam plants on steam turbine units and for auxiliary boilers where steam is used for
equipment supplying primary essential services

(g) Azimuth thrusters which are the sole means for propulsion/steering with lubricating oil pumps, cooling water
pumps, etc.

(h) Electrical equipment for electric propulsion plant with lubricating oil pumps and cooling water pumps

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 8

Part 4 Machinery and Systems
Chapter 1 Machinery, Equipment and Systems
Section 1 General 4-1-1

(i) Electric generators and associated power sources supplying primary essential equipment

(j) Hydraulic pumps supplying primary essential equipment

(k) Viscosity control equipment for heavy fuel oil

(l) Control, monitoring and safety devices/systems of equipment for primary essential services

(m) Fire pumps and other fire extinguishing medium pumps.

(n) Navigation lights, aids and signals.

(o) Internal safety communication equipment.

(p) Lighting system.

(q) Services considered necessary to maintain dangerous spaces in a safe condition

(r) Blow-out preventer control systems

(s) Well control systems

(t) Dynamic positioning systems

(u) Ventilation systems necessary to maintain a safe atmosphere

(v) Elevating (jacking) systems

(w) Ballast control systems (on column stabilized units)

TABLE 4
Secondary Essential Services

(a) Windlass

(b) Fuel oil transfer pumps and fuel oil treatment equipment

(c) Lubrication oil transfer pumps and lubrication oil treatment equipment

(d) Pre-heaters for heavy fuel oil

(e) Starting air and control air compressors

(f) Bilge, ballast and heeling pumps

(g) Ventilating fans for engine and boiler rooms

(h) Fire and gas detection and alarm system

(i) Electrical equipment for watertight and fire-tight closing appliances

(j) Electric generators and associated power sources supplying secondary essential equipment

(k) Hydraulic pumps supplying secondary essential equipment

(l) Control, monitoring and safety devices/systems of equipment for secondary essential services

(m) Inerting systems

(n) Ambient temperature control equipment required by 4-3-1/17.3

(o) Watertight Doors (see 3A-3-2/5)

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 9

 PART 4
CHAPTER 1
Machinery, Equipment and Systems

SECTION 2
Machinery and Equipment

1 Prime Movers

1.1 Application
Prime movers (diesel engines, gas turbines, steam turbines) having a rated power of 100 kW (135 hp) and
over, intended for essential services (see 4-1-1/3.5) or for services related to additional optional notations
requested for the unit, are to be designed, constructed, tested, certified and installed in accordance with the
requirements of Part 4, Chapter 2 of the ABS Rules for Building and Classing Marine Vessels (Marine
Vessel Rules).

Prime movers having a rated power of less than 100 kW (135 hp) are not required to comply with Part 4,
Chapter 2 of the Marine Vessel Rules, but are to be designed, constructed and equipped in accordance with
good commercial and marine practice. Acceptance of such engines will be based on manufacturer’s
affidavit, verification of engine nameplate data, and subject to a satisfactory performance test after
installation conducted in the presence of the Surveyor. Automatic air intake shut-off valves or equivalent
arrangements are to be provided in accordance with 8-2-1/11.

Prime movers having a rated power of 100 kW (135 hp) and over, intended for services not considered
essential (see 4-1-1/3.5) and not related to additional optional notations requested for the unit, are not
required to be designed, constructed and certified by ABS in accordance with the requirements of Part 4,
Chapter 2 of the Marine Vessel Rules. However, they are to comply with safety features, such as crankcase
explosion relief valve, overspeed protection, etc., as provided in 4-2-1/7 of the Marine Vessel Rules, as
applicable. After installation, they are subject to a satisfactory performance test conducted in the presence
of the Surveyor. Automatic air intake shut-off valves or equivalent arrangements are to be provided in
accordance with 8-2-1/11.

Drilling, hydrocarbon production, and other types of units where large amounts of flammable gases may be
present, are to be fitted with automatic air intake shut off valves. Automatic air intake shut-off valves or
equivalent arrangements are to be provided in accordance with 8-2-1/11.

3 Propulsion, Maneuvering and Dynamic Positioning Systems

Self-propelled units and those receiving notations related to propulsion assist thrusters and athwartship
thrusters are to be fitted to thrusters that comply with the following:

● Main propulsion thrusters Section 4-3-5 of the Marine Vessel Rules

● Waterjets Section 4-3-6 of the Marine Vessel Rules

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 10

Part 4 Machinery and Systems
Chapter 1 Machinery, Equipment and Systems
Section 2 Machinery and Equipment 4-1-2

● Podded Propulsors Section 4-3-8 of the Marine Vessel Rules

● Contra-Rotating Propellers Section 4-3-9 of the Marine Vessel Rules

Dynamic positioning systems, including their thrusters, are to comply with the ABS Guide for Dynamic
Positioning Systems.

5 Moving Cantilevers, Skid Beams and Moveable Structures

A description of equipment for moving cantilevers, skid beams or moveable substructures, including
piping and electrical systems, details of mechanical components, including hold-down devices and
applicable strength calculations, is to be submitted for review.

7 Electrical Machinery and Equipment

For electrical machinery and equipment, refer to Section 4-3-4.

9 Certification of Machinery and Equipment

For certification of machinery and equipment required at vendor’s plant, refer to Part 6.

11 Unattended Machinery Spaces

Controls necessary for safe operation are to be provided for machinery spaces which are not normally
manned. Relevant data is to be submitted to permit the assessment of the effect of such controls on the
safety of the unit. See 4-2-4/3.7 for bilge alarm systems and 5-3-1/13 for fire precautions for such spaces.

For self-propelled units where it is intended that propulsion machinery space be periodically unattended
and that propulsion machinery be controlled primarily from the navigation bridge, ✠ACCU notation will
be assigned upon verification of compliance with Section 4-9-6 of the Marine Vessel Rules.

For non-self-propelled units where it is intended that the machinery space(s) and the local centralized
control and monitoring station(s) (if provided) be periodically unmanned, and that the machinery/ systems
be controlled and monitored from a remote control and monitoring center located outside the machinery
space(s), ✠AMCCU notation will be assigned upon verification of compliance with the Section 3 of the
ABS Guide for Automatic or Remote Control and Monitoring for Machinery and Systems (other than
Propulsion) on Offshore Installations.

✠ ACCU and ✠AMCCU notations are not mandatory and will be assigned upon request.

13 Propulsion Redundancy
Units equipped with propulsion and steering systems designed to provide enhanced reliability and
availability through functional redundancy may be granted the optional notation as specified in 4-3-7/3 of
the Marine Vessel Rules, as appropriate, when the unit is designed, built and surveyed in accordance with
Section 4-3-7 of the Marine Vessel Rules.

It is a prerequisite that the units are also to be classed to ✠ACCU notation, in accordance with Part 4,
Chapter 9 of the Marine Vessel Rules.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 11

 PART 4
CHAPTER 2
Pumps and Piping Systems

CONTENTS
SECTION 1 General................................................................................................20
1 Objective.......................................................................................20
1.1 Goal................................................................................. 20
1.2 Functional Requirements.................................................21
1.3 Compliance......................................................................22
2 General Requirements..................................................................22
2.1 Damage Stability..............................................................22
2.3 Segregation of Piping Systems........................................22
3 Definitions .................................................................................... 23
3.1 Piping...............................................................................23
3.3 Piping System..................................................................23
3.5 Piping Components......................................................... 23
3.7 Pipes................................................................................23
3.9 Pipe Schedule..................................................................23
3.11 Tubes............................................................................... 23
3.13 Pipe Fittings..................................................................... 24
3.15 Valves.............................................................................. 24
3.17 Design Pressure of Components.....................................24
3.19 Maximum Working Pressure............................................24
3.21 Maximum Allowable Working Pressure........................... 24
3.23 Design Temperature........................................................ 24
3.25 Maximum Working Temperature......................................24
3.27 Flammable Fluids............................................................ 24
3.29 Toxic Fluids...................................................................... 25
3.31 Corrosive Fluids...............................................................25
5 Classes of Piping Systems .......................................................... 25
7 Plans and Data to Be Submitted...................................................26
7.1 Plans................................................................................26
7.3 All Piping Systems........................................................... 27
7.5 Booklet of Standard Details............................................. 27
9 Material Tests and Inspection....................................................... 27

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 12

 9.1 Specifications and Purchase Orders............................... 27
9.3 Special Materials............................................................. 27
11 General Installation Details...........................................................27
11.1 Protection.........................................................................27
11.3 Pipes Near Switchboards................................................ 27
11.5 Expansion or Contraction Stresses................................. 27
11.7 Molded Expansion Joints.................................................28
11.9 Metallic Bellow Type Expansion Joints............................ 29
11.11 Pipe Joints....................................................................... 30
11.13 Mechanical Joints............................................................ 30
11.15 Bulkhead, Deck or Tank-Top Penetrations.......................30
11.17 Collision-bulkhead Penetrations...................................... 31
11.19 Sluice Valves and Cocks................................................. 31
11.21 Relief Valves.................................................................... 31
11.23 Common Overboard Discharge....................................... 32
11.25 Remote Operation........................................................... 32
11.27 Instruments...................................................................... 32
11.29 Flexible Hoses................................................................. 32
11.31 Control of Static Electricity...............................................32
11.33 Leakage Containment......................................................32

TABLE 1 Classes of Piping Systems ..................................................25

FIGURE 1 Typical Drain Connection .................................................... 23

FIGURE 2 Molded Nonmetallic Expansion Joint................................... 28
FIGURE 3 Metallic Bellow Type Expansion Joint ................................. 30

SECTION 2 Pumps, Pipes, Valves, and Fittings..................................................34

1 Objective.......................................................................................34
1.1 Goals............................................................................... 34
1.2 Functional Requirements.................................................35
1.3 Compliance......................................................................36
2 General......................................................................................... 36
2.1 Service Conditions...........................................................36
2.3 Standards for Valves, Fittings and Flanges..................... 36
3 Certification of Piping Components ............................................. 37
5 Metallic Pipes................................................................................37
5.1 Steel Pipe........................................................................ 37
5.3 Copper and Copper alloys............................................... 38
5.5 Brass Pipe....................................................................... 38
5.6 Other Materials................................................................ 38
5.7 Design..............................................................................38

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 13

 5.9 Design Pressure and Thickness – Alternative
Consideration...................................................................40
7 Plastic Pipes ................................................................................ 44
7.1 General............................................................................ 44
7.2 Definitions........................................................................ 44
7.3 Plans and Data to be Submitted...................................... 45
7.5 Design..............................................................................46
7.7 Installation of Plastic Pipes.............................................. 51
7.9 Manufacturing of Plastic Pipes........................................ 52
7.11 Plastic Pipe Bonding Procedure Qualification................. 53
7.13 Tests by the Manufacturer – Fire Endurance Testing
of Plastic Piping in the Dry Condition (For Level 1
and Level 2)..................................................................... 54
7.15 Test by Manufacturer – Fire Endurance Testing of
Water-Filled Plastic Piping (For Level 3)..........................55
7.16 Tests by the Manufacturer - Wet/Dry Fire Endurance
Testing of FRP Piping Used in Deluge System (For
Level 3 Modified Test - Level 3 WD) (Adopted from
USCG PFM 1-98)............................................................ 58
7.17 Tests by Manufacturer – Flame Spread...........................58
7.19 Testing By Manufacturer – General................................. 59
9 Valves .......................................................................................... 64
9.1 General............................................................................ 64
9.3 Construction.....................................................................64
9.5 Hydrostatic Test and Identification................................... 65
11 Pipe Fittings.................................................................................. 65
11.1 General............................................................................ 65
11.3 Hydrostatic Test and Identification................................... 65
11.5 Nonstandard Fittings........................................................65
13 Welded Nonstandard Valves and Fittings.....................................66
15 Flanges......................................................................................... 66
15.1 General............................................................................ 66
15.3 Class I and II Piping Flanges........................................... 66
15.5 Class III Piping Flanges................................................... 66
17 Material of Valves and Fittings......................................................66
17.1 General............................................................................ 66
17.3 Forged or Cast Steel........................................................67
17.5 Cast Iron.......................................................................... 67
17.7 Nonferrous....................................................................... 67
17.9 Ductile (Nodular) Iron.......................................................67
19 Fluid Power Cylinders ..................................................................67
19.1 General............................................................................ 67
19.3 Non-compliance with a Recognized Standard.................68
19.5 Materials.......................................................................... 68
19.7 Rudder Actuators.............................................................68

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 14

 19.9 Cylinders Below Pressures or Temperatures
Indicated in 4-2-2/19.1..................................................... 68
19.11 Exemptions...................................................................... 68
21 Sea Inlets and Overboard Discharges..........................................69
21.1 Installation........................................................................69
21.3 Valve Connections to Shell.............................................. 69
21.5 Materials.......................................................................... 69
21.7 Shell Reinforcement........................................................ 69
21.9 Shell Valves..................................................................... 69
21.11 Sea Chests...................................................................... 70
23 Scuppers and Drains on Surface-Type and Self-Elevating
Units..............................................................................................70
23.1 Discharges through the Shell...........................................70
23.3 Scuppers and Discharges below the Freeboard Deck
– Shell Penetration.......................................................... 72
23.5 Scuppers from Superstructures or Deckhouses.............. 72
25 Cooler Installations External to the Hull........................................72
25.1 General............................................................................ 72
25.3 Integral Keel Cooler Installations..................................... 72
25.5 Non-integral Keel Cooler Installations............................. 72
27 Penetrations through Watertight Boundaries................................72
27.1 Ventilating Systems......................................................... 72
27.3 Internal Drain System...................................................... 73

TABLE 1 Allowable Stress Values S for Piping N/mm2 (kgf/mm2,

psi) ...................................................................................... 41
TABLE 2 Fire Endurance Requirements Matrix.................................. 60
TABLE 3 Standards for Plastic Pipes – Typical Requirements for
All Systems ......................................................................... 62
TABLE 4 Standards for Plastic Pipes – Additional Requirements
Depending on Service and/or Location of Piping ................ 63

FIGURE 1 Fire Endurance Test Burner Assembly.................................56

FIGURE 2 Fire Endurance Test Stand With Mounted Sample.............. 57
FIGURE 3 Overboard Discharges – Valve Requirements .................... 71

SECTION 3 Tank Vents, Overflows and Sounding.............................................. 74

1 Objective ......................................................................................74
1.1 Goals............................................................................... 74
1.2 Functional Requirements.................................................75
1.3 Compliance......................................................................76
2 Tank Vents, Overflows and Sounding........................................... 76
2.1 General............................................................................ 76
2.3 Progressive Flooding Consideration................................77

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 15

 2.5 Height and Wall Thickness of Vent Pipes........................ 77
2.7 Size..................................................................................77
2.9 Termination of Vent Pipes................................................ 78
2.11 Overflow Pipes.................................................................83
3 Sounding Arrangements .............................................................. 84
3.1 General............................................................................ 84
3.3 Sounding Pipes................................................................84
3.5 Gauge Glasses................................................................ 85
3.7 Level Indicating Device....................................................85

FIGURE 1 Example of Normal Position ................................................81

FIGURE 2 Example of Inclination 40 degrees Opening Facing
Upward ................................................................................82
FIGURE 3 Example of Inclination 40 degrees Opening Facing
Downward ........................................................................... 82
FIGURE 4 Example of Inclination 40 degrees Opening Facing
Sideways .............................................................................83

SECTION 4 Bilge and Ballast Systems and Tanks..............................................86

1 Objective.......................................................................................86
1.1 Goal................................................................................. 86
1.2 Functional Requirements.................................................87
1.3 Compliance......................................................................88
2 General Arrangement of Bilge Systems for Surface-Type Units...88
2.1 General............................................................................ 88
2.3 Number of Bilge Pumps...................................................88
2.5 Direct Bilge Suctions........................................................89
2.7 Emergency Bilge Suctions...............................................89
3 General Arrangement of Bilge Systems for Column-
Stabilized Units and Self-Elevating Units......................................89
3.1 Permanent Systems........................................................ 89
3.3 Void Compartments......................................................... 89
3.5 Chain Lockers..................................................................89
3.7 Bilge Alarm...................................................................... 90
5 Bilge Piping (All Units).................................................................. 90
5.1 General............................................................................ 90
5.3 Installation........................................................................90
5.5 Manifolds, Cocks and Valves...........................................90
5.7 Common-main-type Bilge Systems................................. 90
5.9 Strainers.......................................................................... 90
5.11 Gravity Drains.................................................................. 91
5.13 Bilge Suctions from Hazardous Areas............................. 91
5.15 Exceptions....................................................................... 91
7 Bilge Pumps (All Units)................................................................. 91

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 16

 7.1 General............................................................................ 91
7.3 Arrangement and Capacity.............................................. 91
9 Size of Bilge Suctions................................................................... 91
9.1 Surface-Type Units.......................................................... 91
9.3 Column-Stabilized Units and Self-Elevating Units........... 92
11 Ballast Piping (All Units)............................................................... 93
11.1 General............................................................................ 93
11.3 Installation........................................................................93
11.5 Controls for Ballast Tank Valves...................................... 93
11.7 Exceptions....................................................................... 93
11.9 Ballast Water Treatment Systems................................... 93
13 Ballasting Systems for Column-Stabilized Units...........................94
13.1 General............................................................................ 94
13.3 Manifolds......................................................................... 94
13.5 Pumps..............................................................................94
13.7 Ballast Control Features.................................................. 94

SECTION 5 Fuel Oil Systems and Tanks..............................................................97

1 Objective.......................................................................................97
1.1 Goals............................................................................... 97
1.2 Functional Requirements.................................................98
1.3 Compliance......................................................................99
2 Fuel Oil Piping System – General.................................................99
2.1 Arrangement.................................................................... 99
2.3 Piping, Valves and Fittings.............................................102
2.5 Oil Heating Arrangements............................................. 102
2.7 Fuel Oil Purifiers............................................................ 103
3 Fuel-oil Transfer and Filling ....................................................... 103
3.1 General.......................................................................... 103
3.3 Pipes in Oil Tanks.......................................................... 103
3.5 Control Valves or Cocks................................................ 103
3.7 Valves on Oil Tanks....................................................... 103
5 Fuel-oil Service System for Boilers.............................................104
7 Fuel-oil Service System for Internal Combustion Engines..........104
7.1 Fuel-oil Pumps and Oil Heaters.....................................104
7.3 Oil Tanks and Drains for Fuel Oil Systems.................... 105
7.5 Fuel-oil Pressure Piping.................................................105
7.7 Fuel-oil Injection System................................................105
7.9 Piping Between Booster Pump and Injection Pumps.... 105
7.10 Isolating Valves in Fuel Supply and Spill Piping............ 106
9 Low Flash Point Fuels ............................................................... 106
9.1 General.......................................................................... 106
9.3 Fuel Heating.................................................................. 106

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 17

 9.5 Fuel-tank Vents..............................................................106
11 Additional Measures for Oil Pollution Prevention .......................107
11.1 General.......................................................................... 107
11.3 Tank Protection Requirements.......................................107
13 Class Notation – POT ................................................................ 108

FIGURE 1 Acceptable Fuel Oil Tanks Arrangements Inside

Category A Machinery Spaces ..........................................101

SECTION 6 Other Piping Systems and Tanks................................................... 109

1 Objective.....................................................................................109
1.1 Goal............................................................................... 109
1.2 Functional Requirements............................................... 110
1.3 Compliance.................................................................... 112
2 Lubricating-oil Systems ..............................................................112
2.1 General.......................................................................... 112
2.3 Sight Flow Glasses........................................................ 112
2.5 Turbines and Reduction Gears...................................... 112
2.7 Internal Combustion Engines and Reduction Gears......112
3 Hydraulic Systems ..................................................................... 113
3.1 General.......................................................................... 113
3.3 Valves.............................................................................113
3.5 Piping............................................................................. 114
3.7 Pipe Fittings................................................................... 114
3.9 Flexible Hoses............................................................... 114
3.11 Accumulators................................................................. 114
3.13 Fluid Power Cylinders.................................................... 114
3.15 Segregation of High-Pressure Hydraulic Units.............. 114
5 Fixed Oxygen-Acetylene Systems ............................................. 115
5.1 Application..................................................................... 115
5.3 Gas Storage...................................................................115
5.5 Piping System Components...........................................115
7 Helicopter Refueling Systems ....................................................117
7.1 Fuel Storage and Refueling Equipment Area................ 117
7.3 Spill Containment...........................................................118
9 Starting-air Systems ...................................................................118
9.1 Design and Construction................................................118
9.3 Starting-air Capacity...................................................... 118
9.5 Protective Devices for Starting-air Mains.......................119
11 Cooling-water Systems for Internal Combustion Engines...........119
11.1 General.......................................................................... 119
11.3 Sea Suctions..................................................................119
11.5 Strainers........................................................................ 120

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 18

 11.7 Circulating Water Pumps............................................... 120
13 Exhaust System .........................................................................120
13.1 Exhaust Lines................................................................ 120
13.3 Exhaust Gas Temperature............................................. 120
13.5 Exhaust Emission Abatement Systems......................... 120
15 Valves in Atomizing Lines........................................................... 120
17 Helicopter Deck Drainage Arrangements................................... 120
19 Boilers and Associated Piping.................................................... 121
21 Steering Gear Piping.................................................................. 121
23 Gas Turbine Piping..................................................................... 121
25 Raw Water System for Self-Elevating Units in Elevated
Condition ....................................................................................121
25.1 General.......................................................................... 121
25.3 Raw Water Tower...........................................................121
25.5 Leg Well Suction............................................................121
25.7 Hose Reel...................................................................... 121

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 19

 PART 4
CHAPTER 2
Pumps and Piping Systems

SECTION 1
General

1 Objective

1.1 Goal
The pumps and piping systems covered in this section are to be designed, constructed, operated, and
maintained to:

Goal No. Goal

SAFE 1 promote the occupational health and safety of personnel onboard

SAFE 1.1 minimize danger to persons on board, the vessel, and surrounding equipment/installations from
hazards associated with machinery and systems

FIR 1 prevent the occurrence of fire and explosion.

FIR 2 reduce the risk to life caused by fire

STAB-1 have adequate watertight integrity and restoring energy to prevent capsize in an intact condition

STAB 5 be able to remove accumulated liquids to mitigate the effects of flooding.

STAB 6 provide means to control the overall vessel weight and distribution to maintain adequate trim and
stability.

ENV 1 prevent and minimize oil pollution due to vessel operation and accidents.

AUTO 3 have an alternative means to enable safe operation in the event of an emergency or failure of
remote control.

MGMT 4 establish procedures, plans and instructions for emergency situations concerning the safety of the
personnel, vessel, and protection of the environment

MAT 1 The selected materials’ physical, mechanical and chemical properties are to meet the design
requirements appropriate for the application, operating conditions and environment.

Materials are to be suitable for the intended application in accordance with the following goals and support
the Tier1 goals as listed above.

The goals in the cross-referenced Rules/Regulations are also to be met.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 20

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

1.2 Functional Requirements

In order to achieve the above stated goals, the design, construction, installation and maintenance of the
pumps and piping systems are to be in accordance with the following functional requirements:

Functional Functional Requirement

Requirement No.

Safety of Personnel (SAFE)

SAFE-FR1 (FIR) Design is to protect the safety of non-hazardous areas by effectively segregating hazardous fluids
and preventing ignition sources from coming into contact with combustible materials and
flammable liquids.

SAFE-FR2 Piping is to contain the fluid media and withstand the most severe condition of coincident design
pressure, temperatures, vibration, and loading.

SAFE-FR 3 Piping is to be designed or arranged to enable flexibility in movements while transferring the fluid
media without leakage or failure.

SAFE-FR4 Provide means to prevent a system from being subjected to a pressure that exceed the design
limits.

SAFE-FR5 (ENV) Discharge location and arrangement are not to endanger the safety of persons onboard,
equipment/systems and environment.

SAFE-FR6 (MGMT) Arrangements are to be provided to enable the removal of devices without impairing integrity of
the tanks and pressurized systems.

SAFE-FR7 (FIR) Arrangements are to be provided to prevent build-up of static electricity and reduce the risk of
fire/explosion due to electrostatic discharge.

Materials (MAT)

MAT-FR1 Materials are to be compatible with liquids, solids, gases they are expected to encounter during
the service life.

Fire Safety (FIR)

FIR-FR1 Piping penetrations through fire tight bulkhead are to be by methods which maintain the required
integrity.

FIR-FR2 (ENV) Protect oil tanks from collision and grounding to prevent pollution and fire.

FIR-FR3 Piping is to be designed, arranged, or protected to minimize fire risks.

FIR-FR4 Piping and electrical devices are to be designed, arranged, or protected to minimize fire risk.

FIR-FR5 (SAFE) Provide means of containment and drainage of oils where spillage or leakage is expected to
minimize fire and safety risks.

Stability (STAB)

STAB-FR1 Piping penetrations through watertight bulkheads are to be by methods which maintain the
required integrity.

STAB-FR2 Valves installed on watertight bulkheads to control flooding are to be operable during the
corresponding flooding scenarios.

STAB-FR3 Piping is to be designed, arranged, or protected to minimize the chance of collision damage.

STAB-FR4 Piping is to be designed, arranged, or protected to minimize flooding risks.

STAB-FR5 Penetrations through the collision bulkhead in ship type units are to be limited and designed to
prevent uncontrolled flooding in case of collision.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 21

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

Functional Functional Requirement

Requirement No.

STAB-FR6 Penetrations through watertight bulkheads are to be by methods which maintain the required
integrity.

Automation (Control, Monitoring and Safety Systems) (AUTO)

AUTO-FR1 Provide redundant, manual modes of operation for remotely power-operated valves in case of
power or control failure.

The Functional Requirements in the cross-referenced Rules/Regulations are also to be met.

1.3 Compliance
A unit is considered to comply with the Goals and Functional Requirements when the applicable
prescriptive requirements are complied with or when an alternative arrangement has been approved. Refer
to Part 1D, Chapter 2.

2 General Requirements
Piping systems are to be in accordance with the applicable requirements of this Section. Piping systems
used solely for specific operations associated with class notations and complying with a recognized
standard need not be in accordance with these Rules. All piping systems are to be installed and tested in
accordance with the Rules or recognized standards to the satisfaction of the attending Surveyor.

2.1 Damage Stability

When considering the design and layout of piping systems, consideration is to be given to the damage
stability requirements and the assumed extent of damage for the type of unit, as outlined in 3A-3-2/3.5.

2.3 Segregation of Piping Systems

Piping systems carrying non-hazardous fluids are to be segregated from piping systems which may contain
hazardous fluids. Cross connection of the piping systems may be made where means for avoiding possible
contamination of the non-hazardous fluid system by the hazardous medium are provided.

Where an unsafe condition, due to piping interconnection of hazardous and nonhazardous areas or between
hazardous areas of different classifications, is possible, a loop-seal to trap hazardous gases from reaching
non-hazardous areas or from areas of higher classification to areas of lower classification is to be fitted. If
back-up of hazardous liquid into the non-hazardous areas or from hazardous areas of higher classification
to areas of lower classification is possible, a non-return check valve is to be installed. The height of the
loop-seal is to be not less than 760 mm (30 inches) and the check valve is to be fitted downstream of the
seal. Both the seal and the valve are to be accessible for maintenance by crew.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 22

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

FIGURE 1
Typical Drain Connection

3 Definitions

3.1 Piping
The term Piping refers to assemblies of piping components and pipe supports.

3.3 Piping System

Piping System is a network of piping and any associated pumps, designed and assembled to serve a
specific purpose. Piping systems interface with, but exclude, major equipment, such as boilers, pressure
vessels, tanks, diesel engines, turbines, etc.

3.5 Piping Components

Piping Components include pipes, tubes, valves, fittings, flanges, gaskets, bolting, hoses, expansion joints,
sight flow glasses, filters, strainers, accumulators, instruments connected to pipes, etc.

3.7 Pipes
Pipes are pressure-tight cylinders used to contain and convey fluids. Where the word ‘pipe’ is used in this
section, it means pipes conforming to materials and dimensions as indicated in 2-3-12, 2-3-13, 2-3-16, and
2-3-17 of the ABS Rules for Materials and Welding (Part 2), or equivalent national standards such as
ASTM, BS, DIN, JIS, etc.

3.9 Pipe Schedule

Pipe Schedules are designations of pipe wall thicknesses as given in American National Standard Institute,
ANSI B36.10. For a listing of commercial pipe sizes and wall thicknesses, see 4-6-2/Table 8 of the Marine
Vessel Rules.

3.11 Tubes
Tubes are small-diameter thin-wall pipes conforming to an appropriate national standard. Tubes are to meet
the same requirements as pipes.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 23

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

3.13 Pipe Fittings

Pipe Fittings refer to piping components such as sleeves, elbows, tees, bends, flanges, etc., which are used
to join sections of pipe.

3.15 Valves
The term Valve refers to gate valves, globe valves, butterfly valves, etc., which are used to control the flow
of fluids in a piping system. For the purpose of these Rules, test cocks, drain cocks and other similar
components which perform the same function as valves are considered valves.

3.17 Design Pressure of Components

Design Pressure is the pressure to which each piping component of a piping system is designed. It is not to
be less than the pressure at the most severe condition of coincidental internal or external pressure and
temperature (maximum or minimum) expected during service.

3.19 Maximum Working Pressure

The Maximum Working Pressure is the pressure of a piping system at the most severe condition of
coincidental internal or external pressure and temperature (maximum or minimum) expected during
service, including transient conditions.

3.21 Maximum Allowable Working Pressure

The Maximum Allowable Working Pressure (MAWP) is the maximum pressure permissible of a piping
system determined, in general, by the design pressure of the weakest piping component in the system or by
the relief valve setting.

3.23 Design Temperature

The Design Temperature is the maximum temperature at which each piping component is designed to
operate. It is not to be less than the temperature of the piping component material at the most severe
condition of temperature and coincidental pressure expected during service. For purposes of the Rules, it
may be taken as the maximum fluid temperature for which the piping component is designed.

For piping used in a low-temperature application, the design temperature is to include also the minimum
temperature at which each piping component is designed to operate. It is not to be higher than the
temperature of the piping component material at the most severe condition of temperature and coincidental
pressure expected during service. For the purposes of the Rules, it may be taken as the minimum fluid
temperature.

For all piping components, the design temperature is to be used to determine allowable stresses and
material testing requirements.

3.25 Maximum Working Temperature

The Maximum Working Temperature is the maximum fluid temperature of a piping system at the most
severe condition of temperature and coincidental pressure expected during service, including transient
conditions. The maximum working temperature of a piping system or a section of the system is not to
exceed the design temperature of any piping component in the system or section of the system.

3.27 Flammable Fluids

Any fluid, regardless of its flash point, liable to support a flame is to be treated as a flammable fluid for the
purposes of 4-2-1 through 4-2-6. Aviation fuel, diesel fuel, heavy fuel oil, lubricating oil and hydraulic oil
(unless the hydraulic oil is specifically specified as non-flammable) are all to be considered flammable
fluids.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 24

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

3.29 Toxic Fluids

Toxic fluids are those that are liable to cause death or severe injury or to harm human health if swallowed
or inhaled or by skin contact.

3.31 Corrosive Fluids

Corrosive fluids, excluding seawater, are those possessing in their original state the property of being able
through chemical action to cause damage by coming into contact with living tissues, the vessel or its
cargoes, when escaped from their containment.

5 Classes of Piping Systems

Piping systems are divided into three classes according to service, maximum working pressure and
maximum working temperature, as indicated in 4-2-1/5 TABLE 1. Each class has specific requirements for
joint design, fabrication and testing. The requirements in this regard are given in 4-2-2/5 for metallic
piping. For plastic piping, see 4-2-2/7.

TABLE 1
Classes of Piping Systems

Piping Class Class I Class II Bounded by Class I Class III

P > P2 OR T > T2 and Class III - see chart P ≤ P1 AND T ≤ T1
above

Piping System bar , °C bar, °C bar, °C

(kgf/cm2, psi) (°F) (kgf/cm2, psi) (°F) (kgf/cm2, psi) (°F)

Corrosive fluids Without special safeguards With special safeguard Not applicable

Toxic fluids All Not applicable Not applicable

Flammable liquids heated to Without special safeguards With special safeguards Open-ended piping
above flash point or having
flash point 60°C or less

Liquefied gas Without special safeguards With special safeguards Open-ended piping

Steam 16 300 See chart 7 170

(16.3, 232) (572) (7.1, 101.5) (338)

Thermal oil 16 300 See chart 7 150

(16.3, 232) (572) (7.1, 101.5) (302)

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 25

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

Fuel oil 16 150 See chart 7 60

Lubricating oil (16.3, 232) (302) (7.1, 101.5) (140)
Flammable hydraulic oil

Cargo oil piping in cargo Not applicable Not applicable All

area

Other fluids (including 40 300 16 200

water, air, gases, non- (40.8, 580) (572) See chart (16.3, 232) (392)
flammable hydraulic oil)

Open ended pipes (drains, Not applicable Not applicable All

overflows, vents, exhaust gas
lines, boilers escapes pipes)

Fixed Oxygen-acetylene High pressure Side Not applicable Low pressure Side
System

Notes:

1 The above requirements are not applicable to piping systems intended for liquefied gases in cargo and process
areas.

2 The above requirements are also not applicable to cargo piping systems of units carrying chemicals in bulk.

3 Safeguards are measures undertaken to reduce leakage possibility and limiting its consequences, (e.g., double
wall piping or equivalent, or protective location of piping etc.)

7 Plans and Data to Be Submitted

7.1 Plans
Before proceeding with the work, plans are to be submitted, as applicable, showing clearly the
diagrammatic details or arrangement of the following.

● General arrangement of pumps and piping

● Sanitary system
● Bilge and ballast systems
● Compressed air systems
● Essential control-air systems
● Vent, sounding and overflow pipes
● Fuel-oil filling, transfer and service systems
● Boiler-feed systems
● Steam and exhaust piping
● Lubricating-oil systems
● Hydraulic power piping systems
● Essential seawater and fresh-water service systems
● Starting-air systems
● Fire-main and fire-extinguishing systems (see Part 5, Chapter 2)
● Steering-gear piping systems
● Systems conveying toxic liquids, low flash point below 60°C (140°F) liquids or flammable gas.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 26

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

● Exhaust piping for internal combustion engines and boilers

● Exhaust gas cleaning system (as applicable, see 6-3-1/9.11 of the Marine Vessel Rules
● All Class I and Class II piping systems not covered above, except for those which form part of an
independently manufactured unit.
● A description of the bilge, ballast and drainage systems
● A description of the ballast control system for column-stabilized units
● A description and diagrammatic plans of all piping systems used solely for industrial operations (ie
drilling), including their cross connections.

7.3 All Piping Systems

The plans are to consist of a diagrammatic drawing of each system accompanied by lists of material giving
size, wall thickness, design pressure and material of all pipes and the type, size, construction standards
pressure and temperature ratings and material of valves and fittings. Where superheated steam is used, the
temperatures are also to be given.

7.5 Booklet of Standard Details

A booklet of standard piping practices and details, including such items as bulkheads, deck and shell
penetrations, welding details including dimensions, pipe join details, etc. is to be submitted. Pipe weld
details are to comply with Chapter 4 of the ABS Rules for Materials and Welding (Part 2). Applicable
limitations are to be specified.

9 Material Tests and Inspection

9.1 Specifications and Purchase Orders

The appropriate material to be used for the various pipes, valves and fittings is indicated in 4-2-2/5 to
4-2-2/19. The material is to be made in accordance with the requirements in Chapter 3 of the ABS Rules
for Materials and Welding (Part 2), except that tests of material for valves and fittings and fluid power
cylinders need not be witnessed by the Surveyor. Where electric welding is used, the requirements in
Chapter 4 of the above-referenced Part 2 are also applicable.

9.3 Special Materials

If it is desired to use special alloys or other materials not covered by the Rules, the use of such materials
requires technical assessment and approval by ABS.

11 General Installation Details

11.1 Protection
The installation is to be in accordance with 7A-1-3/11.3.

11.3 Pipes Near Switchboards

The installation is to be in accordance with 7A-1-3/11.5.

11.5 Expansion or Contraction Stresses

Provision is to be made to limit expansion or contraction stresses in pipes due to temperature changes or
working of the hull. Provisions include, but are not limited to, piping bends, elbows, offsets, changes in
direction of the pipe routing or expansion joints. Slip joints of an approved type may be used in systems
and locations where possible leakage will not be critical. See also 4-2-4/5.3 and 4-2-4/11.3.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 27

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

11.7 Molded Expansion Joints

Molded expansion joints may be Type Approved; see 1B-1-A2 of the ABS Rules for Conditions of
Classification - Offshore Units (Part 1B).

11.7.1 Circulating Water Systems

Molded expansion fittings of reinforced rubber or other suitable materials (See 4-2-1/Figure 2)
may be used in Class III seawater piping systems in machinery spaces. Such fittings are to be oil-
resistant. The maximum working pressure is not to be greater than 25% of the hydrostatic bursting
pressure of the fitting as determined by a prototype test. Manufacturer’s name and the month and
year of manufacture are to be embossed or otherwise permanently marked on the outside edge of
one of the flanges or other easily examined area of all flexible expansion joints intended for use in
seawater piping systems over 150 mm (6 in.). Plans of the molded or built-up flexible expansion
joints in seawater piping systems over 150 mm (6 in.), including details of the internal
reinforcement arrangements, are to be submitted for approval.

FIGURE 2
Molded Nonmetallic Expansion Joint

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 28

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

11.7.2 Oil Systems

Where molded expansion joints of composite construction utilizing metallic material, such as steel
or stainless steel or equivalent material, with rubberized coatings inside and/or outside or similar
arrangements are proposed for use in oil piping systems (fuel, lubricating, or hydraulic oil), the
following requirements apply:

11.7.2(a) Expansion joint ratings for temperature, pressure, movements and selection of materials
are to be suitable for the intended service.

11.7.2(b) The maximum allowable working pressure of the system is not to be greater than 25% of
the hydrostatic bursting pressure determined by a burst test of a prototype expansion joint. Results
of the burst test are to be submitted.

11.7.2(c) The expansion joints are to pass the fire-resistant test specified in 4-2-1/11.7.3, below.

11.7.2(d) The expansion joints are to be permanently marked with the manufacturer’s name and
the month and year of manufacture.

11.7.3 Fire Resistant Test

In order for a molded expansion joint of composite construction utilizing metallic material, as
referenced in 4-2-1/11.7.2, to be considered fire-resistant, a prototype of the molded expansion
joint is to be subjected to a fire test for at least 30 minutes at a temperature of not less than 800°C
(1472°F) while water at or above the design pressure is circulated inside. The temperature of the
water at the outlets is not to be less than 80°C (176°F) during the test. The tested molded
expansion joint is to be complete with end fittings, and no leakage is to be recorded during or after
the test. In lieu of maximum working pressure, the fire test may be conducted with the circulating
water at a pressure of at least 5 bar (5.1 kgf/cm2, 72.5 lb/in2), and with a subsequent pressure test
to twice the design pressure. This test may be performed in accordance with ISO 15540 and ISO
15541.

11.9 Metallic Bellow Type Expansion Joints

Metallic bellow type expansion joints (See 4-2-1/Figure 3) may be used in all classes of piping, except that
where used in Classes I and II piping, they are to be approved in each individual case. Detailed plans of the
joint are to be submitted along with calculations and/or test results verifying the pressure temperature
rating and fatigue life.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 29

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

FIGURE 3
Metallic Bellow Type Expansion Joint

11.11 Pipe Joints

Butt welded joints, socket welded joints, slip-on welded sleeve joints, flanged joints and threaded joints are
to comply with the requirements of 4-6-2/5.5 of the Marine Vessel Rules. See also 4-2-2/11.

11.13 Mechanical Joints

Pipe unions (welded and brazed types), compression couplings (swage, press, bite, and flare types) and
slip-on joints (grip, machine grooved and slip types) are to comply with the requirements of 4-6-2/5.9 of
the Marine Vessel Rules. See also 4-2-2/11.

11.15 Bulkhead, Deck or Tank-Top Penetrations

11.15.1 Watertight Integrity
Where it is necessary for pipes to penetrate watertight bulkheads, decks or tank tops, the
penetrations are to be made by methods which maintain the watertight integrity. For this purpose,
bolted connections are to have bolts threaded into the plating from one side; through bolts are not
to be used. Welded connections are either to be welded on both sides or to have full penetration
welds from one side.

Piping penetrations of deep tank bulkhead boundaries are to be welded-type; sealing systems or
block-type are not to be used due to material incompatibility, static and dynamic loads and service
life.

Commentary:

If a special sealing system is proposed for tank boundaries, documents are to be submitted to ABS for special
review and approval.

End of commentary

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 30

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

11.15.2 Firetight Integrity

Where pipes penetrate bulkheads, decks or tank-tops which are required to be firetight or
smoketight, the penetrations are to be made by approved methods which maintain the same degree
of firetight or smoketight integrity.

11.17 Collision-bulkhead Penetrations

Pipes piercing the collision bulkhead on ship type units are to be fitted with suitable valves operable from
above the bulkhead deck and the valve chest is to be secured at the bulkhead generally inside the forepeak.
Gray cast iron is not to be used for these valves. The use of nodular iron, also known as ductile iron or
spheroidal-graphite iron will be accepted, provided the material has an elongation not less than 12%.

Tanks forward of the collision bulkhead on surface-type units are not to be arranged for the carriage of oil
or other liquid substances that are flammable.

11.19 Sluice Valves and Cocks

No valve or cock for sluicing purposes is to be fitted on a collision bulkhead on ship type units. Sluice
valves or cocks may be fitted only on other watertight bulkheads when they are at all times accessible for
examination. The control rods are to be operable from the bulkhead deck and are to be provided with an
indicator to show whether the valve or cock is open or closed. Drains from spaces over deep tanks may be
led to an accessible compartment, provided they do not exceed 89 mm O.D. (3 inches nominal pipe size)
and are fitted with quick-acting self-closing valves accessibly located in the compartment where they
terminate.

Commentary:

Sluice valves may be fitted between deep tanks where weight distribution needs to be adjusted for stability purposes.

End of Commentary

11.21 Relief Valves

All systems which are exposed to pressures greater than that for which they are designed are to be
safeguarded by relief valves or the equivalent. Pressure containers such as evaporators, heaters, etc., which
may be isolated from a protective device in the line are to have other such devices either directly on the
shell, or between the shell and the cut-off valve.

11.21.1 Exceptions
In pumping systems such as boiler feed, oil piping and fire main, where relief valves are ordinarily
required at the pumps, such valves need not be fitted when the systems are served only by
centrifugal pumps so designed that the pressure delivered cannot exceed that for which the piping
is designed.

11.21.2 Relief Valve Discharges

For systems carrying flammable liquids or gases, relief valves are to be arranged to discharge back
to the suction side of the pump or to a tank. In all cases, when discharging directly to
the atmosphere, the discharge is not to impinge on other piping or equipment and is to be
directed away from areas used by personnel.

11.21.3 Setting
Relief valves are to be set at pressures not exceeding the piping design pressure. Hydraulic
systems are to comply with 4-2-6/3.3.2. Steering gear hydraulic piping systems are to comply with
4-3-4/9.1.6 of the Marine Vessel Rules.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 31

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

11.23 Common Overboard Discharge

Various types of systems which discharge overboard are not to be interconnected that is, closed pumping
systems, deck scuppers, soil lines or sanitary drains are not to have a common overboard discharge.

In case of interconnection, ABS technical assessment and approval is required, and justification is to be
submitted considering fire, flooding and health risks, and discharge backpressures of each discharge.

11.25 Remote Operation

Where valves of piping systems are arranged for remote control and are power operated, a secondary
means for either local or remote-manual control is to be provided.

11.27 Instruments
11.27.1 Temperature
Thermometers and other temperature sensing devices registering through pressure boundaries are
to be provided with instrument wells to allow for instrument removal without impairing the
integrity of the pressurized system.

11.27.2 Pressure
Pressure sensing devices are to be provided with valve arrangements to allow for instrument
isolation and removal without impairing the pressurized systems’ integrity.

11.27.3 Tanks
Pressure, temperature and level sensing devices installed on tanks at locations where they are
subjected to a static head of liquid are to be fitted with valves or arranged such that they may be
removed without emptying the tank.

Commentary:

Isolation valves for tank devices do not require remote means of closure stated in 4-2-5/3.9.2.

End of commentary

11.29 Flexible Hoses

Flexible hoses are to comply with the requirements of 4-6-2/5.7 of the Marine Vessel Rules.

Hose connections utilized in cooling systems for engines with cylinder bores equal to or less than 300 mm
(12 in.) require technical assessment and approval by ABS.

11.31 Control of Static Electricity

Piping systems that are routed through hazardous areas are to be grounded either by welding or bolting the
pipes or their supports directly to the hull of the unit or through the use of bonding straps. Reference is
made to 7A-1-7/13.5 with regard to testing and installation details.

Components of alarms and level indicating devices located within tanks are to be designed to account for
conductivity.

11.33 Leakage Containment

11.33.1 Oil Leaks
For areas where leakage may be expected such as oil burners, purifiers, drains and valves under
daily service tanks, etc., means of containing the leakage are to be provided together with
drainage. Where drain pipes are provided from collected leakages, they are to be led to an oil drain
tank not forming part of an overflow system.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 32

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 1 General 4-2-1

11.33.2 Boiler Flats

Where boilers are located in machinery spaces on tween decks and the boiler rooms are not
separated from the machinery space by watertight bulkheads, the tween decks are to be provided
with coamings at least 75 mm (3 in.) in height. This area may be drained to the bilges.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 33

 PART 4
CHAPTER 2
Pumps and Piping Systems

SECTION 2
Pumps, Pipes, Valves, and Fittings

1 Objective

1.1 Goals
The pumps, pipes, valves and fittings covered in this section are to be designed, constructed, operated, and
maintained to:

Goal No. Goal

STAB 1 have adequate watertight integrity and restoring energy to prevent capsize in an intact condition

STAB 2 have adequate subdivision and stability to provide survivability to damage or accidental
conditions.

FIR 1 prevent the occurrence of fire and explosion.

FIR 2 reduce the risk to life caused by fire.

FIR 3 reduce the risk of damage caused by fire to the unit, its cargo and the environment.

SAFE 1.1 minimize danger to persons on board, the vessel, and surrounding equipment/installations from
hazards associated with machinery and systems.

SAFE 1.2 provide means to minimize the risk of strikes against objects/equipment, slips, trips, and falls
within the vessel and overboard.

AUTO 3 have an alternative means to enable safe operation in the event of an emergency or failure of
remote control.

Materials are to be suitable for the intended application in accordance with the following goals in support
of the Tier 1 goals as listed above.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 34

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

Goal No. Goal

MAT 1 The selected materials’ physical, mechanical and chemical properties are to meet the design
requirements appropriate for the application, operating conditions and environment

MAT 2 The manufacturing process is to be capable of producing products to meet the specified quality
and property requirements.

MAT 3 The fabrication and welding process is to be capable of producing products that meet the specified
quality and property requirements.

The goals in the cross-referenced Rules/Regulations are also to be met.

1.2 Functional Requirements

In order to achieve the above stated goals, the design, construction, installation and maintenance of the
pumps, pipes, valves and fittings are to be in accordance with the following functional requirements:

Functional Functional Requirements

Requirement No.
Materials (MAT)

MAT-FR1 Materials are to be compatible with liquids, solids, and gases they are expected to encounter during
the service life.

MAT-FR2 Weldability (Carbon content, Carbon Equivalent) to be considered when the items/components are
welded.

MAT-FR3 For elevated design temperatures, calculations are to consider the effects of temperature on tensile
properties. In case of steels, for temperatures above 121°C (250°F).

MAT-FR4 Formability to be considered for ease of manufacturing and potential loss of ductility and toughness.

MAT-FR5 The manufacturing process is to be of an established practice, documented, and under a QA system
so to generate materials with minimal defects that perform in accordance with the design
assumptions.

MAT-FR6 Fabrication tolerances, alignment and defect inspection are to be in accordance with recognized
standards so that the quality control is maintained, and the finished product performs in accordance
with the design assumptions.

Safety of Personnel (SAFE)

SAFE-FR1 Piping/Equipment is to safely contain the fluid media it conveys and able to withstand the most
severe condition of coincident design pressures, temperatures, vibrations and loadings.

SAFE-FR2 Piping is to be designed or arranged to mitigate hazards due to failure of joints.

SAFE-FR3 Piping is to be adequately supported and properly aligned to prevent excessive stresses.

SAFE-FR4 Provide means to preclude the entry of debris or other contaminants into the systems.

SAFE-FR5 Piping is to be designed, arranged, or protected to minimize chance of mechanical damage.

Fire Safety (FIR)

FIR-FR1 Piping is to be designed, arranged, or protected to minimize fire risk.

FIR-FR2 (SAFE) Limit the fire growth potential in every space of the ship.

FIR-FR3 Piping is to be provided with means to prevent buildup of electrostatic charge.

FIR-FR4 (SAFE) Restrict use of materials that are readily rendered ineffective by heat.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 35

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

Functional Functional Requirements

Requirement No.
FIR-FR5 (SAFE) Reduce the hazard to life from smoke and toxic products generated during a fire in spaces where
persons normally work or live

FIR-FR6 (SAFE) The fire integrity of the divisions shall be maintained at openings and penetrations.

Stability (STAB)

STAB-FR1 Piping is to be designed, arranged, or protected to minimize flooding risks.

STAB-FR2 (AUTO) Valves required to control external flooding and their controls are to be readily accessible and
suitably arranged to enable safe operation by the crew.

STAB-FR3 Piping penetrations through watertight bulkheads are to be by methods which maintain the required
integrity.

STAB-FR4 Provide means to prevent the entry of sea water through the opening when the gravity drain is
directed/discharged overboard.

STAB-FR5 Gravity drains from spaces above freeboard deck not fitted with weathertight/watertight doors are to
discharge overboard and be independent of the unit’s drain system

STAB-FR6 Arrangements are to be made to prevent cross-flooding between spaces and between the unit and the
sea.

Automation (Control, Monitoring and Safety systems) (AUTO)

AUTO-FR1 Apply fail-safe design for control systems and safety systems to prevent dangerous situations due to
single failure.

AUTO-FR2 Power operated piping components are to have means of manual operation in the event of power
failure.

The functional requirements in the cross-referenced Rules/Standards are also to be met.

1.3 Compliance
A unit is considered to comply with the Goals and Functional requirements when the prescriptive
requirements are complied with or when an alternative arrangement has been approved, refer to Part 1D
Chapter 2.

2 General

2.1 Service Conditions

The piping details determined in accordance with 4-2-2/5 to 4-2-2/17, inclusive, are to be based on the
maximum working pressure and temperature to which they may be exposed in service under normal
sustained operating conditions. For boiler-feed and blow-off service, see 4-6-6/3.5, 4-6-6/3.15, and
4-6-6/5.3.1 of the Marine Vessel Rules.

2.3 Standards for Valves, Fittings and Flanges

The following requirements for valves, fittings and flanges are based upon standards of the American
National Standards Institute (ANSI) or American Society of Mechanical Engineers (ASME). The
suitability and application of those manufactured in accordance with other recognized standards will be
considered.

Commentary:

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 36

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

Industrial Systems need not meet these Rules if they comply with an applicable recognized standard. The standards most
often used for Industrial Systems are ASME B31.3 Process Piping Code Section and ASME B31.1 Power Piping Code
Section. Other design standards may also be considered acceptable, provided they are determined to be valid and applicable
to the system being reviewed.

End of Commentary

3 Certification of Piping Components

For certification of piping components required at vendor’s plant, refer to Part 6.

5 Metallic Pipes

5.1 Steel Pipe

5.1.1 Material Specifications
Material specifications for acceptable steel pipes are in Section 2-3-12 of the ABS Rules for
Materials and Welding (Part 2). Materials equivalent to these specifications are subject to ABS
technical assessment and approval.

5.1.2 Application of Seamless and Welded Pipes

The application of seamless and welded pipes is to be in accordance with the following table:

Seamless Pipes Electric Resistance Welded Pipes Furnace Butt Welded Pipes

Class I permitted permitted not permitted

Class II permitted permitted not permitted

Class III permitted permitted permitted (1)

Note: 1 Except for flammable fluids.

5.1.3 Stainless Steels

For sea water piping systems in which sea water may be retained within the piping system in a
stagnant or low flow condition (i.e., less than 1 m/sec), there is a potential for chloride pitting and
the following grades are not to be used for the piping or piping components:
● 304 and 304L stainless steels
● 316 and 316L stainless steels with a molybdenum content of less than 2.5%

Other stainless grades when used are to be confirmed suitable for the application by the
manufacturer.

Where the water spray system is maintained in a dry condition and the system is exposed to
seawater during actual operations of the water spray, 316 and 316L stainless steels with a
molybdenum content of less than 2.5% are acceptable provided there are provisions to
immediately flush the system with fresh water and then dry the internal portions of the system
piping and components. The requirement for flushing and drying of the system and the procedures
to carry out these efforts are to be clearly posted. These requirements are also applicable for piping
systems that are immersed in seawater such as piping passing through seawater tanks or raw water
piping.

5.1.4 Fuel-Oil-Pipe
Steel piping is required for fuel-oil lines and for all pipes passing through fuel-oil tanks.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 37

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

5.3 Copper and Copper alloys

Material specifications for copper and copper alloy pipes and castings are given in Sections 2-3-14, 2-3-16,
2-3-17, 2-3-18, 2-3-19, and 2-3-20 of the ABS Rules for Materials and Welding (Part 2).

Copper and copper alloys are not to be used for fluids having a temperature greater than the following:

Copper-nickel: 300°C (572°F)

High temperature bronze: 260°C (500°F)
All other copper and copper alloys: 200°C (392°F)

Copper and copper alloy pipes are acceptable for Classes I and II systems provided they are of the
seamless drawn type. Seamless drawn and welded copper pipes are acceptable for Class III systems.

However, welded copper and copper alloy pipes are acceptable for Class II non-flammable fluid systems
within the limitations specified in the material specification in accordance with a recognized industrial
standard (e.g., EEMUA 234).

5.5 Brass Pipe

Seamless-drawn brass pipe, unless otherwise specified, is acceptable where the temperature does not
exceed 208°C (406°F).

5.6 Other Materials

Piping containing flammable fluids is to be constructed of steel or other materials approved by ABS. Other
equivalent material with a melting point above 930°C (1706°F) and with an elongation above 12% may be
accepted subject to ABS technical assessment and approval. Aluminum and aluminum alloys which are
characterized by low melting points, below 930°C (1706°F), are considered heat sensitive materials and
are not to be used to convey flammable fluids, except for such piping as arranged inside cargo tanks or heat
exchangers or as otherwise permitted for engine, turbine and gearbox installations, see 4-2-1/7.7 of the
Marine Vessel Rules.

Commentary:

When selecting pumps and piping systems materials, the following should also be taken into consideration:

i To minimize galvanic corrosion, proposed material should be compatible with other materials in the piping system.
ii The proposed material should be able to withstand general and localized corrosion/erosion anticipated during its
service life.
iii The proposed material should be able to withstand selective corrosion e.g., decarburization, denickelification,
dezincification, and graphitic corrosion.

End of Commentary

5.7 Design
5.7.1 Design Pressure and Minimum Thickness
The design pressure and the minimum thickness of pipes are to be determined by the following
equations, due consideration being given to the reduction in thickness at the outer radius of bent
pipes.
KS t − C
W= D−M t−C
WD
t= KS + MW +C

where

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 38

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

K = 20 (200, 2)
W = design pressure, in bar (kgf/cm2, psi). See Note 1. (For feed and blow-off piping, see
4-6-6/3.5, 4-6-6/3.15 and 4-6-6/5.3.1 of the Marine Vessel Rules).
t = minimum thickness of pipe, in mm (in.). See Note 5.
D = actual external diameter of pipe, in mm (in.)
S = maximum allowable fiber stress, in N/mm2 (kgf/mm2, psi), from 4-2-2/5 TABLE 1. See
Note 2.
M = factor from 4-2-2/5 TABLE 1
C = allowance for corrosion, threading, grooving or mechanical strength.
= 1.65 (0.065 in.) for plain-end steel or wrought-iron pipe or tubing up to 115
mm O.D. (4 in. N.P.S.). See Note 3.
= 0.00 mm (0.000 in.) for plain-end steel or wrought-iron pipe or tubing up to 115
mm O.D. (4 in. N.P.S.) used for hydraulic piping systems. See
Note 3.
C = 0.00 mm (0.000 in.) for plain-end steel or wrought-iron pipe or tubing 115 mm
O.D. (4 in. N.P.S.) and larger. See Note 3.
= 1.27 mm (0.05 in.) for all threaded pipe 17 mm O.D. (3/8 in.) and smaller.
= depth of thread h for all threaded pipe over 17 mm O.D. (3/8 in.). See Note 4.
= depth of groove for grooved pipe.
= 0.00 mm (0.000 in.) for plain-end nonferrous pipe or tubing. See Note 3.

Notes:

1 The value of W used in the equations is to be not less than 8.6 bar (8.8 kgf/cm2, 125 psi), except that
for suction and other low-pressure piping of nonferrous material, the actual maximum working
pressure may be applied if a suitable addendum is provided against erosion and outside damage.
However, in no case is the value of W to be less than 3.4 bar (3.5 kgf/cm2, 50 psi) for use in the
equations.

2 Values of S for other materials are not to exceed the stress permitted by ASME B31.1, “Power Piping
Code Section” for marine and utility systems and ASME B31.3, “Process Piping Code Section” for
systems used solely for drilling.

3 Plain-end pipe or tubing includes those joined by any method in which the wall thickness is not
reduced.

4 The depth of thread, h, may be determined by the equation ℎ = 0 . 8/n, where n is the number of
threads per inch, or in metric units by the equation ℎ = 0 . 8n, where n is the number of mm per
thread.

5 If pipe is ordered by its nominal wall thickness, the negative manufacturing tolerance on wall
thickness is to be taken into account.

Commentary:

If the system's service is erosive or corrosive, a corrosion allowance and an erosion allowance as justified by the
designer/manufacturer through analysis or service experience are to be considered in the calculations.

For information, the explanations of allowance c may be found in ASME B31.1 Power Piping Code Section 102.4.

End of Commentary

Commentary:

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 39

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

For information, 12.5% negative manufacturing tolerance is used if information is not available, consistent with
ASTM A530/A530M-18.

End of Commentary

5.7.2 Pipe Bending

Pipe bending is to comply with the requirements in Reference 7A-1-3/11.1.

5.9 Design Pressure and Thickness – Alternative Consideration

The design pressure and the minimum thickness of piping determined from the criteria of applicable
recognized standards are subject to ABS technical assessment and approval.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 40

 Part

Section
Chapter

TABLE 1
2
2
4

Allowable Stress Values S for Piping N/mm2 (kgf/mm2, psi)

Material Tensile Maximum Working Temperature

ABS Gr. Strength
-29°C 372°C 399°C 427°C 455°C 483°C 510°C 538°C 566°C 593°C
ASTM Gr. N/mm2
(0°F) 700°F 750°F 800°F 850°F 900°F 950°F 1000°F 1050°F 1100°F
Nominal kgf/mm2
to
Composition psi
344°C
(650°F)
Machinery and Systems

M 0.8 0.8 0.8 0.8 0.8 0.8 1.0 1.4 1.4 1.4
Pumps and Piping Systems

Gr.1 310 46.9 46.6

53-FBW 31.5 4.78 4.75
Pumps, Pipes, Valves, and Fittings

45000 6800 6500

Gr. 2 330 70.3 68.3 62.8 53.1

A53-A, ERW 33.7 7.17 6.96 6.40 5.41
C, Mn 48000 10200 9900 9100 7700

Gr.2 330 82.8 80.6 73.7 62.1

A53-A, SML 33.7 8.44 8.22 7.52 6.33

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025

C, Mn 48000 12000 11700 10700 9000

Gr.3 415 88.3 84.1 75.8 63.4

A53-B, ERW 42 9.0 8.58 7.73 6.47
C, Mn 60000) 12800 12200 11000 9200

Gr.3 415 103.5 99.2 89.6 74.4

A53-B, SML 42 10.55 10.12 9.14 7.59
C, Mn 60000 15000 14400 13000 10800

Gr.4 330 82.8 80.7 73.7 62.1

A106-A 33.7 8.44 8.23 7.52 6.33
C, Mn, Si 48000 12000 11700 10700 9000

Gr.5 415 103.5 99.2 89.6 74.4

A106-B 42 10.55 10.12 9.14 7.59
C, Mn, Si 60000 15000 14400 13000 10800

41
4-2-2
 Part

Section
Chapter

Material Tensile Maximum Working Temperature

2
2
4

ABS Gr. Strength

-29°C 372°C 399°C 427°C 455°C 483°C 510°C 538°C 566°C 593°C
ASTM Gr. N/mm2
(0°F) 700°F 750°F 800°F 850°F 900°F 950°F 1000°F 1050°F 1100°F
Nominal kgf/mm2
to
Composition psi
344°C
(650°F)

Gr.6 380 95.1 95.1 95.1 93.1 90.3

A355-P1 39 9.70 9.70 9.70 9.49 9.21
1/2 Mo 55000 13800 13800 13800 13500 13100
Machinery and Systems

Gr. 7 380 95.1 95.1 95.1 93.1 90.3 88.3 63.4 40.7
Pumps and Piping Systems

A335-P2 39 9.70 9.70 9.70 9.49 9.21 9.0 6.47 4.15

1/2 Cr 1/2 Mo 55000 13800 13800 13800 13500 13100 12800 9200 5900
Pumps, Pipes, Valves, and Fittings

Gr. 8 330 70.3 68.3 62.8 53.1

A135-A 33.7 7.17 6.96 6.40 5.41
48000 10200 9900 9100 7700

Gr. 9 415 88.3 84.1 75.8 63.4

A135-B 42 9.0 8.58 7.73 6.47
60000 12800 12200 11000 9200

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025

Gr.11 415 103.5 103.5 103.5 103.5 99.2 90.3 75.8 45.4 28.2 20.7
A335-P11 42, 10.55, 10.55, 10.55, 10.55, 10.12, 9.21, 7.73, 4-64, 2.88, 2.11,
1-1/4 Cr 1/2 Mo 60000 15000 15000 15000 15000 14400 13100 11000 6600 4100 3000

Gr. 12 415 103.5 103.5 103.5 101.7 91.9 90.3 75.8 45.5 28.2 19.3
A335-P12 42 10.55 10.55 10.55 10.37 9.98 9.21 7.73 4.64 2.88 1.97
1 Cr 1/2 Mo 60000 15000 15000 15000 14750 14200 13100 11000 6600 4100 2800

Gr. 13 415 103.5 103.5 103.5 103.5 99.2 90.3 75.8 53.7 35.9 28.9
A335-P22 42 10.55 10.55 10.55 10.55 10.12 9.21, 7.73 5.48 3.66 2.95
2-1/4 Cr 1 Mo 60000 15000 15000 15000 15000 14400 13100 11000 7800 5200 4200

Notes:
1 Intermediate values of S and M may be determined by interpolation.
2 For grades of pipe other than those given in this Table, S values may be obtained from ASME B31.1 Pressure Piping Code Section.

42
4-2-2
 Part

Section
Chapter

3 Consideration to be given to the possibility of graphite formation in the following steels: Carbon steel above 427°C (800°F); carbon-molybdenum
2
2
4

steel above 468°C (875°F); chrome-molybdenum steel (with chromium under 0.60%) above 524°C (975°F).
4 For low temperature service, see 2-3-2/11 and 2-3-13 of the ABS Rules for Materials and Welding (Part 2).
Machinery and Systems
Pumps and Piping Systems
Pumps, Pipes, Valves, and Fittings

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025

43
4-2-2
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

7 Plastic Pipes

7.1 General
Note:

Text in italics comes from IMO Resolution. A.753(18), as amended by IMO Resolutions. MSC.313(88) and IMO Res.
MSC.399(95) and are required for classification. The parts which are classification requirements and not based on the Codes
are presented in non-italics type style etc. The term “shall be” is to be understood to read as “is to be” or “are to be” unless
otherwise specified, the term “Administration” is to be read as “ABS”.

Pipes and piping components made of thermoplastic or thermosetting plastic materials, with or without
reinforcement, are acceptable in piping systems referred to in 4-2-2/7.19 TABLE 2, subject to compliance
with the following requirements.

i) These requirements are applicable to piping systems on offshore units, including pipe joints and
fittings, made predominately of other material than metal.
ii) The use of mechanical joints approved for the use in metallic piping systems only is not permitted.
iii) Piping systems intended for non-essential services are to meet only the requirements of recognized
standards and 4-2-2/7.5.2, 4-2-2/7.5.8, 4-2-2/7.7 and 4-2-2/7.9.
Note: “Essential services” are those services essential for propulsion and steering and safety of the unit as specified in
4-3-1/3.5.

7.2 Definitions
Design pressure means the maximum working pressure which is expected under operation conditions or
the highest set pressure of any safety valve or pressure relief device on the system, if fitted.

Essential services, refer to 4-1-1/3.5.

Essential to the safety of the unit means all piping systems that in the event of failure will pose a threat to
personnel and the unit.

Fire endurance means the capability of piping to maintain its strength and integrity (i.e. capable of
performing its intended function) for some predetermined period of time while exposed to fire.

Fittings means bends, elbows, fabricated branch pieces etc. of plastic materials.

Industrial equipment means equipment used in non-marine systems i.e. topsides process system, drilling
system, well-test system, subsea mining system.

Joint means the location at which two pieces of pipe or a pipe and a fitting are connected together. The
joint is made by adhesive bonding, laminating, welding, flanges and mechanical joints.

Nominal pressure means the maximum permissible working pressure which is determined in accordance
with the requirements in 4-2-2/7.5.2.

Pipes/piping systems mean those made of plastic(s) and include the pipes, fittings, system joints, method of
joining and any internal or external liners, coverings and coatings required to comply with the performance
criteria.

Plastic(s) means both thermoplastic and thermosetting plastic materials with or without reinforcement,
such as PVC and fiber reinforced plastics - FRP. Plastic includes synthetic rubber and materials of similar
thermo/mechanical properties.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 44

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

7.3 Plans and Data to be Submitted

Rigid plastic pipes are to be in accordance with a recognized national or international standard acceptable
to ABS. Specification for the plastic pipe, including thermal and mechanical properties and chemical
resistance, is to be submitted for review, together with the spacing of the pipe supports.

The following information for the plastic pipes, fittings and joints is to be also submitted for review.

7.3.1 General Information

i) Pipe and fitting dimensions
ii) Maximum internal and external working pressure
iii) Working temperature range
iv) Intended services and installation locations
v) Level of fire endurance
vi) Electrically conductive
vii) Intended fluids
viii) Limits on flow rates
ix) Serviceable life
x) Installation instructions
xi) Details of marking
7.3.2 Drawings and Supporting Documentation
i) Certificates and reports for relevant tests previously carried out. See 4-2-2/7.9
ii) Details of relevant standards. See 4-2-2/Table 3 and 4-2-2/Table 4
iii) All relevant design drawings, catalogues, data sheets, calculations and functional
descriptions
iv) Fully detailed sectional assembly drawings showing pipe, fittings and pipe connections.
v) Documentation verifying the certification of the manufacturer’s quality system and that
the system addresses the testing requirements in 4-2-2/7.5.1 through 4-2-2/7.5.8. See
4-2-2/7.9 for manufacturing requirements of plastic pipes.
7.3.3 Materials
All material used in the production of plastic piping are to be accompanied by datasheets of
chemistry, mechanical and physical properties. Where it is required by the operating conditions,
the corrosion, ageing and wear resistance characteristics of these pipes are to also be identified.
The following are to be submitted for review as a minimum.

i) Type of plastic, e.g., PVC, CPVC, HDPE.

ii) Resin type
iii) Catalyst and accelerator types and reinforced polyester resin pipes and for epoxy-based
piping the hardener and the mixing ratio to resin
iv) All fiber reinforcements are to be identified. In case of filament winding process the
roving is to carry a reference number related to mass per unit area or by the strand count
(Tex System or other recognized yarn numbering system) ) or alternatively the specific
weight per unit is to be detailed.
v) Full information regarding the type of gel-coat or thermoplastic liner employed during
construction, as appropriate

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 45

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

vi) Cure/post-cure conditions. The cure and post-cure temperatures and times employ for
given resin/reinforcement ratio
vii) Winding angle and orientation of fibers as well as the ratio of resin to fibers by volume or
weight.
viii) Joint bonding procedures and qualification tests results. See 4-2-2/7.11
ix) Inspection procedures utilized during production and at final stage to verify the soundness
of the structure and that the design requirements are fulfilled, see 7A-1-3/13.5.

7.5 Design
7.5.1 Strength
7.5.1.1

The strength of the pipes is to be determined by a hydrostatic test failure pressure of a pipe
specimen under the standard conditions: Atmospheric pressure equal to 1 bar (1 kgf/cm2, 14.5
psi), Relative humidity 30%,

Environmental and carried fluid temperature 2.98 bar (25°C, 77°F).

7.5.1.2

The strength of fittings and joints is to be not less than that of the pipes.

7.5.1.3

The maximum permissible working pressure is to be specified with due regard for maximum
possible working temperatures in accordance with manufacturer’s recommendations.

7.5.2 Nominal Pressure

The nominal pressure is to be determined from the following conditions:

7.5.2.1 Internal Pressure

A pipe is to be designed for an internal pressure to be of the smaller of the following:

Pstℎ Pltℎ
pn int = 4 or pn int = 2.5

where

Pstℎ = short-term hydrostatic test failure pressure

Pltℎ = long-term hydrostatic test failure pressure (> 100,000 hours)

7.5.2.2 External Pressure

External pressure is to be considered for any installation which may be subject to vacuum
conditions inside of the pipe or a head of liquid on the outside of the pipe and for any pipe
installation required to remain operational in case of flooding damage, as per Regulation 8-1 of
SOLAS Chapter II-1, as amended, or for any pipes that would allow progressive flooding to other
compartments through damaged piping or through open ended pipes in the compartments.

For an external pressure:

Pn ext ≤ Pcol /3

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 46

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

where

Pcol = pipe collapse pressure.

In no case is the pipe collapse pressure to be less than 3 bar.

The maximum working external pressure is a sum of the vacuum inside the pipe and a head of
liquid acting on the outside of the pipe.

The collapse test failure pressure is to be verified experimentally or determined by a combination

of testing and calculation methods, which are to be submitted to ABS for approval.

7.5.3 Wall Thickness

Notwithstanding the requirements of 4-2-2/7.5.2.1 or 4-2-2/7.5.2.2 as applicable, the pipe or pipe
layer minimum wall thickness is to follow recognized standards. In the absence of standards for
pipes not subject to external pressure, the requirements of 4-2-2/7.5.2.2 are to be met.

7.5.4 Axial Strength

7.5.4(a) The sum of the longitudinal stresses due to pressure, weight and other dynamic and
sustained loads is not to exceed the allowable stress in the longitudinal direction. Forces due to
thermal expansion, contraction and external loads, where applicable, are to be considered when
determining longitudinal stresses in the system.

7.5.4(b) In the case of fiber reinforced plastic pipes, the sum of the longitudinal stresses is not to
exceed one-half of the nominal circumferential stress derived from the maximum internal pressure
determined according to 4-2-2/7.5.1, through 4-2-2/7.5.3, unless the minimum allowable
longitudinal stress is verified experimentally or by a combination of testing and calculation
methods.

7.5.5 Temperature
The design temperature of a pipe is to be in accordance with the manufacturer’s recommendations,
but in each case it is to be at least 20°C (36°F) lower than the minimum heat distortion
temperature of the pipe material determined according to ISO 75 method A or equivalent (e.g.
ASTMD648). The minimum heat distortion temperature is not to be less than 80°C (176°F).

Where low temperature services are considered, the material properties are to be assessed for its
suitability. Ferrous materials used in piping systems operating at lower than –18°C (0°F) are to
comply with the requirements in Section 2-3-13 of the ABS Rules for Materials and Welding (Part
2). Alternatively, material grades based on recognized codes or standards suitable for low
temperature applications are acceptable.

7.5.6 Impact Resistance

Plastic pipes and joints are to have a minimum resistance to impact in accordance with a
recognized national or international standard such as ASTM D2444, ASTM D6110, ASTM
F2231, ISO14692-2, Clause 6.4.3 or other equivalent standards as appropriate for the resin type.
ASTM D256 may also be considered, provided the average minimum required impact resistance is
961 J/m of width (18 ft-lbf/in of width) as per Test Method E or a value acceptable to the
Surveryor.

7.5.7 Fire Endurance - Design and Testing

Pipes and their associated joints and fittings whose integrity is essential to the safety of units,
including plastic piping required by Regulation 21.4 of SOLAS Chapter II-2 as amended by IMO
Resolutions up to MSC.421(98) (hereinafter the same) to remain operational after a fire casualty,
are required to meet the minimum fire endurance requirements of Appendix 1 or 2, as applicable,
of IMO Resolution A.753(18), as amended by IMO Resolutions MSC.313(88) and MSC.399(95).

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 47

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

Three different levels of fire endurance for plastic are given. These levels consider the different
severities of consequences resulting from the loss of system integrity for the various applications
and locations. The highest fire endurance standard (level 1) will ensure the integrity of the system
during a fullscale hydrocarbon fire and is particularly applicable to systems where loss of
integrity may cause outflow of flammable liquids or spread of fire through duct piping and worsen
the fire situation. The intermediate fire endurance standard (level 2) intends to ensure the
availability of systems essential to the safe operation of the unit after a fire of short duration,
allowing the system to be restored after the fire has been extinguished. The lowest level (level 3) is
considered to provide the fire endurance necessary for a water-filled piping system to survive a
local fire of short duration. The system’s functions should be capable of being restored after the
fire has been extinguished.

4-2-2/7.19 TABLE 2 Fire Endurance Requirements Matrix specifies the fire endurance
requirements piping based upon system and location.

Note: “Essential to the safety of unit” means all piping systems that in event of failure will pose a threat to
personnel, the unit and the environment. Examples for piping systems essential to the safety are provided
by 4-2-2/TABLE 2.
i) Piping systems essential to the safety of the unit and those systems outside machinery
spaces where the loss of integrity may cause outflow of flammable fluid and worsen the
fire situation should be designed to endure a fully developed hydrocarbon fire for a long
duration without loss of integrity under dry conditions. Piping having passed the fire
endurance test specified in Appendix 1 of IMO Resolution A.753(18), as amended by
IMO Resolutions MSC.313(88) and MSC.399(95) for a duration of a minimum of one
hour without loss of integrity in the dry condition is considered to meet level 1 fire
endurance standard (L1). Level 1W – Piping systems similar to Level 1 systems except
these systems do not carry flammable fluid or any gas and a maximum 5% flow loss in
the system after exposure is acceptable (L1W). (See 4-2-2/7.13).
ii) Piping systems essential to the safe operation of the unit should be designed to endure a
fire without loss of the capability to restore the system function after the fire has been
extinguished. Piping having passed the fire endurance test specified in Appendix 1 of
IMO Resolution A.753(18), as amended by IMO Resolutions MSC.313(88) and
MSC.399(95) for a duration of a minimum of 30 minutes in the dry condition is
considered to meet level 2 fire endurance standard (L2). Level 2W – Piping systems
similar to Level 2 systems except a maximum 5% flow loss in the system after exposure
is acceptable (L2W). (See 4-2-2/7.13).
iii) Piping systems essential to the safe operation of the unit should be designed to endure a
fire without loss of the capability to restore the system function after the fire has been
extinguished. Piping having passed the fire endurance test specified in Appendix 2 of
IMO Resolution A.753(18) as amended by IMO Resolutions MSC.313(88) and
MSC.399(95) for a duration of a minimum of 30 minutes in the wet condition is
considered to meet level 3 fire endurance standard (L3). (See 4-2-2/7.15).
iv) Plastic (GRP/FRP) materials used in firewater systems are to pass Level 1 fire endurance
test. However, a plastic piping material that passes Level 3 fire endurance requirements in
lieu of Level 1 requirements may be considered when the additional conditions listed
below are fully met and accepted by the Flag Administration

The following additional requirements are applicable to the plastic material piping that
passes Level 3 in lieu of Level 1 fire endurance tests and is used in the fire main system:

a) Plastic piping is to be located on open decks, on the exterior perimeter of the

units and shielded by primary structural members from potential sources of fire
that may occur on or emanate from the units.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 48

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

b) Plastic piping is to be located so that pooling of flammable liquids below the

piping is not possible. A properly designed drainage system may be provided to
mitigate the pooling of flammable liquid below the piping system.
c) The firewater system design is to be such that the plastic sections are
continuously maintained in the wet condition.
d) The firewater system is to be equipped with an adequate number of isolation and
cut-off valves such that, if a section of the system is to fail, it can be isolated, and
the remainder of the system is still capable of supplying firewater.
v) Plastic (GRP/FRP) materials used in water spray (deluge) systems for process equipment
system are to pass Level 1 fire endurance test. However, a plastic piping material that
passes Level 3 Modified Test – Level 3 WD fire endurance requirements in lieu of Level
1 requirements may be considered acceptable when the following design conditions are
fully met and accepted by the Flag Administration:
a) Plastic piping is installed in open decks or semi-enclosed locations.
b) The water spray piping system is to meet the Level 3 fire endurance requirements
as specified in 4-2-2/7.15.
c) In addition to meeting the Level 3 fire endurance requirements, the water spray
piping system is to meet the requirements of the wet/dry fire endurance testing
specified in 4-2-2/7.16.
d) Other wet/dry fire endurance test methods that may be equivalent to or more
severe than the methods described in 4-2-2/7.16, are acceptable on a case-by-case
basis.
e) An automatic fire detection system is to be installed in areas protected by the
water spray system.
f) The water spray system is to be designed to activate automatically upon detection
by the automatic fire detection system.
g) Each section or area served by a water spray system is to be capable of being
isolated by one (1) water supply valve only. The stop valve in each section is to
be readily accessible, and its location clearly and permanently indicated.
h) The design of the water spray system is to be such that upon fire detection, the
time required to have water flowing through the hydraulically most remote
nozzle is less than one (1) minute. This requirement is to be verified by system
testing at the time of installation and at subsequent annual inspections.
i) The water spray system piping is to be located downstream of the water supply
valve.
j) All piping upstream of the water supply valve is to meet the requirements for fire
main and water spray systems as specified in 4-2-2/7 or be of metallic material.
Commentary:

A risk analysis, subject to the approval by ABS Engineering, may also be proposed to justify the use of Level 3 for
fire main systems and Level 3 WD for water spray (deluge) systems. In addition, considering the diversity of
offshore facilities, the risk analysis may substitute the conditions in 4-2-2/7.5.7 iv) and v) above provided that the
risk analysis is conducted to the satisfaction of ABS Engineering and accepted by the Flag Administration.

End of Commentary

Where a fire protective coating of pipes and fittings is required for achieving the fire endurance
standards required, the following requirements apply.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 49

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

i) Pipes are to be delivered from the manufacturer with the protective coating applied, with
on-site application limited to that necessary for installation purposes (i.e., joints). See
7-1-3/13.5.3.vii regarding the application of the fire protection coating on joints.
ii) The fire protection properties of the coating are not to be diminished when exposed to salt
water, oil or bilge slops. It is to be demonstrated that the coating is resistant to products
likely to come in contact with the piping.
iii) In considering fire protection coatings, such characteristics as thermal expansion,
resistance against vibrations and elasticity are to be taken into account.
iv) The fire protection coatings are to have sufficient resistance to impact to retain their
integrity.
v) Random samples of pipe are to be tested to determine the adhesion qualities of the
coating to the pipe.
7.5.7(a) Test Specimens
i) Representative Specimens
Unless instructed otherwise by the flag Administration, fire endurance tests are to be
carried out with specimen representative for pipes, joints and fittings.

Pipes:

● For sizes with outer diameter < 200 mm: The minimum outer diameter and wall
thickness
● For sizes with outer diameter ≥ 200 mm: One test specimen for each category of t/d
(D = outer diameter, t = structural wall thickness). A scattering of ±10% for t/D is
regarded as the same group. Minimum size approved is equal to the diameter of
specimen successfully tested.

Joints:

● Each type of joint applicable for applied fire endurance level tested on pipe to pipe
specimen.
Note:

A test specimen incorporating several components of a piping system may be tested in a single test.

Test conditions are most demanding for minimum wall thickness and thus larger wall thickness is
covered. A key factor determining the fire performance of a pipe component variant is the thickness-to-
diameter (t/D) ratio and whether it is larger or smaller than that of the variant which has been fire-tested.
If fire-protective coatings or layers are included in the variant used in the fire test, only variants with the
same or greater thickness of protection, regardless of the (t/D) ratio, are to be qualified by the fire test.

ii) Pressure inside the test specimen

Means are to be provided to maintain a constant media pressure inside the test specimen
during the fire test as specified in 4-2-2/7.5.8 or 4-2-2/7.5.9. During the test it is not
permitted to replace media drained by fresh water or nitrogen.

7.5.8 Flame Spread

7.5.8(a) Plastic Pipes.
All pipes, except those fitted on open decks and within tanks, cofferdams, void spaces, pipe
tunnels and ducts if separated from accommodation, permanent manned areas and escape ways by
means of an A class bulkhead, are to have low surface flame spread characteristics. The test
procedures in 4-2-2/7.17 in accordance with IMO Resolution A.753(18) Guidelines for the
application of plastic pipes on ships, as amended by Resolution MSC.399(95), are to be used for

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 50

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

determining the flame spread characteristics. Piping materials giving average values for all of the
flame spread criteria not exceeding the values listed in Resolution A.753(18), as amended by
Appendix of Resolution MSC.399(95), are considered to meet the requirements for low flame
spread.

Surface flame spread characteristics are to be determined using the procedure given in the 2010
FTP Code, Annex 1, Part 5 with regard to the modifications due to the curvilinear pipe surfaces as
also listed in Appendix 3 of IMO Resolution A.753(18), as amended by IMO Resolutions
MSC.313(88) and MSC.399(95).

Surface flame spread characteristics may also be determined using the test procedures given in
ASTM D635, or in other equivalent national standards provided such test is acceptable to the
Administration.

Under the procedure of ASTM D635, a maximum burning rate of 60 mm/min applies. In case of
adoption of other national equivalent standards, the relevant acceptance criteria are to be defined.

7.5.8(b) Multi-core Metallic Tubes Sheathed by Plastic Materials

The multi-core tubes in "bundles" made of stainless steel or copper tubes covered by an outer
sheath of plastic material are to comply with the flammability test criteria of IEC 60332-3-22 or
60332-3-21, for Category A or A F/R, respectively. Alternatively, the tube bundles complying
with at least the flammability test criteria of 60332-1-2 or a test procedure equivalent thereto are
acceptable provided they are installed in compliance with approved fire stop arrangements.

7.5.9 Electrical Conductivity

7.5.9(a) Where plastic piping is to be electrically conductive, the resistance of the pipes and
fittings is not to exceed 1 ×105Ω/m (3 ×104Ω/ft).

7.5.9(b) Regardless of the fluid being conveyed, plastic pipes are to be electrically conductive if
the piping passes through a hazardous area.

7.5.9(c) If the pipes and fittings are not homogeneously conductive, the conductive layers are to be
protected against the possibility of spark damage to the pipe wall.

7.5.10 Marking
Marking on the plastic piping is to be in accordance with the requirements in 7A-1-3/13.5.

Commentary:

When proposing the use of plastic pipes and fittings, in addition to considering maximum internal working
pressure and the external working pressures, other requirements, as applicable, are also to be considered:

i Temperature range
ii Installation locations
iii Eelectrical conductivity (particularly when installed in a hazardous area/location)
iv Level of fire endurance and
v Manufacturer’s recommendations, if any, (available through the manufacturer's specifications and
catalog).

End of Commentary

7.7 Installation of Plastic Pipes

Information to verify compliance with the following requirements is to be submitted for review. Refer also
to 7A-1-3/13.5.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 51

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

7.7.1 Supports
7.7.1(a) Selection and spacing of pipe supports in shipboard systems are to be determined as a
function of allowable stresses and maximum deflection criteria. Support spacing is not to be
greater than the pipe manufacturer’s recommended spacing. The selection and spacing of pipe
supports are to take into account pipe dimensions, length of the piping, mechanical and physical
properties of the pipe material, mass of pipe and contained fluid, external pressure, maximum
working temperature, thermal expansion effects, loads due to external forces, thrust forces, water
hammer and vibrations to which the system may be subjected. Combination of these loads are to
be checked.

7.7.1(b) The supports are to allow for relative movement between the pipes and the unit’s
structure, having due regard to the difference in the coefficients of thermal expansion and
deformations of the unit’s hull and its structure.

7.7.1(c) When calculating the thermal expansion, the system maximum working temperature and
the temperature at which assembling is performed are to be taken into account.

7.7.2 External Loads

When installing the piping, allowance is to be made for temporary point loads, where applicable.
Such allowances are to include at least the force exerted by a load (person) of 980 N (100 kgf, 220
lbf) at mid-span on any pipe more than 100 mm (4 in.) nominal diameter.

Besides providing adequate robustness for all piping including open-ended piping, a minimum
wall thickness, complying with 4-2-2/7.5.3, may be increased taking into account the conditions
encountered during service onboard the unit.

Pipes are to be protected from mechanical damage where necessary.

7.7.3 Shell Connections

Where plastic pipes are permitted in systems connected to the shell of the unit, the valves and the
pipe connection to the shell are to be metallic. The side shell valves are to be arranged for remote
control from outside of the space in which the valves are located. For further details of the shell
valve installation, their connections and material, refer to 4-2-2/21.

7.7.4 Bulkhead and Deck Penetrations

7.7.4(a) The integrity of watertight bulkheads and decks is to be maintained where plastic pipes
pass through them.

7.7.4(b) Where plastic pipes pass through "A" or "B" class divisions, arrangements are to be made
so that the fire endurance is not impaired. For test procedures, see 7A-1-3/13.5. These
arrangements are to be tested in accordance with, Recommendations for fire test procedures for
“A”, “B” and “F” bulkheads specified in Part 3 of Annex 1 to the 2010 FTP Code (Resolution
MSC.307(88) as amended by Resolution MSC.437(99)).

7.7.4(c) If the bulkhead or deck is also a fire division and destruction by fire of plastic pipes may
cause inflow for liquid from tank, a metallic shut-off valve operable from above the bulkhead deck
is to be fitted at the bulkhead or deck.

7.7.4(d) When plastic pipes pass through watertight bulkheads or decks, the watertight integrity of the
bulkhead or deck is to be maintained. For pipes not able to satisfy the requirements in 4-2-2/7.5.2.2, a
metallic shut-off valve operable from above the main deck is to be fitted at the bulkhead or deck.
7.9 Manufacturing of Plastic Pipes
The manufacturer is to have a quality system and be certified in accordance with 1B-1-A2/5.3 and 1B-1-
A2/5.5 of the ABS Rules for Conditions of Classification – Offshore Units and Structures (Part 1B) or ISO
9001 (or equivalent). The quality system is to consist of elements necessary for pipes and components are

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 52

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

to be produced with consistent and uniform mechanical and physical properties in accordance with
recognized standards, including testing to demonstrate the compliance of plastic pipes, fittings and joints
with 4-2-2/7.5.1 through 4-2-2/7.5.8 and 4-2-2/7.19, as applicable.

Where the manufacturer does not have a certified quality system in accordance with 1B-1-A2/5.3 and
1B-1-A2/5.5 of the ABS Rules for Conditions of Classification - Offshore Units and Structures (Part 1B)
or ISO 9001 (or equivalent), the tests in 4-2-2/7.5.1 through 4-2-2/7.5.8 and 4-2-2/7.19, as applicable, is
required using samples from each batch of pipes being supplied for use aboard the unit and are to be
carried out in the presence of the Surveyor.

Each length of pipe and each fitting is to be tested at the manufacturer’s production facility to a hydrostatic
pressure not less than 1.5 times the internal design pressure of the pipe in 4-2-2/7.5.1. Alternatively, for
pipes and fittings not employing hand layup techniques, the hydrostatic pressure test may be carried out in
accordance with the hydrostatic testing requirements stipulated in the recognized national or international
standard to which the pipe or fittings are manufactured, provided that there is an effective quality system in
place.

Depending upon the intended application, ABS reserves the right to require the hydrostatic pressure testing
of each pipe and/or fitting.

If the facility does not have a certified quality system in accordance with 1B-1-A2/5.3 and 1B-1-A2/5.5 of
the ABS Rules for Conditions of Classification – Offshore Units and Structures (Part 1B) or ISO 9001 (or
equivalent), then the production testing is to be witnessed by the Surveyor.

The manufacturer is to provide documentation certifying that all piping and piping components supplied
are in compliance with the requirements of 4-2-2/7.

7.11 Plastic Pipe Bonding Procedure Qualification

7.11.1 Procedure Qualification Requirements
7.11.1(a) To qualify joint bonding procedures, the tests and examinations specified herein are to be
successfully completed. The procedure for making bonds is to include the following:

i) Materials used
ii) Tools and fixtures
iii) Environmental requirements
iv) Joint preparation requirements
v) Cure temperature
vi) Dimensional requirements and tolerances
vii) Test acceptance criteria for the completed assembly

7.11.1(b) Any change in the bonding procedure which will affect the physical and mechanical
properties of the joint will require the procedure to be re-qualified.

7.11.2 Procedure Qualification Testing

7.11.2(a) A test assembly is to be fabricated in accordance with the procedure to be qualified and
it is to consist of at least one pipe-to-pipe joint and one pipe-to-fitting joint. When the test
assembly has been cured, it is to be subjected to a hydrostatic test pressure of 2.5 times the design
pressure of the test assembly for not less than one hour. No leakage or separation of joints is to be
allowed. The test is to be conducted so that the joint is loaded in both longitudinal and
circumferential direction.

7.11.2(b) Selection of pipes used for test assembly is to be in accordance with the following:

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 53

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

i) When the largest size to be joined is 200 mm (8 in.) nominal outside diameter or smaller,
the test assembly is to be the largest pipe size to be joined.
ii) When the largest size to be joined is greater than 200 mm (8 in.) nominal outside
diameter, the size of the test assembly is to be either 200 mm (8 in.) or 25% of the largest
piping size to be joined, whichever is greater.

7.11.2(c) When conducting performance qualifications, each bonder and each bonding operator
are to make up test assemblies, the size and number of which are to be as required above.

7.13 Tests by the Manufacturer – Fire Endurance Testing of Plastic Piping in the Dry
Condition (For Level 1 and Level 2)
7.13.1 Test Method
7.13.1(a) The specimen is to be subjected to a furnace test with fast temperature increase similar
to that likely to occur in a fully developed liquid hydrocarbon fire. The time/temperature is to be
as follows:

Time Temperature

°C °F

At the end of 5 minutes 945 1733

At the end of 10 minutes 1033 1891

At the end of 15 minutes 1071 1960

At the end of 30 minutes 1098 2008

At the end of 60 minutes 1100 2012

7.13.1(b) The accuracy of the furnace control is to be as follows:

i) During the first 10 minutes of the test, variation in the area under the curve of mean
furnace temperature is to be within ±15% of the area under the standard curve.
ii) During the first 30 minutes of the test, variation in the area under the curve of mean
furnace temperature is to be within ±10% of the area under the standard curve.
iii) For any period after the first 30 minutes of the test, variation in the area under the curve
of mean furnace temperature is to be within ±5% of the area under the standard curve.
iv) At any time after the first 10 minutes of the test, the difference in the mean furnace
temperature from the standard curve is to be within ±100°C (±180°F).

7.13.1(c) The locations where the temperatures are measured, the number of temperature
measurements and the measurement techniques are to be approved by ABS, taking into account
the furnace control specification as set out in paragraphs 7.1 to 7.4 of part 3 of annex 1 to the 2010
FTP Code.

7.13.2 Test Specimen

7.13.2(a) The test specimen is to be prepared with the joints and fittings intended for use in the
proposed application.

7.13.2(b) The number of specimens is to be sufficient to test typical joints and fittings, including
joints between non-metal and metal pipes and metal fittings to be used.

7.13.2(c) The ends of the specimen are to be closed. One of the ends is to allow pressurized
nitrogen to be connected. The pipe ends and closures may be outside of the furnace.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 54

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

7.13.2(d) The general orientation of the specimen is to be horizontal and is to be supported by one
fixed support with the remaining supports allowing free movement. The free length between
supports is not to be less than eight times the pipe diameter.

7.13.2(e) Most materials will require a thermal insulation to pass this test. The test procedure is to
include the insulation and its covering.

7.13.2(f) If the insulation contains or is liable to absorb moisture, the specimen is not to be tested
until the insulation has reached an air dry-condition defined as equilibrium with an ambient
atmosphere of 50% relative humidity at 20 ± 5°C (68 ± 9°F). Accelerated conditioning is
permissible, provided the method does not alter the properties of the component material. Samples
are to be used for moisture content determination and conditioned with the test specimen. These
samples are to be so constructed as to represent the loss of water vapor from the specimen having
similar thickness and exposed faces.

7.13.3 Test Condition

A nitrogen pressure inside the test specimen in to be maintained automatically at 0.7 ± 0.1 bar (0.7
± 0.1 kgf/cm2, 10 ± 1.5 psi) during the test. Means are to be provided to record the pressure inside
of the pipe and the nitrogen flow into and out of the specimen in order to indicate leakage.

7.13.4 Acceptance Criteria

7.13.4(a) During the test, no nitrogen leakage from the sample is to occur.

7.13.4(b) After termination of the furnace test, the test specimen together with fire protective
coating, if any, is to be allowed to cool in still air to ambient temperature and then tested to the
design pressure of the pipes, as defined in 4-2-2/7.5.1 and 4-2-2/7.5.2. The pressure is to be held
for a minimum of 15 minutes. Pipes without leakage qualify as Level 1 or 2 depending on the test
duration. Pipes with negligible leakage (i.e., not exceeding 5% flow loss) qualify as Level 1W or
Level 2W depending on the test duration. Where practicable, the hydrostatic test is to be
conducted on bare pipe (i.e., coverings and insulation removed) so that any leakage will be
apparent.

7.13.4(c) Alternative test methods and/or test procedures considered to be at least equivalent,
including open pit testing method, may be accepted in cases where the pipes are too large for the
test furnace.

7.15 Test by Manufacturer – Fire Endurance Testing of Water-Filled Plastic Piping (For
Level 3)
7.15.1 Test Method
7.15.1(a) A propane multiple burner test with a fast temperature increase is to be used.

7.15.1(b) For piping up to and including 152 mm (6 in.) O.D., the fire source is to consist of two
rows of five burners, as shown in 4-2-2/7.15.1 FIGURE 2. A constant heat flux averaging 113.6
kW/m2 (36,000 BTU/hr-ft2) ± 10% is to be maintained 12.5 + 1 cm (5 ± 0.4 in.) above the
centerline of the burner array. This flux corresponds to a pre-mix flame of propane with a fuel
flow rate of 5 kg/hr (11 lb/hr) for a total heat release of 65 kW (3700 BTU/min.). The gas
consumption is to be measured with an accuracy of at least ± 3% in order to maintain a constant
heat flux. Propane with a minimum purity of 95% is to be used.

7.15.1(c) For piping greater than 152 mm (6 in.) O.D., one additional row of burners is to be
included for each 51 mm (2 in.) increase in pipe diameter. A constant heat flux averaging 113.6
kW/m2 (36,000 BTU/hr-ft2) ± 10% is to be maintained 12.5 + 1 cm (5 ± 0.4 in.) above the
centerline of the burner array. This fuel flow is to be increased as required to maintain the
designated heat flux.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 55

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

7.15.1(d) The burners are to be type "Sievert No. 2942" or equivalent which produces an air
mixed flame. The inner diameter of the burner heads is to be 29 mm (1.14 in.). See 4-2-2/7.15.1
FIGURE 1. The burner heads are to be mounted in the same plane and supplied with gas from a
manifold. If necessary, each burner is to be equipped with a valve in order to adjust the flame
height.

7.15.1(e) The height of the burner stand is also to be adjustable. It is to be mounted centrally
below the test pipe with the rows of burners parallel to the pipe’s axis. The distance between the
burner heads and the pipe is to be maintained at 12.5 ± 1 cm (5 ± 0.4 in.) during the test. The free
length of the pipe between its supports is to be 0.8 ± 0.05 m (31.5 ± 2 in.). See 4-2-2/7.15.1
FIGURE 2.

FIGURE 1
Fire Endurance Test Burner Assembly

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 56

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

FIGURE 2
Fire Endurance Test Stand With Mounted Sample

7.15.2 Test Specimen

7.15.2(a) Each pipe is to have a length of approximately 1.5 m (5 ft).

7.15.2(b) The test pipe is to be prepared with permanent joints and fittings intended to be used.
Only valves and straight joints versus elbows and bends are to be tested as the adhesive in the joint
is the primary point of failure.

7.15.2(c) The number of pipe specimens is to be sufficient to test all typical joints and fittings.

7.15.2(d) The ends of each pipe specimen are to be closed. One of the ends is to allow pressurized
water to be connected.

7.15.2(e) If the insulation contains or is liable to absorb moisture, the specimen is not to be tested
until the insulation has reached an air dry-condition defined as equilibrium with an ambient
atmosphere of 50% relative humidity at 20 ± 5°C (68 ± 9°F). Accelerated conditioning is
permissible, provided the method does not alter the properties of the component material. Samples
are to be used for moisture content determination and conditioned with the test specimen. These
samples are to be so constructed as to represent the loss of water vapor from the specimen having
similar thickness and exposed faces.

7.15.2(f) The pipe samples are to rest freely in a horizontal position on two V-shaped supports.
The friction between pipe and supports is to be minimized. The supports may consist of two
stands, as shown in 4-2-2/7.15.1 FIGURE 2.

7.15.2(g) A relief valve is to be connected to one of the end closures of each specimen.

7.15.3 Test Conditions

7.15.3(a) The test is to be carried out in a sheltered test site in order to prevent any draft
influencing the test.

7.15.3(b) Each pipe specimen is to be completely filled with deaerated water to exclude air
bubbles.

7.15.3(c) The water temperature is not to be less than 15°C (59°F) at the start and is to be
measured continuously during the test. The water is to be stagnant and the pressure maintained at
3 ± 0.5 bar (3.1 ± 0.5 kgf/cm2, 43.5 ± 7.25) during the test.

7.15.4 Acceptance Criteria

7.15.4(a) During the test, no leakage from the sample(s) is to occur, except that slight weeping
through the pipe wall may be accepted.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 57

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

7.15.4(b) After termination of the burner test, the test specimen together with fire protective
coating, if any, is to be allowed to cool to ambient temperature and then tested to the design
pressure of the pipes, as defined in 4-2-2/7.5.1 and 4-2-2/7.5.2. The pressure is to be held for a
minimum of 15 minutes without significant leakage [i.e., not exceeding 0.2 1/min. (0.05 gpm)].
Where practicable, the hydrostatic test is to be conducted on bare pipe (i.e., coverings and
insulation removed) so that any leakage will be apparent.

7.16 Tests by the Manufacturer - Wet/Dry Fire Endurance Testing of FRP Piping Used in
Deluge System (For Level 3 Modified Test - Level 3 WD) (Adopted from USCG PFM
1-98)
For requirements on Test by Manufacturer – Wet/Dry Fire Endurance Testing of FRP Piping Used in
Deluge System (For Level 3 Modified Test - Level 3 WD), see 7A-1-3/13.5. The wet/dry fire endurance
testing is to consist of conducting the Level 3 fire endurance testing specified in 4-2-2/7.15, with the
following modifications:

i) For the first five (5) minutes of the test, the piping is to be maintained in the dry condition at
atmospheric pressure in lieu of containing stagnant water.
ii) After completion of the first five (5) minutes of the test, the pipe specimen is to be completely
filled with flowing water.
iii) Air is to be bled from the opposite end of the piping via a test connection, until a steady flow of
water at the specified flow rate and pressure is observed.
iv) The flow rate is not to exceed the minimum pressure and flow rate that will be observed at the
hydraulically most remote nozzle of the specific deluge system installation. The elapsed time
between first introducing water to the test specimen until the specified flow rate and pressure is
obtained, is not to exceed one minute. Testing at the specified flow rate and pressure will qualify
the piping for all flow rates greater than that specified in the test.
v) The total test time including dry and wet time is to be 30 minutes.

All other requirements of Level 3 testing are to be followed without deviation.

7.17 Tests by Manufacturer – Flame Spread

For requirements on Test by Manufacturer – Flame Spread, see 7A-1-3/13.5.

7.17.1 Test Method

Flame spread of plastic piping is to be determined by IMO Resolution A.653(16)
Recommendation on Improved Fire Test Procedures for Surface Flammability of Bulkhead,
Ceiling, and Deck Finish Materials and Resolution A.753(18) Guidelines for the application of
plastic pipes on ships, as amended by Resolution MSC.399(95) as follows.

7.17.1(a)
Tests are to be made for each pipe material and to take into account differences in wall thickness.
When conducting testing of plastic piping, testing need not be conducted on every pipe size.

Testing is to be conducted on pipe sizes with the maximum and minimum wall thicknesses intended
to be used. This will qualify all piping sizes for a specific piping material provided that the wall
thickness falls within the tested range.

7.17.1(b)
For homogenous thermoplastic pipes, the test specimens may be produced as flat plates in the
required wall thickness(es).

7.17.1(c)

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 58

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

The test sample is to be fabricated by cutting pipes lengthwise into individual sections and then
assembling the sections into a test sample as representative as possible of a flat surface. A test
sample is to consist of at least two sections. All cuts are to be made normal to the pipe wall. The
test sample is to be 800 mm ± 5 mm long for tests to 2010 FTP Code, annex 1, part 5. The test
sample is to be 75 mm ± 1 mm square for tests to 2010 FTP Code, annex 1, part 2.

7.17.1(d)
The number of sections that must be assembled together to form a test sample is to be that which
corresponds to the nearest integral number of sections which makes up a test sample with an
equivalent linearized surface width between 155 mm (6 in.) and 180 mm (7 in.). The surface width
is defined as the measured sum of the outer circumference of the assembled pipe sections that are
exposed to the flux from the radiant panel.

7.17.1(e)
The assembled test sample is to have no gaps between individual sections.

7.17.1(f)
The assembled test sample is to be constructed in such a way that the edges of two adjacent
sections coincide with the centerline of the test holder.

7.17.1(g)
The individual test sectionsare to be attached to the backingcalcium silicate board using wire (No.
18 recommended) insertedat 50 mm (2 in.) intervals throughthe board and tightened by twisting at
the back.

7.17.1(h)
The individual pipe sections are to be mounted so that the highest point of the exposed surface is
in the same plane as the exposed flat surface of a normal surface.

7.17.1(i)
The space between the concave unexposed surface of the test sample and the surface of the
calcium silicate backing board is to be left void.

7.17.1(j)
The void space between the top of the exposed test surface and the bottom edge of the sample
holder frame is to be filled with a high temperature insulating wool if the width the of the pipe
segments extend under the side edges of the sample holding frame.

7.19 Testing By Manufacturer – General

Testing is to demonstrate the compliance of plastic pipes, fittings and joints for which approval, in
accordance with 4-2-2/7, is requested. These tests are to be in compliance with the requirements of
relevant standards as per 4-2-2/Table 3 and 4-2-2/Table 4.

Commentary:

During the evaluation of use of plastic piping in firewater systems, the following should be considered:

i Results and conclusions of fire tests

ii Whether firewater system is a wet-pipe system (i.e., water is constantly maintained in the piping)
iii Ability to isolate damaged section of the firewater system (e.g., location of isolation points)
iv Proximity to potential fire or explosion sources or hazards

End of commentary

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 59

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

TABLE 2
Fire Endurance Requirements Matrix

LOCATION
PIPING SYSTEMS
A B C D E F G H I

FLAMMABLE LIQUIDS

1 Oil [flash point ≤ 60°C (140°F)] NA NA L1 0 NA 0 0 NA L1 (2)

1a Cargo Lines X X L1 NA(13) 0 0 0 NA L1

(13)
2 Fuel oil [flash point > 60°C X X L1 NA 0 0 0 L1 L1
(140°F)]

3 Lubricating oil X X L1 NA NA NA 0 L1 L1

4 Hydraulic oil X X L1 0 0 0 0 L1 L1

SEA WATER (See Note 1)

5 Bilge main and branches L1 L1 L1 NA 0 0 0 NA L1

6 Fire main L1 L1 L1 NA NA 0 0 X L1/

L3(9)

6a Water spray (Deluge) for Industrial L1 L1 L1 NA NA 0 0 X L1/L3

Equipment System WD(9)

7 Foam system L1W L1W L1W NA NA NA 0 L1W L1W

8 Sprinkler system L1W L1W L3 NA NA 0 0 L3 L3

9 Ballast L3 L3 L3 0 0 0 0 L2W L2W

10 Cooling water, essential services L3 L3 NA NA NA 0 0 NA L2W

10a Tank cleaning services, fixed NA NA L3 0 NA 0 0 NA L3 (10)

machines

11 Non-essential systems 0 0 NA 0 0 0 0 0

FRESH WATER

12 Cooling water, essential services L3 L3 NA NA 0 0 0 L3 L3

13 Condensate return L3 L3 L3 NA NA NA 0 0 0

14 Non-essential systems 0 0 0 NA 0 0 0 0 0

SANITARY/DRAINS/SCUPPERS

15 Deck drains (internal) L1W L1W NA NA 0 0 0 0 0

(3) (3)

16 Sanitary drains (internal) 0 0 NA NA 0 0 0 0 0

17 Scuppers and discharges 0 (1,5) 0 (1,5) 0 (1,5) 0 0 0 0 0 (1,5) 0

(overboard)

VENTS/SOUNDING

18 Water tanks/dry spaces 0 0 0 0 0 0 0 0 0

19 Oil tanks [flash point > 60°C X X X X 0 0 0 X X

(140°F)]

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 60

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

LOCATION
PIPING SYSTEMS
A B C D E F G H I

20 Oil tanks [flash point ≤ 60°C NA NA NA 0 NA 0 0 NA X

(140°F)]

MISCELLANEOUS

21 Control air L1 (4) L1 (4) L1(4) NA 0 0 0 L1 (4) L1 (4)

22 Service air (non-essential) 0 0 0 NA 0 0 0 0 0

23 Brine 0 0 NA NA NA NA 0 0 0

24 Auxiliary low pressure L2 L2 0(6) 0 0 0 0 0 (6) 0 (6)

steam(Pressure ≤ 7 bar (7 kgf/cm2,
100 psi)

25 Central vacuum cleaners NA NA NA NA NA NA 0 0 0

(1) (1) (1)(7)
26 Exhaust gas cleaning system L3 L3 NA NA NA NA 0 L3 0
effluent line NA

27 Urea Transfer/Supply System L1(8) L1(8) L3 NA NA NA 0 L3(7) 0

(SCR installations) NA

HYDROCARBON & CARGO (Flammable cargoes with flashpoint ≤ 60°C (140°F))

28 Cargo lines NA NA L1 0 NA 0 0 NA L1(10)

29 Crude oil washing lines NA NA L1 0 NA 0 0 NA L1(10)

30 Process lines NA NA NA 0 NA 0 0 NA L1(10)

31 Produced water lines NA NA NA 0 NA 0 0 NA L3(11)

INERT GAS

32 Water seal effluent line NA NA 0(1) 0(1) 0(1) 0(1) 0(1) NA 0

33 Scrubber effluent line 0(1) 0(1) NA NA NA 0(1) 0(1) NA 0

34 Main line 0 0 L1 0 NA NA 0 NA L10

35 Distribution Lines NA NA L1 0 NA NA 0 NA L1(10)

Locations Abbreviations

A Category A machinery spaces L1 Fire endurance test in dry conditions, 60 minutes in

B Other machinery spaces accordance with 4-2-2/7.13
C Cargo pump rooms

D Oil tanks [flashpoint ≤ 60°C (140°F)] L2 Fire endurance test in dry conditions, 30 minutes, in
E Fuel oil tanks [flashpoint > 60°C (140°F)] accordance with 4-2-2/7.13

F Ballast water tanks L3 Fire endurance test in wet conditions, 30 minutes, in

G Cofferdams, void spaces, pipe tunnels and ducts L3 accordance with 4-2-2/7.15
WD Fire endurance test in dry condition, 5 minutes, and in
wet condition 25 minutes, in accordance with
4-2-2/7.15 and 4-2-2/7.16

H Accommodation, service and control spaces 0 No fire endurance test required

I Open decks NA Not applicable (Plastic pipe is not permitted.)

X Metallic materials having a melting point greater than

925°C (1700°F).

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 61

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

Notes:

1 Where nonmetallic piping is used, remotely controlled valves are to be provided at the unit’s side. These
valves are to be controlled from outside of the space.

2 Remote closing valves are to be provided at the tanks.

3 For drains serving only the space concerned, “0” may replace “L1W” .

4 When controlling functions are not required by statutory requirements, “0” may replace “L1” .

5 Scuppers serving open decks in positions 1 and 2, as defined in Regulation 13 of the International
Convention on Load Lines, 1966, are to be “X” throughout unless fitted at the upper end with the means of
closing capable of being operated from a position above the freeboard deck in order to prevent
downflooding.

6 For essential services, such as fuel oil tank heating and whistle, “X” is to replace “0” .

7 L3 in service spaces, NA in accommodation and control spaces.

8 Type Approved plastic piping without fire endurance test (0) is acceptable downstream of the tank valve,
provided this valve is metal seated and arranged as fail-to-closed or with quick closing from a safe position
outside the space in the event of fire.

9 Lower level of fire resistant tests Level 3 may be considered for the fire water main and Level 3 WD for
the water spray (deluge) systems, provided the system arrangement meets the requirements in 4-2-2/7.5.7
iv) and v).

10 Remote closing valves are to be provided at the oil tanks and hydrocarbon liquid and gas retaining
components as applicable.

11 Metallic ESD valves are to be provided together with fire detection, fire fighting and shutdown system.

12 For pipe between machinery space and deck water seal, “0” may replace “L1”.

13 When oil tanks contain flammable liquids with a flash point greater than 60°C (140°F), “0” may replace
“NA” or “X”.

TABLE 3
Standards for Plastic Pipes – Typical Requirements for All Systems

Test Typical Standard Notes

1 Internal pressure (1) 4-2-2/7.5.1 Top, Middle, Bottom (of each

ASTM D 1599, pressure range)
ASTM D 2992 Tests are to be carried out on pipe
ISO 15493 or equivalent spools made of different pipe sizes,
fittings and pipe connections.

2 External pressure (1) 4-2-2/7.5.2 As above, for straight pipes only.

ISO 15493 or equivalent

3 Axial strength (1) 4-2-2/7.5.4 As above.

4 Load deformation ASTM D 2412 or equivalent Top, Middle, Bottom (of each
pressure range)

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 62

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

Test Typical Standard Notes

(1)
5 Temperature limitations 4-2-2/7.5.5 Each type of resin
ISO 75 Method A GRP piping
system:
HDT test on each type of resin acc.
to ISO 75 method A.
Thermoplastic piping systems:
ISO 75 Method A ISO 306 Plastics
– Thermoplastic materials –
Determination of Vicat softening
temperature (VST)
VICAT test according to ISO 2507
Polyesters with an HDT below
80°C is not to be used

6 Impact resistance (1) 4-2-2/7.5.6 Representative sample of each type

ISO 9854, ISO 9653: ISO 15493 of construction
ASTM D 2444, or equivalent

7 Ageing Manufacturer's standard Each type of construction

ISO 9142

8 Fatigue Manufacturer’s standard or service Each type of construction

experience.

9 Fluid absorption ISO 8361

(2)
10 Material compatibility ASTM C581
Manufacturer’s standard

Notes:
1 Where the manufacturer does not have a certified quality system, test to be witnessed by the Surveyor.
See 4-2-2/7.9.
2 If applicable.

TABLE 4
Standards for Plastic Pipes – Additional Requirements Depending on Service
and/or Location of Piping

Test Typical Standard Notes

1 Fire endurance (1,2) 4-2-2/7.5.7 Representative samples of each

type of construction and type of
pipe connection.

2 Flame spread (1,2) 4-2-2/7.5.8 Representative samples of each

type of construction.

3 Smoke generation (2) IMO Fire Test Procedures Code Representative samples of each
type of construction.

4 Toxicity (2) IMO Fire Test Procedures Code Representative samples of each
type of construction.

5 Electrical conductivity (1,2) 4-2-2/7.5.9 Representative samples of each

ASTM F1173-95 or ASTM type of construction
D 257, NS 6126/ 11.2 or equivalent

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 63

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

Notes:
1 Where the manufacturer does not have a certified quality system, test to be witnessed by the Surveyor.
See 4-2-2/7.9.
2 If applicable.

Note: Test items 1, 2 and 5 in 4-2-2/7.19 TABLE 4 are optional. However, if not carried out, the range of approved
applications for the pipes will be limited accordingly (see 4-2-2/7.19 TABLE 2).

9 Valves

9.1 General
9.1.1 Standard Valves
All valves constructed and tested in accordance with a recognized standard are acceptable to ABS,
subject to compliance with 4-2-2/9.5.

9.1.2 Non-Standard Valves

Components not manufactured to a recognized national standard are preferably to be Type
Approved (see 1B-1-A2/5 of the ABS Rules for Conditions of Classification - Offshore Units and
Structures (Part 1B)). They may be considered for acceptance based on manufacturers’ specified
pressure and temperature ratings and on presented evidence, such as design calculations or type
test data, that they are suitable for the intended purpose. For Classes I and II piping applications,
drawings showing details of construction, materials, welding procedures, etc., as applicable, are to
be submitted for those components, along with the basis for the pressure and temperature ratings.

Valves are to be tested to a burst pressure without indication of failure or leakage:

i) Valves of steel other than cast steel - Not less than four (4) times its design pressure
ii) Valves of cast steel, cast iron and ductile iron - Not less than five (5) times its design
pressure
iii) Valves of non-ferrous materials-Not less than four (4) times its design pressure.

9.3 Construction
All valves are to close with a right hand (clockwise) motion of the handwheel when facing the end of the
stem and are to be either of the rising stem type or fitted with an indicator to show whether the valve is
open or closed.

All valves of Class I and II piping systems having nominal diameters exceeding 50 mm (2 in.) are to have
bolted, pressure seal or breech lock bonnets and flanged or welding ends. Welding ends are to be butt
welding type, except that socket welding ends are acceptables to be used for valves having nominal
diameters of 80 mm (3 in.) or less. See 4-2-1/11.11.

All cast iron valves are to have bolted bonnets or are to be of the union bonnet type. For cast iron valves of
union bonnet type, the bonnet ring is to be of steel, bronze or malleable iron.

Stems, discs or disc faces, seats, and other wearing parts of valves are to be of corrosion-resistant materials
suitable for intended service.

Valves are to be designed for the maximum working pressure to which they will be subjected. The design
pressure is to be at least 3.4 bar (3.5 kgf/cm2, 50 psi), except that valves used in open systems, such as vent
and drain lines, and valves mounted on atmospheric tanks which are not part of the tank suction or
discharge piping (for example, level gauge and drain cocks and valves in inert gas and vapor emission
control systems) may be designed for a pressure below 3.4 bar (3.5 kgf/cm2, 50 psi), subject to the

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 64

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

requirements of 4-2-2/9.1. Large fabricated ballast manifolds which connect lines exceeding 200 mm (8
in.) nominal pipe size are acceptable when the maximum working pressure to which they will be subjected
does not exceed 1.7 bar (1.75 kgf/cm2, 25 psi).

All valves for Class I and II piping systems and valves intended for use in steam or oil lines are to be
constructed so that the stem is positively restrained from being screwed out of the body (bonnet). Plug
cocks, butterfly valves and valves employing resilient material are subject to ABS technical assessment
and approval. Valve operating systems for all valves which cannot be manually operated are to be
submitted for approval.

9.5 Hydrostatic Test and Identification

For hydrostatic test and identification requirements, see 7A-1-3/15.7.

11 Pipe Fittings

11.1 General
All fittings in Class I and II piping are to have flanged or welded ends in sizes over 89 mm O.D. (3 in.
N.P.S). Screwed fittings are acceptables in Class I and II piping systems, provided the maximum working
temperature does not exceed 496°C (925°F) and the maximum working pressure does not exceed the
maximum pressure indicated below for the pipe size.

Pipe Size Maximum Pressure

mm O.D. (in. N.P.S.) bar (kgf/cm2, psi)

above 89 (3) not permitted in Class I and II piping service

above 60 (2) through 89 (3) 27.6 (28.10, 400)

above 33 (1) through 60 (2) 41.4 (42.20, 600)

above 27 (0.75) through 33 (1) 82.3 (84.4, 1200)

27 (0.75) and smaller 103 (105.5, 1500)

Flared, flareless and compression fittings are acceptable to be used for tube sizes not exceeding 60 mm
O.D. (2 in. N.P.S.) in Class I and II piping. In Class III piping, screwed fittings and flared, flareless and
compression tube fittings will be accepted without size limitations. Flared fittings are to be used for
flammable fluid systems, except that both flared and flareless fittings of the non-bite type are acceptable to
be used when the tubing system is of steel or nickel-copper or copper-nickel alloys. Only flared fittings are
to be used when tubing for flammable fluid systems is of copper or copper-zinc alloys. See 4-2-6/3.7 for
hydraulic systems. Bite type fittings are not to be used for flammable fluid systems, unless such fittings are
in compliance with a recognized standard or design-approved by ABS. Refer to 4-6-2/Tables 10 and 11 of
Marine Vessel Rules.

11.3 Hydrostatic Test and Identification

For hydrostatic test and identification requirements, see 7A-1-3/17.3.

11.5 Nonstandard Fittings

Fittings which are not certified by the manufacturer to a recognized standard will be subject to ABS
technical assessment and approval. Plans showing details of construction, material and design calculations
or test results are to be submitted for review.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 65

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

13 Welded Nonstandard Valves and Fittings

Nonstandard steel valves and fittings fabricated by means of fusion welding are to comply also with the
requirements of Chapter 4 of the ABS Rules for Materials and Welding (Part 2). However, after a
manufacturer’s procedure in the fabrication of equipment of this kind has been demonstrated by tests to the
satisfaction of a Surveyor to ABS, subsequent tests on the product need not be witnessed, but the
manufacturer’s guarantee that the Rules are complied with are acceptable for other valves and fittings
which conform to standards of the American National Standards Institute or other recognized standards.

15 Flanges

15.1 General
Flanges are to be designed and fabricated in accordance with a recognized national or international
standard. Slip-on flanges from flat plate are acceptable in lieu of hubbed slip-on flanges in Group II piping
systems.

Commentary:

Flanges of dimensions, configuration, construction and testing in accordance to the recognized standard and used at or below
the pressure-temperature rating are considered standard flanges. If such flanges are used above the pressure-temperature
rating, or if their dimensions or configurations are modified, they should be considered as non-standard flanges.

End of commentary

15.3 Class I and II Piping Flanges

In Class I and II piping, flanges may be attached to the pipes by any of the following methods appropriate
for the material involved.

15.3.1 Steel Pipe

Over 60 mm O.D. (2 in. N.P.S.) steel pipes are to be expanded into steel flanges, or they may be
screwed into the flanges and seal-welded. They may in all cases be attached by fusion welding in
compliance with the requirements of 2-4-4/5.7 of the ABS Rules for Materials and Welding (Part
2). Smaller pipes may be screwed without seal-welding, but in steam and oil lines are, in addition,
to be expanded into the flanges for uniformly tight threads.

15.3.2 Nonferrous Pipe

In Class I and II, nonferrous pipes are to be brazed to composition or steel flanges, and in sizes of
60 mm O.D. (2 in. N.P.S.) and under, they may be screwed.

15.5 Class III Piping Flanges

Similar attachments are also to be used in Class III piping. However, modifications are permitted for
welded flanges, as noted in 2-4-4/5.7 of the ABS Rules for Materials and Welding (Part 2), and screwed
flanges of suitable material are acceptable to be used in all sizes.

17 Material of Valves and Fittings

17.1 General
The physical characteristics of such material are to be in accordance with the applicable requirements of
section 2-3-1 of the ABS Rules for Materials and Welding (Part 2). or such other appropriate material
specification as may be approved in connection with a particular design for the stresses and temperatures
to which they may be exposed. Manufacturers are to make physical tests of each melt and, upon request,
are to submit the results of such tests to ABS.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 66

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

17.3 Forged or Cast Steel

In any system, forged or cast steel is acceptable to be used in the construction of valves and fittings for all
pressures and temperatures.

Reduction of strength and hardness are to be considered in the design for the following steels due to
graphite formation when exposed to elevated temperatures for extended periods.

Material degradation due to creep and graphite formation at elevated temperatures are to be considered
when the following steels are used above the temperatures indicated.

Grade Temperature

Carbon steel* ≥ 425°C (797°F)

Carbon-molybdenum steel ≥ 470°C (878°F)

Chrome-molybdenum steel (with chromium under 0.60%) ≥ 525°C (977°F)

Note: * Electric-resistance-welded steel pipe may be used for temperatures up to 343°C (650°F)

17.5 Cast Iron

For temperatures not exceeding 232°C (450°F), cast iron of the physical characteristics specified in
Section 2-3-11 of the ABS Rules for Materials and Welding (Part 2) are acceptable to be used in the
construction of valves and fittings, except as noted in 4-2-1/11.17, 4-2-2/21.5 and 4-2-5/3.7.

17.7 Nonferrous
Brass or bronze having the physical characteristics as specified in Section 2-3-1 of the ABS Rules for
Materials and Welding (Part 2) are acceptable to be used in the construction of valves and fittings intended
for temperatures up to 208°C (406°F). For temperatures greater than 208°C (406°F), but not in excess of
288°C (550°F), high-temperature bronze is to be used and the chemical and physical characteristics are to
be submitted for approval.

Commentary:

Valves, fittings and flanges made of nonferrous material may be attached to nonferrous pipe by an approved soldering
method.

End of Commentary

For pressures up to 6.9 bar (7 kgf/cm2, 100 psi) and temperatures not exceeding 93°C (200°F), ordinary
solder is acceptable, but for higher pressures and temperatures, the method and the quality of solder to be
used will be subject to ABS technical assessment and approval in each case.

17.9 Ductile (Nodular) Iron

Nodular-iron applications for valves and fittings are subject to ABS technical assessment and approval
where the temperature does not exceed 343°C (650°F).

19 Fluid Power Cylinders

19.1 General
Fluid power cylinders subject to pressures or temperatures greater than those indicated below are to be
designed, constructed and tested in accordance with a recognized standard for fluid power cylinders.

● Hydraulic fluid – flammable: 7 bar (7.1 kgf/cm², 101.5 psi) or 60°C (140°F)
● Hydraulic fluid – non-flammable: 16 bar (16.3 kgf/cm², 232 psi) or 200°C (392°F)
● Air: 16 bar (16.3 kgf/cm², 232 psi) or 200°C (392°F)

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 67

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

Acceptance is based on the manufacturer’s certification of compliance and on verification of permanent

identification on each cylinder bearing the manufacturer's name or trademark, standard of compliance and
design pressure and temperature.

19.3 Non-compliance with a Recognized Standard

Cylinders subject to pressures or temperatures higher than those indicated above which are not constructed
to a recognized standard may be accepted based on the following:

i) Regardless of diameter, the design of the cylinder is to be shown to comply with one of the
following:

● A recognized pressure vessel code,

● Section 4-4-1 of the Marine Vessel Rules. For instance, the cylinder is to have a wall thickness
not less than that given by equation 2 of 4-4-1-A1/3.1 the Marine Vessel Rules, and the
cylinder ends are to meet the requirements of flat heads in 4-4-1-A1/5.7 the Marine Vessel
Rules, or
● Verification through burst tests. Steel cylinders (other than cast steel) are to withstand not less
than 4 times the design pressure, while cast steel, cast iron and nodular iron cylinders are to
withstand not less than 5 times the maximum allowable working pressure.

Documentation in this regard is to be submitted for review. See 7A-1-3/21 for survey
requirements.
ii) Each individual unit is to be hydrostatically tested to 1.5 times the design pressure (2 times, for
cast iron and nodular iron cylinders) by the manufacturer. A test certificate is to be submitted.
iii) Each cylinder is to be affixed with a permanent nameplate or marking bearing the manufacturer’s
name or trademark and the design pressure and temperature.

19.5 Materials
i) The materials of the cylinders are to comply with the requirements of the standard or code to
which they are designed and constructed. Where the design is verified though burst tests, the
materials of the cylinder are to comply with 4-4-1/3 of the Marine Vessel Rules or other acceptable
standards.
ii) Ordinary cast iron having an elongation of less than 12% is not to be used for cylinders expected
to be subjected to shock loading.
iii) Copies of certified mill test reports are to be made available to the Surveyor upon request.

19.7 Rudder Actuators

Rudder actuators are to be in accordance with the requirements of 4-3-4/7.3.1 of the Marine Vessel Rules.

19.9 Cylinders Below Pressures or Temperatures Indicated in 4-2-2/19.1

Cylinders subject to pressures and temperatures at or below those indicated in 4-2-2/19.1 are acceptable in
accordance with the manufacturer’s rating and verification of suitability for the intended service.

19.11 Exemptions
Fluid power cylinders that do not form part of the unit's piping systems covered in Part 4, Chapter 2 and
Part 6, Chapter 1 are exempt from the requirements of 4-2-2/19. However, those fluid power cylinders
which are integrated into piping systems associated with optional classification notations are to comply
with the requirements of 4-2-2/19 and the applicable requirements specified in the applicable ABS Rules
and Guides.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 68

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

21 Sea Inlets and Overboard Discharges

21.1 Installation
Piping connections bolted to the shell plating are to have the bolt heads countersunk on the outside and the
bolts threaded through the plating. Where a reinforcing ring of sufficient thickness is riveted or welded to
the inside of the shell, studs are acceptable to be used.

Threaded connections outboard of the shell valves are not considered an acceptable method of connecting
pipe to the shell.

21.3 Valve Connections to Shell

Pipe connections fitted between the shell and the valves are to have a minimum wall thickness not less
than that specified below and be as short as possible. Wafer-type valves are not to be used for any
connections to the unit’s shell unless subjected to ABS technical assessment and approval.

Nominal Size, d Min. Wall Thickness

d ≤ 65 mm (2.5 in.) 7 mm (0.276 in.)

d = 150 mm (6 in.) 10 mm (0.394 in.)

d ≥ 200 mm (8 in.) 12.5 mm (0.492 in.)

For intermediate nominal pipe sizes, the wall thicknesses are to be obtained by linear interpolation as
follows:

For 65 < d < 150: 7 + 0.035 (d - 65) mm or 0.28 + 0.034 (d - 2.5) in.

For 150 < d < 200: 10 + 0.05 (d - 150) mm or 0.39 + 0.05 (d - 6.0) in.

21.5 Materials
All shell fittings and the valves required by 4-2-2/21.9 and 4-2-2/23 are to be of steel, bronze or other
approved ductile material. Valves of ordinary cast iron or similar material are not acceptable. The use of
nodular iron, also known as ductile iron or spheroidal-graphite iron, is acceptable, provided the material
has an elongation not less than 12%. All pipes to which this subsection refers are to be of steel or other
equivalent material, subject to ABS technical assessment and approval.

21.7 Shell Reinforcement

Overboard discharges are to have spigots extending through the shell plate. Boiler and evaporator blow-off
overboard discharges are to have doubling plates or heavy inserts fitted. The spigot is to extend through the
doubling and the shell and the external doubling plate, when fitted, but the spigot need not project beyond
the outside surface of the unit.

21.9 Shell Valves

Shell valves are to comply with the following requirements:

Positive closing valves are to be fitted at the shell in inlet and discharging piping. The controls are to be
readily accessible and are to be provided with indicators showing whether the valves are open or closed.
Refer to 7A-1-3/23.3 with regard to controls accessibility.

Materials readily rendered ineffective by heat are not to be used for connection to the shell where the
failure of the material in the event of a fire would give rise to danger of flooding.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 69

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

Gaskets and valve seats used in shell connections are not required to be a fire-resistant type. However,
where the possibility of significant flooding is expected due to the gasket failure, ABS technical
assessment and approval are required.

Power-operated valves are to meet the requirements in 4-2-1/11.25. Position indicating systems for
seawater inlet and discharge valves are to be independent of the valves’ control systems. Additionally,
seawater valves necessary for the operation of propulsion machinery or generation of power required in
4-3-2/3.1 are to be designed to remain in the last ordered position upon loss of control power.

Shell valves are also to be in accordance with the following, as applicable.

21.9.1 Column-Stabilized Units

Sea-water inlets and discharges below the assigned load line are to be provided with valves which
can be remotely operated from an accessible position outside of the space.

21.9.2 Self-Elevating and Surface-Type Units

Sea-water inlets and discharges in spaces below the assigned load line which are not intended to
be normally manned are to be provided with valves which can be remotely operated from an
accessible position outside of the space. If the valves are readily accessible, the spaces containing
the inlets and discharges may be provided with bilge alarms in lieu of remote operation of the
valves.

21.9.3 Self-Elevating Units

Mud pit discharges are to be provided with valves which can be operated from an accessible
position. These valves are to be normally closed and a sign to this effect is to be posted near the
operating position. Non-return valves need not be provided.

21.11 Sea Chests

The locations of sea chests are to be such as to minimize the probability of blanking off the suction, and
they are to be so arranged that the valves are operable from the floors or gratings.

Sea chests are to be fitted with strainer plates at the shell. The strainers are to have a clear area of at least
1.5 times the area of the sea valves, and means are to be provided for clearing the strainers.

23 Scuppers and Drains on Surface-Type and Self-Elevating Units

23.1 Discharges through the Shell

Discharges led through the shell either from spaces below the freeboard deck or from within
superstructures and deckhouses on the freeboard deck, fitted with doors complying with the requirements
of 3-2-11/5 of the Marine Vessel Rules, are to be fitted with efficient and accessible means for preventing
water from passing inboard.

Normally, each separate discharge is to have one automatic non-return valve with a positive means of
closing it from a position above the freeboard deck, or bulkhead deck, whichever is higher. Alternatively,
one non-return valve and one positive closing valve controlled from above the freeboard deck may be
accepted.

23.1.1
Where, however, the vertical distance from the load water-line to the inboard end of the discharge
pipe exceeds 0.01L, the discharge may have two automatic non-return valves without positive
means of closing, provided that the inboard valves are always accessible for examination under
service conditions. The inboard valve is to be above the deepest load waterline. If this is not

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 70

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

practicable, then, provided a locally controlled stop valve is interposed between the two non-
return valves, the inboard valve need not be fitted above the deepest load waterline.

23.1.2
Where that vertical distance from the summer load waterline to the inboard end of the discharge
pipe exceeds 0.02L, a single automatic non-return valve without positive means of closing may be
accepted provided it is located above the deepest load waterline. If this is impracticable, a locally
operated positive closing valve may be provided below the single non-return valve in which case
the non-return valve need not be located above the specified deepest load waterline. The means for
operating the positive-action valve is to be readily accessible and provided with an indicator
showing whether the valve is open or closed.

See 3A-1-1/13 for definition of freeboard deck.

L is defined in 3-1-1/3 of the Marine Vessel Rules or 3-1-1/3 of the Barge Rules.

23.1.3
Where sanitary discharges and scuppers lead overboard through the shell in way of machinery
spaces, the fitting to shell of a locally operated positive closing valve, together with a non-return
valve inboard, is acceptable.

See 4-2-2/FIGURE 3 for acceptable arrangements of scuppers, inlets and discharges.

FIGURE 3
Overboard Discharges – Valve Requirements

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 71

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

23.3 Scuppers and Discharges below the Freeboard Deck – Shell Penetration
Scuppers and discharge pipes originating at any level and penetrating the shell either more than 450 mm
(17.5 in.) below the freeboard deck or less than 600 mm (23.5 in.) above the summer load waterline are to
be provided with a non-return valve at the shell.
Commentary:

The valve mentioned above may be omitted if the piping has a wall thickness at least equal to the thickness of the shell
plating or extra-heavy pipe (see 4-2-1/3.9), whichever is less.

End of Commentary

23.5 Scuppers from Superstructures or Deckhouses

Scuppers leading from superstructures or deckhouse not fitted with doors complying with the requirements
of 3-2-11/5 of the Marine Vessel Rules are to be led overboard.

25 Cooler Installations External to the Hull

25.1 General
The inlet and discharge connections of external cooler installations are to be in accordance with 4-2-2/21.1,
4-2-2/21.3, 4-2-2/21.5 and 4-2-2/21.9, except that wafer type valves are acceptable. If a flexible hose or
joint is fitted, it is to be fire rated when located within the machinery space of Category A and located
inboard of the isolation valve.

25.3 Integral Keel Cooler Installations

The positive closing valves required by 4-2-2/27.1 need not be provided if the keel (skin) cooler
installation is integral with the hull. To be considered integral with the hull, the installation is to be
constructed such that channels are welded to the hull with the hull structure forming part of the channel.
The channel material is to be at least of the same thickness and quality as that required for the hull, and the
forward end of the cooler is to be faired to the hull with a slope of not greater than 4 to 1.

If positive closing valves are not required at the shell, all flexible hoses or joints are to be positioned above
the deepest load waterline or be provided with an isolation valve.

25.5 Non-integral Keel Cooler Installations

Where non-integral keel coolers are used, if the shell penetrations are not fully welded, the penetration is to
be encased in a watertight enclosure.

27 Penetrations through Watertight Boundaries

At the boundaries required to be maintained watertight for damage stability, means are to be provided or
piping is to be arranged to prevent progressive flooding. Such means, for example, remotely operated
valves or watertight closures (see 3A-3-2/5). Check valves and spring or gravity-actuated, non-return
valves are not considered effective in preventing progressive flooding. Watertight closures or valves and
their control and position-indicating systems are to be provided as follows:

27.1 Ventilating Systems

Non-watertight ducts passing through subdivision bulkheads and watertight ducts servicing more than one
watertight compartment or which are within the extent of damage, (see 3A-3-2/3.5), are to be provided
with valves, or other approved positive means of closure such as watertight dampers, at the subdivision
boundary.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 72

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 2 Pumps, Pipes, Valves, and Fittings 4-2-2

Materials readily rendered ineffective by heat are not to be used in the construction of the valves or the
closure mechanism to ensure effective closure facility in the event of fire. Electric cables, where used, are
to be fire-resistant, meeting the requirements of IEC Publication 60331.

Valve operators are to be fitted with position indicators. Control of valves is to be from one of the
following areas:

i) Ballast control room or other normally manned spaces.

ii) Readily accessible locations which are above the calculated immersion line in the damaged
condition (see 3A-3-2/1.3).

27.3 Internal Drain System

27.3.1
Where drain systems are led to a separate, watertight compartment fitted with a bilge suction,
positive closing valves with position indicators are to be provided. Control of these valves is to be
from locations listed in 4-2-2/27.1.

27.3.2
Where the installation of a remote valve operator is impractical, drain lines may be fitted with
quick-acting, self-closing valves at the boundary of the space which is equipped with a bilge
suction.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 73

 PART 4
CHAPTER 2
Pumps and Piping Systems

SECTION 3
Tank Vents, Overflows and Sounding

1 Objective

1.1 Goals
The tank vents, overflows and sounding covered in this section shall be designed, constructed, operated,
and maintained to:

Goal No. Goal

STAB 1 have adequate watertight integrity and restoring energy to prevent capsize in an intact condition.

STAB 2 have adequate subdivision and stability to provide survivability to damage or accidental
conditions.

STAB 4 detect accumulated liquids.

STRU 1 in the intact condition, have sufficient structural strength to withstand the environmental
conditions, loading conditions, and operational loads anticipated during the design life.

FIR 1 prevent the occurrence of fire and explosion.

ENV 1 prevent and minimize oil pollution due to unit operation and accidents.

PROP 2 provide redundancy and/or reliability to maintain propulsion.

POW 3 enable all electrical services necessary for maintaining the vessel in normal operational and
habitable conditions to be available without recourse to the emergency source of power.

SAFE 1.1 minimize danger to person on board, the unit, and surrounding equipment/installation from
hazards associated with machinery and systems.

Materials are to be suitable for the intended application in accordance with the following goals in support
of the Tier 1 goals as listed above.

Goal No. Goal

MAT 1 The physical, mechanical and chemical properties of base material and weldments are to meet the
design requirements appropriate for the application and operating environment.

The goals in the cross-referenced Rules are also to be met.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 74

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

1.2 Functional Requirements

In order to achieve the above stated goals, the design, construction, installation and maintenance of the
tank vents, overflows and sounding are to be in accordance with the following functional requirements:

Functional Functional Requirements

Requirement No.

Stability (STAB)

STAB-FR1 Provide means to prevent inadvertent flooding of an internal space.

STAB-FR2 Provide means to prevent entry of sea water through openings of vents/overflows such that the unit
still complies with the applicable damage stability criteria.

STAB-FR3 There are to be arrangements to prevent progressive flooding for piping/tanks that is arranged within
the assumed damage zone such that the unit still complies with the applicable damage stability
criteria.

STAB-FR4 Provide means to prevent progressive flooding during damage of tanks and to satisfy the applicable
intact and damage stability criteria.

STAB-FR5 Provide means to protect overflows against water ingress.

STAB-FR6 Provide means to determine amount of liquid in all tanks, cofferdams and all normally dry
compartments, such as cargo holds, which are not easily accessible, and which have the possibility
of water accumulation.

STAB-FR7 Sounding pipes are to be suitably located to determine amount of liquid under all operational
conditions and to be protected from mechanical damage.

STAB-FR8 (MAT) Sounding devices are to have adequate size and strength, and materials are to be suitable for the
intended liquids.

STAB-FR9 Provide means to protect sounding device against water ingress.

Structure (STRU)

STRU-FR1 Vents without any manual devices are to be suitably located and be of sufficient size to prevent over
or underpressurization of tanks during storage, filling or discharge operation.

STRU-FR2 Overflow piping is to be designed and sufficiently sized to prevent over or underpressurization of
tanks.

STRU-FR3 Vents are to be designed to withstand external environment on the exposed deck.

STRU-FR4 Tank bottom is to be suitably protected against damage from repeated striking by sounding device.

Protection of Environment (ENV)

ENV-FR1 Provide means to prevent oil pollution from oil tanks in the event of inadvertent overflow.

ENV-FR2 (STRU) Provide multi-step arrangements to limit and warn of the level at which the tank can be filled to
allow free flow of air and to prevent overfill or flooding hazards.

ENV-FR3 Provide arrangements such that the overflows from oil tanks are not discharged overboard. ENV-
FR5 Designed to prevent transfer of sludge to the bilge and associated systems.

ENV-FR4 Arrangements are to be provided to prevent overfilling due to failure of the sounding device/system.

ENV-FR5 Designed to prevent transfer of sludge to the bilge and associated systems.

Propulsion, Maneuvering, Station Keeping (PROP)

PROP-FR1 (POW) Damage to vents is not to affect fuel service tanks to propulsion and essential services.

Fire Safety (FIR)

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 75

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

Functional Functional Requirements

Requirement No.

FIR-FR1 Vents and sounding devices for combustible/flammable liquids are to be installed away from sources
of ignition.

FIR-FR2 Provide means to prevent sparks/flame from entering vent opening of oil tanks.

FIR-FR3 (SAFE) Sounding devices are to be protected or arranged to prevent leakage and to minimize risk of fire or
mechanical damage.

FIR-FR4 (STAB) Provide means to prevent release of contents due to failure/maintenance of the sounding device.

FIR-FR5 Arrangements are to be provided to enable the removal of devices without impairing the integrity of
the pressurized system.
Safety of Personnel (SAFE)

SAFE-FR1 Provide means to prevent entry of foreign objects into the water tanks.

SAFE-FR 2 Vents for oil tanks are to be arranged to prevent ingress of water due to vent damage.

SAFE-FR3 Vents are to be terminated away from machinery to minimize risk of damage.

Materials (MAT)

MAT-FR1 Vents are to be constructed of materials that are compatible with the media they are expected to
encounter during the service life.
MAT-FR2 Chemical Composition is to be considered for corrosion resistance, weldability, and final mechanical
properties.

The Functional Requirements in the cross-referenced Rules are also to be met.

1.3 Compliance
A unit is considered to comply with the Goals and Functional Requirements when the prescriptive
requirements are complied with or when an alternative arrangement has been approved. Refer to Part 1D,
Chapter 2.

2 Tank Vents, Overflows and Sounding

2.1 General
Except for comparatively small compartments that are not fitted with a fixed means of drainage, vent pipes
are to be fitted to all tanks, cofferdams, voids, tunnels and compartments which are not fitted with other
ventilation arrangements.

In all units, the structural arrangement in double-bottom and other tanks is to be such as to permit the free
passage of air and gases from all parts of the tanks to the vent pipes. Tanks having a comparatively small
surface, such as fuel-oil settling tanks, cofferdams, voids and tunnels to be fitted with one vent pipe, while
all other tanks are to be fitted with at least two vent pipes, one of which is to be located at the highest part
of the tank. Vent pipes are to be arranged to provide drainage under normal conditions. No shutoff valve or
a closing device that can prevent the venting from a tank is to be installed in vent piping.

All vent and overflow pipes terminating in the weather are to be fitted with return bends (gooseneck), or
equivalent, and the vent outlet is to be provided with an automatic means of closure i.e., close
automatically upon submergence (e.g., ball float or equivalent), complying with 4-2-3/2.9.5.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 76

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

2.3 Progressive Flooding Consideration

Tank vents and overflows are to be located to maintain unit stability and the extent of watertight integrity
provided in the plans submitted in accordance with 4-2-1/7.1. They are to terminate above the extent of
watertight integrity. Those terminating within the extent of weathertight integrity are to be fitted with
automatic means of closure such as a ball check valve or equivalent.

Commentary:

The vent of a permanently filled compartment may terminate within the extent of watertight integrity. Automatic means of
closures are not required for vents of such compartments.

End of commentary

For the purpose of positioning vent and overflow ends, damage to the space from which they emanate need
not be considered.

Progressive flooding through tank vents and overflows, regardless of the automatic means of closure
mentioned above, is to be considered in damage stability calculations when tank vents and overflows from
intact spaces are routed within an assumed extent of a damage or vice versa.

2.5 Height and Wall Thickness of Vent Pipes

See 4-2-3/2.3 for damage stability requirements.

2.5.1 Vents Exposed to Weather

Vent pipes on decks exposed to the weather are to have the following heights:

i) 760 mm (30 in.) for those on the freeboard deck; and

ii) 450 mm (17.5 in.) for those on the superstructure deck.

The height is to be measured from the deck to the point where water may have access below.

Commentary:

Where these heights interfere with the working of the unit, a lower height may be accepted, provided that the
closing arrangements and justifications are submitted to ABS for technical assessment and approval.

End of Commentary

The wall thicknesses of vent pipes where exposed to the weather are to be not less than that
specified below.

Nominal Size, d Min. Wall Thickness

d ≤ 65 mm (2.5 in.) 6.0 mm (0.24 in.)

65 mm (2.5 in.) < d < 150 mm (6 in.) by interpolation (1)

d ≥ 150 mm (6 in.) 8.5 mm (0.33 in.)

Note:
1 6 + 0.029(d – 65) mm or 0.24 + 0.026(d – 2.5) in.

2.7 Size
The minimum internal diameter of vent pipes for any tank is not to be less than 50 mm (2 in.). However,
vent pipes of small water/oil tanks of less than 1 m3 (36 ft.3), voids, tunnels and cofferdams are allowed to
have a minimum internal diameter of 38 mm (1.5 in.).

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 77

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

Where tanks are to be filled by pump pressure, the aggregate area of the vents in the tank is to be at least
125% of the effective area of the filling line, except that when overflows are fitted, the area of the overflow
is to be at least 125% of the effective area of the filling line and the vents need not exceed the above
minimum sizes. Notwithstanding the above, the pump capacity and pressure head are to be considered in
the sizing of vents and overflows. When high capacity and/or high head pumps are used, calculations
demonstrating the adequacy of the vent and overflows are to be submitted.

2.9 Termination of Vent Pipes

2.9.1 Termination on or Above Freeboard Deck
Vent pipes for all tanks, double bottoms and other compartments which extend to the shell of the
unit are to be led above the freeboard deck. In addition, vents for ballast tanks and fuel oil tanks
are to be led to the weather.

2.9.2 Termination in Machinery Spaces

Vents for other tanks not adjacent to the shell of the unit are allowed to terminate within the
machinery space but are to be located preclude the possibility of overflowing on electric
equipment, engines or high temperature piping. For low flash point fuel oil, see 4-2-5/9.5.

2.9.3 Sea Chest Vent

Where vent pipes for sea chests are provided, they may terminate with return bends (gooseneck)
above the freeboard deck provided a positively closing shut-off valve is fitted on the vent pipe at
the sea-chest.

Alternatively, the vent pipe terminating with return bends (gooseneck) in the vicinity of the sea-
chest area is acceptable, provided at least two positively closing shut-off valves are fitted on the
vent pipe, such that one valve is located at the sea-chest while the other is as close as practicable
to the shut-off valve at the sea-chest. The above referenced shut-off valve(s) are to comply with
4-2-2/21.1 to 4-2-2/21.9 of these Rules. The vent piping is to be made of extra strong thickness
pipe and is to be attached to the sea-chest by full penetration welds.

Where the vent pipe is terminated below the freeboard deck or in way of the sea-chest area, a
warning plate, stating "The sea chest vent line shut-off valve(s) is/are to be kept closed at all
times, except when used with the operator in attendance" is to be posted in a conspicuous place
near the sea chest shutoff valves.

2.9.4 Protection for Fuel Oil and Lubricating Oil Tanks

Vent pipes for fuel oil service tanks, fuel oil settling tanks and lubricating oil tanks which directly
serve the engines for propulsion and auxiliary generator engines are to be so located and arranged
that in the event of a broken vent pipe, this does not directly lead to the risk of ingress of sea water
splashes or rain water into the above mentioned tanks.

2.9.5 Fuel Oil Tanks Vent Outlets

Vent outlets from fuel oil tanks are to be fitted with corrosion-resistant flame screens having clear
area through the mesh of not less than the required area of the vent pipe and are to be located
where the possibility of ignition of gases issuing from the vent outlets is remote. Either a single
screen of corrosion-resistant wire of at least 12 by 12 meshes per lineal cm (30 by 30 mesh per
lineal inch), or two screens of at least 8 by 8 meshes per lineal cm (20 by 20 mesh per lineal inch)
spaced not less than 13 mm (0.5 inch) nor more than 38 mm (1.5 inch) apart are acceptable.

See also 4-2-3/2.3 for progressive flooding considerations.

Note:

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 78

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

Mesh count is defined as a number of openings in a lineal cm (inch) counted from the center of any wire to the
center of a parallel wire.

2.9.6 Vent Outlet Closing Devices

2.9.6(a) General
Where vent outlets are required by 4-2-3/2.1 to be fitted with automatic closing devices, they are
to comply with the following:

2.9.6(b) Design
i) Vent outlet automatic closing devices are to be so designed that they withstand both
ambient and working conditions, and be suitable for use at inclinations up to and
including ±40°.
ii) Vent outlet automatic closing devices are to be constructed to allow inspection of the
closure and the inside of the casing, as well as changing the seals.
iii) Efficient ball or float seating arrangements are to be provided for the closures. Bars, cage
or other devices are to be provided to prevent the ball or float from contacting the inner
chamber in its normal state and made in such a way that the ball or float is not damaged
when subjected to water impact due to a tank being overfilled.
iv) Vent outlet automatic closing devices are to be self-draining.
v) The clear area through a vent outlet closing device in the open position is to be at least
equal to the area of the inlet.
vi) An automatic closing device is to:

● Prevent the free entry of water into the tanks,

● Allow the passage of air or liquid to prevent excessive pressure or vacuum
developing in the tank.
vii) In the case of vent outlet closing devices of the float type, guides are to be provided to
allow unobstructed operation under all working conditions of heel and trim [see
4-2-3/2.9.6.b.i].
viii) The maximum allowable tolerances for wall thickness of floats is not to exceed ±10% of
thickness.
ix) The inner and outer chambers of an automatic air pipe head is to be of a minimum
thickness of 6 mm (0.24 in). Where side covers are provided and their function is integral
to providing functions of the closing device as outlined in 4-2-3/2.9.6.vi, they are to have
a minimum wall thickness of 6 mm (0.24 in). If the air pipe head can meet the tightness
test in 4-2-3/2.9.6.d.i without the side covers attached, then the side covers are not
considered to be integral to the closing device, in which case a wall thickness of less than
6 mm (0.24 in) is acceptable for side covers.
2.9.6(c) Materials
i) Casings of vent outlet closing devices are to be of approved metallic materials protected
against corrosion.
ii) For galvanized steel air pipe heads, the zinc coating is to be applied by the hot dip method
and the thickness is to be 70 to 100 micrometers (2.756 to 3.937 mil).
iii) For areas of the head susceptible to erosion (e.g. those parts directly subjected to ballast
water impact when the tank is being pressed up, for example the inner chamber area
above the air pipe, plus an overlap of 10° or more to either side) an additional harder
coating is to be applied. This is to be an aluminum bearing epoxy, or other equivalent
coating, applied over the zinc.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 79

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

iv) Closures and seats made of non-metallic materials are to be compatible with the media
intended to be carried in the tank and to seawater, and suitable for operating at ambient
temperatures between -25°C and 85°C (-13°F and 185°F).
2.9.6(d) Type Testing
i) Testing of Vent Outlet Automatic Closing Devices. Each type and size of vent outlet
automatic closing device is to be type tested at the manufacturer’s works or other
acceptable location.

The minimum test requirements for a vent outlet automatic closing device are to include
the determination of the flow characteristics of the vent outlet closing device, the
measurement of the pressure drop versus the rate of volume flow using water and with
any intended flame or insect screens in place and also tightness tests during immersion/
emerging in water, whereby the automatic closing device is to be subjected to a series of
tightness tests involving not less than two (2) immersion cycles under each of the
following conditions:

● The automatic closing device is to be submerged slightly below the water surface at a
velocity of approximately 4 m/min (13.12 ft/min) and then returned to the original
position immediately. The quantity of leakage is to be recorded.
● The automatic closing device is to be submerged to a point slightly below the surface
of the water. The submerging velocity is to be approximately 8 m/min (26.24 ft/min)
and the air pipe vent head is to remain submerged for not less than 5 minutes. The
quantity of leakage is to be recorded.
● Each of the above tightness tests are to be carried out in the normal position as well
as at an inclination of 40 degrees under the strictest conditions for the device. In cases
where such strictest conditions are not clear, tests shall be carried out at an inclination
of 40 degrees with the device opening facing in three different directions: upward,
downward, sideways (left or right). See 4-2-3/Figures 1 to 4.

The maximum allowable leakage per cycle is not to exceed 2 ml/mm (1.312 × 10-2 gal/
inch) of nominal diameter of inlet pipe during any individual test.
ii) Discharge/Reverse Flow Test. The air pipe head is to allow the passage of air to prevent
excessive vacuum developing in the tank. A reverse flow test shall be performed. A
vacuum pump or another suitable device shall be connected to the opening of the air pipe
leading to the tank. The flow velocity shall be applied gradually at a constant rate until
the float gets sucked and blocks the flow. The velocity at the point of blocking shall be
recorded. 80% of the value recorded will be stated in the certificate. Each type and size of
vent outlet automatic closing device is to be surveyed and type tested at the
manufacturer’s works or other acceptable location.
iii) Testing of Nonmetallic Floats. Impact and compression loading tests are to be carried out
on the floats before and after pre-conditioning as follows:

Test temperature °C (°F): -25°C (-13°F) 20°C (68°F) 85°C (185°F)

Test conditions

Dry Yes Yes Yes

After immersing in water Yes Yes Yes

After immersing in fuel oil NA Yes NA

Immersion in water and fuel oil is to be for at least 48 hours.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 80

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

Impact Test. The test may be conducted on a pendulum type testing machine. The floats
are to be subjected to 5 impacts of 2.5 N-m (1.844 lbf-ft) each and are not to suffer
permanent deformation, cracking or surface deterioration at this impact loading.

Subsequently, the floats are to be subjected to 5 impacts of 25 N-m (18.44 lbf-ft) each. At
this impact energy level some localized surface damage at the impact point may occur. No
permanent deformation or cracking of the floats is to appear.

Compression Loading Test. Compression tests are to be conducted with the floats
mounted on a supporting ring of a diameter and bearing area corresponding to those of
the float seating with which it is intended that the float shall be used. For a ball type float,
loads are to be applied through a concave cap of the same internal radius as the test float
and bearing on an area of the same diameter as the seating. For a disc type float, loads are
to be applied through a disc of equal diameter as the float.

A load of 3430 N (350 kgf, 770 lbf) is to be applied over one minute and maintained for
60 minutes. The deflection is to be measured at intervals of 10 minutes after attachment
of the full load.

The record of deflection against time is to show no continuing increase in deflection and,
after release of the load, there is to be no permanent deflection.
iv) Testing of Metallic Floats. The above described impact tests are to be carried out at room
temperature and in the dry condition.

FIGURE 1
Example of Normal Position

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 81

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

FIGURE 2
Example of Inclination 40 degrees Opening Facing Upward

FIGURE 3
Example of Inclination 40 degrees Opening Facing Downward

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 82

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

FIGURE 4
Example of Inclination 40 degrees Opening Facing Sideways

2.11 Overflow Pipes

Overflow pipes discharging through the unit’s side are to be located as far above the deepest load line as
practicable and are to be provided with non-return valves located on the unit’s side. Where the overflow
does not extend above the freeboard deck, an additional efficient and accessible means to prevent water
ingress is to be provided. Such means may consist of another non-return valve located in an accessible
position above the deepest load line. Where it is impracticable to locate the inner valve in an accessible
position, one non-return valve with positive means for closing from an accessible position above the
freeboard or bulkhead deck is acceptable, provided there are arrangements to prevent the valve from being
closed by unauthorized persons and a notice is posted in a conspicuous place at the operating station to the
effect that the valve not to be closed, except as required in an emergency.

Tanks containing combustible and flammable liquids are not to be fitted with overflows discharging
overboard. Overflow pipes from these tanks are to lead to an overflow tank or to a storage tank with
sufficient excess capacity (normally 10 minutes at transfer pump capacity) to accommodate the overflow.
The overflow tank is to be provided with a high-level alarm. Where a sight flow glass is also provided in
the overflow pipe, then such sight glasses are to be fitted only in vertical sections of overflow pipes and be
in readily visible positions.

Where a common vent/overflow header is provided for fuel oil storage and day tanks, the vent/overflow
header need not be fitted with a separate vent pipe leading directly to atmosphere. The individual tanks and
the common vent/overflow header may be vented through the overflow tank vent line to atmosphere,
provided the common vent/overflow header arrangement has the following features/conditions:

i) Each vent/overflow line from the tank to the common header, the vent/overflow common headers
and the vent line from the overflow tank to the atmosphere are to be sized in order to provide a
venting area of at least 125% of the effective fill line area of the shore filling line or onboard
transfer line, whichever is greater. Fuel oil tank scantlings are to consider the height of the
overflow tank vent.
ii) Each storage tank is to be fitted with a high-level alarm and a high-high level alarm. Both level
alarms are to provide visual and audible indication of the alarm condition at a continuously
manned station (such as central control station, engine control room or an equivalent station) from
where filling/transfer operation is controlled.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 83

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

iii) The drop lines from the common headers to the overflow tank are to terminate above the
maximum liquid level in the overflow tank (i.e., above the alarm point where the liquid reaches a
predetermined level in the overflow tank to give the high-level warning).
iv) The venting arrangement of the overflow tank is to permit the free passage of air from the
individual tanks, the vent/overflow headers and the overflow tank vent to atmosphere under all
conditions.
v) The storage tanks are not to be filled by using a cascade filling arrangement (i.e., tanks are not to
be filled by overflowing from one to another).
vi) The fueling station(s) is/are to be manned at all times during bunkering and/or fuel oil transfer
operations.
vii) In lieu of items i) through vi); the overflow line common header may be vented to the atmosphere
in accordance with 4-2-3/2.5 and 4-2-3/2.7, in addition to the overflow tank being fitted with a
dedicated vent pipe.

3 Sounding Arrangements

3.1 General
All tanks, except as noted below, are to be provided with separate sounding pipes or with approved tank-
level indicating apparatus. Where a tank-level indicating system is used, a supplementary manual means of
sounding is to be provided, for tanks which are not always accessible.

Void compartments adjacent to the sea or to tanks containing liquids, and void compartments through
which piping carrying liquids pass are to be fitted with separate sounding pipes, approved tank liquid level
indicating apparatus, or be fitted with means to determine if the void tanks contain liquids. Voids as
defined above which do not comply with this requirement are to be accounted for in the unit’s stability
analysis. See 3-3-2/1.3.4.

3.3 Sounding Pipes

Sounding pipes are not to be less than 32 mm (1.25 in.) internal diameter. Where a sounding pipe exceeds
20 m (65.6 ft) in length, the internal diameter is to be at least 50 mm (2 in.). They are to be led as straight
as possible from the lowest part of the tank or compartment to the bulkhead deck or to a position which is
always accessible. If sounding pipes terminate below the freeboard deck, they are to be provided with
means for closing in the following manner.

Provision is to be made to prevent injuring the unit’s plating by the striking of the sounding
rod. Sounding pipes are not to pass through bilge wells. Alternatively, the pipe is to be at least extra strong
in the bilge well. (See 4-2-1/3.9). Sounding pipes for combustible or flammable fluids are not to terminate
in accommodation spaces.

3.3.1 Oil Tanks

For oil tanks, with quick-acting, self-closing valves.

3.3.2 Other Tanks

For tanks other than oil tanks, with gate valves or a screw cap secured to the pipe with a chain.

3.3.3 Ignition of Spillage

3.3.3(a) Fuel Oil Tanks
Sounding pipes for fuel oil tanks are not to terminate in any space where the risk of ignition of
spillage may exist. They shall not to terminate in machinery spaces or in close proximity to
internal combustion engines, generators, major electric equipment or surfaces with temperatures in
excess of 220°C (428°F) in other spaces. Alternatively Sounding pipes from fuel oil tanks
terminating in machinery spaces, are acceptable provided the following are met:

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 84

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 3 Tank Vents, Overflows and Sounding 4-2-3

i) The sounding pipes terminate in locations remote from ignition hazards or effective
precautions such as shielding are taken to prevent fuel oil spillage from coming into
contact with a source of ignition;
ii) The terminations of sounding pipes are fitted with quick-acting, self-closing valves and
with a small-diameter self-closing test cock or equivalent located below the valve for the
purpose of ascertaining that fuel oil is not present before the valve is opened. Provisions
are to be made so as to prevent spillage of fuel oil through the test cock from creating an
ignition hazard.
iii) An oil level gauge is provided. However, short sounding pipes are acceptable for tanks
other than double bottom tanks without the additional closed level gauge, provided an
overflow system is fitted, see 4-2-3/2.11.
3.3.3(b) Lubricating Oil Tanks
Sounding pipes from lubricating oil tanks terminating in machinery spaces are acceptable
provided that the following are met:

i) The sounding pipes are to terminate in locations remote from the ignition hazards, or
effective precautions, such as shielding, are taken to prevent oil spillage from coming into
contact with a source of ignition.
ii) The termination of sounding pipes is fitted with a quick-acting self-closing valve.
Alternatively, for lubricating oil tanks that cannot be filled by a pump, the sounding pipes
fitted with a appropriate means of closure such as a shut-off valve or a screw cap attached
by chain to the pipe are acceptable.

3.5 Gauge Glasses

Tanks fitted with gauge glasses are acceptable, provided the gauge glasses are fitted with a valve at each
end and protected from mechanical damage.

Tanks containing flammable or combustible fluids are to be fitted with gauge glasses of the flat glass type
having approved self-closing valves at each end. For hydraulic oil tanks located in spaces other than
machinery spaces of Category A, cylindrical gauge glasses with approved self-closing valves at each end
are acceptable, provided such spaces do not contain internal combustion engines, generators, major
electrical equipment or piping having a surface temperature in excess of 220°C (428°F).

Tanks integral with the shell which are located below the deepest load waterline fitted with gauge glasses
are acceptable, provided they are of the flat glass type having approved self-closing valves at each end.

See 5-1-1/3.9.2.6 for the definition of machinery space of Category A.

Commentary:

A self-closing valve for the upper end of the gauge glass is not required if the end is above the maximum liquid level in the
tank. Only a positive closing valve is required for removal of gauge glass in case of maintenance.

End of Commentary

3.7 Level Indicating Device

Where a level-indicating device or system is provided for determining the level in a tank containing
flammable or combustible liquid, failure of the device/system is not to result in the release of the content of
the tank through the device. Penetrations for level switches below the tank top are acceptable provided
they are contained in a steel enclosure or other enclosures not capable of being destroyed by fire. However,
level switches are not be used in place of required level indicating devices. Where the device is located
such that it is subjected to a head of oil, a valve is to be fitted to allow for its removal. If an overflow is not
fitted, means are also to be provided to prevent overfilling of the tank in the event of malfunctioning of the
indicating device/system.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 85

 PART 4
CHAPTER 2
Pumps and Piping Systems

SECTION 4
Bilge and Ballast Systems and Tanks

1 Objective

1.1 Goal
The bilge and ballast systems covered in this section shall be designed, constructed, operated and
maintained to:

Goal No. Goal

STAB 4 detect accumulated liquids.

STAB 5 be able to remove accumulated liquids to mitigate the effects of flooding.

STAB 6 provide means to control the overall unit weight and distribution to maintain adequate trim and
stability.

FIR 1 prevent the occurrence of fire and explosion.

FIR 4 detect, contain, control and suppress or swiftly extinguish a fire in the compartment of origin.

ENV 1 prevent and minimize oil pollution due to unit operation and accidents.

ENV 8 have provisions in place to control/minimize the introduction of unwanted aquatic organisms and
pathogens into the marine environment from units’ ballast waters and sediment discharges.

AUTO 1 perform its functions as intended and in a safe manner.

AUTO 2 indicate the system operational status and alert operators of any essential machinery/systems
deviate from its defined design/operating conditions or intended performance.
AUTO 3 have an alternative means to enable safe operation in the event of an emergency or failure of
remote control.

AUTO 4 provide the equivalent degree of safety and operability from a remote location as those provided
by local controls.

AUTO 5 provide a safety system that shall automatically lead machinery controlled to a fail-safe state in
response to a fault which may endanger the safety of persons on board, machinery/equipment or
environment.

AUTO 6 independently perform different functions, such that a single failure in one system will not render
the others inoperative.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 86

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 4 Bilge and Ballast Systems and Tanks 4-2-4

Materials are to be suitable for the intended application in accordance with the following Goals and
support the Tier 1 goals listed above.

Goal No. Goal

MAT 1 The physical, mechanical and chemical properties of base materials and weldments are to meet
the design requirements appropriate for the application, operating conditions and environment.

1.2 Functional Requirements

In order to achieve the above-stated Goals, the design, construction, installation and maintenance for the
bilge and ballast systems are to be in accordance with the following Functional Requirements:

Functional Functional Requirements

Requirement No.

Stability (STAB)

STAB-FR1 Provide means to dispose of or clear accumulated liquids in spaces within the unit due to
condensation, leakage, washing, or fire fighting.

STAB-FR2 Provide emergency or backup means to control flooding quickly as a result of damage to piping
systems in the propulsion machinery space.

STAB-FR3 Provide means to enhance the bilge/ballast system availability and redundancy of the system such
that it is available and operable under all defined seagoing and environmental conditions including
damage conditions.

STAB-FR4 Provide accessible means to preclude the entry of debris or other contaminants into the systems
during normal operations.

STAB-FR5 (AUTO) On column stabilized units, provide means to control the bilge system in a centralized location
together with the ballast system.

STAB-FR6 (AUTO) On column stabilized units, provide suitable and duplicated monitoring and warning devices from a
centralized location for normally inaccessible compartments where high bilge levels are expected.

STAB-FR7 (ENV/ Reduce the risk of failure of joints and risk of flooding/contamination caused by damage to piping
MAT) and mitigate hazards upon failure.

STAB-FR8 (AUTO) Valves required to control flooding/ballasting and their controls are to be readily accessible and
suitably arranged to enable safe operation by the crew. Means are to be provided to close remote
control valves in the event of loss of control power.

STAB-FR9 Provide means to prevent damaged piping causing cross-flooding in case the valves are in open
position during loss of power or incidental damage.

STAB-FR10 Provide means to prevent backflow from a drain tank to the other drain lines and spaces.

STAB-FR11 Provide a ballast system to adjust trim, heel and displacement of the unit for the stability purposes.

STAB-FR12 Provide backup means of communication, operations and emergency disconnection at the
(AUTO) centralized control station in case of loss of remote control of ballast system.

STAB-FR13 Provide local centralized control that can be operated in the event of loss of remote control of ballast
(AUTO) system.

STAB-FR14 Ballast system is to be designed with independence of power supply, components, or subsystems
(AUTO) such that failure of power, component or subsystem are in failsafe status and allow other subsystems
to continue their operations.

STAB-FR15 Provide sufficient information relating to unit stability for effective ballast control at the centralized
(AUTO) ballast control station.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 87

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 4 Bilge and Ballast Systems and Tanks 4-2-4

Functional Functional Requirements

Requirement No.

Fire Safety (FIR)

FIR-FR1 Provide means to prevent the escape of the fire extinguishing medium for the protected space
through gravity drain lines.

FIR-FR2 Be arranged or be provided with means to prevent the ignition of flammable gases and liquids.

Protection of Environment (ENV)

ENV-FR1 Prevent the transportation of unwanted marine organisms and pathogens between different
geographical areas through the unit’s ballast water.

ENV-FR2 Minimize risk of cross-contamination and oil pollution when switching to bilge/ballast operations.

Automation (Control, Monitoring and Safety Systems) (AUTO)

AUTO-FR1 Remote control of bilge/ballast system is to be complemented by suitable display and monitoring of
the system at the remote location for effective control.

The Functional Requirements covered in the cross-referenced Rules are also to be met.

1.3 Compliance
A unit is considered to comply with the Goals and Functional Requirements when the prescriptive
requirements are complied with or when an alternative arrangement has been approved. Refer to Part 1D,
Chapter 2.

2 General Arrangement of Bilge Systems for Surface-Type Units

2.1 General
A bilge system is to be provided in all units capable of pumping from and draining any compartment when
the unit is on an even keel and either upright or listed 5 degrees. For this purpose, wing suctionsare
required except in narrow compartments at the ends of the unit. Arrangements are to be made whereby
water in the compartment drains to the suction pipes. Means are to be provided for draining water from all
tank tops and other watertight flats. Peak tanks and comparatively small compartments, such as chain
lockers, echo sounder spaces and decks over peak tanks, etc., are acceptable to be drained by ejectors or
hand pumps. Where ejectors are used for this purpose, the overboard discharge arrangements are to comply
with 4-2-2/23. See also 3-2-4/19.3 of the Marine Vessel Rules. For cases where a suction line is led through
the forepeak bulkhead, see 4-2-1/11.17.

Notes:

For the purpose of this Section, comparatively small compartments are those which meet the following criteria:

i The volume of the compartment is not to exceed

(LBD)/1000

where L, B and D as defined in 4-2-4/9.1.2; and

ii The wetted surface of the compartment, excluding stiffening members, when its volume is half-filled with water is
not to exceed 100 m2 (1076 ft2)

2.3 Number of Bilge Pumps

At least two power-driven bilge pumps are to be provided, one of which may be attached to the propulsion
unit.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 88

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 4 Bilge and Ballast Systems and Tanks 4-2-4

2.5 Direct Bilge Suctions

One of the independent power pumps is to be fitted with a suction led directly from the main machinery-
space bilge to the suction valve chest of the pump so arranged that it can be operated independently of the
bilge system. The size of this line is to be such that the pump delivers its full capacity. If watertight
bulkheads separate the main machinery space into compartments, such a direct suction is to be fitted to
each compartment unless the pumps available for bilge service are distributed throughout these
compartments, in which case, at least one pump in each such compartment is to be fitted with a direct
suction in its compartment. The direct bilge suction is to be controlled by a stop-check valve.

2.7 Emergency Bilge Suctions

In addition to the direct bilge suction required by 4-2-4/2.5, emergency bilge suction is to be fitted for the
main machinery space for surface-type units 55 m (180 ft) or more in length. The emergency bilge suction
is to be directly connected to the largest independently driven pump in the main machinery space, other
than the required bilge pumps. Where this pump is not suitable, the second largest suitable pump in the
main machinery space are acceptable used for this service, provided that the selected pump is not one of
the required bilge pumps and its capacity is not less than that of the required bilge pump.

The emergency bilge line is to be provided with a suction stop-check valve, which is to be so located as to
enable rapid operation and a suitable overboard discharge line. For the emergency bilge inlet, the distance
between the open end of the suction inlet and the tank top is to allow a full flow of water. The hand wheel
of emergency bilge suction valve is to be positioned not less than 460 mm (18 in.) above the floor plates.

In addition, the following arrangements are also to be complied with, as applicable:

i) For internal-combustion-engine propulsion machinery spaces, the area of the emergency bilge
suction pipe is to be equal to the full suction inlet of the pump selected.
ii) For steam propulsion machinery spaces, the main cooling water circulating pump is to be the first
choice for the emergency bilge suction, in which case, the diameter of the emergency bilge suction
is to be at least two-thirds the diameter of the cooling water pump suction.

3 General Arrangement of Bilge Systems for Column-Stabilized Units

and Self-Elevating Units

3.1 Permanent Systems

Except as indicated in 4-2-4/3.3 and 4-2-4/3.5 below, all compartments are to have a permanently installed
bilge or drainage system. Compartments below the bulkhead deck containing essential equipment for
operation and safety of the unit are to be capable of being pumped out by at least two power-driven bilge
pumps or equivalent. In addition for column stabilized units, the bilge system in each pump room is to be
operable from the central ballast control station.

3.3 Void Compartments

Void compartments adjacent to the sea or to tanks containing liquids, and void compartments through
which piping conveying liquids pass, are to be drained by permanently installed bilge or drainage systems
or by portable means. If portable pumps are used, two are to be provided and both pumps and
arrangements for pumping are to be readily accessible. Void compartments as defined above which are not
provided with bilge or drainage systems complying with the above are to be accounted for in the unit’s
stability analysis. See 3-3-2/1.3.4 and 4-2-2/27.3.

3.5 Chain Lockers

Chain lockers are to be drained by permanently installed bilge or drainage systems or by portable means.
Means are to be provided for removal of mud and debris.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 89

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 4 Bilge and Ballast Systems and Tanks 4-2-4

3.7 Bilge Alarm

Propulsion rooms and pump rooms in lower hulls of column-stabilized units are to be provided with two
independent systems of high bilge water level detection, giving an audible and visual alarm at the central
ballast control station.

5 Bilge Piping (All Units)

5.1 General
The arrangement of the bilge pumping system is to be such as to prevent the possibility of water or oil
passing into the machinery spaces, or from one compartment to another, whether from the sea, water
ballast or oil tanks. The bilge mains are to have separate control valves at the pumps.

5.3 Installation
Bilge pipes passing through compartments intended for the carriage of oil are to be of either steel or
wrought iron. Where bilge pipes pass through deep tanks, means are to be provided to prevent the flooding
of other spaces in the event of a pipe breaking or joint leaking in the tanks. Such means may consist of an
oiltight or watertight tunnel, or making the lines of extra-strong steel pipe (see 4-2-1/3.9) properly installed
to take care of expansion and having all joints within the tank welded or extra-strong flanged joints (e.g.,
one pressure rating higher). The number of flanged joints is to be kept to a minimum. When a tunnel is not
employed and the line runs through a deep tank, bilge pipes are to have non-return valves fitted at the open
ends.

5.5 Manifolds, Cocks and Valves

All manifolds, cocks and manually operated valves in connection with the bilge pumping arrangement are
to be in positions which are accessible at all times under ordinary circumstances. Where such valves are
located in normally unmanned spaces below the assigned load line and which are not provided with high
bilge water level alarms, then the valves are to be operable from outside such spaces.

All valves in the machinery space controlling the bilge suctions from the various compartments are to be of
the stop-check type. If valves are fitted in the open ends of bilge pipes, they are to be of the non-return
type.

Remote control of bilge valves is to be clearly marked at the control station and means are to be provided
to indicate whether the valves are open or closed. The indicator is to rely on movement of the valve
spindle, or be otherwise arranged with equivalent reliability.

5.7 Common-main-type Bilge Systems

Where permitted, this type of system is to have the fore-and-aft piping installed inboard of the assumed
penetration zone, as defined in 3-3-2/3.5. The control valves required in the branches from the bilge main
are to be accessible at all times and are to be of the stop-check type with an approved type of remote
operator. Remote operators are to be located in a manned machinery space, at an accessible position above
the freeboard deck, or along underdeck walkways. Remote operators may be of the hydraulic, pneumatic
or reach-rod type.

5.9 Strainers
Bilge lines in machinery spaces other than emergency suctions are to be fitted with strainers, easily
accessible from the floor plates, and are to have straight tail pipes to the bilges. The open ends of the bilge
lines in other compartments are to be fitted with suitable strainers having an open area of not less than
three (3) times the area of the suction pipe. In addition, strainers are to be fitted in accessible positions
between the bilge manifolds and the pumps.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 90

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 4 Bilge and Ballast Systems and Tanks 4-2-4

5.11 Gravity Drains

Gravity drains that penetrate the main machinery space watertight bulkheads below the freeboard deck and
terminate within the main machinery space are to be fitted with a valve operable from above the freeboard
deck or with quick-acting, self-closing valves. The remotely operated valve is to be located in the main
machinery space. Other locations are to be proposed with justification for ABS technical assessment and
approval. When gravity drains from other spaces are terminated in cargo holds, the cargo hold bilge well is
to be fitted with a high-level alarm. Gravity drains which terminate in spaces which are protected by fixed
gas extinguishing systems are to be fitted with means to prevent the escape of extinguishing medium.

5.13 Bilge Suctions from Hazardous Areas

Hazardous and non-hazardous areas are to be provided with separate drainage or pumping arrangements.

5.15 Exceptions
The bilge arrangements of units intended for restricted or special services that do not meet the
requirements in 4-2-4/5 are to be submitted with justification to ABS for technical assessment and
approval.

7 Bilge Pumps (All Units)

7.1 General
Sanitary, ballast and general-service pumps are acceptable as independent power bilge pumps, provided
they are of the required capacity and are fitted with stop valves so that when a pump is used for one
service, the other services are isolated. Where centrifugal pumps are installed, means for priming are to be
provided.

7.3 Arrangement and Capacity

Each bilge pump is to be capable of giving a speed of water through the bilge main, required by 4-2-4/9.1
or 4-2-4/9.3, as applicable, of not less than 2 m (6.6 ft) per second. The pump capacity, Q, in this case is to
be determined from the following equation.

Q = 5 . 66d2 /103 m3/hr

Q = 16 . 1d2 gpm

where

d = diameter of main-bilge-line suction, mm (in.), required by 4-2-4/9.

When more than two pumps are connected to the bilge system, their arrangement and aggregate capacity
are not to be less effective.

9 Size of Bilge Suctions

9.1 Surface-Type Units

The least internal diameter of bilge suction pipes is to be that of the nearest commercial size within 6 mm
(0.25 in.) of the diameter determined by the following equations.

9.1.1 Main Line

For the diameter of main-bilge-line suctions and direct bilge suctions to the pumps:

d = 25 + 1 . 68 L B + D mm

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 91

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 4 Bilge and Ballast Systems and Tanks 4-2-4

d = 1 + L B + D /2500 in.

9.1.2 Branch Lines

For the equivalent diameter of the combined branch suctions to a compartment:

d = 25 + 2 . 16 c B + D mm

d = 1 + c B + D /1500 in.

where

d = internal diameter of pipe, in mm (in.)

L = length of unit, in m (ft)
B = breadth of unit, in m (ft)
D = molded depth to bulkhead or freeboard deck, in m (ft)
c = length of compartment, in m (ft)

L, B, and D are defined in Section 3-1-1 of the Marine Vessel Rules for ship-type units and Section
3-1-1 of the Barge Rules for barge-type units.

Note:

For comparatively small compartments as defined in 4-2-4/1.1, the equation in 4-2-4/9.3.2 may be used as an
alternative in the calculation of the required size of branch lines.

9.1.3 Main Line Reductions

In units where engine room bilge pumps are fitted primarily for drainage within the engine room,
L may be reduced by the combined length of the tanks. In such cases, the cross sectional area of
the bilge main is not to be less than twice the required cross sectional area of the engine room
branch lines.

9.1.4 Size Limits

No main suction piping is to be less than 63 mm (2.5 in.) internal diameter. No branch piping need
be more than 100 mm (4 in.) I.D., nor is it to be less than 51 mm (2 in.) I.D. in diameter, except
that for drainage of small pockets or spaces 38 mm (1.5 in.) I.D. pipe is acceptable.

9.3 Column-Stabilized Units and Self-Elevating Units

9.3.1 Main Line
The cross sectional area of the bilge main is not to be less than the combined areas of the two
largest required branch suctions.

9.3.2 Branch Lines

The size of branch suctions and drains from each compartment is not to be less than that
determined from the following equation:

d = 2 . 15 A + 25 mm

d= A/1500 + 1 in.

where

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 92

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 4 Bilge and Ballast Systems and Tanks 4-2-4

d = internal diameter of the branch suction to the nearest 5 mm (0.20 in.)

A = wetted surface in m2 (ft2) of
i) Single compartment drained by the branch suction, excluding stiffening
members, when the compartment is half-filled.
ii) The two largest compartments, excluding stiffening members, when the
compartments are half-filled where multiple compartments are drained
together.
9.3.3 Size Limits
The internal diameter of any bilge line is not to be less than 50 mm (2 in.).

11 Ballast Piping (All Units)

11.1 General
The arrangement of the ballast pumping system is to be such as to prevent the possibility of water or oil
passing into the machinery spaces, or from one compartment to another, whether from the sea, water
ballast or oil tanks. The ballast mains are to be provided with a stop valve, so that when the pump is used
for one service, the other services are isolated.

11.3 Installation
Ballast pipes passing through compartments intended for the carriage of oil are to be either steel or
wrought iron. Where ballast pipes pass through deep tanks, means are to be provided to prevent the
flooding of other spaces in the event of a pipe breaking or joint leaking in the tanks.

Such means may consist of an oiltight or watertight tunnel, or making the lines of extra-strong steel pipe
(see 4-2-1/3.9) installed with expansion bends and having all joints within the tank welded or extra-strong
flanged joints (e.g., one pressure rating higher). The number of joints is to be kept to a minimum. Slip
joints are not permitted.

11.5 Controls for Ballast Tank Valves

Ballast tank valves are to be arranged so that they remain closed at all times, except when ballasting. For
this purpose, manual screw thread operated valves or positive holding arrangements for butterfly type
valves or other approved arrangement is acceptable. Where installed, remote controlled valves are to be
either arranged so that they close and remain closed upon loss of control power or arranged so they remain
in their last position and are provided with a readily accessible manual means of closing in case of loss of
power to the valve control system. Remote control of ballast valves is to be clearly marked at the control
station and means are to be provided to indicate whether the valve is open or closed.

11.7 Exceptions
The ballast arrangements of units intended for restricted or special services that do not meet the
requirements in 4-2-4/11 are to be submitted with justification to ABS for technical assessment and
approval.

11.9 Ballast Water Treatment Systems

Where a ballast water treatment system is to be installed, it is to comply with the requirements in Part 6
Chapter 6 of Marine Vessel Rules, as applicable, and the same is to be verified by the ABS Surveyor.

When a system is installed during new construction, the unit is to also comply with the ABS Guide for
Ballast Water Exchange if used as a contingency measure during situations when the ballast water
treatment system needs repairs, is out of service, or unavailable. The use of ballast water exchange as a
contingency measure is subject to approval from the flag Administration or the Port State Authority. The
ballast water management plan is to include instructions for the Master to seek permission from the port

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 93

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 4 Bilge and Ballast Systems and Tanks 4-2-4

being visited prior to commencing ballast exchange as a contingency measure in case of inoperability of
the ballast water treatment system.

13 Ballasting Systems for Column-Stabilized Units

13.1 General
The ballast system is to be designed and arranged such that the system can take suction from and deballast
any ballast tank under normal operating and transit conditions. The system is to be capable of restoring the
unit to a normal operating or transit draft and a level trim condition, when subject separately to each of the
following:

i) The assumed damaged conditions as specified in 3A-3-2/1.3.2(a) with any one pump inoperable.
ii) The flooding specified in 3A-3-2/1.3.2(b).

In addition, the system is to be capable of raising the unit, starting from a level trim condition at deepest
normal operating draft, either a distance of 4.6 m (15 ft) or to the severe storm draft, whichever distance is
greater, within three hours (calculations are to be submitted). The ballasting procedure is to be submitted
for information and is to be provided to the unit’s operating personnel.

13.3 Manifolds
Ballast suctions are to be led from readily accessible manifolds unless independent pumps are provided for
each tank. Ballast systems are to be arranged to prevent the inadvertent transfer of ballast water from one
quadrant to any other quadrant of the unit.

13.5 Pumps
13.5.1 Number
At least two independent ballast pumps are to be capable of taking suction on each ballast tank. In
the case of units with two lower hulls, each hull is to be provided with at least two independently
driven ballast pumps. Units with more than two lower hulls or of unusual configuration are subject
to ABS technical assessment and approval.

13.5.2 Pump Performance

At least two pumps are to be capable of effectively emptying each intact tank at maximum normal
operating draft when the unit is subject to the assumed damage conditions specified in
3A-3-2/1.3.2. [Note: Loss of a pump(s) due to flooding of a pump room is to be considered in
meeting this requirement.] Each of the pumps utilized in meeting the above requirement is to have
adequate head/capacity characteristics and available net positive suction head (NPSHa) to operate
at the angles of heel and trim associated with the conditions specified in 3A-3-2/1.3.2 at a capacity
of not less than 50% of the capacity required from that pump to meet the criteria of 4-2-4/13.1.
Counter-flooding is not to be considered as a means to improve the suction head available to the
ballast pumps.

Pump data and calculations substantiating compliance with this requirement are to be submitted.
The use of submersible pumps are subject to ABS technical assessment and approval

13.7 Ballast Control Features

13.7.1 Centralized Control Station
13.7.1(a) Location.
A centralized control station is to be provided. It is to be located above the worst damage
waterline and in a space clear of the assumed extent of damage specified in 3A-3-2/3.5.2,
protected from weather and readily accessible when the unit is subjected to the severe storm and
damage, as defined in 3A-3-2/1.3.1 and 3A-3-2/1.3.2.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 94

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 4 Bilge and Ballast Systems and Tanks 4-2-4

13.7.1(b) Controls and Indications.

The central ballast control station is to be fitted with the following control and indicating systems,
having appropriate audible and visual alarms.

i) Ballast pump control system

ii) Ballast pump status indicating system
iii) Ballast valve control system
iv) Ballast valve position indicating system
v) Draft indicating system
vi) Tank level indicating system
vii) Heel and trim indicators
viii) Electric power availability system (main and emergency)
ix) Ballast control hydraulic or pneumatic pressure indicating system, where applicable.
x) Bilge system in each pump room. See 4-2-4/3.1
xi) Bilge alarms of propulsion and pump rooms in lower hulls. See 4-2-4/3.7.
13.7.1(c) Communication.
A means of communication, which is independent of the unit’s service electrical system, is to be
provided between the central ballast control station and those spaces containing the local controls
for ballast pumps and associated ballast valves.

13.7.1(d) Back-up Station.

Back-up station is not required but if fitted, it is to comply with the requirements in
4-2-4/13.7.1(a) and 4-2-4/13.7.1(c), except that the back-up station need not be located above the
worst damaged waterline.

13.7.2 Independent Local Control

All ballast pumps and valves are to be fitted with independent local control operable in the event
of failure of the remote control from the central ballast control station. These independent local
controls need not be power operated. The independent local controls for each ballast pump and its
associated valves are to be from the same location. For communication, see 4-2-4/13.7.1(c).

13.7.3 Safety Features

13.7.3(a) Independency.
i) All Systems. The systems listed in 4-2-4/13.7.1(b) are to function independently of one
another or have sufficient redundancy so that a failure in one system does not jeopardize
the operation of any of the other systems.
ii) Pump/Valve Control Systems. The ballast pump and ballast valve control systems are to be
arranged such that loss of any one component does not cause loss of operation of the
other pumps or valves. This requirement does not apply to those parts of a control system
dedicated to a single ballast valve nor does it apply to manifolds serving exclusively those
dedicated systems.
13.7.3(b) Dual Power Source.
For those systems listed in 4-3-2/5.3.10(a), the source of any electrical power is to comply with
the requirements in 4-3-2/5.3. Where the power source is pneumatic or hydraulic, there are to be at
least two power units designed to function at the inclination angles in 4-3-2/5.5.1.

13.7.3(c) Disconnects.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 95

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 4 Bilge and Ballast Systems and Tanks 4-2-4

Means are to be provided at the central ballast control station to isolate or disconnect the ballast
pump control and ballast valve control systems from their sources of electrical, pneumatic or
hydraulic power.

13.7.3(d) Electronic Systems.

Where microprocessor, computer-operated or multiplex type systems form part of the control
system, they are to have back-up capability for continued operation upon loss of any single major
component.

13.7.3(e) Valve Controls.

The ballast valve control system is to be designed and arranged so that there is not continuing
transfer of ballast upon loss of power. See also 4-2-4/13.3. Ballast tank valves are to close
automatically upon loss of power. They are to remain closed upon reactivation of control power
until they are intentionally opened.

13.7.4 Valve Position Indicating Systems

A means to indicate whether a valve is open or closed is to be provided at each location from
which the valve is controlled. The indicators are to rely on movement of the valve spindle or be
otherwise arranged with equivalent reliability.

13.7.5 Draft Indicating System

The draft indicating system is to indicate the draft at each corner of the unit.

13.7.6 Tank Level Indicating System

The tank level indicating system is to indicate the liquid levels in all ballast tanks and in other
tanks, such as fuel oil, fresh water, drilling water or liquid storage tanks, the filling of which could
affect the stability of the unit. Tank level sensors are not to be located in the tank suction lines.

A secondary means of determining levels in ballast tanks, which may be a sounding pipe, is also
to be provided.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 96

 PART 4
CHAPTER 2
Pumps and Piping Systems

SECTION 5
Fuel Oil Systems and Tanks

1 Objective

1.1 Goals
The fuel oil systems and tanks covered in this section is to be designed, constructed, operated, and
maintained to:

Goal No. Goal

STRU 1 in the intact condition, have sufficient structural strength to withstand the environmental
conditions, operational loads anticipated during the design life.

PROP 2 provide redundancy and/or reliability to maintain propulsion.

POW 3 provide means to control the overall unit weight and distribution to maintain adequate trim and
stability.

POW 4 enable all electrical services required for safety to be available during emergency condition.

FIR 1 prevent the occurrence of fire and explosion.

FIR 2 reduce the risk of life caused by fire.

FIR 3 reduce the risk of damage caused by fire to the unit, its cargo and the environment.

ENV 1 prevent and minimize oil pollution due to unit operation and accidents.

SAFE 1.1 minimize danger to person on board, the unit, and surrounding equipment/installation from
hazards associated with machinery and systems.

AUTO 2 indicate the system operational status and alert operators of any essential machinery/systems
deviate from its defined design/operating conditions or intended performance.

AUTO 4 provide the equivalent degree of safety and operability from a remote location as those provided
by local controls.

Materials are to be suitable for the intended application in accordance with the following goals and support
the Tier 1 goals listed above.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 97

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

Goal No. Goal

MAT 1 The physical, mechanical and chemical properties of base materials and weldments are to meet
the design requirements appropriate for the application, operating conditions and environment.

1.2 Functional Requirements

In order to achieve the above-stated goals, the design, construction, and maintenance of the fuel oil
systems and tanks are to be in accordance with the following functional requirements:

Functional Functional Requirements

Requirement No.

Structure (STRU)

STRU-FR1 (FIR) Structural integrity is to be provided for fuel oil tanks to minimize fire risk in the tanks and adjacent
spaces.

Propulsion (PROP)

PROP-FR1 Fuel systems for propulsion and essential services are to be designed and arranged so that there is
sufficient supply of fuel at defined operating conditions upon single failure.

PROP-FR2 Provide redundancy and/or reliability requirements to minimize loss of propulsion and essential
services of the unit in the event of a single failure.

PROP-FR3 Provide means to remove contaminants in the system to prevent equipment damage.

PROP-FR4 Operation is not to be affected when the equipment/component is isolated for repair or maintenance.

Power Generation & Distribution (POW)

POW-FR1 Means of closure for fuel tanks used for emergency services are to be independent of means of
closure of other fuel tanks so that emergency source of power remains available.

POW-FR2 Design is to prevent major loss of emergency or essential services in the event of failure in the
remote control valve system.

Materials (MAT)

MAT-FR1 (FIR) Material is to be compatible with fluid media conveyed, external environment exposed to and is to
withstand the effects of heat/fire.

Protection of Environment (ENV)

ENV-FR1 (FIR) Provide means of containment and drainage where spillage or leakage is expected during normal
operations.

ENV-FR2 Oil tanks are to be arranged in suitable locations to prevent and minimize oil pollution in the event
of accidents.

ENV-FR3 (FIR) Fuel oil piping is to be independent of other piping system to prevent oil pollution and cross-
contamination.

Fire Safety (FIR)

FIR-FR1 Be arranged or be provided with means to prevent the ignition of flammable gases and liquids.

FIR-FR2 Provide arrangements to maintain the temperature of heating devices below auto-ignition point.

FIR-FR3 Provide means to prevent backflow and backpressure across the piping affecting the systems and
machinery spaces.

FIR-FR4 Piping design is to mitigate hazards due to the failure of joints.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 98

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

Functional Functional Requirements

Requirement No.

FIR-FR5 Provide means to isolate fuel system of each engine during a fire in order not to affect the operation
of the other engines.

FIR-FR6 (AUTO) Provide means to control leaks by restricting fuel supply with local control and remote closure from
a protected location, such that they can be safely closed in the event of fire in the space to prevent
further escalation of hazards.

FIR-FR7 Means shall be provided to limit the accumulation of flammable vapors.

FIR-FR8 (AUTO) Provide means to detect the contamination of the heating medium by flammable fluids.

FIR-FR9 (AUTO) Provide means to check and monitor the temperature of low flash point fuel such that it does not
reach its flash point during all defined operating conditions.

Safety of Personnel (SAFE)

SAFE-FR1 (FIR) Provide means to prevent oil spray or oil leakage into machinery air intakes or other sources of
ignition.

The functional requirements in the cross-referenced Rules/Regulations are also to be met.

1.3 Compliance
A unit is considered to comply with the goals and functional requirements when the applicable prescriptive
requirements are complied with or when an alternative arrangement has been approved. Refer to Part 1D,
Chapter 2.

2 Fuel Oil Piping System – General

2.1 Arrangement
2.1.1 Tanks
2.1.1(a) Structural Tanks
Fuel-oil tanks are to be part of the structure and located outside of machinery spaces of Category
A. Where fuel-oil tanks, other than double bottom tanks, are necessarily located adjacent to or
within machinery spaces of Category A. the arrangements are to reduce the area of the tank
boundary common with the machinery space of category A to not more than two sides and to
comply with the following:

i) Fuel tanks having boundaries common with machinery spaces of category A are not to
contain fuel oils having flash point of 60°C (140°F) or less.
ii) At least one of their vertical sides is to be contiguous to the machinery space boundary.
The arrangements in 4-2-5/2.1 FIGURE 1 are acceptable for structural tanks provided the
requirements of 4-2-5/11 are complied with. (The side shell is not being included in
contiguous boundary of the machinery space of Category A.)
iii) The bottom of the fuel oil tank is not to be so exposed that it comes in direct contact with
flame should there be a fire in a Category A machinery space of Category A. The fuel
tank is to extend to the double bottom. Alternatively, the bottom of the fuel oil tank is to
be fitted with a cofferdam. The cofferdam is to be fitted with suitable drainage
arrangements to prevent accumulation of oil in the event of oil leakage from the tank.
2.1.1(b) Independent or Free Standing Tanks
Free standing tanks are completely self-supporting and do not form part of the unit's structure. The
use of free standing fuel oil tanks is to be avoided. See the intent of 4-2-5/2.2.1(a). Where this is

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 99

Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

unavoidable free-standing fuel oil tanks in machinery spaces of Category A are to be kept to a
minimum and their construction and installation are to be as follows:

Free- standing fuel oil tanks are to be placed in an oil tight spill tray of ample size (e.g., large
enough to cover leakage points such as manholes, drain valves, gauge glasses, etc.), which drains
to a suitable drain tank.

Free- standing fuel oil tanks are not to be located in areas where spillages or leakages on heated
surfaces can constitute a hazard. In particular, they are not to be located over boilers.

i) Free- standing fuel tanks are to be of approved metal construction.

ii) Free- standing Atmospheric Tanks
a) For tanks over 1510 liters (400 gallons), the design head is not to be less than
hydrostatic load at the tank vent outlet or1.2m (4 ft ) above the tank top,
whichever is greater, and the design safety factor is to be four on the ultimate
strength of the material used.
b) The plate thickness is not to be less than 5 mm (0.2 in.) for the tanks with
capacity more than 570 liters (150 gallons). For the tanks with capacity 570 liters
(150 gallons) or less, the minimum allowable plate thickness is not to be less than
3 mm (0.12 in.).
c) The tanks are to be pressure tested to 1.5 times the design head, but no case less
than 0.35 bar (5 psi).
iii) Free- standing Pressurized Tanks. Pressurized tanks are to be designed, constructed and
tested in accordance with Section 4-4-1 of the Marine Vessel Rules, as applicable.
iv) Additional consideration for free-standing tank design. The tank design is also to consider
the stresses due to external nozzle loads and dynamic loads arising out of the unit ship
motion. These stresses are to be within the allowable limits specified under
4-2-5/2.2.1(b)ii) and 4-2-5/2.2.1(b)iii) above.
v) Special attention is to be given to the mounting, securing arrangement, and electrical
bonding of the tanks.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 100
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

FIGURE 1
Acceptable Fuel Oil Tanks Arrangements Inside Category A Machinery Spaces

2.1.2 Spillage
No fuel oil tank is to be situated where spillage or leakage therefrom can constitute a hazard by
falling on heated surfaces or electrical equipment. Precautions are to be taken to prevent any oil
that may escape under pressure from any pump, filter or heater from coming into contact with
heated surfaces.

To prevent the ignition of fuel oil, all hot surfaces, e.g. steam and exhaust piping, turbochargers,
exhaust gas boilers, etc. likely to reach a temperature above 220°C (428°F) during service are to
be insulated with non-combustible, and preferably non-oil-absorbent, materials. Such insulation
materials, if not impervious to oil, are to be encased in oil-tight steel sheathing or equivalent. The
insulation assembly is to be well installed and supported having regard to its possible deterioration
due to vibration.

2.1.3 Service and Settling Tanks

At least two fuel oil service tanks are to be provided for propulsion and essential services. The
capacity, with one service tank unavailable, is to be sufficient for at least eight hours operation of
the propulsion plant, if any, at maximum continuous rating and the generator plant (excluding
emergency generator) at the normal sea load. See also 4-2-3/2.9.4.

Where the propulsion plant and auxiliary machinery are supplied by different service tanks, or
where more than one type of fuel is used onboard the unit, the number and capacity of the fuel oil
service tanks is to be sufficient such that the propulsion plant, including all auxiliary machinery
vital for propulsion, and the generator plant have both a main fuel oil supply and a back-up fuel oil
supply. The capacity of the tanks, with one service tank unavailable, is to be sufficient to provide
the machinery it serves with enough fuel oil for at least eight hours operation, as required above.

A service tank is a fuel tank which contains only fuel of a quality ready for use, that is, fuel of a
grade and quality that meets the specification required by the equipment manufacturer. A service
tank is to be declared as such and is not to be used for any other purpose.

Commentary:

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 101
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

For examples of acceptable arrangements, refer to the latest revision of the IACS UR SC 123.

1) EXAMPLE 1

i) Main and Auxiliary Engines and Boiler(s) operating with Heavy Fuel Oil (HFO) (one-fuel
unit)

HFO Service Tank Capacity HFO Service Tank Capacity MDO Tank For initial cold
for at least 8 h Main Engine for at least 8 h Main Engine starting or repair work of
+ Auxiliary Boiler + + Auxiliary Boiler + Engines/Boilers
Auxiliary Engine Auxiliary Engine

ii) Equivalent Arrangement

HFO Service Tank Capacity for at least 8 h MDO Service Tank Capacity for at least 8 h
Main Engine + Auxiliary Boiler + Auxiliary Main Engine + Auxiliary Boiler + Auxiliary
Engine Engine

iii) This arrangement only applies where main and auxiliary engines can operate with heavy fuel
oil under all load conditions and, in the case of main engines, during maneuvering. For pilot
burners of Auxiliary Boilers, if provided, an additional MDO tank containing fuel for 8 hours
of operation is necessary.

2) EXAMPLE 2

i) Main Engine(s) and Auxiliary Boiler(s) operating with HFO and Auxiliary Engine operating
with Main Diesel Oil (MDO)

HFO Service Tank HFO Service Tank MDO Service Tank MDO Service Tank
Capacity for at least 8 Capacity for at least 8 Capacity for at least 8 Capacity for at least 8
h Main Engine + h Main Engine + h Auxiliary Engines h Auxiliary Engines
Auxiliary Boiler Auxiliary Boiler

ii) Equivalent Arrangement

HFO Service Tank MDO Service Tank Capacity MDO Service Tank Capacity for at
Capacity for at least 8 for at least highest of: 4 h Main least highest of: 4 h Main Engine +
h Main Engine + Engine + Auxiliary Engine + Auxiliary Engine + Auxiliary
Auxiliary Boiler Auxiliary Boiler or 8 h Boiler or 8 h Auxiliary Engine +
Auxiliary Engine + Auxiliary Auxiliary Boiler
Boiler

iii) The equivalent arrangements in 1.ii) and 2.ii) apply provided the dual-fuel propulsion systems
support rapid fuel changeover and are capable of operating under all normal operating
conditions at sea with dual fuels (MDO and HFO).

End of Commentary

2.3 Piping, Valves and Fittings

Fuel oil pipes, valves and fittings are to be of steel or other approved materials.

2.5 Oil Heating Arrangements

2.5.1 Oil Heaters
Where steam heaters or heaters using other heating media are provided in fuel oil systems they are
to be fitted with a temperature control and with a high temperature alarm, except where the
maximum temperature of the heating medium does not exceed 220°C (428°F).

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 102
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

When heating coils are fitted, and oil leakage into the returns can contaminate the boiler feed
water, provision is to be made to detect this leakage by running the returns from the heating coils
to an inspection tank or other approved oil detector before being led to the boiler feed system.

Where electric heaters are fitted, the heating elements are to be arranged to be submerged at all
times during operation, and are to be fitted with automatic means of preventing the surface
temperature of the heating element from exceeding 220°C (428°F). This automatic feature is to be
independent of the fuel oil temperature control and is to be provided with manual reset.

2.5.2 Tanks
Fuel oil in storage tanks is not to be heated to temperatures within 10°C (18°F) below the flash
point of the fuel oil.

Where heating arrangements are provided, the control and alarm requirements of 4-2-5/1.5.1 are
applicable.

2.7 Fuel Oil Purifiers

Where fuel oil purifiers for heated oil are installed, the arrangement is to be in accordance with 5-3-1/11.

3 Fuel-oil Transfer and Filling

3.1 General
The fuel-oil pumping arrangements are to be distinct from the other pumping systems, and the means
provided for preventing dangerous interconnection in service are to be thoroughly effective.

3.3 Pipes in Oil Tanks

Oil pipes and other pipes, where passing through oil tanks, are to be of steel, except that other materials are
acceptable subject to ABS technical assessment and approval where it is demonstrated that the material is
suitable for the intended service. All packing is to be of a composition not affected by oil.

3.5 Control Valves or Cocks

Valves or cocks controlling the various suctions are to be located close to the bulkhead where the suctions
enter the machinery spaces and, wherever practicable, directly over the gutterway in way of deep and
settling tanks. Pumps, strainers, etc., requiring occasional examination are to have drip pans.

3.7 Valves on Oil Tanks

3.7.1 Required Valves
Where pipe lines emanate from fuel oil tanks at such a level that they are subjected to a static head
of oil from the tank, they are to be fitted with positive closing valves. The valves are to be secured
at the tank. A short length of Extra Strong pipe connecting the valve to the tank is also acceptable.
Where the fuel oil piping passes through adjacent tanks, the valve required above may be located
where the pipe run exits the adjacent tank(s) provided the piping in the adjacent tanks is Extra-
Heavy and has all welded connections. However, if the adjacent tank is a fuel oil tank, the pipe run
within the fuel oil tank is to be at least Standard thickness.

If the valves are installed on the outside of the tank, they are not to be of cast iron. The use of
nodular iron, also known as ductile iron or spheroidal-graphite iron, are acceptable, provided the
material has an elongation not less than 12%. Arrangements are to be provided for closing them at
the valve and for tanks having a capacity of 500 liters (132 U.S. gal.) or greater, from a readily
accessible and safe location outside of the compartment in which the valve is located.

If the positive closing valve required above is situated in a shaft tunnel, pipe tunnel or similar
space, arrangements for closing may be affected by means of an additional valve on the pipe

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 103
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

outside of the tunnel or similar space. If such an additional valve is fitted in the machinery space it
is to be operated from a position outside of this space. Where independent filling lines are fitted,
they are to enter at or near the top of the tank, but if this is impracticable, they are to be fitted with
non-return valves at the tank. Also see 5-3-1/9.5.

3.7.2 Remote Means of Closure

The valves required above are to be remotely operated by reach rods or by electric, hydraulic or
pneumatic means. The source of power to operate these valves is to be located outside of the space
in which the valves are located. The positioning of the valve by either local or remote means is not
to interfere with the ability of the other means to close the valve. This remote means of closure is
to override all other means of valve control.

The controls for the remote means of closure of the valves of the emergency generator fuel tank
and the emergency fire pump fuel tank, as applicable, are to be grouped separately from those for
other fuel oil tanks.

Remote operation of readily accessible normally closed tank valves in open ended service such as
sampling or drains, is not required if the valves are fitted with blind, plug, or cap.

Where tanks are supplying fuel to diesel engines of essential or emergency services, the use of an
electric, hydraulic or pneumatic system to keep the valve directly in the open position is not
acceptable. Materials readily rendered in effective by heat are not to be used in the construction of
the valves or the closure mechanism within the space unless protected to ensure effective closure
facility in the event of fire. If electric cables are utilized, they are to be fire-resistant, meeting the
requirements of IEC 60331. See 4-3-4/7.

Hydraulic systems are to be in accordance with 4-2-6/3 for both Class I and II piping systems. For
a pneumatic system, the air supply is acceptable to be from a source from within the space,
provided an air receiver complying with the following is located outside of the space.

i) Sufficient capacity to close all connected valves twice

ii) Fitted with low air pressure alarm
iii) Air supply line is fitted with a non-return valve adjacent to the receiver

5 Fuel-oil Service System for Boilers

Where boilers are located in machinery spaces, they are to be fitted with guard plates and drip pans in way
of furnaces. Boilers installed for the purpose of providing power for auxiliaries are to have at least two
means of feeding and two fuel-oil service pumps. The construction of all boilers is to comply with the
requirements of Section 4-4-1 and Appendix 4-4-1-A1 of the Marine Vessel Rules.

7 Fuel-oil Service System for Internal Combustion Engines

7.1 Fuel-oil Pumps and Oil Heaters

7.1.1 Transfer Pumps
Two fuel-oil transfer pumps are to be provided and one of them is to be independent of the main
engine.

7.1.2 Booster Pumps

A standby fuel-oil booster pump is to be provided for main engines having independently driven
booster pumps. For main engines having attached booster pumps, a complete pump carried as a
spare is acceptable in lieu of the standby pump.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 104
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

7.1.3 Heaters
When fuel-oil heaters are required for main engine operation, at least two heaters of
approximately equal size are to be installed. The combined capacity of the heaters is to be not less
than that required to supply the main engine(s) at full power.

7.3 Oil Tanks and Drains for Fuel Oil Systems

Drain tanks for waste oil, fuel oil overflows, drains from fuel and lube oil drip pans, and fuel injection
piping, etc. are to be fitted with air and sounding pipes. Non-return valves are to be fitted in drain lines
entering the drain tanks, except where backflow does not present a hazard. Means are to be provided for
pumping out these drain tanks.

Oil tanks not forming a part of the unit’s structure, where permitted by 4-2-5/2.2.1, are to have suitable
drip pans with adequate means of drainage, in accordance with 4-2-1/11.33.1.

7.5 Fuel-oil Pressure Piping

Pipes from booster pumps to injection systems are to be at least Standard seamless steel (see 4-2-1/3.9).
Pipes conveying heated oil are to be at least Standard seamless or electric resistance welded steel. ERW
pipe is to be straight seam type and fabricated with no filler metal (e.g., ABS Grade 2 or 3 ERW). Valves
and fittings of screwed type are acceptable in sizes up to and including 60 mm O.D. (2 in. N.P.S.), but
screwed unions are not to be used on pressure lines in sizes 33 mm O.D. (1 in. N.P.S.) and over. Valves are
to be so constructed as to permit packing under pressure.

7.7 Fuel-oil Injection System

7.7.1 General
Strainers are to be provided in the fuel-oil injection-pump suction line. For main propulsion
engines, the arrangement is to be such that the strainers can be cleaned without interrupting the
fuel supply to the engine. For auxiliary engines, the arrangement is to be such that the strainers
can be cleaned without undue interruption of power necessary for propulsion. Multiple auxiliary
engines, each fitted with a separate strainer and arranged such that changeover to a standby unit
can be accomplished without loss of propulsion capability, are acceptable for this purpose.

Where strainers are fitted in parallel to enable cleaning without disrupting the oil supply, means
are to be provided to minimize the possibility of a strainer under pressure being opened
inadvertently. Strainers are to be provided with means for venting when being put in operation and
being depressurized before being opened. Valves or cocks with drain pipes led to a safe location
are to be used for this purpose. Strainers are to be so located that in the event of leakage, oil
cannot be sprayed onto the exhaust manifold or surfaces with temperatures in excess of 220°C
(428°F).

Cut-out valves are to be located at the service tanks and be so arranged as to be operable from the
engine-room floor plates and, from outside the engine compartment. See also 4-2-5/3.7. The
injection line is to be of seamless pipe and fittings are to be extra strong. The material used may be
either steel or nonferrous, as approved in connection with the design.

7.7.2 Piping Between Injection Pump and Injectors

See 6-1-3/3.1.

7.9 Piping Between Booster Pump and Injection Pumps

Spray shields are to be fitted around flanged joints, flanged bonnets and any other flanged or threaded
connections in fuel oil piping systems under pressure exceeding 1.8 bar (1.84 kgf/cm2, 26 psi) which are
located above or near units of high temperature, including boilers, steam pipes, exhaust manifolds,
silencers or other equipment required to be insulated by 5-3-1/13.i, and to also avoid, oil spray or oil
leakage into machinery air intakes or other sources of ignition. The number of joints in such piping
systems is to be kept to a minimum.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 105
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

7.10 Isolating Valves in Fuel Supply and Spill Piping

In multi-engine installations which are supplied from the same fuel source, a means of isolating the fuel
supply and spill (return) piping to individual engines is to be provided. The means of isolation is not to
affect the operation of the other engines and is to be operable from a position not rendered inaccessible by
a fire on any of the engines. Method of isolation may include the following:

i) Isolating valves located approximately 5 m (16.4 ft) away from engines in any direction. Where a
distance of 5 m (16.4 ft) is not physically possible or practical, the operating position of the valves
is to be protected by an obstruction considered acceptable to ABS.
ii) Remotely controlled isolating valves. Location of the remote actuation for the fuel oil supply and
spill (return) valves is to be approximately 5m away from the engines in any direction. Where a
distance of 5 m (16.4 ft) is not physically possible or practical, the remote operating position is to
be protected by an obstruction considered acceptable to ABS.

9 Low Flash Point Fuels

9.1 General
Fuel oils with a flash point of 60°C (140°F) closed cup or below are acceptable for the following:

9.1.1
Fuel oil with flash point of 60°C (140°F) or below, but not less than 43°C (110°F) are acceptable
for units classed for restricted service within areas having a climate such that ambient
temperatures of spaces where such fuel oil is stored does not rise within 10°C (18°F) below its
flash point.

9.1.2
Installations complying with the ABS Requirements for Burning Crude Oil and Slops in Main and
Auxiliary Boilers, regarding the use of crude oil as fuel.

9.1.3
For emergency generators or emergency fire pump prime movers, fuel oil with a flash point of not
less than 43°C (110°F) are acceptable, subject to the following:

i) Fuel oil tanks except those arranged in double bottom compartments are located outside
of machinery spaces of category A.
ii) Means for measurement of oil temperature are provided on the suction pipe of fuel oil
pump.
iii) Stop valves and/or cocks are provided on the inlet side and outlet side of the fuel oil
strainers.
iv) Pipe joints of welded construction circular cone type union joint, or spherical type union
joint are to be used. Other joints are subject to ABS technical assessment and approval.

See 4-3-2/5.5.2.iii

9.3 Fuel Heating

For oil heating arrangements, see 4-2-5/2.5.2.

9.5 Fuel-tank Vents

Vent pipes are to extend at least 1 m (3 ft) above the operating deck unless otherwise required by damage
stability considerations or the International Convention on Load Lines.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 106
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

11 Additional Measures for Oil Pollution Prevention

11.1 General
11.1.1 Application
The requirements of 4-2-5/11 provide the arrangement of fuel oil tanks location for compliance
with MARPOL 73/78, as amended. They are to be applied to all types of mobile units classed with
ABS.

11.1.2 Submission of Plans

Plans showing compliance with the applicable requirements in 4-2-5/11.3 are to be submitted for
review.

11.3 Tank Protection Requirements

11.3.1 General
The requirements of 4-2-5/11 apply to offshore units having an aggregate fuel oil capacity
(including tanks of 30 m3 (1060 ft3) or less) of 600 m3 (21190 ft3) and above. However, the
requirements need not be applied to individual fuel oil tanks with a capacity not greater than 30 m3
(1060 ft3), provided that the aggregate capacity of such excluded tanks is not greater than 600 m3
(21190 ft3). Further, individual fuel oil tanks are not to have capacity greater than 2500 m3 (88290
ft3).

Fuel oil tanks of any volume are not to be used for ballast water.

Fuel oil tank means a tank in which fuel oil is carried, but excludes those tanks which would not
contain fuel oil in normal operation, such as overflow tanks. Fuel oil capacity means the volume
of a tank in cubic meters (cubic feet) at 98% tank filling.

Fuel oil means any oil used as fuel in connection with the propulsion and auxiliary machinery of
the unit in which such oil is carried.

11.3.2 Protective Location of Tanks

The protective locations for the tanks specified in 4-2-5/11.3.1 above are to be as follows:

11.3.2(a) Deterministic Approach.

All applicable tanks are to be located not less than the distance as specified in 4-2-5/11.3.2(a)i), ii)
and iii), as relevant, from the unit’s bottom or side shell plating. Small suction wells may extend
below fuel oil tank’s bottom if they are as small as possible and the distance between the unit’s
bottom plate and the suction well bottom is not reduced by more than half of the distance required
by 4-2-5/11.3.2(a).i.

i) For all offshore units, except of the self-elevating type, having an aggregate fuel oil
capacity of 600 m3 (21190 ft3) and above, all tanks, including those in the unit’s pontoons,
are to be arranged above the unit’s molded line of bottom shell plating at the distance ℎ as
specified below:

ℎ = B/20 m (ft), or

ℎ = 2 . 0 m (6.6 ft), whichever is smaller

where

B is the breadth of the unit or, if applicable, the pontoon, in m (ft).

ℎ is in no case to be less than 0.76 m (2.5 ft).

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 107
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 5 Fuel Oil Systems and Tanks 4-2-5

ii) For all offshore units having an aggregate fuel oil capacity greater than or equal to 600 m3
(21190 ft3) but less than 5000 m3 (176570 ft3), tanks are to be arranged inboard of the
molded line of side plating not less than the distance w as specified below:

w = 0 . 4 + 2 . 4C/20000 m

w = 1 . 31 + 7 . 87C/706290 ft

where

C = unit’s total volume of fuel oil (including tanks of 30m3 or less) in m3 (ft3) at
98% tank filling;
w = at least 1.0 m (3.3 ft)
for individual tanks smaller than 500 m3 (17657 ft3), w is to be at least 0.76 m
(2.5 ft)
iii) For all offshore units having an aggregate fuel oil capacity of 5000 m3 (176570 ft3) and
above, tanks are to be arranged inboard of the molded line of side plating not less than the
distance w, as specified below:

w = 0 . 5 + C/20000 m w = 1 . 64 + C/706290 ft, or

w = 2 . 0 m (6.6 ft), whichever is smaller

where C is the unit’s total volume of fuel oil (including tanks of 30 m3 or less) in m3 (ft3)
at 98% tank filling.

The minimum value of w = 1 . 0 m (3.3 ft).

iv) When applying 4-2-5/11.3.2(a) to column-stabilized units, the tank protection specified
by paragraphs 4-2-5/11.3.2(a).ii and by 4-2-5/11.3.2(a).iii applies only to those areas
subject to damage as per 3-3-2/3.5.2.
11.3.2(b) Probabilistic Approach.
As an alternative to the deterministic approach of 4-2-5/11.3.2(a), arrangements complying with
the level of protection for both side and bottom damage in accordance with the accidental oil fuel
outflow performance standard of Regulation 12A, Annex I, MARPOL 73/78, as amended, are
acceptable.

13 Class Notation – POT

In addition to the requirements for fuel oil tank protection as specified in 4-2-5/11.1 utilizing the
deterministic approach of 4-2-5/11.3.2(a), where lubricating oil tanks with a capacity greater than 30 m3
(1060 ft3) (other than tanks for lubricating oil under main engines) are also arranged in the same manner as
required by the deterministic approach [4-2-5/11.3.2(a)] for fuel oil tanks, offshore units are to be eligible
for the optional Class notation, POT – Protection of Fuel and Lubricating Oil Tanks. Further, the following
exemptions are applicable to lubrication oil tanks:

i) In application of equation in 4-2-5/11.3.2(a).ii or 4-2-5/11.3.2(a).iii, total volume of lubricating oil

tanks need not be accounted for C (unit’s total volume of oil fuel in m3 (ft3) at 98% tank filling).
ii) Tanks used as propulsion engine lubricating oil drain tanks need not be located in a protected
location away from the unit side or bottom plates.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 108
 PART 4
CHAPTER 2
Pumps and Piping Systems

SECTION 6
Other Piping Systems and Tanks

1 Objective

1.1 Goal
The other piping systems and tanks covered in this section shall be designed, constructed, operated, and
maintained to:

Goal No. Goal

PROP 2 provide redundancy and/or reliability to maintain propulsion.

POW 2 provide power to enable the machinery/equipment/electrical installation to perform its required
functions necessary for the safe operation of the unit.

FIR 1 prevent the occurrence of fire and explosion.

FIR 2 reduce the risk of life caused by fire.

FIR 3 reduce the risk of damage caused by fire to the unit, its cargo and the environment.

ENV 1 prevent and minimize oil pollution due to unit operation and accidents.

SAFE 1.1 minimize danger to person on board, the unit, and surrounding equipment/installation from
hazards associated with machinery and systems.

STRU 1 in the intact condition, have sufficient structural strength to withstand the environmental
conditions, loading conditions, and operational loads anticipated during the design life.

AUTO 2 indicate the system operational status and alert operators of any essential machinery/systems
deviate from its defined design/operating conditions or intended performance.

AUTO 4 provide the equivalent degree of safety and operability from a remote location as those provided
by local controls.

OTH SG 5 enable safe helicopter operations.

MGMT 4 establish procedures, plans and instructions for emergency situations concerning the safety of the
personnel, vessel, and protection of the environment.

Materials are to be suitable for the intended application in accordance with the following goals in support
of the Tier 1 goals as listed above.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 109
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

Goal No. Goal

MAT 1 The physical, mechanical and chemical properties of base material and weldments are to meet the
design requirements appropriate for the application and operating environment. Refer to Part 2-
A1-2 to identify the applicable material properties.

The goals in the cross-referenced Rules are also to be met.

1.2 Functional Requirements

In order to achieve the above stated goals, the design, construction, installation and maintenance of the
other piping systems and tanks are to be in accordance with the following functional requirements:

Functional Functional Requirements

Requirement No.

Structure (STRU)

STRU-FR1 (FIR) Withstand the maximum working stresses to which tanks may be subjected in all service conditions

Protection of Environment (ENV)

ENV-FR1 (FIR) Provide means of containment and drainage where spillage or leakage is expected during normal
operations.

ENV-FR2 Means to detect overflow from lubricating-oil tanks are to be installed at accessible and effective
locations.

ENV-FR3 (SAFE/ Fuel oil piping is to be independent of other piping systems to prevent oil pollution and cross-
FIR) contamination.

Propulsion, Maneuvering, Station Keeping (PROP)

PROP-FR1 (POW) Provide redundancy and/or reliability of critical components to minimize loss of propulsion and/or
power generation of the unit in the event of failure.

PROP-FR2 (POW) Provide means to remove contaminants in the system to prevent equipment damage.

PROP-FR3 Operation is not to be affected when the equipment/component is isolated for repair or maintenance.

PROP-FR4 System and equipment are to be capable of satisfactory operation under all defined operating
conditions.

PROP-FR5 Provide arrangements to prevent water ingress into exhaust lines to avoid engines from
malfunctioning or breaking down.

PROP-FR6 (POW) Be provided with sufficient sources or capacity for the starting of essential propulsion services
without recharging.

Fire Safety (FIR)

FIR-FR1 Be arranged or be provided with means to prevent the ignition of flammable gases and liquids..

FIR-FR2 (SAFE) Piping design is to mitigate hazards due to the failure of joints.

FIR-FR3 (AUTO) Provide means to control leaks by restricting fuel supply and for local/remote closure from a
protected location, such that they can be safely closed in the event of fire in the space to prevent
further escalation of hazards.

FIR-FR4 Provide means to prevent flammable fluid from self-igniting or being ignited by flame/spark with
due regard to leakages, spillage, and hot surfaces.

FIR-FR5 Electrical equipment is to be of appropriate type for the hazardous areas that they operate in and are
arranged to minimize fire risk when located in such areas.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 110
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

Functional Functional Requirements

Requirement No.

FIR-FR6 Provide arrangements to maintain the level of flammable gases or vapors below 30% of their lower
explosive limits (LEL).

FIR-FR7 Be arranged to separate helicopter fuel from safe areas to prevent spread of fire and to allow escape.

FIR-FR8 Provided with arrangements to prevent build-up of static electricity and increased risk of fire/
explosion due to electrostatic discharge.

FIR-FR9 Provide means of collection and drainage of flammable liquid leakages to limit the fire growth
potential.

FIR-FR10 (PROP) Provide means to prevent backflow and backpressure across the piping affecting the systems and
machinery spaces.

FIR-FR11 (PROP) Piping design is to be suitable for the intended service and not rendered ineffective by heat.

FIR-FR12 Provided with arrangements to prevent build-up of static electricity and increased risk of fire/
explosion due to electrostatic discharge.

Safety of Personnel (SAFE)

SAFE-FR1 (PROP/ Operation of the safety shutdown is not to cause damage to propulsion and essential equipment.
FIR)

SAFE-FR2 Provide means to isolate and depressurize piping components prior to maintenance.

SAFE-FR3 Provide protective devices if the system/equipment can be subjected to a pressure more than its
design pressure.

SAFE-FR4 Piping and equipment are to safely contain the fluid media being conveyed and able to withstand the
most severe condition of coincident design pressures, temperatures, and loadings.

SAFE-FR5 Minimize danger to persons on board, due regard to toxicity, asphyxiation, flammability and high-
temperature surfaces.

SAFE-FR6 Piping is to be adequately supported and designed, arranged, or protected to minimize chance of
mechanical damage and corrosion.

SAFE-FR7 (FIR) Discharge arrangement of pressure relief devices is not to endanger the safety of persons onboard,
equipment/systems and environment.

SAFE-FR8 (FIR/ Provide arrangements to collect and drain fuel spillage to a safe location which does not interfere
ENV) with normal operation.

Automation (Control, monitoring and safety systems) (AUTO)

AUTO-FR1 (PROP) Provide monitoring of system parameters and alarms for the safe operation of the system/machinery.

Others (OTH)

OTH-FR1 (MGMT) Provide information at appropriate locations to advise of hazards associated with helicopter
refueling.

Safety Management (MGMT)

MGMT-FR1 (POW) Information is to be provided onboard regarding deployment of hose reels to allow non-hazardous
liquids to be supplied to units in elevated condition (i.e. raw water supply).

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 111
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

Functional Functional Requirements

Requirement No.

Materials (MAT)

MAT-FR1 Physical Properties typically considered when selecting materials for a given application:
a. Density
b. Specific heat
c. Electric resistivity
d. Melting or boiling point
e. Thermal Conductivity
f. Coefficient of thermal expansion
g. Coefficient of friction

The functional requirements in the cross-referenced Rules are also to be met.

1.3 Compliance
A unit is considered to comply with the goals and functional requirements when the prescriptive
requirements are complied with or when an alternative arrangement has been approved. Refer to Part 1D,
Chapter 2.

2 Lubricating-oil Systems

2.1 General
The lubricating-oil piping is to be entirely separated from other piping systems. In addition, the
requirements of 4-2-5/2.2.2, 4-2-5/2.3, and 4-2-5/2.5 are applicable.

Normally opened valves on lubricating oil tanks are to comply with the same requirements as those for fuel
oil tanks given in 4-2-5/3.9. However, arrangements for remotely closing the valve from a position outside
of the compartment need not be provided if inadvertent valve can could result in damage to the running
machinery due to lack of lubricating-oil. Where the machinery is arranged for automatic shutdown upon
loss of lubricating-oil, the valve required by 4-2-5/3.7 is to be provided with means to close it from a
readily accessible and safe location outside of the compartment in which the valve is located.

For surface-type units, the lubricating systems are to be so arranged that they function under the conditions
specified in 4-1-1/7.

2.3 Sight Flow Glasses

Sight flow glasses are to be fitted only in the vertical sections of lubricating oil overflow pipes, provided
that they are in a readily visible position.

2.5 Turbines and Reduction Gears

For turbines and their reduction gears, see 4-6-6/9.7.1 and 4-6-6/9.3.1 of the Marine Vessel Rules.

2.7 Internal Combustion Engines and Reduction Gears

Lubricating-oil systems for internal-combustion engines and their reduction gears are to be in accordance
with the following.

2.7.1 Lubricating-oil Pumps

In cases where forced lubrication is used for propulsion engines and reduction gears, one
independently driven stand-by pump is to be provided in addition to the necessary pumps for
normal operation. Two separate means are to be provided for water circulation where oil coolers
are fitted (see 4-2-6/11.7). Where the size and design of an engine is such that lubrication before

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 112
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

starting is not necessary and an attached pump is normally used, an independently driven stand-by
pump is not required if a complete duplicate of the attached pump is carried as a spare. The above
requirements are applicable to diesel propulsion engines and for reduction gears associated with
single diesel propulsion engines with a maximum operating speed above 400 RPM driving a
single shaft (single and multiple screw). For reduction gears associated with diesel propulsion
engines with a maximum operating speed of 400 RPM and below and reduction gears associated
with multiple diesel engines driving a single shaft (single and multiple screw), see 4-6-5/5.3.1 of
the Marine Vessel Rules.

2.7.2 Filters
Oil filters are to be provided. In the case of main propulsion engines which are equipped with full-
flow-type filters, the arrangements are to be such that the filters can be cleaned without
interrupting the oil supply. For auxiliary engines, the arrangement is to be such that the filters may
be cleaned without undue interruption of power necessary for propulsion. Multiple auxiliary
engines, each fitted with a separate filter and arranged such that change over to a standby unit can
be accomplished without loss of propulsion capability, are acceptable for this purpose. The
arrangement of the valving is to be such as to avoid release of debris into the lubricating-oil
system upon activation of the relieving mechanism.

Where filters are fitted in parallel to enable cleaning without disrupting the oil supply, means are
to be provided to minimize the possibility of a filter under pressure being opened inadvertently.
Filters are to be provided with suitable means for venting when being put in operation and being
depressurized before being opened. Valves and cocks with drain pipes led to a safe location are to
be used for this purpose. Filters are to be so arranged as to prevent, in the event of leakage,
spraying of oil onto the exhaust manifold and surfaces with temperatures in excess of 220°C
(428°F).

2.7.3 Low-oil-pressure Alarm

An alarm device with audible and visual signals for failure of the lubricating-oil system is to be
fitted for propulsion and auxiliary engines having a rated power greater than 37 kW (50 hp).

2.7.4 Drain Pipes

Lubricating oil drain pipes from the engine sump to the drain tank are to be submerged at their
outlet ends.

No interconnection is to be made between the drain pipes from the crankcases of two or more
engines.

3 Hydraulic Systems

3.1 General
The arrangements for Class I and II hydraulic piping systems are to be in accordance with the requirements
of this section, except that hydraulic systems which form part of an independent device or equipment not
covered by these Rules and which does not form part of the unit’s piping system (such as a crane) are not
covered by this Section, unless it is relevant to an optional notation or certification requested for the unit.
Plans showing clearly the arrangements and details are to be submitted for review. The requirements for
fuel oil tanks contained in 4-2-5/2.1.2 and 4-2-5/2.3 are also applicable for tanks containing hydraulic
fluid.

3.3 Valves
3.3.1 General
Valves are to comply with the requirements of 4-2-2/9 and 4-2-2/17.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 113
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

3.3.2 Relief Valves

Relief valves are to be provided for the protection of the hydraulic system. Each relief valve is to
be capable of relieving not less than full pump flow with a maximum pressure rise of not more
than 10% of the relief valve setting.

3.5 Piping
Piping is to meet the requirements of 4-2-1/9 and 4-2-2/5, except that mill tests need not be witnessed by
the Surveyor. In such cases, mill certificates are to be provided.

3.7 Pipe Fittings

Fittings and flanges are to meet the requirements of 4-2-2/11 and 4-2-2/15, except as follows.

3.7.1 Non-standard Fittings

Fittings which are not constructed to a recognized standard are subject to ABS technical
assessment and approval. Plans showing details of construction, material and design calculations
or test results are to be submitted for review.

3.7.2 Split Flanges

Split flanges are not to be used in steering gear systems and certified thruster systems for
propulsion or station keeping service. The use of split flanges for all other applications will be
specially considered.

3.7.3 Straight Thread O Ring Connections

Straight thread O ring type connections are acceptable for connections to equipment such as
pumps, valves, cylinders, accumulators, gauges and hoses. Such connections are not to be used for
joining sections of pipe.

3.7.4 Taper Thread Connections

Taper thread connections up to and including 89 mm O.D. (3 in. N.P.S.) are acceptable without
limitation for connections to equipment such as pumps, valves, cylinders, accumulators, gauges
and hoses.

Such connections are not to be used for joining sections of pipe, except where permitted by
4-2-2/11.1.

3.9 Flexible Hoses

Hose assemblies are to be in accordance with 4-2-1/11.29.

3.11 Accumulators
Accumulators are to meet the requirements of 4-6-7/3 of the Marine Vessel Rules. Each accumulator which
may be isolated is to be protected by suitable relief valves. Where a gas charging system is used, a relief
valve is to be provided on the gas side of the accumulator.

3.13 Fluid Power Cylinders

Fluid power cylinders are to meet the requirements of 4-2-2/19.

3.15 Segregation of High-Pressure Hydraulic Units

Hydraulic units with maximum working pressures above 15.5 bar (15.8 kgf/cm2, 225 psi) installed within
machinery spaces are to be placed in separate room or rooms or shielded as necessary to prevent any oil or
oil mist that may escape under pressure from coming into contact with surfaces with temperatures in
excess of 220°C (428°F), electrical equipment or other sources of ignition. For the purposes of this
requirement, a hydraulic unit includes the power pack and all components of the hydraulic piping system.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 114
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

5 Fixed Oxygen-Acetylene Systems

5.1 Application
Requirements of 4-2-6/3 apply to fixed oxygen-acetylene systems that have two or more cylinders of
oxygen and acetylene, respectively. Spare cylinders of gases need not be counted for this purpose.
Requirements of 4-2-6/5.5 and 7A-1-4/41.9, as applicable, are to be complied with for fixed system
regardless of the number of cylinders.

5.3 Gas Storage

5.3.1 Storage of Gas Cylinders
5.3.1(a) Storage room.
The gas cylinders are to be stored in rooms dedicated for this purpose only. A separate room is to
be provided for each gas. The rooms are to be on or above the upper-most continuous deck and are
to be constructed of steel. Access to the rooms is to be from the open deck and the door is to open
outwards. The boundaries between the rooms and other enclosed spaces are to be gastight.
Drainage of the storage room is to be provided.

5.3.1(b) Open area.

Where no storage room is provided, the gas cylinders may be placed in an open storage area-with
weather protection (particularly from heavy seas and heat) and effectively protected from
mechanical damage. Drainage of the open storage area is to be provided.

5.3.2 Ventilation of Storage Room

Acetylene cylinder storage rooms are to be fitted with ventilation systems capable of providing at
least six air changes per hour based on the gross volume of the room. The ventilation system is to
be independent of ventilation systems of other spaces. The space within 3 m (10 ft) from the
power ventilation exhaust or 1 m (3 ft) from the natural ventilation exhaust is to be considered a
hazardous area. The fan is to be of non-sparking construction. See 4-3-3/9.7.

Commentary:

Small storage spaces provided with large openings for natural ventilation need not be fitted with mechanical
ventilation.

End of Commentary

5.3.3 Electrical Installation in Storage Room

Electrical equipment installed within the acetylene storage room, including the ventilation fan
motor, is to be of the certified safe type. Electrical equipment installed within the storage room are
to be of the types indicated in 4-3-3/9.1.2(b) and is to be at least ISO/IEC 80079-20-1 group IIC
class T2.

In explosive gas atmospheres containing acetylene, equipment protection by flameproof

(explosion proof) enclosures “Ex d” for external mounting, where constructed of copper or copper
alloys, is to be:

i) Coated with tin, nickel, or other coating; or

ii) Alternatively, the maximum copper content of the alloy is to be limited to 60%.

Flameproof entry devices are not considered an enclosure surface requiring coating or copper
content restriction.

5.5 Piping System Components

5.5.1 Pipe and Fittings
5.5.1(a) General.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 115
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

All oxygen and acetylene pipes, pipe fittings, pipe joints and valves are to be in accordance with
Section 4-2-1 and Section 4-2-2, except as modified below.

5.5.1(b) Piping materials.

Materials for acetylene on the high-pressure side between the cylinders and the regulator are to be
steel. Copper or copper alloys containing more than 65% copper are not to be used in acetylene
piping (high or low pressure). Materials for oxygen on the high-pressure side are to be steel or
copper. All pipes, both high- and low-pressure sides, are to be seamless.

5.5.1(c) Design pressure

Pipes, pipe fittings and valves on the oxygen high-pressure side are to be designed for not less
than 207 bar (211 kgf/cm2, 3000 psi). Pipes used on the low-pressure side are to be at least of
standard wall thickness.

5.5.1(d) Pipe joints.

All pipe joints outside of the storage room or open storage area are to be welded.

5.5.1(e) Flexible hoses.

Flexible hoses used to connect oxygen or acetylene gas cylinders to a fixed piping system or
manifold are to comply with an acceptable standard and be suitable for the intended pressure and
service. Further, the internal surface of a hose used to connect an acetylene tank is to be of a
material that is resistant to acetone and dimethylformamide decomposition.*

Where a flexible hose is connected from an oxygen cylinder to the piping system or manifold
directly (i.e., no intervening pressure regulator), the internal liner of the oxygen hose is to be of a
material that has an autoignition temperature of not less than 400°C (752°F) in oxygen.*

Note:

* Criteria based on ISO 14113:1997 Gas welding equipment - rubber and plastic hoses assembled for compressed
or liquefied gases up to a maximum design pressure of 450 bar.

5.5.2 Pressure Relief Devices

Pressure relief devices are to be provided in the gas piping if the maximum allowable working
pressure of the piping system can be exceeded. These devices are to be set to discharge at not
more than the maximum allowable working pressure of the piping system to a location in the
weather remote from sources of vapor ignition or openings to spaces or tanks. The area within 3 m
(10 ft) of the pressure relief device discharge outlet is to be regarded as a hazardous area. The
pressure relief devices are to be either a relief valve or a rupture disc.

5.5.3 System Arrangements

Where two or more gas cylinders are connected to a manifold, high pressure piping between each
gas cylinder and the manifold is to be fitted with a non-return valve. The piping is not to run
through unventilated spaces or accommodation spaces. Outlet stations are to be fitted with shut-off
valves. Outlet stations are to be provided with protective devices to prevent back flow of gas and
the passage of flame into the supply lines.

5.5.4 Gas Cylinders

Gas cylinders are to be designed, constructed and certified in accordance with the requirements of
4-4-1/1.11.5 of the Marine Vessel Rules. Each cylinder is to be fitted with a suitable pressure relief
device such as a fusible plug or a rupture disc. If each cylinder is not provided with such a
pressure relief device, all valves installed between the cylinders and the pressure relief device in
4-2-6/5.5.2 are to be locked in the open position to protect the cylinders.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 116
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

The area within 3 m (10 ft) of the pressure relief device discharge outlet from an acetylene gas
cylinder is to be regarded as a hazardous area.

7 Helicopter Refueling Systems

Helicopter Refueling Systems for fuels with a flash point at or below 60°C (140°F) close cup test are to
comply with 4-2-6/7. For fuels with a flash point of above 60°C (140°F), the requirements for fuel oil
storage and transfer system in 4-2-5 and for spill containment in 4-2-6/7.3 here under are applicable.

7.1 Fuel Storage and Refueling Equipment Area

7.1.1 Isolation
Fuel storage and transfer facilities are to be remote or suitably isolated from areas which contain a
source of vapor ignition and are not to be located on landing areas. The storage and transfer area is
to be permanently marked as an area where smoking and open flames are not permitted.

7.1.2 Hazardous Areas

The requirements for hazardous areas are applicable to fuel with a flash point at or below 60°C
(140°F) closed-cup test. Hazardous area classification for fuel storage tanks and refueling
equipment are defined under 4-3-6/6.5. See 4-3-3/9 for acceptable certified safe equipment. This
equipment is to be at least ISO/IEC 80079-20-1 Group IIA, Class T3.

Enclosed spaces containing refueling equipment are to meet the following requirements:

7.1.2(a) Ventilation Capacity.

The enclosed space is to be provided with a power ventilation system sufficient to provide at least
six air changes per hour.

7.1.2(b) Exhaust Ventilation Duct and Fan.

The exhaust duct is to be regarded as a Zone 1 hazardous area and the outlet from any exhaust
duct is to be sited in a safe location, having regard to other possible sources of ignition. See
4-3-6/5.3.ii and 4-3-6/5.5.iv. Exhaust fans are to be of non-sparking construction complying with
4-3-3/9.7.

7.1.2(c) Dewatering System.

Where a gravity drain system is fitted, the system is to comply with the requirements of 4-2-2/23.
Where a bilge pumping system is fitted, the system is to comply with the requirements of 4-2-4/2
through 4-2-4/7 as applicable.

7.1.3 Independent or Free Standing Fuel Storage Tank Construction

Independent or Free standing tanks are completely self-supporting and do not form part of the
unit's structure. Independent fixed fuel storage tanks are to be of approved metal construction and
meet 4-2-5/2.2.1(b)ii) through 4-2-5/2.2.1(b)v), as applicable.

7.1.4 Fuel Storage Tank Vents

Tank vents are to be sized in accordance with 4-2-3/2.7, API Standard 2000, “Venting
Atmospheric and Low-Pressure Storage Tanks”, or other approved criteria. Vent outlets are to be
located such that vapors disperse freely.

7.1.5 Fuel Storage Tank Valves

Storage tank outlet valves are to be provided with a means of remote closure in the event of fire.
Means are also to be provided for remote shutdown of the fuel transfer unit.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 117
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

7.3 Spill Containment

To contain spillage and retain fire extinguishing agents, a coaming at least 150 mm (6 in.) in height is to be
provided. The coaming is to surround the fuel storage area, which consists of the fuel tank, associated
piping and any pumping unit adjacent to the storage tank. Where the pumping unit or any other unit such
as dispenser/coalescer unit is remote from the tank, a separate coaming around each unit is to be provided.
A coaming will not be required around the fuel storage tank where the installation is such that the tank is
cantilevered from the platform and arranged to be jettisoned.

Drainage is to be provided for the area enclosed by the coaming complying with the following:

7.3.1
The area within the coaming is to be sloped toward the drain line.

7.3.2
Drainage from the area within the coaming is to be led through a valve designed for selective
output (e.g., three-way valve) either to a holding tank complying with 4-2-6/7.1.2 and 4-2-6/7.1.3
or directly overboard. No other valves is to be fitted in the drain line.

7.3.3
The cross sectional area of the drain line from the fuel tank coaming is to be at least twice that of
the fuel storage tank outlet connection.

Fuel tank coamings not provided with drainage arrangements in accordance with the above are to be sized
to contain the full volume of the fuel storage tank plus 150 mm (6 in.) of foam.

9 Starting-air Systems

9.1 Design and Construction

The design and construction of all air reservoirs and piping systems are to be in accordance with the
applicable requirements of Section 4-4-1 and Appendix 4-4-1-A1 of the Marine Vessel Rules. The piping
system is to be in accordance with the applicable requirements of Section 4-2-2 of these Rules. The air
reservoirs are to be so installed as to make the drain connections effective under extreme conditions of
trim. Compressed-air systems are to be fitted with relief valves and each air reservoir which can be isolated
from a relief valve is to be provided with its own safety valves or equivalent. Connections are also to be
provided for cleaning the air reservoir and pipe lines.

All discharge pipes from starting air compressors are to be led directly to the starting air reservoirs, and all
starting pipes from the air reservoirs to main or auxiliary engines are to be entirely separate from the
compressor discharge piping system.

9.3 Starting-air Capacity

Units having internal combustion engines arranged for air starting are to be provided with at least two
starting-air reservoirs of approximately equal size. The total capacity of the starting-air reservoirs is to be
sufficient to provide, without recharging the air reservoirs, at least the number of consecutive starts stated
below. If other compressed air systems, such as control air, are supplied from starting-air reservoirs, the
aggregate capacity of the air reservoirs is to be sufficient for continued operation of these systems after the
air necessary for the required number of starts has been used.

9.3.1 Diesel Propulsion

The minimum number of consecutive starts (total) required to be provided from the starting-air
reservoirs is to be based upon the arrangement of the engines and shafting systems as indicated in
the following table.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 118
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

Single Screw Unit Multiple Screw Unit

One engine coupled Two or more engines One engine coupled Two or more engines
to shaft directly or coupled to shaft to each shaft directly coupled to each shaft
through reduction through clutch and or through reduction through clutch and
gear reduction gear gear reduction gear

Reversible Engines 12 16 16 16

Non-reversible Engines 6 8 8 8

Note:
In the case of reversible multi-engines coupled to one propeller or multiple propellers, 12 starts (total) for propulsion
engines may be acceptable provided that the total capacity of the starting air receivers is sufficient for a minimum of 3 starts
for each engine.
End of Commentary

9.3.2 Diesel-electric Propulsion

The minimum number of consecutive starts required to be provided from the starting-air reservoirs
is to be determined from the following equation.

S=6+G G−1

where

S = total number of consecutive starts

G = number of engines necessary to maintain sufficient electrical load to permit unit transit
at full seagoing power and maneuvering. The value of G need not exceed 3.
9.3.3 Non-Self-Propelled Units
The minimum number of consecutive starts required to be provided from the starting-air reservoirs
is three (3) per auxiliary engine, but the total capacity of the starting-air reservoirs dedicated to the
auxiliary engines need not exceed eight (8) consecutive starts.

9.5 Protective Devices for Starting-air Mains

Where engine starting is by direct injection of air into engine cylinders, in order to protect starting-air
mains against explosions arising from improper functioning of starting valves, an isolation non-return
valve or equivalent is to be installed at the starting-air supply connection to each engine. Where engine
bores exceed 230 mm (9 in.), a bursting disc or flame arrester is to be fitted in way of the starting valve of
each cylinder for direct reversing engines having a main starting manifold or at the supply inlet to the
starting-air manifold for non-reversing engines.

The above requirement is not intended to apply to engines utilizing air starting motors.

11 Cooling-water Systems for Internal Combustion Engines

11.1 General
Means are to be provided to ascertain the temperature of the circulating water at the return from each
engine and to indicate that the proper circulation is being maintained. Drain cocks are to be provided at the
lowest point of all jackets. For relief valves, see 4-2-1/11.21.

11.3 Sea Suctions

At least two independent sea suctions are to be provided for supplying water to the engine jackets or to the
heat exchangers.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 119
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

11.5 Strainers
Where sea water is used for direct cooling of the engine, strainers are to be fitted between the sea valves
and the pump suctions and are to be either of the duplex type or otherwise so arranged that they can be
cleaned without interrupting the cooling-water supply. This applies also to the emergency circulating water
to the engine.

11.7 Circulating Water Pumps

There are to be at least two means for supplying cooling water to main and auxiliary engines, compressors,
coolers, reduction gears, etc. One of these means is to be independently driven and may consist of a
connection from a pump normally used for other purposes, such as a general service pump, or in the case
of fresh-water circulation, one of the unit’s fresh-water pumps. Where, due to the design of the engine, the
connection of an independent pump is impracticable, the independently driven stand-by pump is not
required if a complete duplicate of the attached pump is carried as a spare. Multiple auxiliary engine
installations utilizing attached pumps need not be provided with spare pumps.

13 Exhaust System

13.1 Exhaust Lines

The exhaust pipes are to be water-jacketed or effectively insulated. Exhaust pipes of several engines are
not to be connected together, but are to be run separately to the atmosphere unless arranged to prevent the
return of gases to an idle engine. Exhaust lines which are led overboard near the waterline are to be
protected against the possibility of water finding its way inboard. The exhaust gas system is to be designed
such that the back-pressure across the piping is within the allowable limits stated by the engine and fired
equipment manufacturer under all expected operating conditions. Boiler uptakes and engine-exhaust lines
are not to be connected.
Commentary:

Where boiler uptakes or engine exhaust lines are interconnected, such as in the case of boilers arranged to utilize waste heat
from the engines, the arrangement may be acceptable subject to ABS technical assessment and approval.

End of commentary

13.3 Exhaust Gas Temperature

Propulsion engines with bores exceeding 200 mm (8 in.) are to be fitted with a means to display the
exhaust gas temperature of each cylinder.

13.5 Exhaust Emission Abatement Systems

Where a unit is fitted with an exhaust emission abatement system and the optional vessel notations detailed
under 6-3-1/9.3 through 6-3-1/9.9 of the Marine Vessel Rules are not requested, the installed exhaust
emission abatement system is to comply with the minimum requirements prescribed in 6-3-1/13 TABLE 1
of the Marine Vessel Rules and is to be verified by an ABS Surveyor during installation. This is applicable
to new construction and existing unit conversions.

15 Valves in Atomizing Lines

Where air or steam is used to atomize well bore fluids prior to flaring, a non-return valve is to be fitted in
the line. This valve is to be part of the permanently installed piping, readily accessible and as close as
possible to the burner boom.

17 Helicopter Deck Drainage Arrangements

Helicopter decks are to be arranged and provided with means to prevent the collection of liquids and to
prevent liquids from spreading to or falling on other parts of the unit. Drainage piping from helicopter

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 120
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

decks is to be constructed of steel. Drainage facilities in way of helidecks are to be lead directly overboard
independent of any other system.

19 Boilers and Associated Piping

Boilers and their associated steam, exhaust and feed systems are to be in accordance with the applicable
requirements of Part 4, Chapters 4 and 6 of the Marine Vessel Rules.

21 Steering Gear Piping

Piping systems associated with steering gear systems are to be in accordance with Section 4-3-4 of the
Marine Vessel Rules.

23 Gas Turbine Piping

Piping systems associated with gas turbines are to be in accordance with 4-2-3/9 of the Marine Vessel
Rules.

25 Raw Water System for Self-Elevating Units in Elevated Condition

Raw water systems supplying seawater to essential services on a self-elevating unit in elevated condition
are to be approved by ABS. Raw water towers, leg well suctions and hose reels are acceptable
arrangements for raw water systems.

25.1 General
At least two means of supplying water to essential services, such as cooling water system for main power
generation or fire main system, are to be provided. Pump capacity, system pressure and piping installation
are to be as required for the specific system or systems supplied. The pumps are to be sized to provide their
full required water demand with one pump out of service. See 4-2-6/11 and 5-2-2/1.1.

The use of hoses from the discharge of the submersible pump to the connection to the fixed seawater
system on board the unit is permitted, provided that the hose is suitable for the intended service. The hoses
are to be fire resistant, except when they are separated such that a single incident (fire, blast, etc.) would
not damage all the raw water hoses.

25.3 Raw Water Tower

The strength of the raw water tower and its components to withstand the maximum design environmental
conditions for the unit in elevated condition is to be assessed and calculations in this regard are to be
submitted for review.

25.5 Leg Well Suction

The raw water system is to be suitably supported to the unit’s leg and protected against mechanical damage
due to the operation of the legs.

25.7 Hose Reel

In lieu of utilizing either raw water towers or leg well suctions, submersible pumps installed on a hose reel
and lowered into the sea are acceptable means of water supply onboard a self-elevating unit, subject to the
following conditions:

25.7.1 Arrangement
There are to be at least two hose reels provided. The hose reel units are to be adequately separated
by either distance or primary structure such that a single incident (fire, blast, etc.) would not
render both pumping systems inoperable.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 121
Part 4 Machinery and Systems
Chapter 2 Pumps and Piping Systems
Section 6 Other Piping Systems and Tanks 4-2-6

25.7.2 Pump Power

Each hose reel pump unit is to be powered independently, such that a single failure in the power
distribution system would not render both units inoperable.

25.7.3 Design
The design of the hose reel/pump skid is to be submitted for review, including verification of the
skid and reel strength and component suitability (piping and electrical). In particular, details of the
hoses, including type, standard, material and capability to withstand the maximum design
environmental loads, are to be submitted for review. Collapsible type hoses are not acceptable for
this service.

25.7.4 Isolation
In order to isolate a damaged pump/hose from the rest of the sea water system, an isolation valve
is to be provided, capable of being operated during or immediately after the incident (fire, blast,
etc.) in such a way that the water supply is not interrupted.

25.7.5 Location
The reels are not to be located in a hazardous zone and each reel is to be positioned directly next
to the deck edge or opening utilized to lower the pumps overboard.

25.7.6 Operation
All hose reels provided are to be deployed at all times the unit is in the elevated condition.
Instructions in this regard are to be included in the Operating Manual.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 122
 PART 4
CHAPTER 3
Electrical Installations

CONTENTS
SECTION 1 General..............................................................................................130
1 Objective.....................................................................................130
1.1 Goals............................................................................. 130
1.2 Functional Requirements...............................................130
1.3 Compliance....................................................................131
2 General....................................................................................... 131
3 Definitions................................................................................... 131
3.1 Earth.............................................................................. 131
3.3 Earthed Distribution System.......................................... 131
3.5 Essential Services......................................................... 131
3.7 Explosion-proof (Flameproof) Equipment...................... 131
3.9 Hull-return System......................................................... 132
3.11 Inhomogeneous Field.................................................... 132
3.13 Intrinsically safe............................................................. 132
3.15 Increased Safety............................................................132
3.17 Nominal Voltage.............................................................132
3.19 Non-Periodic Duty Rating.............................................. 132
3.21 Non-sparking Fan.......................................................... 132
3.23 Overvoltage Category....................................................133
3.25 Overvoltage Withstand Test...........................................133
3.27 Periodic Duty Rating...................................................... 133
3.29 Pollution Degree............................................................ 133
3.31 Portable Apparatus........................................................ 133
3.33 Pressurized Equipment..................................................133
3.35 Semi-enclosed Space....................................................133
3.37 Separate Circuit............................................................. 133
3.39 Short Circuit................................................................... 133
3.41 Short-time Rating...........................................................133
5 Plans and Data to Be Submitted ................................................133
7 Standard Distribution System .................................................... 134
9 Voltage and Frequency Variations ............................................. 134

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 123
 11 Materials..................................................................................... 135
13 Grounding Arrangements .......................................................... 135
15 Degree of Protection for Enclosure ............................................135
17 Temperature Ratings.................................................................. 137
17.1 General.......................................................................... 137
17.3 Reduced Ambient Temperature..................................... 137
19 Clearances and Creepage Distances......................................... 137

TABLE 1 Voltage and Frequency Variations [See 4-3-1/9] ...............134

TABLE 2 Degree of Protection – Indicated by the First
Characteristic Numeral [See 4-3-1/15]...............................135
TABLE 3 Degree of Protection – Indicated by the Second
Characteristic Numeral [See 4-3-1/15] ..............................136

SECTION 2 Electrical Systems........................................................................... 138

1 Objective.....................................................................................138
1.1 Goals............................................................................. 138
1.2 Functional Requirements...............................................139
1.3 Compliance....................................................................141
2 Plans and Data to be Submitted................................................. 141
2.1 Wiring.............................................................................141
2.3 Short-circuit Data........................................................... 142
2.5 Protective Device Coordination..................................... 142
2.7 Load Analysis................................................................ 142
2.9 High Voltage Systems....................................................143
3 Main Service Source of Power................................................... 143
3.1 Power Supply by Generators.........................................143
3.3 Generator Driven by Propulsion Unit............................. 145
3.5 Sizing of AC Generator..................................................146
5 Emergency Source of Power...................................................... 146
5.1 General.......................................................................... 146
5.3 Emergency Power Supply............................................. 147
5.5 Emergency Sources...................................................... 149
5.7 Transitional Source of Power.........................................150
5.9 Emergency Switchboard................................................151
5.11 Ballast Pumps................................................................151
5.13 Arrangements for Periodic Testing.................................151
5.15 Starting Arrangements for Emergency Generator Sets. 152
5.17 Alarms and Safeguards for Emergency Diesel Engines152
5.19 Requirements by the Governmental Authority...............153
7 Distribution System.....................................................................153
7.1 Main Service Distribution System.................................. 153
7.3 Hull Return System........................................................155
7.5 Earthed Distribution Systems........................................ 156

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 124
 7.7 External or Shore Power Supply Connection................ 156
7.9 Harmonics......................................................................156
9 Circuit Protection System........................................................... 157
9.1 System Design...............................................................157
9.3 Protection for Generators.............................................. 159
9.5 Protection for Alternating-current (AC) Generators....... 160
9.7 Protection for Direct Current (DC) Generators.............. 160
9.9 Protection for Accumulator Batteries............................. 161
9.11 Protection for External or Shore Power Supply............. 161
9.13 Protection for Motor Branch Circuits..............................161
9.15 Protection for Transformer Circuits................................ 163
9.17 Protection for Meters, Pilot Lamps and Control Circuits 163
9.18 Harmonic Distortion for Unit Electrical Distribution
System including Harmonic Filters................................ 163
9.19 Protection of Harmonic Filter Circuits............................ 164
11 Systems for Steering Gear Installed in Self-propelled Units.......165
11.1 Power Supply Feeder.................................................... 165
11.3 Protection for Steering Gear Motor Circuit.....................165
11.5 Emergency Power Supply............................................. 166
11.7 Controls, Instrumentation, and Alarms.......................... 166
13 Lighting and Navigation Light Systems.......................................166
13.1 Lighting System............................................................. 166
13.3 Navigation Light System................................................ 167
15 Interior Communication Systems ...............................................168
15.1 Navigation Bridge.......................................................... 168
15.3 Main Propulsion Control Stations.................................. 168
15.5 Voice Communications.................................................. 168
15.7 Emergency and Interior-communication Switchboard... 169
15.9 Public Address System..................................................169
17 Manually Operated Alarms......................................................... 169
17.1 General Emergency Alarm Systems..............................169
17.3 Engineers’ Alarm........................................................... 170
17.5 Refrigerated Space Alarm............................................. 170
17.7 Elevator..........................................................................170
19 Fire Protection and Fire Detection Systems............................... 171
19.1 Emergency Stop............................................................ 171
19.3 Fire Detection and Alarm System.................................. 171
21 Remote Camera System............................................................ 171

TABLE 1 Alarms and Safeguards for Emergency Diesel

Engines[See 4-3-2/5.17] ................................................... 153

SECTION 3 Onboard Installation........................................................................ 172

1 Objective.....................................................................................172

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 125
 1.1 Goals............................................................................. 172
1.2 Functional Requirements...............................................173
1.3 Compliance....................................................................174
2 Plans and Data to be Submitted................................................. 174
2.1 Booklet of Standard Details........................................... 174
2.3 Arrangement of Electrical Equipment............................ 175
2.5 Electrical Equipment in Hazardous Areas..................... 175
2.7 Emergency Shutdown Procedures................................ 175
2.9 Maintenance Schedule of Batteries............................... 175
2.11 Cable Transit Seal System Register.............................. 175
3 Equipment Installation and Arrangement....................................176
3.1 General Consideration...................................................176
3.3 Generators.....................................................................179
3.5 Motors for Essential Services........................................ 179
3.7 Accumulator Batteries....................................................180
3.9 Switchboard................................................................... 183
3.11 Distribution Boards........................................................ 183
3.13 Motor Controllers and Control Centers.......................... 184
3.15 Resistors for Control Apparatus.....................................184
3.17 Lighting Fixtures............................................................ 184
3.19 Heating Equipment........................................................ 184
3.21 Magnetic Compasses.................................................... 185
3.23 Portable Equipment and Outlets....................................185
3.25 Receptacles and Plugs of Different Ratings.................. 185
3.27 Installation Requirements for Recovery from Dead
Ship Condition............................................................... 185
3.29 Services Required to be Operable Under a Fire
Condition........................................................................185
3.31 High Fire Risk Areas......................................................186
5 Cable Installation........................................................................ 186
5.1 General Considerations................................................. 186
5.3 Insulation Resistance for New Installation..................... 187
5.5 Protection for Electromagnetic Induction....................... 187
5.7 Joints and Sealing......................................................... 188
5.9 Support and Bending..................................................... 188
5.11 Cable Run in Bunches................................................... 189
5.13 Deck and Bulkhead Penetrations.................................. 190
5.15 Mechanical Protection................................................... 191
5.17 Emergency and Essential Feeders................................191
5.19 Battery Room.................................................................192
5.21 Splicing of Electrical Cables.......................................... 192
5.23 Splicing of Fiber Optic Cables....................................... 193
5.25 Cable Junction Box........................................................193
7 Earthing...................................................................................... 193

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 126
 7.1 General.......................................................................... 193
7.3 Permanent Equipment................................................... 194
7.5 Connections...................................................................194
7.7 Portable Cords...............................................................195
7.9 Cable Metallic Covering.................................................195
9 Equipment and Installation in Hazardous Area...........................195
9.1 General Consideration...................................................195
9.3 Certified-safe Type and Pressurized Equipment and
Systems......................................................................... 197
9.5 Paint Stores................................................................... 198
9.7 Non-sparking Fans........................................................ 199

TABLE 1 Minimum Degree of Protection [See 4-3-3/3.1.1] ..............178

TABLE 2 Size of Earth-continuity Conductors and Earthing
Connections[See 4-3-3/7.5] .............................................. 194

FIGURE 1 Example of Area Affected by Local Fixed Pressure

Water-sprayingWater mist Fire Extinguishing System in
Machinery Spaces .............................................................177
FIGURE 2 Cables within High Fire Risk Areas ...................................192

SECTION 4 Machinery and Equipment.............................................................. 201

1 Objective.....................................................................................201
1.1 Goals............................................................................. 201
1.2 Functional Requirement.................................................201
1.3 Compliance....................................................................202
2 Certification of Electrical Machinery and Equipment ................. 202
3 Battery Systems and Uninterruptible Power Systems (UPS)..... 202
3.1 References.................................................................... 202
3.3 Engine-starting Battery.................................................. 203
3.5 Location......................................................................... 203
3.7 Performance.................................................................. 203
5 Computer-Based System (CBS).................................................203
6 Cyber Resilience.........................................................................204
7 Cables and Wires....................................................................... 204
7.1 Cable Construction........................................................ 204
7.3 Portable and Flexing Electric Cables.............................206
7.5 Mineral-insulated, Metal-sheathed Cable...................... 206

TABLE 1 Types of Cable Insulation [See 4-3-4/7.1.4] ...................... 205

TABLE 2 Maximum Current Carrying Capacity for Cables ...............206

SECTION 5 Specialized Installations................................................................. 210

1 Objective.....................................................................................210

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 127
 1.1 Goals............................................................................. 210
1.2 Functional Requirements............................................... 211
1.3 Compliance....................................................................213
2 High Voltage Systems.................................................................213
2.1 General.......................................................................... 213
2.3 System Design...............................................................215
2.5 Circuit Breakers and Switches – Auxiliary Circuit
Power Supply Systems for Operating Energy............... 216
2.7 Circuit Protection........................................................... 216
2.9 Equipment Installation and Arrangement.......................217
2.11 Cable Construction........................................................ 220
2.13 Design Operating Philosophy........................................ 220
2.15 Preliminary Operations Manual..................................... 221
3 Electric Propulsion System......................................................... 223
3.1 General.......................................................................... 223
3.3 System Design...............................................................224
3.5 Propulsion Power Supply Systems................................225
3.7 Circuit Protection........................................................... 226
3.9 Protection for Earth Leakage......................................... 227
3.11 Electric Propulsion Control............................................ 227
3.13 Instrumentation at the Control Station........................... 228
3.15 Equipment Installation and Arrangement.......................229
3.17 Machinery and Equipment............................................. 229
5 Three-wire Dual-voltage DC System.......................................... 230
5.1 Three-wire DC Unit’s Generators.................................. 230
5.3 Neutral Earthing.............................................................230
5.5 Size of Neutral Conductor..............................................230
7 Emergency Shutdown Arrangements......................................... 230
7.1 Emergency Shutdown Facilities.....................................231
9 Energy Storage Systems............................................................ 232
9.1 Lithium-ion Batteries...................................................... 232
9.3 Supercapacitors.............................................................232

TABLE 1 High Voltage Equipment Locations and Minimum

Degree of Protection.......................................................... 222

SECTION 6 Hazardous Areas..............................................................................233

1 Objective.....................................................................................233
1.1 Goals............................................................................. 233
1.2 Functional Requirements...............................................233
1.3 Compliance....................................................................234
2 Definitions................................................................................... 234
2.1 Hazardous Areas........................................................... 234
2.3 Enclosed Space.............................................................235

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 128
 2.5 Semi-Enclosed Location................................................ 235
2.7 Outdoor Location........................................................... 235
3 Plans and Data to be Submitted ................................................ 235
5 Classification of Areas (Non-Drilling and Production Related)... 235
5.1 Hazardous Areas Zone 0 Include:................................. 235
5.3 Hazardous Areas Zone 1 Include:................................. 235
5.5 Hazardous Areas Zone 2 Include:................................. 236
6 Classification of Miscellaneous Areas ....................................... 236
6.1 Paint Stores................................................................... 236
6.3 Battery Rooms............................................................... 236
6.5 Helicopter Refueling Facilities....................................... 237
6.7 Oxygen-acetylene Storage Rooms................................237
7 Openings, Access, and Ventilation Conditions Affecting the
Extent of Hazardous Zones........................................................ 237
7.1 Enclosed Space with Direct Access to any Zone 1
Location......................................................................... 238
7.3 Enclosed Space with Direct Access to any Zone 2
Location......................................................................... 238
7.5 Enclosed Space with Access to any Zone 1 Location... 239
7.7 Ventilation Alarms.......................................................... 240
7.9 Hold-back Devices.........................................................240
9 Ventilation .................................................................................. 241
9.1 General.......................................................................... 241
9.3 Ventilation of Hazardous Areas..................................... 241
9.5 Ventilation of Non-hazardous Areas.............................. 241
11 Machinery Installations in Hazardous Areas ..............................241

FIGURE 1 Hazardous Zones...............................................................238

FIGURE 2 Hazardous Zones...............................................................239
FIGURE 3 Hazardous Zones...............................................................240

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 129
 PART 4
CHAPTER 3
Electrical Installations

SECTION 1
General

1 Objective

1.1 Goals
The electrical installations covered in this section is to be designed, constructed, operated, and maintained
to:

Goal No. Goal

POW 1 provide safe and reliable storage and supply of fuel/energy/power.

POW 2 provide power to enable the machinery/equipment/electrical installation to perform its required
functions necessary for the safe operation of the unit.

POW 5 enable supply/power for essential services to be restored after malfunction.

SAFE 1-1 minimize danger to persons on board, the unit, and surrounding equipment/installations from
hazards associated with machinery and systems.

FIR 3 reduce the risk of damage caused by fire to the ship, its cargo and the environment.

Materials are to be suitable for the intended application in accordance with the following goals and support
the Tier 1 goals as listed above.

Goal No. Goal

MAT 1 The selected materials’ physical, mechanical and chemical properties are to meet the design
requirements appropriate for the application, operating conditions and environment.

The goals in the cross-referenced Rules/Standards are also to be met.

1.2 Functional Requirements

In order to achieve the above-stated goals, the design, construction, installation and maintenance of the
electrical installations are to be in accordance with the following functional requirements:

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 130
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 1 General 4-3-1

Functional Functional Requirement

Requirement No.

Power Generation and Distribution (POW)

POW1 Provide electrical distribution scheme for Alternating Current (AC) and Direct Current (DC)
systems suitable for offshore units and safe for onboard personnel.

POW2 Design to withstand normally occurring variations in voltage and frequency.

Materials (MAT)

MAT-FR1 (FIR/POW) Be designed and be constructed of materials that are able to withstand the marine and operating
environment, maximum design ambient temperature and stresses without deterioration.

Safety of Personnel (SAFE)

SAFE-FR1 (POW) Provide design or arrangement to prevent unintentional electric discharge, short circuit and
electric shock.

SAFE-FR2 (POW) Provide enclosure with suitable degree of protection against ingress of foreign objects and liquids
based on location of installation.

The functional requirements covered in the cross-referenced Rules/Standards are also to be met.

1.3 Compliance
A unit is considered to comply with the goals and functional requirements when the applicable prescriptive
requirements are complied with or when an alternative arrangement has been approved, refer to Part 1D,
Chapter 2.

2 General
Electrical apparatus and wiring systems are to be constructed and installed in accordance with the
requirements of this Section.

3 Definitions
The following definitions apply for the purpose of this Section.

3.1 Earth
A large conducting body, such as the metal hull of the ship, used as an arbitrary zero of potential.

3.3 Earthed Distribution System

A system in which one pole of a single phase system or the neutral point of a three phase system is earthed
but the earthing connection does not normally carry current.

3.5 Essential Services

For definition of essential services, see 4-1-1/3.5.

3.7 Explosion-proof (Flameproof) Equipment

Explosion-proof equipment is equipment:

i) Having an enclosure capable of:

● withstanding an explosion within it of a specified flammable gas or vapor, and

● preventing the ignition of the specified flammable gas or vapor in the atmosphere surrounding
the enclosure by sparks, flashes or explosions of the gas or vapor within, and

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 131
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 1 General 4-3-1

ii) Operates at such an external temperature that a surrounding flammable atmosphere will not be
ignited.

Where explosion-proof equipment is required by these Rules, equipment certified as being flameproof as
defined in IEC Publication 60079 series or other recognized standard can be accepted.

3.9 Hull-return System

A system in which insulated conductors are provided for connection to one pole or phase of the supply, the
hull of the unit or other permanently earthed structure being used for effecting connections to the other
pole or phase.

3.11 Inhomogeneous Field

An electric field which does not have a constant voltage gradient between electrodes.

3.13 Intrinsically safe

A circuit or part of a circuit is intrinsically safe when any spark or any thermal effect produced in the test
conditions prescribed in a recognized standard (such as IEC 60079-11) is incapable of causing ignition of
the prescribed explosive gas atmosphere.

3.13.1 Category “ia”

Apparatus which is incapable of causing ignition in normal operation, or with a single fault, or
with any combination of two faults applied, with the following safety factors:

In normal operation: 1.5

With one fault: 1.5
With two faults: 1.0

Above safety factors are applied to the current, voltage or their combination, as specified in 5.2 of
IEC 60079-11.

3.15 Increased Safety

Type of protection applied to electrical apparatus that does not produce arcs or sparks in normal service, in
which additional measures are applied so as to give increased security against the possibility of excessive
temperatures and of the occurrence of arc and sparks. See IEC 60079-7.

3.17 Nominal Voltage

Nominal Voltage (Un) – The nominal value assigned to a circuit or system for the purpose of conveniently
designating its voltage class (as 120/240 V, 480/277 V, 600 V). The actual voltage at which a circuit
operates can vary from the nominal within a range that permits satisfactory operation of equipment.

Uo (as relates to cable voltage rating) – The rated power frequency voltage between conductor and earth or
metallic screen for which the cable is designed.

3.19 Non-Periodic Duty Rating

A rating at which the machine is operated continuously or intermittently with varying the load and speed
within the permissible operating range. The load and speed variations include the overloads applied
frequently, which may greatly exceed the full load rating of the machine.

3.21 Non-sparking Fan

A fan consisting of a combination of impeller and housing which are unlikely to produce sparks by static
electricity or by entry of foreign objects in both normal and abnormal conditions. See also 4-3-3/9.7.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 132
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 1 General 4-3-1

3.23 Overvoltage Category

Overvoltage Category (of a circuit or within an electrical system) – Conventional number based on
limiting the values of prospective transient overvoltages occurring in a circuit and depending on the means
employed to influence the overvoltages.

3.25 Overvoltage Withstand Test

Overvoltage Withstand Test (layer test) – Test intended to verify the power-frequency withstand strength
along the winding under test and between its phase (strength between turns and between layers in the
windings).

3.27 Periodic Duty Rating

A rating at which the machine is operated repeatedly on cycle of sequential loading with starting, electric
braking, no-load running, rest and de-energized periods, where applicable. The time for the duration of
operating cycle (duty cycle) is to be 10 minutes and the ratio (i.e., cyclic duration factor) between the
period of loading (including starting and electric braking) and the duty cycle is to be one of the values of
15%, 25%, 40% or 60%.

3.29 Pollution Degree

Pollution Degree (of environmental conditions) – A conventional number based on the amount of
conductive or hygroscopic dust, ionized gas or salt, and on the relative humidity and its frequency of
occurrence resulting in hygroscopic absorption or condensation of moisture leading to reduction in
dielectric strength and/or surface resistivity of the insulating materials of devices and components.

3.31 Portable Apparatus

Portable apparatus is any apparatus served by a flexible cord.

3.33 Pressurized Equipment

Equipment having an enclosure in which positive pressure is maintained to prevent against the ingress of
external atmosphere and complying with the requirements in 4-3-3/9.3.3.

3.35 Semi-enclosed Space

A space limited by decks and/or bulkheads in such a manner that the natural conditions of ventilation in
the space are notably different from those obtained on open deck.

3.37 Separate Circuit

A circuit which is independently protected by a circuit protection device at the final subcircuit and is
dedicated to a single load.

3.39 Short Circuit

A short circuit is an abnormal connection through a negligible impedance, whether made accidentally or
intentionally, between two points of different potential in a circuit.

3.41 Short-time Rating

A rating at which the machine is operated for a limited period which is less than that required to reach the
steady temperature condition, followed by a rest and de-energized period of sufficient duration to re-
establish the machine temperature within 2°C (3.6°F) of the coolant.

5 Plans and Data to Be Submitted

See 4-3-/2, 4-3-3/2, 4-3-4/2 and 4-3-5/3.1.2, and 4-3-6/3. Refer to 6-1-7/3 for electrical equipment
certification.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 133
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 1 General 4-3-1

7 Standard Distribution System

The following are recognized as standard systems of distribution. Distribution systems differing from these
will be reviewed on a case-by-case basis in accordance with applicable industry standards and this section.

● Two-wire direct current

● Three-wire direct current
● Two-wire single-phase alternating current
● Three-wire three-phase alternating current*
● Four-wire three-phase alternating current with solidly earthed neutral but not with hull return

*Three-wire single-phase AC can be used in conjunction with this system for lighting.

9 Voltage and Frequency Variations

Electrical appliances supplied from the main or emergency systems, are to be so designed and
manufactured that they are capable of being operated satisfactorily under the normally occurring variations
in voltage and frequency. Unless otherwise stated in national or international standards, the variations from
the rated value can be taken from 4-3-1/9 TABLE 1. Any special system, such as electronic circuits, which
cannot operate satisfactorily within the limit shown in 4-3-1/9 TABLE 1, is not to be supplied directly from
the system but by alternative means, such as through a stabilized supply.

For generators, see 6-1-3/3.3.1, 6-1-3/3.5.1, and 6-1-7/5.17.2.

TABLE 1
Voltage and Frequency Variations [See 4-3-1/9]

Voltage and Frequency Variations for AC Distribution Systems

Quantity in Operation Permanent Variation Transient Variation

(Recovery Time)

Frequency ±5% ±10% (5 s)

Voltage +6%, -10% ±20% (1.5 s)

Voltage Variations for DC Distribution Systems

(such as systems supplied by DC generators or rectifiers)

Parameters Variations

Voltage tolerance (continuous) ±10%

Voltage cyclic variation deviation 5%

Voltage ripple (AC rms over steady DC voltage) 10%

Voltage Variations for Battery Systems

Type of System Variations

Components connected to the battery during charging (see Note) +30%, –25%

Components not connected to the battery during charging +20%, –25%

Note:
Different voltage variations as determined by the charging/discharging characteristics, including the ripple voltage from the
charging device,can be considered.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 134
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 1 General 4-3-1

11 Materials
All electrical equipment is to be constructed of durable and flame-retardant materials. Materials are to be
resistant to corrosion, moisture, high and low temperatures, and are to have other qualities necessary to
prevent deterioration in the ambient conditions that the equipment may be expected to encounter.

13 Grounding Arrangements
Where not obtained through normal construction, arrangements are to be provided to effectively ground
metal structures of derricks, masts and helicopter decks. See also 4-2-6/7.1.3 for fuel storage for helicopter
facilities. Grounding arrangements are also to be provided for tending vessels.

15 Degree of Protection for Enclosure

The designation to indicate the degree of protection consists of the characteristic letters IP followed by two
numerals (the “characteristic numerals”) indicating conformity with conditions stated in 4-3-1/9 TABLE 2
and 4-3-1/9 TABLE 3. The test and inspection for determining the degree of protection can be carried out
in accordance with IEC Publication 60529 by the manufacturer whose certificate of tests will be acceptable
and is to be submitted upon request from ABS. Type of enclosure required for protection of equipment is
to be suitable for the intended location. See 4-3-3/3.1.1 for selection of protective enclosure for electrical
equipment based on location condition. Equipment in compliance with recognized national standards will
also be considered. For high voltage equipment see 4-3-5/7 TABLE 1.

TABLE 2
Degree of Protection – Indicated by the First Characteristic Numeral
[See 4-3-1/15]

Degree of Protection

First Characteristic Short Description Definition

Numeral

0 Non-protected No special protection

1 Protected against solid objects A large surfacing of the body, such as a hand (but no
greater than 50 mm (2 in.) protection against deliberate access). Solid object exceeding
50 mm (2 in.) in diameter.

2 Protected against solid objects Fingers or similar objects not exceeding 80 mm (3.15 in.) in
greater than 12 mm (0.5 in.) length. Solid objects exceeding 12 mm (0.5 in.) in diameter.

3 Protected against solid objects Tools, wires, etc., of diameter or thickness greater than 2.5
greater than 2.5 mm (0.1 in.) mm (0.1 in.). Solid objects exceeding 2.5 mm (0.1 in.) in
diameter.

4 Protected against solid objects Wires or strips of thickness greater than 1 mm (0.04 in.).
greater than 1 mm (0.04 in.) Solid objects exceeding 1 mm (0.04 in.) in diameter.

5 Dust protected Ingress of dust is not totally prevented, but dust does not
enter in sufficient quantity to interfere with satisfactory
operation of the equipment.

6 Dust-tight No ingress of dust

[Designation]

The degree of protection is designated as shown in the following examples:

When it is required to indicate the degree of protection by only one characteristic numeral which shows either degree of
protection against foreign bodies and electrical shock or against liquid, the omitted numeral is to be replaced by the
letter X.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 135
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 1 General 4-3-1

Examples:

1 IP56 The first characteristic numeral of "5".

The second characteristic numeral of "6".

2 IPX5 Degree of protection against only liquid.

3 IP2X Degree of protection against foreign bodies and electrical shock.

TABLE 3
Degree of Protection – Indicated by the Second
Characteristic Numeral [See 4-3-1/15]

Degree of Protection

Second Characteristic Short Description Definition

Numeral

0 Non-protected No special protection

1 Protected against dripping water Dripping water (vertically falling drops) is to have no
harmful effect.

2 Protected against dripping water Vertically dripping water is to have no harmful effect when
when tilted up to 15 deg. the enclosure is tilted at any angle up to 15 deg. from its
normal position.

3 Protected against spraying water Water falling as spray at an angle up to 60 deg. from the
vertical is to have no harmful effect.

4 Protected against splashing water Water splashed against the enclosure from any direction is to
have no harmful effect.

5 Protected against water jets Water projected by a nozzle against the enclosure from any
direction is to have no harmful effect.

6 Protected against heavy seas Water from heavy seas or water projected in powerful jets is
not to enter the enclosure in harmful quantities.

7 Protected against the effects of Ingress of water in a harmful quantity is not to be possible
immersion when the enclosure is immersed in water under defined
conditions of pressure and time.

8 Protected against submersion The equipment is suitable for continuous submersion in

water under conditions which are to be specified by the
manufacturer.
Note: Normally, this will mean that the equipment is
hermetically sealed. However, with certain types of
equipment, it can mean that water can enter but only in such
a manner that it produces no harmful effects.

9 Protected against high pressure and Water projected at high pressure and high temperature
high temperature water jets against the enclosure from any direction is to have no
harmful effect.

See Designation and examples in 4-3-1/9 TABLE 2.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 136
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 1 General 4-3-1

17 Temperature Ratings

17.1 General
For the purposes of rating of equipment a maximum ambient air temperature of 45°C (113°F) is to be
assumed.

Where ambient temperatures in excess of 45°C (113°F) are expected the rating of equipment is to be based
on the actual maximum ambient air temperature.

The use of lower ambient temperatures can be considered provided the total rated temperature of the
equipment is not exceeded and where the lower values can be demonstrated. The use of a value for
ambient temperature less than 40°C (104°F) is only permitted in spaces that are environmentally
controlled.

17.3 Reduced Ambient Temperature

17.3.1 Environmentally Controlled Spaces
Where electrical equipment is installed within environmentally-controlled spaces, the ambient
temperature for which the equipment is to be rated can be reduced from 45°C and maintained at a
value not less than 35°C, provided:

i) The equipment is not to be used for emergency services.

ii) Temperature control is achieved by at least two independent cooling systems so arranged
that in the event of loss of one cooling system for any reason, the remaining system(s) is
capable of satisfactorily maintaining the design temperature. The cooling equipment is to
be rated for a 45°C ambient temperature.
iii) The equipment is to be able to initially start to work safely at a 45°C ambient temperature
until such a time that the lesser ambient temperature may be achieved.
iv) Audible and visual alarms are provided, at a continually-manned control station, to
indicate any malfunction of the cooling systems.
17.3.2 Rating of Cables
In accepting a lesser ambient temperature than 45°C, it is to be ensured that electrical cables for
their entire length are adequately rated for the maximum ambient temperature to which they are
exposed along their length.

17.3.3 Ambient Temperature Control Equipment

The equipment used for cooling and maintaining the lesser ambient temperature is to be classified
as a secondary essential service, in accordance with 4-3-1/3.5, and the capability of cooling is to
be witnessed by the Surveyor at trials.

19 Clearances and Creepage Distances

The distances between live parts of different potential and between live parts and the case or other earthed
metal, whether across surfaces or in air, are to be adequate for working voltage, having regard to the nature
of the insulating material and the conditions of service. See 4-3-5/2.1.3 and 6-1-7/9.9.6 for additional
requirements for switchboard and high voltage systems.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 137
 PART 4
CHAPTER 3
Electrical Installations

SECTION 2
Electrical Systems

1 Objective

1.1 Goals
The power generation and distribution systems covered in this section are to be designed, constructed,
operated, and maintained to:

Goal No. Goal

PROP 2 provide redundancy and/or reliability to maintain propulsion.

POW 1 provide safe and reliable storage and supply of fuel/energy/power.

POW 2 provide power to enable the machinery/equipment/electrical installation to perform its required
functions necessary for the safe operation of the unit.

POW 3 enable all electrical services necessary for maintaining the unit in normal operational and
habitable conditions to be available without recourse to the emergency source of power.

POW 4 enable all electrical services required for safety to be available during emergency conditions.

POW 5 enable supply/power for essential services to be restored after malfunction.

SAFE 1-1 minimize danger to persons on board, the unit, and surrounding equipment/installations from
hazards associated with machinery and systems.

SAFE 2 provide suitable and readily available illumination.

FIR 1 prevent the occurrence of fire and explosion.

FIR 3 reduce the risk of damage caused by fire to the unit, its cargo and the environment.

AUTO 5 provide a safety system that will automatically lead machinery controlled to a fail-safe state in
response to a fault which may endanger the safety of persons on board, machinery/equipment or
environment

COMM 2 provided with means for internal communications.

COMM 2.1 enable essential safety services of the communication installations to be maintained and be
available at all times.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 138
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

Goal No. Goal

COMM 2.2 provide reliable communication equipment so as to minimize risk of malfunction.

NAV 1 be navigated independently and safely while at sea, minimizing the risk of collision, grounding,
floundering and adverse impact to the marine environment.

The goals in the cross-referenced Rules are also to be met.

1.2 Functional Requirements

In order to achieve the above stated goals, the design, construction, installation and maintenance of the
power generation and distribution systems are to be in accordance with the following Functional
Requirements:

Functional Functional Requirements

Requirement No.

Power Generation and Distribution (POW)

POW-FR1 Provide sufficient power capacity and quantity to supply maximum expected conditions with all
main sources of power and to achieve continuity of power at normal operational and habitable
condition with at least one source of power in standby.

POW-FR2 Power generation and distribution equipment to be designed with redundancy to prevent loss of
essential/emergency services upon a single failure.

POW-FR3 Means to be provided to protect the main source of power from sustained overload.

POW-FR4 The emergency source of electrical power is to be capable of functioning at the worst case heel angle
in a damaged condition of the unit.

POW-FR5 Design and arrange emergency power such that a casualty of a space containing the main source of
power, propulsion engines and high fire risk will not affect the emergency power.

POW-FR6 Provide a power source independent of the main source of power to support emergency services for
applicable duration.

POW-FR7 Provide transitional power to supply emergency safety systems that are not to be interrupted
significantly upon loss of either the main or emergency source of power.

POW-FR8 Maintain the integrity of emergency power and associated electrical distribution equipment.

POW-FR9 Provide redundancies and enhance reliability for emergency generator starting.

POW-FR10 Provide continuous power supply to communication systems such that the final supply power
circuits are independent of other systems.

POW-FR11 Provide electrical distribution scheme for Alternating Current (AC) and Direct Current (DC)
systems suitable for offshore units and safe for onboard personnel.

POW-FR12 Provide conductors with sufficient current carrying capacity to support connected loads and within
the ratings of overload protection

POW-FR13 Provide vessel essential and emergency loads with dedicated power supply feeders from main or
emergency power distribution as applicable.

POW-FR14 Provide redundancy for steering gear power supply feeders such that a single failure will not result
in loss of steering.

POW-FR15 The main and emergency lighting systems are to be independent such that a single failure of one
system will not result in loss of the other.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 139
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

Functional Functional Requirements

Requirement No.

POW-FR16 Primary essential services and secondary essential services necessary for safety are to be provided
with arrangements to automatically restart upon restoration of main source of power.

POW-FR17 (PROP) Provide sufficient fuel capacity for power generation and propulsion system to achieve continuity of
power for intended operation.

POW-FR18 Provide system/equipment redundancy such that a single failure will not disable the essential and
emergency services.

POW-FR19 Restrict heating appliances connected to a subcircuit to prevent overloading.

POW-FR20 The total harmonic distortion in the distribution system is not to exceed the design limits of the
distribution equipment and consumers.

POW FR21 (PROP) Provide means to start the propulsion and auxiliary services in the event of dead ship condition.

Fire Safety (FIR)

FIR-FR1 Provide protection for indicating and measuring devices to prevent fire in the control circuit.

FIR-FR2 Provide means to shut down the power ventilation system in the event of emergency. The means of
shutdown are to be in an accessible location outside the affected space, not likely to be cut off in the
event of fire.

FIR-FR3 Arrange batteries, other than those for engine-starting, away from other electrical equipment
including related battery distribution equipment to minimize fire risk.

Safety of Personnel (SAFE)

SAFE-FR1 Provide designs and arrangements that allow for the safe use of hull return and earthing systems.

SAFE-FR2 Provide adequate illumination of the unit for safe working conditions in all modes of vessel
operation.

SAFE-FR3 Provide segregation of ventilation systems serving different functional categories of spaces such that
shutdown of one group will not affect the other.

SAFE-FR4 Provide necessary information, instrumentation, and interlocks for safe use of shore connection with
electrical distribution system.

SAFE-FR5 Provide control, monitoring and alarms for navigation lights grouped in a centralized interface at the
navigation bridge.

SAFE-FR6 Provide protection to prevent accidental contact with live parts of the assembly.

Communications (COMM)

COMM-FR1 Provide effective and efficient means of communication from the navigation bridge to essential
interior locations.

COMM-FR2 Provide means of visual indication of the orders and responses in the bridge and machinery space
control stations.

COMM-FR3 Provide a general alarm capable of distinguishable audio signals that is audible throughout all
accommodation and normal crew working areas for summoning passengers and crew to muster
stations.

COMM-FR4 Provide means to initiate alarm from the centralized propulsion machinery control stations to alert
the engineers not on duty.

COMM-FR5 Provide means to initiate alarm from the refrigerated space and elevator such that the normally
(SAFE) manned control station is alerted of an emergency.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 140
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

Functional Functional Requirements

Requirement No.

COMM-FR6 Provide a broadcast system that is audible in all spaces where passengers and personnel are normally
present to notify them of an emergency and actions to be taken.

Automation (Control, monitoring and safety systems) (AUTO)

AUTO-FR1 (POW) Provide overload protection to emergency generator when used to supply the non-emergency
services or arranged for feedback operation as to safeguard the power supply to the required
emergency loads.

AUTO-FR2 (POW) Provide fail-safe safety measures and alarms at suitable remote locations to protect the emergency
generator.

AUTO-FR3 (POW) Provide protection against overload, undervoltage and short circuit conditions to prevent damage to
equipment and maintain continuity of power to remaining circuits.

AUTO-FR4 (POW) The circuit protection devices are to be able to withstand the prospective short circuit current values
at the point of installation.

AUTO-FR5 (POW) Provide coordination for all protective devices to allow the system to open the protective device
closest to the fault first to protect the healthy portion of the system.

AUTO-FR6 (POW) Provide arrangements for reverse power and undervoltage protection when sources of power are
arranged for parallel operation.

AUTO-FR7 (POW) Provide safety measures and alarms to protect the electrical distribution system from harmonics.

AUTO-FR8 (POW) Provide means to initiate shutdown of equipment and be designed such that a single failure will not
result in the loss of duplicated essential equipment.

AUTO-FR9 (POW) Provide means to monitor the emergency shutdown circuits to alert the crew of any failures.

AUTO-FR10 Provide protection against undervoltage and short circuit conditions for steering gear circuit to
(POW) maintain the steering capability.

AUTO-FR11 Provide automatic means of selecting sources of power and alarm at manned control station to
(POW) maintain continuity of power.

The functional requirements covered in the cross-referenced Rules are also to be met.

1.3 Compliance
A unit is considered to comply with the goals and functional requirements when the prescriptive
requirements are complied with or when an alternative arrangement has been approved. Refer to Part 1D,
Chapter 2.

2 Plans and Data to be Submitted

2.1 Wiring
2.1.1 Systems
One line diagrams for the following electrical systems are to be submitted for review.

● Power Supply and Distribution

● Lighting including Navigation Light
● Internal Communication
● General Emergency Alarm
● Fire Detection and Alarm

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 141
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

● Steering Gear Control (for self-propelled unit)

● Intrinsically-safe Equipment
● Emergency Generator Starting
2.1.2 Data for Wiring Systems
The one line diagrams are to show the circuit designation, type and size of cables, cable grouping
and banking, trip setting and rating of the circuit protection devices, the location of electrical
equipment accompanied by list of components, complete feeder list, rated load current for each
branch circuit, and voltage drop for longest run of each size cable. The one line diagram for power
supply and distribution systems is to indicate the following component details.

● Generator: kW rating, voltage, rated current, frequency, number of phases, power

factor

● Batteries: type, voltage, capacity, conductor protection (when required)

● Motors: kW rating, remote stops (when required)

● Transformers: kVA rating, rated voltage and current on primary and secondary side,
connection method

The one line diagram for power supply and distribution systems is also to include a list of
sequential start of motors and equipment having emergency tripping or preferential tripping
features.

2.3 Short-circuit Data

In order to establish that the protective devices on the main and emergency switchboards have sufficient
short-circuit breaking and making capacities, data are to be submitted giving the maximum calculated
short-circuit current in symmetrical rms and asymmetrical peak values available at the main bus bars
together with the maximum allowable breaking and making capacities of the protective device. Similar
calculations are to be made at other points in the distribution system where necessary to determine the
adequacy of the interrupting capacities of protective devices.

Refer to IEC Publication 61363-1 Electrical Installations of Ships and Mobile and Fixed Offshore Units –
Part 1: Procedures for Calculating Short-Circuit Currents in Three-Phase A.C.

2.5 Protective Device Coordination

A protective device coordination study is to be submitted for review. This protective device coordination
study is to consist of an organized time-current study of all protective devices in series from the utilization
equipment to the source for all circuit protection devices having different setting or time-current
characteristics for long-time delay tripping, short-time delay tripping and instantaneous tripping, where
applicable. Where an overcurrent relay is provided in series and adjacent to the circuit protection device,
the operating and time-current characteristics of the relay are to be considered for coordination. See
4-3-2/9.1.5.

2.7 Load Analysis

An electric-plant load analysis is to be submitted for review. The electric-plant (including high voltage unit
main service transformers or converters, where applicable per 4-3-2/7.1.6) load analysis is to cover all
operating conditions of the unit, including normal seagoing (if applicable) and emergency operations.

The analyses are to include:

● The simultaneous operation of loads on the emergency switchboard as per 4-3-2/5.3. Where the
emergency generator capacity is less than the sum of all of the nameplate rated loads, which can be
simultaneously connected to the emergency switchboard, then the analysis is to be supported by a
justification for each reduced or non-simultaneous load used.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 142
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

● High/low voltage ship service transformers or converters, where applicable as per 4-3-2/7.1.6 showing
they have sufficient capacity to support the connected loads.
● Identifying the loads to be tripped to provide continuity of supply per 4-3-2/3.1.6 (a), 4-3-2/3.3.2 iv)
and 4-3-2/9.3.3.
● Where optional DPS-2 or DPS-3 notation is requested, the load analysis is to include a detailed
analysis for all dynamic positioning modes and including during and following a single bus section
failure in different configurations (open or closed bus).

2.9 High Voltage Systems

2.9.1 Documents
High Voltage Design Operating Philosophy Document (See 4-3-5/1.13)

2.9.2 Analysis
Arc-flash hazard analyses [See 6-1-7/15.3.2(f)]

2.9.3 Operating Manual

Preliminary Operation Manual for the high voltage system and equipment (See 4-3-5/1.15)

2.9.4 General Arrangement

General Arrangement of the switchboards and distribution boards

2.9.5 Spaces
General Arrangement of spaces containing high voltage switchboards showing the location of:

i) Access and operating locations

ii) The equipment in 4-3-2/2.9.4 above, with equipment access doors closed, open,
maximum extent of withdrawable circuit breakers and associated cradles/dollies
iii) Doors to the room
iv) Location of work areas associated with the activities described in 4-3-5/2.13 and
4-3-5/2.15
v) Location and inventory of personal protective equipment (PPE) and safety equipment
vi) First aid equipment
2.9.6 Analysis and Data
An analysis or data for the estimated voltage transients to show that the insulation of power
transformers is capable of withstanding the estimated voltage transients.

2.9.7 Standards
The applicable standard of construction and the rated withstand voltage of the insulation for power
transformers. (This information is in addition to the information required in 6-1-7/11.)

3 Main Service Source of Power

3.1 Power Supply by Generators

3.1.1 Number of Generators
Units are to be provided with at least two main generator sets with combined capacity sufficient to
maintain the unit in normal operations (including the drilling mode) and habitable conditions to
include at least adequate services for cooking, heating, domestic refrigeration, mechanical
ventilation, sanitary and fresh water.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 143
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

3.1.2 Capacity of Generators

In addition to 4-3-2/3.1.1, the capacity of the generator sets is to be sufficient to maintain the unit
in normal operational and habitable conditions, excluding drilling equipment, with any one main
generator in reserve. The capacity of main generators is to be determined without recourse to the
emergency source of power. See 4-3-2/5 for emergency power source requirements. Also, for self-
propelled units, the generating sets are to be such that with any one generator or its primary source
of power out of operation, the remaining generating sets are capable of providing the electrical
services necessary to start the main propulsion plant in conjunction with other machinery, as
appropriate, from a dead ship condition within 30 minutes, as defined in 4-1-1/3.9 See also
4-3-2/3.1.4.

3.1.3 Multiple Generators

For units having multiple generating sets providing power for both propulsion and auxiliary
services, the propulsion loads considered for normal operation need only include those necessary
to propel the unit at 3.6 m/s (7 kn) or one-half the design speed in calm water, whichever is the
lesser. See 6-1-3/3.7 and 6-1-7/17.3.1 for details of propulsion generator.

3.1.4 Starting from "Dead Ship" Condition

In restoring the propulsion from a dead ship condition (see 4-1-1/3.9) for self-propelled units, no
stored energy is to be assumed available for starting the propulsion plant, the main source of
electrical power and other essential auxiliaries. It is assumed that means are available to start the
emergency generator at all times.

The emergency source of electrical power may be used to restore the propulsion, provided its
capacity either alone or combined with that of any other available source of electrical power is
sufficient to provide at the same time those services required to be supplied by 4-3-2/5.3.1 through
4-3-2/5.3.7.

The emergency source of electrical power and other means needed to restore the propulsion are to
have a capacity such that the necessary propulsion starting energy is available within 30 minutes
from a dead ship condition, as defined in 4-1-1/3.9. Emergency generator stored starting energy is
not to be directly used for starting the propulsion plant, the main source of electrical power and/or
other essential auxiliaries (emergency generator excluded).

See also 4-3-2/3.1.2 above.

3.1.5 Fuel Capacity for Generator Prime Mover

For self-propelled units where the fuel for any unit’s main service generator prime mover differs
from the fuel for the main propulsion plant, fuel capacity for that unit’s service generator prime
mover with margins is to be provided for the longest anticipated run of the unit between fueling
ports.

3.1.6 System Arrangement

3.1.6(a) General.
For self-propelled units where the main source of electrical power is necessary for propulsion and
steering and the safety of the unit, the system is to be so arranged that the electrical supply to
equipment necessary for these services is maintained or is capable of being restored in the case of
loss of any one of the generators in service in accordance with the requirements in 4-3-2/3.1.6(b)
or 4-3-2/3.1.6(c).

Load shedding of nonessential services, and where necessary, secondary essential services (see
4-1-1/3.5) or other arrangements, as may be necessary, are to be provided to protect the generators
against the sustained overload. For main bus bar subdivision, see 6-1-7/9.13.2.

3.1.6(b) Single Generator Operation.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 144
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

Where the electrical power is normally supplied by a single generator, provision is to be made
upon loss of power for automatic starting and connecting to the main switchboard of a stand-by
generator(s) of sufficient capacity with automatic restarting of the essential auxiliaries in
sequential operation, if necessary, to permit propulsion steering and to the safety of the unit.
Starting and connection to the main switchboard of the standby generator is to be preferably
within 30 seconds after loss of the electrical power supply but in no case in more than 45 seconds.

3.1.6(c) Multiple Generator Operation.

Where the electrical power is normally supplied by more than one generator set simultaneously in
parallel operation, the system is to be so arranged that in the event of the loss of any one of the
generators in service, the electrical supply to equipment necessary for propulsion, steering and the
safety of the unit will be maintained by the remaining generator(s) in service. See also 4-3-2/3.1.3.

3.3 Generator Driven by Propulsion Unit

3.3.1 Constant Speed Drive
A generator driven by a main propulsion unit (shaft generator) capable of operating continuously
at a constant speed, e.g., a system where the unit speed and direction are controlled only by
varying propeller pitch, may be considered to be one of the generators required by 4-3-2/3.1.1,
provided that the arrangements stated in i) to iii) below are complied with:

i) The generator and the generating systems are capable of maintaining the voltage and
frequency variation within the limits specified in 6-1-7/5.17.2 and 4-3-1/9 TABLE 1
under all weather conditions during sailing or maneuvering and also while the unit is
stopped.
ii) The rated capacity of the generator and the generating systems is safeguarded during all
operations given under i), and is such that the services required by 4-3-2/3.1.2 can be
maintained upon loss of any generator in service.
iii) An arrangement is made for starting a standby generator and connecting it to the
switchboard, in accordance with 4-3-2/3.1.6.
3.3.2 Variable Speed Drive
Shaft generator installations not capable of operating continuously at a constant speed may be
used for normal operational and habitable conditions of the unit, provided that the arrangements
stated in i) to v) below are complied with. This type of generator will not be counted as one of the
generators required by 4-3-2/3.1.2.

i) In addition to this type of generator, generators of adequate rating are provided, which
constitute the main source of electrical power required by 4-3-2/3.1.2.
ii) When the frequency variations at the main bus bar exceed the following limits due to the
speed variation of the propulsion machinery which drives the generator, arrangements are
made to comply with 4-3-2/3.1.6.

● Permanent frequency variation: ±5.5%

● Transient frequency variation: ±11% (5 sec)
iii) The generators and the generating systems are capable of maintaining the voltage and
frequency variation within the limits specified in 6-1-7/5.17.2 and 4-3-1/9 TABLE 1.
iv) Where load-shedding arrangements are provided, they are fitted in accordance with
4-3-2/9.3.3.
v) Where the propulsion machinery is capable of being operated from the navigation bridge,
means are provided or procedures are in place such that power supply to essential services
is maintained during maneuvering conditions in order to avoid a blackout situation.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 145
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

3.5 Sizing of AC Generator

In selecting the capacity of an alternating-current generating plant, particular attention is to be given to the
starting current of motors forming part of the system. Under normal operating conditions of the unit with
one generator held in reserve as a standby, the remaining generator sets operating in parallel and initially
carrying the minimum load necessary for operating the unit are to have sufficient capacity with respect to
the largest idle motor on the unit so that the motor can be started and the voltage drop occasioned by its
starting current will not cause any already running motor to stall or control equipment to drop out.

5 Emergency Source of Power

5.1 General
5.1.1 Basic Requirement
A self-contained emergency source of electrical power – together with its associated power
transformer, if any, transitional source of emergency power, emergency switchboard, and
emergency lighting switchboard, and the fuel oil tank for emergency generator prime mover – is to
be installed in a non-hazardous space and is to be located above the worst damage waterline (see
3A-3-2/1.3.2), aft of the collision bulkhead, if any, and in a space which is not within the assumed
extent of damage defined in 3A-3-2/3.5. The space is to contain only machinery and equipment
supporting the normal operation of the emergency power source. Its location is to be readily
accessible from the open deck. The arrangement is to be such that a fire, flooding or other failure
in a space containing the main source of electrical power, or in any space containing internal
combustion machinery for propulsion, any oil-fired or oil-fuel unit, or internal combustion
machinery with an aggregate total power of 375 kW (500 hp) or more, will not interfere with the
supply or distribution of emergency power.

5.1.2 Boundary
Where the "boundaries" of spaces containing the emergency sources of electrical power,
associated power transformer, transitional source of emergency power, emergency switchboard,
emergency lighting switchboard, and the fuel oil tank for emergency generator prime mover are
contiguous to boundaries of internal combustion machinery for propulsion, an oil-fired, or oil-fuel
unit, or internal combustion machinery with an aggregate total power of 375 kW (500 hp) or more,
or to spaces of Zone 1 or Zone 2, the contiguous boundaries are to be in compliance with Section
5-1-1.

5.1.3 Alternate Arrangements

Where the main source of electrical power is located in two or more spaces which have their own
systems, including power distribution and control systems, completely independent of the systems
in other spaces and such that a fire or other casualty in any other of the spaces will not affect the
power distribution from the others, or to the services required in 4-3-2/5.3, the requirements for
self-contained emergency source of power may be considered satisfied without an additional
emergency source of electrical power, provided that:

i) There are at least two generating sets meeting the inclination design requirements of
4-3-2/5.5.1;
ii) Each set is of sufficient capacity to meet the requirements of 4-3-2/5.3;
iii) The generating sets are located in each of at least two spaces;
iv) The arrangements required by 4-3-2/5.1.3 in each such space are equivalent to those
required by 4-3-2/5.5.2, 4-3-2/5.9 and 4-3-2/5.15 so that a source of electrical power is
available at all times for the services required by 4-3-2/5.3; and
v) The location of each of the spaces referred to in 4-3-2/5.1.3.iii is in compliance with
4-3-2/5.1.1 and the boundaries meet the requirements of 4-3-2/5.1.2, except that
contiguous boundaries should consist of an “A-60” bulkhead and a cofferdam, or a steel
bulkhead insulated to class “A-60” on both sides.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 146
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

5.1.4 Units with Dynamic Positioning Systems Notation (DPS 2 and 3)

For Units with optional DPS notation, an emergency source of power is required in accordance
with 4-3-2/5.1.1 and 4-3-2/5.1.2. Alternate arrangements without a dedicated emergency source of
power, in accordance with 4-3-2/5.1.3, will be considered, provided the unit also meets the
requirements of optional EHS-P notation in accordance with 8/3.1 of ABS Guide for Dynamic
Positioning Systems.

5.3 Emergency Power Supply

The electrical power available is to be sufficient to supply all those services that are essential for safety in
an emergency, due regard being paid to such services as may have to be operated simultaneously. Where
the sum of the loads on the emergency generator switchboard exceeds the power available, an analysis
demonstrating that the power required to operate the services simultaneously is to be produced. The
analysis is to be submitted for review in support of the sizing of the emergency generator. Having regard to
starting currents and the transitory nature of certain loads, the emergency source of electrical power is to be
capable of supplying simultaneously at least the services listed in 4-3-2/5.3.1 through 4-3-2/5.3.12 for the
period specified, if they depend upon an electrical source for their operation.

5.3.1 Emergency Lighting

For a period of 18 hours, emergency lighting:

5.3.1(a)
At every survival craft embarkation station, on deck, at the launching appliances and over the side
to illuminate the surface of the water where the survival craft will enter the water. If fixed metal
ladders or stairways are provided from the deck to the surface of the water for embarkation
purposes, emergency lighting is to be provided for the fixed metal ladder and sea areas in their
vicinity.

5.3.1(b) In all service and accommodation alleyways, stairways and exits, personnel elevators and
their trunks.

5.3.1(c) In the machinery spaces and main generating stations, including their control positions.

5.3.1(d) In all control stations, machinery control rooms, and at each main and emergency
switchboard.

5.3.1(e) In all spaces from which control of the drilling process is performed and where controls of
machinery essential for the performance of this process, or devices for emergency switching-off of
the power plant are located.

5.3.1(f) At all stowage positions for fire-fighters' outfits.

5.3.1(g) At the sprinkler pump, if any, at one of the fire pumps, if dependent upon emergency
generator for its source of power, at the emergency bilge pump, if any, and at the starting positions
of their motors.

5.3.1(h) On helideck, to include perimeter and helideck status lights, wind direction indicators
illumination, and related obstruction lights, if any.

5.3.1(i) At every location where an abandonment system is deployed or operated and onto the
water where personnel leaving the abandonment system will reach the water level.

5.3.2 Navigation Lights and Signals

For a period of 18 hours, the navigation lights, other lights and sound signals required by the
International Regulations for the Prevention of Collisions at Sea in force.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 147
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

5.3.3 Marking of Offshore Structures

For a period of four days, signaling lights and sound signals required for marking of offshore
structures.

5.3.4 Internal Communications

For a period of 18 hours, all internal communication systems required in an emergency (see Note
1 below).

5.3.5 Fire and Gas Detection and Alarm Systems

For a period of 18 hours, the required fire and gas detection and alarm systems (see Note 1 below).

5.3.6 Emergency Signals

For a period of 18 hours, intermittent operation of the manually operated call points and all
internal signals that are required in an emergency (see Note 1 below).

5.3.7 Blow-Out Preventer (BOP) and Well Disconnection

For a period of 18 hours, blow-out preventer control systems and means for disconnecting the unit
from the well-head arrangement, if electrically controlled (see Note 1 below).

5.3.8 Fire Pump and Fire Extinguishing Systems

For a period of 18 hours, one of the fire pumps and other fire extinguishing systems, if dependent
upon the emergency generator for its source of power.

5.3.9 Diving Equipment

Permanently installed diving equipment necessary for safe conduct of diving operations, if
dependent on the unit’s electrical power.

5.3.10 Column-Stabilized Units

On column-stabilized units, for a period of 18 hours:

5.3.10(a) Ballast valve control system, ballast valve position indicating system, draft level
indicating system and tank level indicating system.

5.3.10(b) The largest single ballast pump required by 4-2-4/13.5.1. See also 4-3-2/5.11.

5.3.11 Self-propelled Units

On self-propelled units:

5.3.11(a) For a period of 18 hours, emergency lighting at the steering gear.

5.3.11(b) For a period of 18 hours, navigational aids as required by Chapter V of the 1974 SOLAS
Convention, as amended (see Note 1 below).

5.3.11(c) For a period of 18 hours, intermittent operation of the daylight signaling lamp and the
unit's whistle (see Note 1 below).

5.3.11(d) For a period of at least 10 minutes continuous operation of the steering gear (see
4-3-2/11.5).

5.3.11(e) For a period of 18 hours, the radio communication equipment as required by Chapter IV
of the 1974 SOLAS Convention, as amended (see Note 1 below).

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 148
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

5.3.12 Other Emergency Services

5.3.12(a) For a period of 30 minutes, operation of watertight doors referred to in 3-3-2/5.3 (but not
necessarily all of them simultaneously), including their controls and indicators, unless an
independent temporary source of stored energy is provided.

5.3.12(b) For a period of 30 minutes, free-fall lifeboat secondary launching appliance, if the
secondary launching appliance is not dependent on gravity, stored mechanical power or other
manual means.

5.3.12(c) For a period of 18 hours, intermittent operation of the general emergency alarm system
and other manually operated alarms required in 4-3-2/17.

Note:
1 Unless they have an independent supply from an accumulator battery suitably located for use in an emergency and
sufficient for the period of 18 hours.

5.5 Emergency Sources

5.5.1 General
The emergency source of electrical power may be either a generator or an accumulator battery in
accordance with 4-3-2/5.5.2 or 4-3-2/5.5.3. The emergency generator and its prime mover and any
emergency accumulator battery are to be designed to function at full rated power when upright and
when inclined in static condition up to a maximum angle of heel in the intact and damaged
condition, as determined in accordance with Section 3-3-2. In no case need the equipment be
designed to operate when inclined in static condition more than:

● 25° in any direction on a column-stabilized unit;

● 15° in any direction on a self-elevating unit, and
● 22.5° about the longitudinal axis and/or when inclined 10° about the transverse axis on a
surface unit.

In all cases, the emergency source of electrical power is to be designed to operate as a minimum
under the angles of inclination defined in 4-1-1/7.1.

5.5.2 Generator
Where the emergency source of electrical power is a generator, it is to be:

i) Driven by a prime mover with all necessary auxiliary systems independent from the main
source of electrical power systems. The auxiliary systems, which may include fuel oil
system, starting equipment, cooling system, lubricating oil system and air supply, are to
be installed as near as is practicable to the generator prime mover, preferably located in
the same space as the generator prime mover unless the operation of the generator prime
mover would be thereby impaired; and
ii) Started automatically upon failure of the main source of electrical power supply and
connected automatically to the emergency switchboard—then, those services referred to
in 4-3-2/5.7 are to be connected automatically to the emergency generator as quickly as is
safe and practicable subject to a maximum of 45 seconds, or

Provided with a transitional source of emergency electrical power as specified in

4-3-2/5.7 unless an emergency generator is provided capable both of supplying the
services referred to in 4-3-2/5.7 of being automatically started and supplying the required
load as quickly as is safe and practicable subject to a maximum of 45 seconds, and
iii) An adequate capacity of fuel oil for the emergency generator prime mover, having a
flashpoint (closed cup test) of not less than 43°C (110°F), is to be provided. The use of

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 149
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

fuel oil having a flashpoint of less than 60°C (140°F) but not less than 43°C (110°F) is to
be subject to the provisions of 4-2-5/9.1.3.
iv) Where fuels with a flash point (closed cup test) of less than 43°C (110°F) are intended to
be used for prime movers, the additional risks due to the use of these low flashpoint fuels
(e.g., hazardous area risks) are to be evaluated and addressed in accordance with
recognized industry standards. The risk assessment and details of the mitigating measures
are to be submitted for review.
Commentary:

Using fuel with flash point less than 43°C (110°F) is subject to be approved by the unit’s flag Administration.

End of Commentary

5.5.3 Accumulator Battery

Where the emergency source of electrical power is an accumulator battery, it is to be capable of:

i) Carrying the emergency electrical load without recharging while maintaining the voltage
of the battery throughout the discharge period within 12% above or below its nominal
voltage,
ii) Automatically connecting to the emergency switchboard in the event of failure of the
main source of electrical power; and
iii) Immediately supplying at least those services specified in 4-3-2/5.7.
5.5.4 Emergency Generator for Non-emergency Services
Provided that suitable measures are taken for safeguarding independent emergency operations
under all circumstances, the emergency generator may be used, exceptionally, and for short
periods, to supply non-emergency circuits during the blackout situation (see 4-1-1/3.11), dead ship
condition (see 4-1-1/3.9), and routine use for testing (see 4-3-2/5.13). The generator is to be
safeguarded against overload by automatically shedding such non-emergency services so that
supply to the required emergency loads is always available. See also 4-3-2/5.9.5.

5.5.5 Lithium-Ion Batteries

Where the emergency source of electrical power is lithium-ion batteries, it is to comply with the
requirements given in the ABS Requirements for Use of Lithium-ion Batteries in the Marine and
Offshore Industries. [see 2/1.9 of that document]

5.7 Transitional Source of Power

The transitional source of emergency electrical power, where required by 4-3-2/5.5.2.ii, is to consist of an
accumulator battery which is to operate without recharging while maintaining the voltage of the battery
throughout the discharge period within 12% above or below its nominal voltage, and be of sufficient
capacity and is to be so arranged as to supply automatically in the event of failure of either the main or the
emergency source of electrical power for half an hour at least the following services if they depend upon
an electrical source for their operation:

i) The lighting required by 4-3-2/5.3.1 and 4-3-2/5.3.2. For this transitional phase, the required
emergency electric lighting, in respect of the machinery space and accommodation and service
spaces, may be provided by permanently fixed, individual, automatically charged, relay operated
accumulator lamps; and
ii) All services required by 4-3-2/5.3.4 through 4-3-2/5.3.7 unless such services have an independent
supply for the period specified from an accumulator battery suitably located for use in an
emergency.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 150
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

5.9 Emergency Switchboard

5.9.1 General
The emergency switchboard is to be installed as near as is practicable to the emergency source of
electrical power.

5.9.2 Emergency Switchboard for Generator

Where the emergency source of electrical power is a generator, the emergency switchboard is to
be located in the same space unless the operation of the emergency switchboard would thereby be
impaired.

5.9.3 Accumulator Battery

No accumulator battery fitted in accordance with 4-3-2/5.5.3 or 4-3-2/5.7 is to be installed in the
same space as the emergency switchboard. An indicator is to be mounted on the main switchboard
or in the machinery control room to indicate when these batteries are being discharged.

5.9.4 Interconnector Feeder Between Emergency and Main Switchboards

The emergency switchboard is to be supplied during normal operation from the main switchboard
by an interconnector feeder which is to be protected at the main switchboard against overload and
short circuit. The interconnector feeder is to be disconnected automatically at the emergency
switchboard upon failure of the main source of electrical power. Where the system is arranged for
feedback operation, the interconnector feeder is also to be protected at the emergency switchboard
against short circuit. In addition, the circuit protection device at the emergency switchboard on the
interconnector feeder is to trip to prevent overloading of the emergency generator.

In designs where the main switchboard voltage is different from that of the emergency
switchboard the power to the emergency switchboard is to be supplied from the main vessel
service switchboard.

As far as practicable, the circuit coordination is to be arranged such that the outgoing circuits from
the main vessel service switchboard will coordinate with the transformer circuit breakers to
prevent the supply to the emergency switchboard from being unavailable due to a fault on one of
the other outgoing circuits from the main vessel service switchboard.

Note:

For the purpose of this Rule, the main vessel service switchboard is a switchboard which is connected to the
secondary of step-down transformer producing the required voltage.

5.9.5 Disconnection of Non-emergency Circuits

For ready availability of the emergency source of electrical power, arrangements are to be made
where necessary to disconnect automatically non-emergency circuits from the emergency
switchboard so that electrical power is to be automatically available to the emergency circuits.

5.11 Ballast Pumps

On column-stabilized units, it is to be possible to supply each ballast pump required by 4-2-4/13.5.1 from
the emergency source of power. The arrangement is to be such that one of the pumps is connected directly
to the main switchboard and the other pump is connected directly to the emergency switchboard. For
systems utilizing independent pumps in each tank, all pumps are to be capable of being supplied from an
emergency source of power. When sizing the emergency source of power in accordance with 4-3-2/5.3, the
largest ballast pump capable of being supplied from this source is to be assumed to be operating
simultaneously with the loads specified in 4-3-2/5.3, allowing for suitable load and diversity factors.

5.13 Arrangements for Periodic Testing

Provision is to be made to enable the periodic testing of the complete emergency system, and is to include
the testing of automatic starting arrangements.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 151
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

5.15 Starting Arrangements for Emergency Generator Sets

5.15.1 Cold Conditions
Emergency generating sets are to be capable of being readily started in their cold condition at a
temperature of 0°C (32°F). If this is impracticable or if lower temperatures are likely to be
encountered, heating arrangements are to be provided for ready starting of the generating sets.

5.15.2 Number of Starts

Each emergency generator that is arranged to be automatically started is to be equipped with
approved starting devices with a stored energy capability of at least three consecutive starts.
Unless a second independent means of starting is provided, the source of stored energy is to be
protected to preclude critical depletion by automatic starting system, i.e., the automatic starting
system is only allowable for consumption of the stored energy source to a level that would still
provide the capability for starting the emergency generator upon intervention by personnel. In
addition, a second source of energy is to be provided for an additional three starts within 30
minutes unless manual starting can be demonstrated to be effective to the Surveyor.

5.15.3 Charging of Stored Energy

The stored energy is to be maintained at all times, as follows:

5.15.3(a)
Electrical and/or hydraulic starting systems are to be maintained from the emergency switchboard;

5.15.3(b) Compressed air starting systems may be maintained by the main or auxiliary compressed
air receivers through a suitable non-return valve or by an emergency air compressor which, if
electrically driven, is supplied from the emergency switchboard;

5.15.3(c) All of these starting, charging and energy storing devices are to be located in the
emergency generator space. These devices are not to be used for any purpose other than the
operation of the emergency generating set. This does not preclude the supply to the air receiver of
the emergency generating set from the main or auxiliary compressed air system through the non-
return valve fitted in the emergency generator space.

5.15.4 Manual Starting

Where automatic starting is not required, manual (hand) starting is permissible, such as manual
cranking, inertia starters, manually charged hydraulic accumulators or power charge cartridges,
where they can be demonstrated as being effective to the Surveyor.

When manual (hand) starting is not practicable, the requirements of 4-3-2/5.15.2 and 4-3-2/5.15.3
are to be complied with, except that starting may be manually initiated.

5.17 Alarms and Safeguards for Emergency Diesel Engines

5.17.1 Information to be Submitted
Information demonstrating compliance with these requirements is to be submitted for review. The
information is to include instructions to test the alarm and safety systems.

5.17.2 Alarms and Safeguards

5.17.2(a) Alarms and safeguards are to be fitted in accordance with 4-3-2/5 TABLE 1.

5.17.2(b) The safety and alarm systems are to be designed to ‘fail safe’. The characteristics of the
‘fail safe’ operation are to be evaluated on the basis not only of the system and its associated
machinery, but also the complete installation, as well as the unit.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 152
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

5.17.2(c) Regardless of the engine output, if shutdowns additional to those specified in 4-3-2/5
TABLE 1 are provided, except for the overspeed shutdown, they are to be automatically
overridden when the engine is in automatic or remote control mode.

5.17.2(d) The alarm system is to function in accordance with 4-9-2/3.1.2 and 4-9-2/7 of the
Marine Vessel Rules, with additional requirements that grouped alarms are to be arranged on the
bridge. For units that are not self-propelled, the grouped alarms are to be arranged at an
emergency control station (see 8-2-1/11.7)

5.17.2(e) In addition to the fuel oil control from outside the space, a local means of engine
shutdown is to be provided.

5.17.2(f) Local indications of at least those parameters listed in 4-3-2/5 TABLE 1 are to be
provided within the same space as the diesel engines and are to remain operational in the event of
failure of the alarm and safety systems.

TABLE 1
Alarms and Safeguards for Emergency Diesel Engines
[See 4-3-2/5.17]

Systems Monitored Parameters A Auto Shut Notes

Down [ A = Alarm; x = apply ]

Fuel oil A1 Leakage from pressure pipes x

Lubricating oil B1 Temperature –high x For engines having a power of 220 kW or more.

B2 Lubricating oil pressure –low x

B3 Oil mist in crankcase, mist x For engines having a power of 2250 kW (3000
concentration – high; or hp) and above or having a cylinder bore of
Bearing temperature - high; or more than 300 mm (11.8 in.).
Alternative arrangements See 4-2-1/7.2 of the Marine Vessel Rules.

Cooling medium C1 Pressure or flow –low x For engines having a power of 220 kW or more.

C2 Temperature –high x

Engine D1 Overspeed activated x x For engines having a power of 220 kW or more.

5.19 Requirements by the Governmental Authority

Attention is directed to the requirements of the governmental authority of the country whose flag the unit
flies for the emergency services and the accumulator batteries required in various types of units.

7 Distribution System

7.1 Main Service Distribution System

7.1.1 General
Current-carrying parts with potential to earth are to be protected against accidental contact.

For recognized standard distribution systems, see 4-3-1/7. Separate feeders are to be provided for
essential and emergency services.

7.1.2 Method of Distribution

The output of the unit’s service generators may be supplied to the current consumers by way of
either branch system, meshed network system or ring main system. The cables of a ring-main or

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 153
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

other looped circuit (e.g., interconnecting section boards in a continuous circuit) are to be formed
of conductors having sufficient current-carrying and short-circuit capacity for any possible load
and supply configuration.

7.1.3 Through-feed Arrangements

The size of feeder conductors is to be uniform for the total length, but may be reduced beyond any
intermediate section board and distribution board, provided that the reduced size section of the
feeder is protected by an overload device.

7.1.4 Motor Control Center

Feeder cables from the main switchboard or any section board to the motor control centers are to
have a continuous current-carrying capacity not less than 100% of the sum of the nameplate
ratings of all the motors supplied. Feeder cables of lesser current capacity are permitted, where the
design is such that connected consumers are not operated simultaneously, under any operating
mode.

7.1.5 Motor Branch Circuit

A separate circuit is to be provided for each fixed motor having a full-load current rating of 6
amperes or more and the conductors are to have a carrying capacity of not less than 100% of the
motor full-load current rating. No branch circuit is to have conductors less than 1.5 mm2 wire.
Circuit-disconnecting devices are to be provided for each motor branch circuit and are to be in
accordance with 4-3-3/3.13.2 and 6-1-7/9.15.2.

7.1.6 Power Supply Through Transformers and Converters

7.1.6(a) Continuity of Supply.
Where transformers and/or converters form a part of the unit’s main service electrical system
supplying essential services and services necessary for minimum comfortable conditions of
habitability, the number and capacity of the transformers and/or converters are to be such that with
any one transformer or converter or any one single phase of a transformer out of service, the
remaining transformers and/or converters or remaining phases of the transformer are capable of
supplying power to these loads under normal seagoing conditions.

See 4-3-5/1.3.6 for the additional requirements applicable for high voltage transformers.

7.1.6(b) Arrangements.
Each required transformer is to be located in a separate enclosure or equivalent, and is to be served
by separate circuits on the primary and secondary sides. When installed in the same space, the
transformers are to be adequately separated to suitably protect and preclude damage by fire or
other incident at one of the transformers.

Each of the secondary circuits is to be provided with a multipole isolating switch. This multipole
isolating switch is not to be installed on the transformer casing or its vicinity (in so far as
practicable) in order to preclude its damage by fire or other incident at the transformer. A circuit
breaker provided in the secondary circuit in accordance with 4-3-2/9.15.1, will be acceptable in
lieu of a multipole isolating switch.

7.1.6(c) Transformers and Converters for Battery Charger.

Where batteries connected to a single battery charger are the sole means of supplying DC power to
equipment for essential services, as defined in 4-3-1/3.5, failure of the single battery charger under
normal operating conditions should not result in total loss of these services once the batteries are
depleted. In order to ensure continuity of the power supply to such equipment, one of the
following arrangements is to be provided:

i) Duplicate battery chargers; or

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 154
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

ii) A single battery charger and a transformer/rectifier (or switching converter) which is
independent of the battery charger, provided with a change-over switch; or
iii) Duplicate transformer/rectifier (or switching converter) units within a single battery
charger, provided with a change-over switch.

The above requirements are not applicable for the following:

● The equipment for the essential services, which contains a single transformer/
rectifier with a single AC power supply feeder to such equipment.
● The services which are not used continuously, such as battery chargers for engine
starting batteries, etc.
7.1.6(d) Automatic Bus Transfer
Where an Automatic Bus Transfer (ABT) is provided between the secondary side of the
transformers and the load center panel connected directly without a multipole isolating switch or
protective device, the ABT may be considered as the multipole isolating switch if it is provided
with manual transfer operation lockable in either position. Details of the ABT is to be submitted
for reference upon request.

7.1.7 Heating Appliances

Each heater is to be connected to a separate final subcircuit. However, a group of up to 10 heaters
whose total current does not exceed 16A may be connected to a single final subcircuit.

7.1.8 Transformer Cable Sizing

Cables provided for primary and secondary circuits of transformers are to have current carrying
capacities not less than the rated primary and secondary currents, respectively.

7.1.9 Generator Cable Sizing

Generator cable is to have a current carrying capacity of not less than the rated current or the rated
continuous overload current of the generator.

7.3 Hull Return System

7.3.1 General
The hull return system is not to be used for power, heating or lighting, except that the following
systems may be used:

i) Impressed current cathodic protective systems;

ii) Limited and locally earthed systems, provided that any possible resulting current does not
flow directly through any hazardous areas; or
iii) Insulation level monitoring devices, provided the circulation current does not exceed 30
mA under all possible conditions.

Current-carrying parts with potential to earth are to be protected against accidental contact.

7.3.2 Final Subcircuits and Earth Wires

Where the hull return system is used, all final subcircuits (i.e., all circuits fitted after the last
protective device) are to consist of two insulated wires, the hull return being achieved by
connecting to the hull one of the bus bars of the distribution board from which they originate. The
earth wires are to be in accessible locations to permit their ready examination and to enable their
disconnection for testing of insulation.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 155
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

7.5 Earthed Distribution Systems

System earthing is to be effected by means independent of any earthing arrangements of the non-current-
carrying parts. Means of disconnection is to be provided in the neutral earthing connection of each
generator so that the generator may be disconnected for maintenance. In distribution systems with neutral
earthed or for generators intended to be run with neutrals interconnected, the machines are to be designed
to avoid circulating currents exceeding the prescribed value. Transformer neutral is not to be earthed unless
all corresponding generator neutrals are disconnected from the system (e.g., during shore supply). See
4-3-3/7.5.2.

7.7 External or Shore Power Supply Connection

7.7.1 General
Where arrangements are made for the supply of electricity from a source on shore or other
external source, a termination point is to be provided on the unit for the reception of the flexible
cable from the external source. Fixed cables of adequate rating are to be provided between the
termination point and the main or emergency switchboard. Means for disconnecting the external
or shore power supply are to be provided at the receiving switchboard. See 4-3-2/9.11 for the
protection of external or shore power supply circuit.

Commentary:

For shore connections where the shore connection box is not utilized, direct connection to the switchboard may be
considered provided the connection can be put into service safely with interlock arrangements and instrumentation
as indicated below (4-3-2/7.7.2 through 4-3-2/7.7.5 as well as 4-3-2/9.11.2).

End of Commentary

7.7.2 Earthing Terminal

An earth terminal is to be provided for connecting the hull to an external earth.

7.7.3 Indicators
The external connection supply or shore connection is to be provided with a pilot lamp and a
voltmeter (and frequency meter for AC) at main or emergency switchboard to show energized
status of the cable.

7.7.4 Polarity or Phase Sequence

Means are to be provided for checking the polarity (for DC) or the phase sequence (for three-
phase AC) of the incoming supply in relation to the unit’s system.

7.7.5 Information Plate

Refer to 7-1-6/7.7.1.

7.9 Harmonics
The total harmonic distortion (THD) in the voltage waveform in the distribution systems is not to exceed
8% and any single order harmonics not to exceed 5%. Other higher values may be accepted provided the
distribution equipment and consumers are designed to operate at the higher limits. This relaxation on THD
limits is to be documented (harmonic distortion calculation report) and made available on board as a
reference for the surveyor at each periodical survey. Where higher values of harmonic distortion are
expected, any other possible effects, such as additional heat losses in machines, network resonances, errors
in control and monitoring systems are to be considered. See also 4-3-2/9.18 and 4-3-2/9.19.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 156
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

9 Circuit Protection System

9.1 System Design

9.1.1 General
Electrical installations are to be protected against accidental overload and short circuit, except

i) As permitted by 4-3-2/11.3,
ii) Where it is impracticable to do so, such as engine starting battery circuit, and
iii) Where by design, the installation is incapable of developing overload, in which case it
may be protected against short circuit only.

The protection is to be by automatic protective devices for:

i) Continued supply to remaining essential circuits in the event of a fault, and

ii) Minimizing the possibility of damage to the system and fire.

Three-phase, three-wire alternating current circuits are to be protected by a triple-pole circuit

breaker with three overload trips or by a triple-pole switch with a fuse in each phase. All branch
circuits are to be protected at distribution boards only and any reduction in conductor sizes is to be
protected. Dual-voltage systems having an earthed neutral are not to have fuses in the neutral
conductor, but a circuit breaker which simultaneously opens all conductors may be installed when
desired. In no case is the dual-voltage system to extend beyond the last distribution board.

9.1.2 Protection Against Short-circuit

9.1.2(a) Protective Devices.
Protection against short-circuit is to be provided for each non-earthed conductor by means of
circuit breakers or fuses.

9.1.2(b) Rated Short-circuit Making Capacity.

The rated short-circuit breaking capacity of every protective device is not to be less than the
maximum available fault current at that point. For alternating current (AC), the rated short-circuit
breaking capacity is not to be less than the root mean square (rms) value of the AC component of
the prospective short-circuit current at the point of application. The circuit breaker is to be able to
break any current having an AC component not exceeding its rated breaking capacity, whatever
the inherent direct current (DC) component may be at the beginning of the interruption.

9.1.2(c) Rated Short-circuit Making Capacity.

The rated short-circuit making capacity of every switching device is to be adequate for maximum
peak value of the prospective short-circuit current at the point of installation. The circuit breaker is
to be able to make the current corresponding to its making capacity without opening within a time
corresponding to the maximum time delay required.

9.1.3 Protection Against Overload

9.1.3(a) Circuit Breakers.
Circuit breakers or other mechanical switching devices for overload protection are to have a
tripping characteristic (overload-trip time) adequate for the overload capacity of all elements in
the system to be protected and for any discrimination requirements.

9.1.3(b) Fuses .
The fuse of greater than 320 amperes is not to be used for overload protection.

9.1.3(c) Rating.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 157
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

Fuse ratings and rating (or settings, if adjustable) of time-delay trip elements of circuit breakers
are not to exceed the rated current capacity of the conductor to be protected as listed in 4-3-4/7
TABLE 2, except as otherwise permitted for generator, motor and transformer circuit protection in
4-3-2/9.3, 4-3-2/9.13 and 4-3-2/9.15. If the standard ratings or settings of overload devices do not
correspond to the rating or the setting allowed for conductors, the next higher standard rating or
setting may be used, provided it does not exceed 150% of the allowable current carrying capacity
of the conductor, where permitted by the Standard to which the feeder cables have been
constructed. Except as otherwise permitted for motor and transformer branch-circuit protection,
adjustable-trip circuit breakers of the time-delay or instantaneous type are to be set to operate at
not more than 150% of the rated capacity of the conductor to be protected.

9.1.3(d) Indication.
The rating or setting of the overload protective device for each circuit is to be permanently
indicated at the location of the protective device.

9.1.4 Back-up Protection

9.1.4(a) Back-up Fuse Arrangements.
Circuit breakers having breaking and/or making capacities less than the prospective short-circuit
current at the point of application will be permitted, provided that such circuit breakers are
backed-up by fuses which have sufficient short-circuit capacity for that application. The fuse is to
be specifically designed for back-up combinations with the circuit breaker and the maximum fault
rating for the combination is to be provided.

9.1.4(b) Cascade Protection.

Cascade protection may be permitted, subject to special consideration. Such special consideration
is not intended for new construction units, however, may be granted when modifications are
performed to existing units. The cascade protection is to be arranged such that the combination of
circuit protective devices has sufficient short-circuit breaking capacity at the point of application
(see 4-3-2/9.1.2(b)). All circuit protective devices are to comply with the requirements for making
capacity (see 4-3-2/9.1.2(c)). Cascade protection is not to be used for circuits of primary essential
services. Where cascade protection is used for circuits of secondary essential services, such
services are to be duplicated, provided with means of automatic transfer and the automatic transfer
is to alarm at a manned location. Cascade protection may be used for circuits of non-essential
services.

9.1.5 Coordinated Tripping

Coordinated tripping is to be provided between generator, bus tie, bus feeder and feeder protective
devices. See also 4-3-2/9.3.2 and 4-3-2/9.7.1. Except for cascade system (backup protection) in
4-3-2/9.1.4, the coordinated tripping is also to be provided between feeder and branch-circuit
protective devices for essential services. Continuity of service to essential circuits under short-
circuit conditions is to be achieved by discrimination of the protective devices as follows:

9.1.5(a) The tripping characteristics of protective devices in series are to be coordinated.

9.1.5(b) Only the protective device nearest to the fault is to open the circuit, except for cascade
system (back-up protection) as specified in 4-3-2/9.1.4(a).

9.1.5(c) The protective devices are to be capable of carrying, without opening, a current not less
than the short-circuit current at the point of application for a time corresponding to the opening of
the breaker, increased by the time delay required for discrimination.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 158
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

9.3 Protection for Generators

9.3.1 General
Generators of less than 25 kW not arranged for parallel operation may be protected by fuses. Any
generators arranged for parallel operation and all generators of 25 kW and over are to be protected
by a trip-free circuit breaker whose trip settings are not to exceed the thermal withstand capacity
of the generator. The long-time over-current protection is not to exceed 15% above either the full-
load rating of continuous-rated machines or the overload rating of special-rated machines. The
shutting down of the prime mover is to cause the tripping of the unit main service generator circuit
breaker.

9.3.2 Trip Setting for Coordination

The instantaneous and short-time overcurrent trips of the generators are to be set at the lowest
values of current and time which will coordinate with the trip settings of feeder circuit breakers.
See also 4-3-2/9.1.5, 4-3-2/9.5.1, and 4-3-2/9.5.2(a).

9.3.3 Load Shedding Arrangements

9.3.3(a) Provision for Load Shedding Arrangements.
In order to safeguard continuity of the electrical power supply, automatic load-shedding
arrangements or other equivalent arrangements are to be provided:

i) Where only one generating set is normally used to supply power for propulsion and
steering of the unit, and a possibility exists that due to the switching on of additional
loads, whether manually or automatically initiated, the total load exceeds the rated
generator capacity of the running generator, or
ii) Where electrical power is normally supplied by more than one generator set
simultaneously in parallel operation for propulsion and steering of the unit, upon the
failure of one of the parallel running generators, the total connected load exceeds the total
capacity of the remaining generator(s).
9.3.3(b) Services not Allowed for Shedding.
Automatic load-shedding arrangements or other equivalent arrangements are not to automatically
disconnect the following services. See 4-1-1/3.5 for the definition of essential services.

i) Primary essential services that, when disconnected, will cause immediate disruption to
propulsion and maneuvering of the unit,
ii) Emergency services as listed in 4-3-2/5.3, and
iii) Secondary essential services that, when disconnected, will:

● Cause immediate disruption of systems required for safety and navigation of the unit,
such as:

– Lighting systems,
– Navigation lights, aids and signals,
– Internal communication systems required by 4-3-2/15, etc.
● Prevent services necessary for safety from being immediately reconnected when the
power supply is restored to its normal operating conditions, such as:

– Fire pumps, and other fire extinguishing medium pumps,

– Bilge pumps,
– Ventilation fans for engine and boiler rooms.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 159
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

9.3.4 Emergency Generator

The emergency generator is also to comply with 4-3-2/9.1, 4-3-2/9.3, 4-3-2/9.5 and 4-3-2/9.7,
where applicable. See also 4-3-2/5.9.

9.5 Protection for Alternating-current (AC) Generators

9.5.1 Short-time Delay Trip
Short-time delay trips are to be provided with circuit breakers for AC generators. See also
4-3-2/9.3.2. The current setting of the short time delay trip is to be less than the steady state short
circuit current of the generator.

For generators with a capacity of less than 200 kW having prime movers such as diesel engines or
gas turbines which operate independently of the electrical system, consideration may be given to
omission of short-time delay trips, if instantaneous trips and long time overcurrent protection (see
4-3-2/9.3.1) are provided. When the short time delay trips are omitted, the thermal withstand
capacity of the generator is to be greater than the steady state short-circuit current of the generator,
until activation of the tripping system.

9.5.2 Parallel Operation

Where AC generators are arranged for parallel operation with other AC generators, the following
protective devices are to be provided.

9.5.2(a) Instantaneous Trip.

Instantaneous trips are to be installed and set in excess of the maximum short-circuit contribution
of the individual generator where three or more generators are arranged for parallel operation.
Alternative suitable protection, such as generator differential protection, which will trip the
generator circuit breaker in the event of a fault in the generator or in the supply cable between the
generator and its circuit breaker, would also be acceptable. See also 4-3-2/9.3.2.

9.5.2(b) Reverse Power Protection.

A time-delayed reverse active power protection or other devices which provide adequate
protection is to be provided. The setting of protective devices is to be in the range of 8% to 15% of
the rated power for diesel engines. A setting of less than 8% of the rated power of diesel engines
may be allowed with a suitable time delay recommended by the diesel engine manufacturer. A fall
of 50% in the applied voltage is not to render the reverse power protection inoperative, although it
may alter the setting to open the breaker within the above range.

9.5.2(c) Undervoltage Protection.

Means are to be provided to prevent the generator circuit breaker from closing if the generator is
not generating, and to open the same when the generator voltage collapses.

In the case of an undervoltage release provided for this purpose, the operation is to be
instantaneous when preventing closure of the breaker, but is to be delayed for discrimination
purposes when tripping a breaker.

9.7 Protection for Direct Current (DC) Generators

9.7.1 Instantaneous Trip
DC generator circuit breakers are to be provided with an instantaneous trip set below the generator
maximum short-circuit current and are to coordinate with the trip settings of feeder circuit
breakers supplied by the generator.

9.7.2 Parallel Operation

9.7.2(a) Reverse Current Protection.
DC generators arranged for parallel operation with other DC generators or with an accumulator
battery are to be provided with instantaneous or short-time delayed reverse current protection. The

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 160
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

setting of the protection devices is to be within the power range specified by 4-3-2/9.5.2(b). When
the equalizer connection is provided, the reverse current device is to be connected on the pole
opposite to the equalizer connection where the series compound winding for the generator is
connected. Reverse current protection is to be adequate to deal effectively with reverse current
conditions emanating from the distribution system (e.g., electric driven cargo winches).

9.7.2(b) Generator Ammeter Shunts.

Generator ammeter shunts are to be so located that the ammeters indicate total generator current.

9.7.2(c) Undervoltage Protection.

Requirements for AC generator in 4-3-2/9.5.2(c) are also applicable to DC generator.

9.9 Protection for Accumulator Batteries

Accumulator (storage) batteries, other than engine starting batteries, are to be protected against overload
and short circuits by devices placed as near as practicable to the batteries but outside of the battery rooms,
lockers or boxes, except that the emergency batteries supplying essential services are to have short circuit
protection only. Fuses may be used for the protection of emergency lighting storage batteries instead of
circuit breakers up to and including 320 amperes rating. The charging equipment, except converters, for all
batteries with a voltage more than 20% of the line voltage is to be provided with reverse current protection.

Where equipment or DC distribution panel is fed from two feeders or sources of DC battery power
connected in parallel from separate battery charger systems, the batteries are to be protected from reverse
power by means of:
● Manual change over switch as applicable
● Automatic change over from one source to the other provided in the equipment as required
● Power diodes in the feeder circuit
● Diode relay switching units

9.11 Protection for External or Shore Power Supply

9.11.1 General
Where arrangements are made for the supply of electricity from a source on shore or other
external source, permanently fixed cables from the external supply or shore connection box to the
main or emergency switchboard are to be protected by fuses or circuit breakers located at the
connection box.

9.11.2 Interlocking Arrangement

Where the generator is not arranged for parallel operation with the external or shore power supply,
an interlocking arrangement is to be provided for the circuit breakers or disconnecting devices
between generator and the external or shore power supply in order to safeguard from connecting
unlike power sources to the same bus.

9.13 Protection for Motor Branch Circuits

9.13.1 General
Trip elements of circuit breaker for starting and for short-circuit protection are to be in accordance
with 4-3-2/9.13.2 or 4-3-2/9.13.3, except that circuit breakers having only instantaneous trips may
be provided as part of the motor control center. Where circuit breakers having only instantaneous
trips are provided, the motor running protective device is to open all conductors, and the motor
controller is to be capable of opening the circuit without damage to itself resulting from a current
up to the setting of the circuit breaker. Circuit-disconnecting devices are to be provided for each
motor branch circuit and are to be in accordance with 4-3-3/3.13.2 and 6-1-7/9.15.2.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 161
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

9.13.2 Direct-current Motor Branch Circuits

The maximum fuse rating or the setting of the time-delay trip element is to be 150% of the full-
load rating of the motor served. If that rating or setting is not available, the next higher available
rating or setting may be used.

9.13.3 Alternating-current Motor Branch Circuits

The maximum fuse rating or setting of the trip element is to be the value stated below. If that
rating or setting is not available, the next higher available rating or setting may be used.

Type of Motor Rating or Setting in % Motor Full-load

Current

Squirrel-cage and Synchronous Full-voltage, Reactor or Resistor- 250

starting

Autotransformer Starting 200

Wound Rotor 150

When fuses are used to protect polyphase motor circuits, it is to be arranged to protect against
single-phasing.

The setting of magnetic instantaneous trips for short-circuit protection only is to exceed the
transient current inrush of the motor, and is to be the standard value nearest to, but not less than,
10 times full-load motor current.

9.13.4 Motor Running Protection

Running protection is to be provided for all motors having a power rating exceeding 0.5 kW,
except that such protection is not to be provided for steering motors (see 4-3-2/11.3). The running
protection is to be set between 100% and 125% of the motor rated current.

9.13.5 Undervoltage Protection and Undervoltage Release

Undervoltage protection is to be provided for motors having power rating exceeding 0.5 kW (0.7
hp) to prevent undesired restarting upon restoration of the normal voltage, after a stoppage due to
a low voltage or voltage failure condition.

Undervoltage release is to be provided for the following motors unless the automatic restart upon
restoration of the normal voltage will cause hazardous conditions:

a) Primary essential services (see 4-1-1/7 TABLE 3).

b) Only those secondary essential services (see 4-1-1/7 TABLE 4) necessary for safety, such
as:

i) Bilge pumps.
ii) Ventilating fans for engine and boiler rooms where they may prevent the normal
operation of the propulsion machinery (See Note 1 below)
c) Where the design of the consumers listed in 4-3-2/9.13.5 a) and b) are demonstrated to
show that the operation of such consumers is not immediately essential to maintain the
vessel’s propulsion, steering and a minimum level of safety, undervoltage protection in
lieu of undervoltage release may be acceptable.

Special attention is to be paid to the starting currents due to a group of motors with undervoltage
release controllers being restarted automatically upon restoration of the normal voltage. Means
such as sequential starting is to be provided to limit excessive starting current, where necessary.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 162
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

Note:
1 Undervoltage protection is to be provided for ventilation fans for engine and boiler room, which are
supplied by an emergency source of power for the purpose of removing smoke from the space after a fire
has been extinguished.

9.13.6 Jacking Gear Motors

For group installations of jacking gear motors, see the special arrangements permitted in 6-1-9/15.

9.15 Protection for Transformer Circuits

9.15.1 Setting of Overcurrent Device
Each power and lighting transformer feeder is to be protected by an overcurrent device rated or set
at a value not more than 125% of rated primary current. When a transformer is provided with an
overcurrent device in the secondary circuit rated or set at not more than 125% of rated secondary
current, the feeder overcurrent device may be rated or set at a value less than 250% of the rated
primary current.

9.15.2 Parallel Operation

When the transformers are arranged for parallel operation, means are to be provided to disconnect
the transformer from the secondary circuit. Where power can be fed into secondary windings,
short-circuit protection (i.e., short-time delay trips) is to be provided in the secondary connections.
In addition, when the disconnecting device in primary side of the transformer is opened due to any
reason (e.g., the short-circuit protection, overload protection, or manual operation for opening),
the disconnecting device in the secondary side of the transformer is to be arranged to open the
circuit automatically.

9.17 Protection for Meters, Pilot Lamps and Control Circuits

Indicating and measuring devices are to be protected by means of fuses or current limiting devices. For
devices such as voltage regulators where interruption of the circuit may have serious consequences, fuses
are not to be used. If fuses are not used, means are to be provided to prevent fire in an unprotected part of
the installation. Fuses are to be placed as near as possible to the tapping from the supply.

9.18 Harmonic Distortion for Unit Electrical Distribution System including Harmonic Filters
9.18.1 Monitoring
Where the electrical distribution system on board a unit includes harmonic filters, such units are to
be fitted with facilities to continuously monitor the levels of harmonic distortion experienced on
the main bus bar as well as alert the crew should the level of harmonic distortion exceed the
acceptable limits. Where the engine room is provided with automation systems, this reading is to
be logged electronically, otherwise it is to be recorded in the engine log book for future inspection
by the Surveyor. However, harmonic filters installed for single application frequency drives such
as pump motors may be excluded from the requirements of this section.

9.18.2 Measurement
As a minimum, harmonic distortion levels of main bus bar on board such existing ships are to be
measured annually under seagoing conditions as close to the periodical machinery survey as
possible so as to give a clear representation of the condition of the entire plant to the Surveyor.
Harmonic distortion readings are to be carried out when the greatest amount of distortion is
indicated by the measuring equipment. An entry showing which equipment was running and/or
filters in service is to be recorded in the log so this can be replicated for the next periodical survey.
Harmonic distortion levels are also to be measured following any modification to the ship’s
electrical distribution system or associated consumers by suitably trained ship’s personnel or from
a qualified outside source. Records of all the above measurements are to be made available to the
surveyor at each periodical survey in accordance with Part 7A of the Rules.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 163
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

9.18.3 Validation of Calculated Harmonic

Where the electrical distribution system on board a unit includes harmonic filters, the system
integrator of the distribution system is to show, by calculation, the effect of a failure of a harmonic
filter on the level of harmonic distortion experienced.

The system integrator of the distribution system is to provide the unit owner with guidance
documenting permitted modes of operation of the electrical distribution system while maintaining
harmonic distortion levels within acceptable limits during normal operation as well as following
the failure of any combination of harmonic filters.

The calculation results and validity of the guidance provided are to be verified by the Surveyor
during trials.

9.18.4 Filter Protection Alarm

Arrangements are to be provided to alert the crew in the event of activation of the protection of a
harmonic filter circuit.

A harmonic filter is to be arranged as a three-phase unit with individual protection of each phase.
The activation of the protection arrangement in a single phase is to result in automatic
disconnection of the complete filter. Additionally, there is to be installed a current unbalance
detection system independent of the overcurrent protection alerting the crew in case of current
unbalance.

Consideration is to be given to additional protection for the individual capacitor element as (e.g.,
relief valve or overpressure disconnector) in order to protect against damage from rupturing. This
consideration is to take into account the type of capacitors used.

9.19 Protection of Harmonic Filter Circuits

Notwithstanding the requirements of 4-3-2/9.18 above, harmonic filters circuits are to be protected against
overload and short-circuit. An alarm is to be initiated in a continuously manned location in the event of an
activation of overload or short-circuit protection.

In cases where multiple harmonic filter circuits are used in series or in parallel, current imbalance between
the different filter circuits is to be continuously monitored. The total rms current into each phase of a
passive harmonic filter circuit is also to be monitored. Detection of a current imbalance is to be alarmed in
a continuously manned location. If the current imbalance exceeds the ratings of the individual filter circuit
components, the appropriate circuits shall automatically trip and be prevented from interacting with other
parts of the electrical network.

Harmonic filters that contain capacitors are to have means of monitoring and of providing advance
warning of capacitor(s) deterioration. Harmonic filters containing oil filled capacitors are to be provided
with suitable means of monitoring oil temperature or capacitor internal pressure. Refer to 5-2-3/13 for
additional requirements. Detection of capacitor(s) deterioration is to be alarmed locally at the equipment
and in a continuously manned location. Power to the harmonic filter circuit containing the deteriorated
capacitor(s) is to be automatically disconnected and the capacitor discharged safely upon detection of
deterioration.

In cases where provisions for automatic/manual switching and/or disconnection of harmonic filter circuits
are provided, there are to be provisions to prevent transient voltages in the system and to automatically
discharge the capacitors in the harmonic filter circuits before they can be put back on-line.

Capacitors used in harmonic filters/capacitor banks are to be prevented from producing a leading system
power factor which could potentially lead to generator(s) becoming self-excited. In cases where a leading
power factor condition approaches the point of the generator(s) becoming self-excited, the appropriate
capacitive circuits are to be automatically disconnected and prevented from interacting with the rest of the
electrical network.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 164
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

11 Systems for Steering Gear Installed in Self-propelled Units

11.1 Power Supply Feeder

Each electric or electro-hydraulic steering gear is to be served by at least two exclusive circuits fed directly
from the main switchboard. However, one of the circuits may be supplied through the emergency
switchboard.

For self-propelled units fitted with alternative propulsion and steering arrangements, such as azimuthing
propulsors, where the propulsion power exceeds 2,500 kW per thruster unit, see 4-3-4/1.10 of the Marine
Vessels Rules.

An auxiliary electric or electro-hydraulic steering gear associated with a main electric or electro-hydraulic
steering gear may be connected to one of the circuits supplying this main steering gear. The circuits
supplying an electric or electro-hydraulic steering gear are to have adequate rating for supplying all
motors, control systems and instrumentation which are normally connected to them and operated
simultaneously. The circuits are to be separated throughout their length as widely as is practicable.

11.3 Protection for Steering Gear Motor Circuit

11.3.1 Short Circuit Protection
Each steering gear feeder is to be provided with short-circuit protection which is to be located at
the main or emergency switchboard. Long-term overcurrent protection is not to be provided for
steering gear motors.

11.3.1(a) Direct Current (DC) Motors.

For DC motors, the feeder circuit breaker is to be set to trip instantaneously at not less than 300%
and not more than 375% of the rated full-load current of the steering-gear motor, except that the
feeder circuit breaker on the emergency switchboard may be set to trip at not less than 200%.

11.3.1(b) Alternating Current (AC) Motors.

For AC motors, the protection against excess current, including starting current, if provided, is to
be for not less than twice the full load current of the motor or circuit so protected, and is to be
arranged to permit the passage of the appropriate starting currents.

11.3.1(c) Fuses as Motor-feeder Protection.

The use of fuses instead of circuit breakers for steering gear motor feeder short circuit protection
is not permitted.

Commentary:

The following is from IACS Unified Interpretation SC187:

Steering gear motor circuits obtaining their power supply via an electronic converter, e.g. for speed control, and
which are limited to full load current are exempt from the requirement to provide protection against excess current,
including starting current, of not less than twice the full load current of the motor. The required overload alarm is
to be set to a value not greater than the normal load of the electronic converter. Normal load is the load in normal
mode of operation that approximates as close as possible to the most severe conditions of normal use in
accordance with the manufacturer's operating instructions.

End of Commentary

11.3.2 Undervoltage Release

Power unit motor controllers and other automatic motor controllers are to be fitted with
undervoltage release.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 165
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

11.5 Emergency Power Supply

Where the rudder stock is required by 3-2-14/7.1 of the Marine Vessel Rules to be over 230 mm (9 in.)
diameter using Ks = 1 . 0 in way of the tiller, excluding strengthening for navigation in ice, an alternative
power supply, sufficient at least to supply the steering gear power unit and also its associated control
system and rudder angle indicator, is to be provided automatically within 45 seconds either from the
emergency source of electrical power or from an independent source of power located in the steering gear
compartment. The steering gear power unit under alternative power supply is to be capable of moving the
rudder from 15 degrees on one side to 15 degrees on the other side in not more than 60 seconds with the
unit at the line draft while running at one half the maximum speed ahead or 7 knots, whichever is the
greater. This independent source of power is to be used only for this purpose. The capacity is to be
sufficient for at least 10 minutes of continuous operation.

11.7 Controls, Instrumentation, and Alarms

See 4-3-4/5.7, 4-3-4/13, 4-3-4/15 and 4-3-4/17 of the Marine Vessel Rules.

13 Lighting and Navigation Light Systems

13.1 Lighting System

13.1.1 Main Lighting System
A main electric lighting system is to provide illumination throughout those parts of the unit
normally accessible to and used by crew. It is to be supplied from the main source of electrical
power.

13.1.2 System Arrangement

13.1.2(a) Main Lighting System.
The arrangement of the main electric lighting system is to be such that a fire or other casualty in
spaces containing the main source of electrical power, associated transforming equipment, if any,
the main switchboard and the main lighting switchboard will not render the emergency electric
lighting system required by 4-3-2/5.3.1 and 4-3-2/5.3.11(a) inoperative.

13.1.2(b) Emergency Lighting System.

The arrangement of the emergency electric lighting system is to be such that a fire or other
casualty in spaces containing the emergency source of electrical power, associated transforming
equipment, if any, the emergency switchboard and the emergency lighting switchboard will not
render the main electric lighting system required by 4-3-2/13.1.1 inoperative.

13.1.3 Lighting Circuits

13.1.3(a) Machinery Space and Accommodation Space.
In spaces such as:

● Public spaces
● Category A machinery spaces
● Galleys
● Corridors
● Stairways leading to boat-decks, including stair towers and escape trunks

there is to be more than one final subcircuit for lighting, one of which may be supplied from the
emergency switchboard, in such a way that failure of any one circuit does not leave these spaces in
darkness.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 166
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

13.1.4 Protection for Lighting Circuits

Lighting circuits are to be protected against overload and short circuit. Overload protective
devices are to be rated or set at not more than 30 amperes. The connected load is not to exceed the
lesser of the rated current carrying capacity of the conductor or 80% of the overload protective
device rating or setting. The control switches are to be rated for the load controlled.

13.1.5 Lighting Distribution Boards

i) To prevent the simultaneous loss of main and emergency lighting distribution boards due
to localized fire or other casualty, these distribution boards are to be installed as widely
apart as practicable in the machinery spaces.
ii) For spaces other than the machinery space (e.g., accommodation space, cargo spaces,
etc.), these lighting distribution boards are to be installed at locations which are separated
by a boundary wall. The boundary wall separation is to be a non-combustible partition
complying with as a minimum a C-class panel division.
iii) For the central control room, the main and emergency lighting distribution boards are not
to be installed in the same compartment of the navigation console or panel.
iv) Cables emanating from the main or emergency lighting switchboard to the main or
emergency lighting distribution board, respectively, are also to be installed as widely
apart as practicable.
v) The emergency lights in the engine room enclosed escape route are not to be fed from the
engine room lighting distribution boards, if located in the engine room. This requirement
may not be waived based on the use of fire resistant cables. Where battery backup fixtures
are used, the location of exit path illumination power source panel in engine room may be
considered on a case by case basis.

13.3 Navigation Light System

13.3.1 Feeder
Navigation lights (mast head, side and stern lights) are to be fed by their own exclusive
distribution board located on the bridge. The distribution board is to be supplied from the main as
well as from the emergency source of power (see 4-3-2/5.3.2). A means to transfer the power
source is to be fitted on the bridge. Automatic switch over to alternative source of power is
permitted.

13.3.2 Branch Circuit

Each navigation light is to have its own branch circuit, and each branch circuit is to be fitted with
a protective device.

13.3.3 Duplicate Lamp

Each navigation light is to be fitted with duplicate lamps.

13.3.4 Control and Indication Panel

A control and indication panel for the navigation lights is to be provided on the navigation bridge.
The panel is to be fitted with the following functions:
i) A means to disconnect each navigation light.
ii) An indicator for each navigation light.
iii) Automatic visual and audible warning in the event of failure of a navigation light. If a
visual signal device is connected in series with the navigation light, the failure of this
device is not to cause the extinction of the navigation light. The audible device is to be
connected to a separate power supply so that the audible alarm may still be activated in
the event of power or circuit failure to the navigation lights.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 167
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

Commentary:

A separate source of power supply to the audible device required by 4-3-2/13.3.4 is not necessary where the
audible device is integral with the indicator panel which also contains a visual alarm.

End of Commentary

15 Interior Communication Systems

15.1 Navigation Bridge

15.1.1 General
At least two independent means are to be provided for communicating orders from the navigation
bridge to the position in the machinery space or in the control room from which the speed and
direction of thrust of the propellers are normally controlled. Appropriate means of communication
are to be provided to any other positions from which the main propulsion machinery may be
controlled. See 4-3-2/5.3.4 for power supply.

15.1.2 Engine Order Telegraph

One of the communicating means between navigation bridge and the main propulsion control
position is to be an engine room telegraph which provides visual indication of the orders and
responses both in the machinery space and on the navigation bridge. Final subcircuit for power
supply to this system is to be independent of other electrical systems and control, monitoring and
alarm systems. See 4-3-2/5.3.4 for power supply. Communication network and power supply
circuit for this may be combined with the engine order telegraph system specified in 4-3-2/15.3.

15.3 Main Propulsion Control Stations

A common talking means of voice communication and calling or engine order telegraph repeater is to be
provided between the main propulsion control station and local control positions for main propulsion
engines and controllable pitch propellers. Voice communication systems are to provide the capability of
carrying on a conversation while the unit is being navigated. Final subcircuit for power supply to these are
to be independent of the other electrical system and the control, monitoring and alarm systems.
Communication network and power supply circuit for the voice communication system may be combined
with the system required in 4-3-2/15.5.

15.5 Voice Communications

15.5.1 Propulsion and Steering Control Stations
A common talking means of voice communication and calling is to be provided between the
navigation bridge, main propulsion control station and the steering gear compartment so that the
simultaneous talking among these spaces is possible at all times and the calling to these spaces is
always possible even if the line is busy.

15.5.2 Communication in Case of an Emergency

Means of voice communication is to be available for transfer of information between all locations
where action may be necessary in case of an emergency. Such locations include the emergency
control stations required by 8-2-1/17.5, machinery spaces, SCR rooms and all locations vital to the
safety of the unit. Simultaneous talking among these locations is to be possible at all times and the
calling to these locations is always to be possible even if the line is busy.

15.5.3 Elevator
Where an elevator is installed, a telephone is to be permanently installed in all cars and connected
to a continuously manned area. The telephone may be sound powered, battery operated or
electrically powered from the emergency source of power.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 168
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

15.5.4 Jacking System

A voice communication system is to be provided between the central jacking control station and a
location at each leg in self-elevating units.

15.5.5 Independence of Power Supply Circuit

Final subcircuit for power supply to these voice communication systems is to be independent of
other electrical systems and control, monitoring and alarm systems. See 4-3-2/5.3.4 for power
supply.

15.7 Emergency and Interior-communication Switchboard

Emergency and interior-communication switchboards, when fitted, are to comply with the applicable parts
of 6-1-7/9, and attention is directed to the requirements of the governmental authority whose flag the unit
flies.

15.9 Public Address System

The public address system is to comply with subparagraphs 4-3-2/15.9.1 through 4-3-2/15.9.4 as follows:

15.9.1 System Requirements

The system is to be a loud speaker installation enabling the broadcast of messages which are
clearly audible in all parts of the unit. The system is to provide for the broadcast of messages from
the navigation bridge, emergency control stations (see 8-2-1/17.5) and other strategic points with
an override function so that all emergency messages may be broadcast if any loudspeaker in the
locations concerned has been turned off, its volume has been turned down or the public address
system is in use for other purposes.

15.9.2 Minimum Sound Levels

With the unit underway or in normal operating conditions, the minimum sound levels for
broadcasting emergency announcements are to be:

i) In interior locations, 75 dB (A) and at least 20 dB (A) above the speech interference level.
ii) In exterior locations, 80 dB (A) and at least 15 dB (A) above the speech interference
level.
15.9.3 Emergency Source of Power
The system is to be connected to the emergency source of power.

15.9.4 Public Address System Combined with General Alarm System

Where a single system serves for both public address and general emergency alarm functions, the
system is to be arranged so that a single failure is not to cause the loss of both systems and is to
minimize the effect of a single failure. The major system components, such as power supply unit,
amplifier, alarm tone generator, etc., are to be duplicated. Power supply is to comply with
4-3-2/17.1.2(b) and 4-3-2/17.1.2(c). The coverage provided by the arrangement of the system
loops and speakers is to be such that after a single failure, the announcements and alarms are still
audible in all spaces. Duplication of system loops and speakers in each room or space is not
required provided the announcements and alarms are still audible in all spaces.

17 Manually Operated Alarms

17.1 General Emergency Alarm Systems

17.1.1 General
A general alarm system complying with requirements of 4-3-2/17.1.2 is to be provided to summon
crew to muster stations and initiate actions included in the muster list. The system is to be
supplemented by instructions over a public address system meeting the requirements of

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 169
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

4-3-2/15.9. Any entertainment sound system is to be automatically turned off when the general
emergency alarm is activated.

17.1.2 System Requirements

17.1.2(a) The general emergency alarm system is to be capable of sounding the general
emergency alarm signal, fire alarm signal and abandon unit signal on an electrically operated bell
or klaxon or other equivalent warning system, which is to be powered from the unit’s main supply
and the emergency source of electrical power required by 4-3-2/5.

17.1.2(b) There are to be not less than two sources of power supply for the electrical equipment
used in the operation of the General Emergency Alarm System, one of which is to be from the
emergency switchboard and the other from the main switchboard. The supply is to be provided by
separate feeders reserved solely for that purpose. Such feeders are to run to an automatic change-
over switch situated in, without passing through any other distributing switchboard, or adjacent to,
the main general emergency alarm control panel.

17.1.2(c) An alarm is to be provided in a normally manned control station to indicate when there
is a loss of power in any one of the feeders required by 4-3-2/17.1.2(b).

17.1.2(d) As an alternative to two feeders as described in 4-3-2/17.1.2(b), a battery may be

considered as one of the required sources, provided the battery has the capacity of at least 30
minutes of continuous operation for alarming and 18 hours in standby. A low voltage alarm for the
battery and the battery charger output is to be provided. The battery charger is to be supplied from
the emergency switchboard.

17.1.2(e) The system is to be capable of operation from the navigation bridge, emergency control
stations (see 8-2-1/17.5) and from other strategic points. The system is to be clearly audible in all
parts of the unit. The alarm is to continue to function after it has been triggered until it is manually
turned off or is temporarily interrupted by a message on the public address system. Self-propelled
units are to be capable of sounding the general emergency alarm on the unit’s whistle, but which
need only be capable of operation from the navigation bridge.

17.1.2(f) For minimum sound levels for the emergency alarm tone required to be verified onboard,
see 7A-1-6/17.1.

17.3 Engineers’ Alarm

An engineers’alarm operable from the main propulsion control station or at the maneuvering platform, as
appropriate, is to be provided. See 7A-1-6/17.3 for minimum sound level and 4-3-2/5.3.12(c) for power
supply.

17.5 Refrigerated Space Alarm

Fan and diffuser rooms serving subfreezing compartments are to be provided with a device capable of
activating an audible and visual alarm in a manned control center and operable from within the latter space
for the protection of personnel. See 4-3-2/5.3.12(c) for power supply.

17.7 Elevator
A device which will activate an audible and visual alarm in a manned control center is to be provided in all
cars. Such alarm system is to be independent of power and control systems of the elevator. See
4-3-2/5.3.12(c) for power supply.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 170
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 2 Electrical Systems 4-3-2

19 Fire Protection and Fire Detection Systems

19.1 Emergency Stop

Wiring break monitoring device is to be provided for normally de-energized (i.e., normally open circuits)
emergency shutdown systems. The arrangement of the emergency shutdown system is to be such that no
single failure will cause loss of duplicated essential equipment such as fuel and lubricating oil pumps
which may cause loss of main power generation or main propulsion.

19.1.1 Ventilation System

19.1.1(a) General.
All electrical ventilation systems are to be provided with means for stopping the motors in case of
fire or other emergency. These requirements do not apply to closed recirculating systems within a
single space. See also 5-3-1/9.1.

19.1.1(b) Propulsion Machinery Space Ventilation.

The main machinery-space ventilation is to be provided with means for stopping the ventilation
fans. The means for stopping the power ventilation serving machinery spaces is to be entirely
separate from the means for stopping the ventilation of spaces in 4-3-2/19.1.1(c) and
4-3-2/19.1.1(d).

19.1.1(c) Machinery Spaces other than Propulsion Machinery Spaces.

Power ventilation systems serving these spaces are to be fitted with means for stopping the
ventilation fan motors in the event of fire. The means for stopping the power ventilation serving
these spaces is to be entirely separate from the means for stopping the ventilation of spaces in
4-3-2/19.1.1(b) and 4-3-2/11.9.1(d). See 5-3-1/9.1.1.

19.1.1(d) Accommodation Spaces, Service Spaces, Control Stations and Other Spaces.
The means for stopping all other power ventilation systems including the small/independent
ventilation fans in accommodation spaces is to be located in the fire-control room or navigation
bridge, or in an accessible position leading to, but outside of the space ventilated.

19.1.2 Other Auxiliaries

See 5-3-1/9.3 for emergency tripping and emergency stop for other auxiliaries, such as forced and
induced draft fans, electric motor pressurization fans, oil fuel transfer pumps, oil fuel unit pumps.

19.3 Fire Detection and Alarm System

See 5-2-5/1.1.

21 Remote Camera System

When permitted by the flag Administration, a remote camera system may be accepted as means for
achieving the view of the self-propelled unit's side from the bridge wing or suitable location with specific
requirements as prescribed in the IACS UI SC235.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 171
 PART 4
CHAPTER 3
Electrical Installations

SECTION 3
Onboard Installation

1 Objective

1.1 Goals
The electrical installations covered in this section is to be designed, constructed, operated and maintained
to:

Goal No. Goal

POW 1 provide safe and reliable storage and supply of fuel/energy/power.

STAB 2 have adequate subdivision and stability to provide survivability to damage or accidental
conditions.

POW 2 provide power to enable the machinery/equipment/electrical installation to perform its required
functions necessary for the safe operation of the unit

POW 4 enable all electrical services required for safety to be available during emergency conditions.

SAFE 1.1 minimize danger to persons on board, the unit, and surrounding equipment/installations from
hazards associated with machinery and systems.

SAFE 2 provide suitable and readily available illumination.

FIR 1 prevent the occurrence of fire and explosion.

FIR 2 reduce the risk to life caused by fire.

FIR 3 reduce the risk of damage caused by fire to the unit, its cargo and the environment.

MGMT 1 provide for safe practices in unit operation and a safe working environment.

MGMT 5 design and construct unit, machinery, and electrical systems to facilitate safe access, ease of
inspection, survey, and maintenance.

AUTO 1 perform its functions as intended and in a safe manner.

AUTO 7 enable rational human machine interface without unintended errors due to the layout or
arrangement of machinery/equipment

Materials are to be suitable for the intended application in accordance with the following goals and support
the Tier 1 goals as listed above.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 172
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

Goal No. Goal

MAT 1 The selected materials’ physical, mechanical and chemical properties are to meet the design
requirements appropriate for the application, operating conditions and environment.

1.2 Functional Requirements

In order to achieve the above stated goals, the design, construction, installation and maintenance of the
electrical installations are to be in accordance with the following functional requirements:

Functional Functional Requirements

Requirement No.

Power Generation & Distribution (POW)

POW-FR1 Enable machinery recovery from the dead ship condition without external aid.

POW-FR2 (SAFE) Provide proper storage locations for lead-acid or alkaline batteries as well as low-hydrogen-emission
batteries according to the total output of battery chargers.

POW-FR3 Batteries are to be segregated and identified by the battery types and maintained regularly to supply
essential and emergency services when required.

POW-FR4 Provide cables with sufficient current carrying capacity to support connected loads and within the
ratings of overload protection.

Fire Safety (FIR)

FIR-FR1 Electrical equipment and cables installed in hazardous areas are to be suitable for the environment
(gas group and temperature classification) in which they operate

FIR-FR2 Provide cable design and routing such that emergency and essential services are operable under a
fire condition.

FIR-FR3 Provide adequate ventilation to maintain the flammable gases within the battery room to a level with
acceptable margin below the lower explosive limit.

FIR-FR4 (SAFE) Prevent electric shock, fire and other hazards of electrical origin where operations or maintenance
are expected.

FIR-FR5 Cables are to be protected from damage due to hot surfaces, fire or explosion hazards and
mechanical damage.

FIR-FR6 (MGMT/ Where cables penetrate watertight or fire-rated boundaries, means are to be provided to maintain the
STAB) watertight integrity or fire-rating.

FIR-FR7 (MGMT) Cable support systems constructed of materials readily rendered ineffective by heat are to be
designed to support safe working load and to be prevented from falling in a fire and causing injuries
or obstruction.

FIR-FR8 Design and arrange components and their materials to prevent the risk of electrostatic discharge and
ignition.

FIR-FR9 Electrical and electronic equipment within areas affected by fire extinguishing media are to be
suitable for use in the affected area.

FIR-FR10 Arrange flammable gases away from sources of ignition.

Safety of Personnel (SAFE)

SAFE-FR1 (POW) Provide enclosures with suitable degree of protection against ingress of foreign objects and liquids
based on location of installation.

SAFE-FR2 Protect against accidental contact and unauthorized operation of essential and emergency equipment
boards.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 173
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

Functional Functional Requirements

Requirement No.

SAFE-FR3 (FIR) Electrical installations in hazardous areas are to be restricted to minimize the potential risks that
might affect the safety of the unit, persons on board and equipment.

Safety Management (MGMT)

MGMT-FR1 Prevent unwanted electromagnetic interference from electrical equipment affecting operations of
(SAFE) other machinery or essential equipment.

MGMT-FR2 Design and arrange signal, single conductor or multiple conductor cables to avoid the harmful
effects of electromagnetic induction or interference.

MGMT-FR3 (POW/ Provide support for cable installation to avoid chafing and undue stress in the cable.
SAFE)

MGMT-FR4 (POW/ Means used to connect lengths of cables are to be suitable for the intended purposes, maintain the
SAFE) watertightness, firetightness and integrity of the cables.

Materials (MAT)

MAT-FR1 (POW) Be constructed of materials that are able to withstand the marine and operating environment,
maximum design ambient temperature and stresses without deterioration.

MAT-FR2 (POW/ Cables and electrical conductors are to be constructed of high conductivity and flame-retardant
FIR) material and sized to prevent any damage due to temperature rise during normal operation.

Automation (Control, monitoring and safety systems) (AUTO)

AUTO-FR1 (SAFE/ Provide protection against overload, undervoltage and short circuit conditions to prevent damage to
POW) equipment and maintain continuity of power to remaining circuits.

AUTO-FR2 Electrical equipment is to be in well supported location with adequate clearance for ease of
(MGMT/POW) operation and maintenance.

AUTO-FR3 Provide properly located and reliable means of disconnecting the electrical power circuits from
(MGMT/POW) power source for maintenance, or to isolate faults in electrical circuits.

The functional requirements covered in the cross-referenced Rules/Standards are also to be met.

1.3 Compliance
A unit is considered to comply with the goals and functional requirements when the prescriptive
requirements are complied with or when an alternative arrangement has been approved. Refer to Part 1D,
Chapter 2.

2 Plans and Data to be Submitted

2.1 Booklet of Standard Details

A booklet of the standard wiring practices and details, including such items as cable supports, earthing
details, bulkhead and deck penetrations, cable joints and sealing, cable splicing, watertight and explosion-
proof connections to equipment, earthing and bonding connections, etc., is to be submitted. Where cable
penetration methods for A- or B-class decks or bulkheads are shown, an evidence of approval by an
Administration signatory to 1974 SOLAS as amended is also to be submitted.

For high voltage systems, see installation requirements given in 4-3-5/2.9.3.

For high voltage cables, the minimum cable bending radii and securing arrangements, taking the relevant
recommendations of the cable manufacturer into consideration, are to be included. Cable tray segregation
(HV to HV and HV to LV arrangements) are also to be included.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 174
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

2.3 Arrangement of Electrical Equipment

A general arrangement plan showing the location of at least the following electrical equipment is to be
submitted for review.

● Generator, Essential Motor, and Transformer

● Battery
● Switchboard, Battery Charger, and Motor Controller
● Emergency Lighting Fixture
● General Emergency Alarm Device and Alarm Actuator
● Detector, Manual Call Point and Alarm Panel for Fire
● Detection and Alarm System
● Certified-safe Type Equipment

Where cable splices or cable junction boxes are provided, locations of the splices and cable junction boxes
together with the information of their services are also to be submitted for review.

2.5 Electrical Equipment in Hazardous Areas

A plan showing hazardous areas, as defined in Section 4-3-6, is to be submitted for review together with
the following:

● A list/booklet of intended electrical equipment in the indicated hazardous areas, including a

description of the equipment, applicable degree of protection and ratings. See 4-3-3/9.3.
● The list/booklet indicated above is to include any equipment listed in 4-3-5/7.1.4 in exterior locations
(in non-hazardous area) operable after emergency shutdown.
● For intrinsically-safe systems, also wiring plans, installation instructions with any restrictions imposed
by the certification agency.
● Detail of installation for echo sounder, speed log and impressed current cathodic protection system
where located in these areas.

When the selection of the equipment has been finalized, a list/booklet identifying all equipment in the
hazardous areas, their method of protection (flameproof, intrinsically safe, etc.), rating (flammable gas
group and temperature class), manufacturer’s name, model number and evidence of certification is to be
submitted for review. See 7A-1-6/9, 7A-2-5/7.1, and 4-3-3/9.1.

2.7 Emergency Shutdown Procedures

Details of the emergency shutdown procedures for electrical equipment as referred to in 8-2-1/17.5. See
also 4-3-5/7.1.

In addition, the following documents are to be submitted for review:

i) The ESD Functional Design Basis Document (FDS) Operation Manual (see 4-3-5/7.1.1)
ii) Gas Detection / ESD System Cause and Effect Chart (see 4-3-5/7.1.2)

2.9 Maintenance Schedule of Batteries

Maintenance schedule of batteries for essential and emergency services. See 4-3-3/3.7.5.

2.11 Cable Transit Seal System Register

A Cable Transit Seal Systems Register (Register) is to be provided by the shipbuilder for all watertight
cable transits fitted to the MOU. See 4-3-3/5.13.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 175
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

Note: Refer to IACS UR Z28.

3 Equipment Installation and Arrangement

3.1 General Consideration

3.1.1 Equipment Location
3.1.1(a) General.
Electrical equipment is to be so placed or protected as to minimize the probability of mechanical
injury or damage from the accumulation of dust, oil vapors, steam or dripping liquids. Equipment
liable to generate arc is to be ventilated or placed in a compartment ventilated to avoid
accumulation of flammable gases, acid fumes and oil vapors. See 4-3-3/3 TABLE 1 for required
degree of protection for various locations.

3.1.1(b) Equipment in Areas Affected by Local Fixed Pressure Water-spraying or Local Water-mist Fire
Extinguishing System in Machinery Spaces.
Electrical and electronic equipment within areas affected by Local Fixed Pressure Water-spraying
or Local Water-mist Fire Extinguishing Systems are to be suitable for use in the affected area. See
4-3-3/3.1 FIGURE 1. Where enclosures have a degree of protection lower than IP44, evidence of
suitability for use in these areas is to be submitted to ABS taking into account:

i) The actual Local Fixed Pressure Water-spraying or Local Water-mist Fire Extinguishing
system being used and its installation arrangements, and
ii) The equipment design and layout (e.g., position of inlet ventilation openings, filters,
baffles, etc.) to prevent or restrict the ingress of water mist/spray into the equipment. The
cooling airflow for the equipment is to be assured.
Notes:

Additional precautions may be required to be taken with respect to:

a) Tracking as the result of water entering the equipment

b) Potential damage as the result of residual salts from sea water systems

c) High voltage installations

d) Personnel protection against electric shock

Equipment may require maintenance after being subjected to water mist/spray.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 176
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

FIGURE 1
Example of Area Affected by Local Fixed Pressure Water-spraying orWater
mist Fire Extinguishing System in Machinery Spaces

3.1.2 Installations subject to Surveyor Satisfaction

Equipment is to be installed in accordance with the manufacturer's installation instructions, as
applicable.

Location of electrical equipment is to account for access for operation, maintenance, repair,
inspection and proper ergonomics of the equipment for operation and maintenance. (Guidance
notes of the Application of Ergonomics to Marine Systems, Publication no. 86, provides guidance
for proper installations).

In general, bulkhead mounted equipment are not to be installed in passageways and stairwells. If
installed, the equipment are not to impede the egress for personnel or danger to personnel
transiting the area subject to motions of the unit.

Bulkhead mounted equipment in passageways are not to reduce the required passageway width as
required by SOLAS, as applicable.

Splices or junction boxes located behind joiner bulkheads are to be provided with hinged or
removable access covers for accessibility and inspection.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 177
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

Location of splices or junction boxes located above drop down ceiling panels are to have
nameplates by the closest removable panels indicating the location of equipment.

Where cable entrance to equipment needs to be from the top or side, the enclosure cable
penetrations are not to reduce the required degree of protection of the enclosure.

Location requirements for optional Class notations, as applicable.

Located as not to interfere or require removal within structural WERP (Welded Equipment
Removal Plate) and BERP (Bolted Equipment Removal Plate) areas.

Electrical receptacles and switches in dry accommodation areas are not to be located immediately
adjacent to routinely used exterior doors allowing rain, sleet, snow or splashing sea water entering
the space and damage to equipment, or be provided with a higher degree of protection.

TABLE 1
Minimum Degree of Protection [See 4-3-3/3.1.1]

(For high voltage equipment see 4-3-5/7.1 TABLE 1)

Switchboards, Distribution Boards, Motor Control Centers &

Controllers (See 4-3-3/3.9 to 4-3-3/3.13)

Generators (See 4-3-3/3.3)

Motors (See 4-3-3/3.5)

Example Condition
Transformers, Converters
of of
Location Location Lighting Fixtures (See
4-3-3/3.17)

Heating Appliances
(See 4-3-3/3.19)

Accessories (2)

Dry accommodation space Danger of touching live parts IP20 - IP20 IP20 IP20 IP20 IP20
only
Dry control rooms (4) IP20 - IP20 IP20 IP20 IP20 IP20

Control rooms Danger of dripping liquid and/or IP22 - IP22 IP22 IP22 IP22 IP22
moderate mechanical damage
Machinery spaces above floor IP22 IP22 IP22 IP22 IP22 IP22 IP44
plates (5)

Steering gear rooms IP22 IP22 IP22 IP22 IP22 IP22 IP44

Refrigerating machinery rooms IP22 - IP22 IP22 IP22 IP22 IP44

Emergency machinery rooms IP22 IP22 IP22 IP22 IP22 IP22 IP44

General store rooms IP22 IP22 IP22 IP22 IP22 IP22 IP22

Pantries IP22 - IP22 IP22 IP22 IP22 IP44

Provision rooms IP22 - IP22 IP22 IP22 IP22 IP22

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 178
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

Bathrooms & Showers Increased danger of liquid and/or - - - - IP34 IP44 IP55(8)
mechanical damage
Machinery spaces below floor - - IP44 - IP34 IP44 IP55 (3)
plates

Closed fuel oil or lubricating IP44 - IP44 - IP34 IP44 IP55 (3)
oil separator rooms

Ballast pump rooms Increased danger of liquid and/or IP44 - IP44 IP44 IP34 IP44 IP55
mechanical damage
Refrigerated rooms - - IP44 - IP34 IP44 IP55

Galleys and Laundries IP44 - IP44 IP44 IP34 IP44 IP44 (7)

Open decks Exposure to heavy seas IP56 - IP56 - IP55 IP56 IP56

Bilge wells Exposure to submersion - - - - IPX8 - IPX8

Notes:

1 Empty spaces shown with “–” indicate installation of electrical equipment is not recommended.

2 "Accessory" includes switches, detectors, junction boxes, etc. Accessories which are acceptable for use in hazardous
areas are limited by the condition of the areas. Specific requirements are given in the Rules. See 4-3-3/3.23.

3 Socket outlets are not to be installed in machinery spaces below the floor plates, enclosed fuel and lubricating oil
separator rooms. Plugs and sockets that are present in a hazardous area are to be certified for use in the particular zone.

4 For the purpose of this Table, the wheelhouse may be categorized as a “dry control room”, and consequently, the
installation of IP20 equipment would suffice therein, provided that: (a) the equipment is located as to preclude being
exposed to steam, or dripping/spraying liquids emanating from pipe flanges, valves, ventilation ducts and outlets, etc.,
installed in its vicinity, and (b) the equipment is placed to preclude the possibility of being exposed to sea or rain.

5 See 4-3-3/3.1.1(b) where the equipment is located within areas protected by local fixed pressure water-spraying or
water-mist fire extinguishing system and its adjacent areas.

6 Electrical equipment used for the power operation, remote control and status indication of watertight doors and located
below the worst damage waterline is to provide suitable protection against the ingress of water, as follows:
i) Electrical motors, associated circuits and control components: protected to IPX7 standard
ii) Door position indicators and associated circuit components: protected to IPX8 standard (The water pressure
testing of the enclosure is to be based on the pressure that may occur at the location of the component during
flooding for a period of 36 hours)
iii) Door movement warning signals: protected to IPX6 standard.
7 Socket outlets in galleys and laundries are to maintain their protection against splashed water when not in use.

8 lower degree of protection may be accepted provided the equipment is not directly exposed to water splash.

3.3 Generators
All generators on ship-type units are to be located with their shafts in a fore-and-aft direction on the unit
and are to operate satisfactorily in accordance with the inclination requirements of 4-1-1/7.1. Where it is
not practicable to mount the generators with the armature shafts in the fore-and-aft direction, their
lubrication requires special consideration. Provision is to be made to prevent oil or oil vapor from passing
into the machine windings.

3.5 Motors for Essential Services

3.5.1 General
Motors for use in the machinery space above the floor plate or spaces where subject to mechanical
injury, or dripping of oil or water are to have an enclosure of at least IP22 protection in accordance
with 4-3-3/3 TABLE 1. However, where they are protected by drip covers, they can have an

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 179
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

enclosure of a lower protection grade than IP22. The motors having a protection enclosure of IP22
or lower are to be installed at a location high enough to avoid bilge water. Motors below the level
of the floor plates are to have an enclosure of at least IP44 protection. Where motors intended for
service at sea are not mounted with the rotor shafts in the fore-and-aft direction, the type of
bearing and lubrication require special consideration.

3.5.2 Pump Motors

Motors for operating plunger and close-coupled pumps are to have the driving end entirely
enclosed or designed to prevent leakage from entering the motor.

3.5.3 Motors on Weather Decks

Motors for use on weather decks are to have an enclosure of at least IP56 protection or are to be
enclosed in watertight housings.

3.5.4 Motors Below Decks

Motors below decks are to be installed at a location as dry as practicable and away from steam,
water, and oil piping. The suitability of the location is to be verified onboard to the satisfaction of
the attending Surveyor.

3.7 Accumulator Batteries

3.7.1 General
The following requirements are applicable to permanently installed power, control and monitoring
storage batteries of acid or alkaline types. Batteries are to be so arranged that the trays are
accessible and provided with not less than 254 mm (10 in.) headroom. Where a relief valve is
provided for discharging excessive gas due to overcharge, arrangements are to be made for
releasing the gas to the weather deck away from any source of ignition.

3.7.2 Battery Installation and Arrangements

3.7.2(a) Large Batteries.
Large storage batteries, those connected to a charging device with an output of more than 2 kW,
are to be installed in a room assigned to the battery only, but can be installed in a deck locker if
such a room is not available. No electrical equipment is to be installed in the battery rooms unless
essential for the operational purposes and certified safe for battery room atmosphere. Electrical
equipment installed in battery rooms can be any of the types indicated in 4-3-3/9.1.2(b) and is to
be ISO/IEC 80079-20-1 Group IIC Class T1.

3.7.2(b) Moderate-size Batteries.

Batteries of moderate size, those connected to a charging device with a power output of 0.2 kW up
to and including 2 kW, can be installed in the battery room or can be installed in battery lockers or
deck boxes in the emergency generator room, machinery space or other suitable location.
Cranking batteries are to be located as closely as possible to the engine or engines served.
Batteries are to be protected from mechanical damage, dripping water and condensation where
necessary. In general, batteries are to be installed away from sources of ignition.

Notes:
In order for the space considered "well ventilated" in the context of battery installation, the following requirements
are to be met:
i A detailed calculation showing adequate ventilation for the space is to be submitted to the ABS technical
office for review and approval.
ii The ventilation system would be considered adequate if the calculation indicates a liberated hydrogen
gas concentration not exceeding 1 percent by volume of the proposed space. Please refer to IEC
standards 62485-2 or 60079-10.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 180
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

iii The calculation is to represent worst case scenario assuming all batteries are releasing gases at the same
time.
iv The ventilation system is to be arranged to provide adequate air movement in the general battery areas to
diffuse generation of hydrogen gas and to maintain that pockets of trapped hydrogen gas do not occur
particularly at the top of the space (or ceiling).

3.7.2(c) Small Batteries.

Small batteries are to be installed in a battery box and can be located as desired, except they are
not to be located in sleeping quarters unless hermetically sealed.

3.7.2(d) Low-hydrogen-emission Battery Installations.

A low-hydrogen-emission battery installation with a battery charger having a charging rate of a
large or moderate battery size installation can be treated as a moderate or small battery
installation, respectively, if the following are met:

i) Calculations under the worst case charging conditions are submitted which demonstrate
that the low-hydrogen-emission battery installation does not emit more hydrogen under
similar charging conditions than a bank of standard lead acid batteries supplied by a 2 kW
charger for a moderate battery installation or 0.2 kW charger for a small battery
installation, and
ii) A warning notice is placed to notify maintenance personnel that additional batteries are
not to be installed, and batteries are only to be replaced by other batteries of the same or
lower hydrogen emission rate.
3.7.2(e) Battery trays and battery locker shelves.
Trays or shelves for batteries are to be chocked with wood strips or equivalent to prevent
movement and each tray is to be fitted with nonabsorbent insulating supports on the bottom and
with similar spacer blocks at the sides or with equivalent provision to secure air-circulation space
all around each tray.

3.7.2(f) Identification of Battery Types.

Lead-acid batteries and alkaline batteries, when placed in the same battery compartment, are to be
effectively identified as to type and segregated.

3.7.3 Ventilation
3.7.3(a) Battery Rooms.
Battery rooms are to be ventilated to avoid accumulation of flammable gas. Natural ventilation
can be employed for moderate and small battery installations if ducts are run directly from the top
of the battery room to the open air above.

If natural ventilation is impractical, mechanical exhaust ventilation is to be provided with fan

intake at the top of the room. Fans are to be of non-sparking construction in accordance with
4-3-3/9.7 and capable of completely changing the air in the battery room in not more than two
minutes. Alternatively, a lesser ventilation rate can be considered, provided that satisfactory
calculations are submitted substantiating that adequate ventilation is available to maintain the
flammable gases within the battery room to a level below the lower explosive limit (L.E.L.) at the
maximum battery charging current. Where the ventilation rate is based on low hydrogen emission
type batteries, a warning notice to this effect is to be provided in a visible place in the battery
room. Openings for air inlet are to be provided near the floor. The battery chargers are to be
interlocked with the power ventilation system to prevent charging and release of gas when the fan
is not running.

3.7.3(b) Battery Lockers.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 181
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

Battery lockers are to be ventilated, if practicable, similarly to battery rooms by a duct led from
the top of the locker to the open air or to an exhaust ventilation duct. Louvers or equivalent are to
be provided near the bottom for entrance of air.

3.7.3(c) Deck Boxes.

Deck boxes are to be provided with a duct from the top of the box, terminating in a goose neck,
mushroom head or equivalent to prevent entrance of water. Holes for air inlet are to be provided
on at least two opposite sides of the box. The entire deck box, including openings for ventilation,
is to be weathertight to prevent entrance of spray or rain.

3.7.3(d) Small Battery Boxes.

Boxes for small batteries require no ventilation other than openings near the top to permit escape
of gas.

3.7.4 Protection from Corrosion

The interiors of battery rooms, including the structural parts and shelves therein, as well as
ventilation inlets and outlets are to be painted with corrosion-resistant paint. Shelves in battery
rooms or lockers for acid batteries are to have a watertight lining of sheet lead not less than 1.6
mm (1/16 in.) on all sides. For alkaline batteries, the shelves are to be similarly lined with steel not
less than 0.8 mm (1/32 in.) thick. Alternatively, a battery room can be fitted with a watertight
corrosion resistant material or lead pan, steel for alkaline batteries, over the entire deck, carried up
not less than 152 mm (6 in.) on all sides. Details of manufactured corrosive resistant materials are
to be provided upon request. Deck boxes are to be lined in accordance with the above alternative
method. Boxes for small batteries are to be lined to a depth of 76 mm (3 in.) consistent with the
methods described above.

3.7.5 Maintenance of Batteries

3.7.5(a) Maintenance Schedule of Batteries.
Where batteries are fitted for use for essential and emergency services, a maintenance schedule of
such batteries is to be provided and maintained.

The schedule is to include all batteries used for essential and emergency services, including
system batteries installed in battery rooms, battery lockers and deck boxes as well as batteries
installed within vendor supplied equipment. Examples of batteries included with equipment are:

● Computer equipment and programmable logic controllers (PLC) use in computer based
systems and programmable electronic systems, when used for essential or emergency services.
● Radiocommunication equipment, such as the equipment required by the IMO MODU Code,
Chapter 11.

The schedule is to be submitted for review, during their plan approval or the new building survey,
and is to include at least the following information regarding the batteries.

● Type and manufacturer’s type designation.

● Voltage and ampere-hour rating.
● Location.
● Equipment and/or system(s) served.
● Maintenance/replacement cycle dates.
● Date(s) of last maintenance and/or replacement.
● For replacement batteries in storage, the date of manufacture and shelf life (See Note below)

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 182
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

Note:

Shelf life is the duration of storage under specified conditions at the end of which a battery retains the ability
to give a specified performance.
3.7.5(b) Procedure of Maintenance.
Procedures are to be put in place to show that, where batteries are replaced, they are to be of an
equivalent performance type. Details of the schedule, procedures, and the maintenance records are
to be included in the unit’s maintenance system and integrated into the unit’s operational
maintenance routine, as appropriate, which are to be verified by the Surveyor.

3.7.6 Replacement of Batteries

Where a vented type battery (See item 1 in commentary) replaces a valve-regulated, sealed type
battery (See item in commentary 2), the requirements in 4-3-3/3.7.2 and 4-3-3/3.7.3 are to be
complied with on the basis of the charging capacity.

Commentary:
1 A vented battery is one in which the cells have a cover provided with an opening through which products
of electrolysis and evaporation are allowed to escape freely from the cells to atmosphere.
2 A valve-regulated battery is one in which cells are closed but have an arrangement (valve) which allows
the escape of gas if the internal pressure exceeds a predetermined value.

End of Commentary

3.9 Switchboard
Switchboards are to be so arranged as to give easy access, as needed, to apparatus and equipment without
danger to personnel. Switchboards are to be located in a dry place so as to provide a clear working space of
at least 900 mm (35 in.) at the front of the switchboard and a clearance of at least 600 mm (24 in.) at the
rear, which can be reduced to 457 mm (18 in.) in way of stiffeners or frames, except that for switchboards
which are enclosed at the rear and are fully serviceable from the front, clearance at the rear is not required
unless necessary for cooling. Switchboards are to be secured to a solid foundation. They are to be self-
supported or are to be braced to the bulkhead or the deck above. In case the last method is used, means of
bracing is to be flexible to allow deflection of the deck without buckling the assembly structure.

3.11 Distribution Boards

3.11.1 Location and Protection
Distribution boards are to be located in accessible positions. Distribution boards can be located
behind panels/linings within accommodation spaces, including stairway enclosures, without the
need to categorize the space to a fire integrity standard, provided no provision is made for storage.
Distribution boards are to have approved noncombustible non-hygroscopic enclosures. Metal
enclosures and all exposed metal parts in nonmetallic enclosures are to be earthed to the unit’s
structure. All cases are to be of adequate mechanical strength.

3.11.2 Switchboard-type Distribution Boards

Distribution boards of the switchboard type, unless installed in machinery spaces or in
compartments assigned exclusively to electric equipment and accessible only to authorized
personnel, are to be completely enclosed or protected against accidental contact and unauthorized
operation.

3.11.3 Safety-type Panels

If the method of operation demands the handling of switches by persons unfamiliar with electrical
equipment, the distribution board is to be of the safety type. This type of distribution board is to be
used for controlling branch lighting circuits. Dead front type panels are to be used where voltage
to earth is in excess of 50 volts DC or 50 volts AC rms between conductors.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 183
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

3.13 Motor Controllers and Control Centers

3.13.1 Location and Installation
Motor control centers are to be located in a dry place. Clear working space is to be provided
around motor control centers to enable doors to be fully opened and equipment removed for
maintenance and replacement. Motor control centers are to be secured to a solid foundation, be
self-supported or be braced to the bulkhead.

3.13.2 Disconnecting Arrangements

3.13.2(a) Device.
Means are to be provided for disconnecting the motor and controller from all supply conductors,
except that a manually operated switch or circuit breaker can serve as both controller and
disconnecting means (see 6-1-7/9.15.2).

3.13.2(b) Location.
The disconnecting device may be in the same enclosure with the controller or may be in a separate
enclosure, and is to be externally operated. Except for remotely controlled fire extinguishing
purpose motors, the branch-circuit switch or circuit breaker on the power-distribution board or
switchboard may serve as the disconnect device if in the same compartment with the controller.

3.13.2(c) Locking Means.

If the disconnecting device is not within sight of both motor and controller, or if it is more than
15.25 m (50 ft) from either, it is to be arranged for locking in the open position. For remotely
controlled fire extinguishing purpose motors, the locking means are to be provided at the feeder
circuit breaker for such motors.

3.13.2(d) Identification Plate.

The disconnect switch, if not adjacent to the controller, is to be provided with an identification
plate.

3.13.2(e) Open and Close Indications.

The disconnect device is to indicate by a position of the handle, or otherwise, whether it is open or
closed.

3.13.3 Indicating-light Circuits

Where indicating-light circuits are employed, their potential is to be limited to 150 volts if the
opening of the foregoing disconnecting devices does not de-energize the indicating circuit.

3.15 Resistors for Control Apparatus

The resistor is to be protected against corrosion, either by rust-proofing or embedding in a protective
material. Resistors are to be located in well-ventilated compartments and are to be mounted with ample
clearances, about 305 mm (12 in.) to prevent excessive heating of an adjacent unit’s structure or dangerous
overheating of unprotected combustible material. The arrangement of the electrical equipment and wiring
located within these spaces is to be such as to prevent their exposure to ambient temperatures in excess of
that for which they have been designed.

3.17 Lighting Fixtures

Lighting fixtures are to be so arranged as to prevent temperature rises which could damage the cables and
wiring, and to prevent surrounding material from becoming excessively hot.

3.19 Heating Equipment

Electric radiators, if used, are to be fixed in position and be so constructed as to reduce fire risks to a
minimum. Electric radiators of the exposed-element type are not to be used.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 184
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

3.21 Magnetic Compasses

Precautions are to be taken in connection with apparatus and wiring in the vicinity of the magnetic
compass to prevent disturbance of the needle from external magnetic fields.

3.23 Portable Equipment and Outlets

Portable equipment are not to be used in hazardous areas nor are portable lights to be used for berth lights
in accommodations.

3.25 Receptacles and Plugs of Different Ratings

Receptacles and plugs of different electrical ratings are not to be interchangeable. In cases where it is
necessary to use 230 volts portable equipment, the receptacles for their attachment are to be of a type
which will not permit attaching 115 volts equipment.

Where plugs and receptacles are located in hazardous areas, they are to be suitable for use in the particular
Zone and have mechanical and/or electrical interlocking to prevent an ignition source occurring during
insertion or removal of the plug.

3.27 Installation Requirements for Recovery from Dead Ship Condition

Means are to be provided to ensure that machinery for self-propelled units can be brought into operation
from the dead ship condition without external aid. See 4-1-1/7.3.

Where the emergency source of power is an emergency generator which complies with 4-3-2/5.15 and
4-3-2/3.1.4, this emergency generator can be used for restoring operation of the main propulsion plant,
boilers and auxiliary machinery.

Where there is no emergency generator installed, the arrangements for bringing main and auxiliary
machinery into operation are to be such that the initial charge of starting air or initial electrical power and
any power supplies for engine operation can be developed onboard the unit without external aid. If for this
purpose an emergency air compressor or an electric generator is required, these units are to be powered by
a hand-starting oil engine or a hand-operated compressor.

The arrangements for bringing the main and auxiliary machinery into operation are to have a capacity such
that the starting energy and any power supplies for propulsion engine operation are available within 30
minutes from a dead ship condition.

3.29 Services Required to be Operable Under a Fire Condition

For the purpose of 4-3-3/5.17.2, services required to be operable under a fire condition include, but not
limited thereto, are the following:

i) Fire and general alarm system

ii) Fire extinguishing system including fire extinguishing medium release alarms
iii) Emergency Fire Pump
iv) Fire detection system
v) Control and power systems for all power operated fire doors and their status indicating systems
vi) Control and power systems for all power operated watertight doors and their status indicating
systems
vii) Emergency lighting
viii) Public address system
ix) Remote emergency stop/shutdown arrangement for systems which can support the propagation of
fire and/or explosion

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 185
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

3.31 High Fire Risk Areas

For the purpose of 4-3-3/5.17, the examples of the high fire risk areas are the following:

i) Machinery spaces as defined by 4-1-1/3.3, except spaces having little or no fire risk such as
machinery spaces which do not contain machinery having a pressure lubrication system and where
storage of combustibles is prohibited (e.g., ventilation and air-conditioning rooms, windlass room,
steering gear room, stabilizer equipment room, electrical propulsion motor room, rooms
containing section switchboards and purely electrical equipment other than oil-filled electrical
transformers (above 10 kVA), shaft alleys and pipe tunnels, and spaces for pumps and
refrigeration machinery not handling or using flammable liquids).
ii) Spaces containing fuel treatment equipment and other highly flammable substances
iii) Galleys and pantries containing cooking appliances, saunas, paint lockers and store rooms having
areas of 4 m2 or more, spaces for the storage of flammable liquids, and workshops other than those
forming part of the machinery spaces.
iv) Laundry containing drying equipment
v) Enclosed drilling and industrial spaces requiring a fixed fire extinguishing system by 8-2-1/15.3.

5 Cable Installation

5.1 General Considerations

5.1.1 Continuity of Cabling
Electric cables are to be installed in continuous lengths between terminations at equipment or in
cable junction boxes. See 4-3-3/5.25. However, approved splices will be permitted at interfaces of
new construction modules, when necessary to extend existing circuits for a unit undergoing repair
or alteration, and in certain cases to provide for cables of exceptional length (See 4-3-3/5.21).

5.1.2 Choice of Cables

The rated operating temperature of the insulating material is to be at least 10°C (18°F) higher than
the maximum ambient temperature likely to exist, or to be produced, in the space where the cable
is installed.

5.1.3 Cable Voltage Drop for New Installation

The cross-sectional area of conductors is to be so determined that the drop in voltage from the
main or emergency switchboard bus-bars to any and every point of the installation when the
conductors are carrying the maximum current under normal steady conditions of service, will not
exceed 6% of the nominal voltage. For supplies from batteries with a voltage not exceeding 55 V,
this figure can be increased to 10%.

The above values are applicable under normal steady conditions. Under special conditions of short
duration, such as motor starting, higher voltage drops may be accepted, provided the installation is
capable of withstanding the effects of these higher voltage drops.

5.1.4 Restricted Location of Cabling

Cables and wiring are to be installed and supported in such a manner as to avoid chafing or other
damage. Cables are to be located with a view to avoiding, as far as practicable, spaces where
excessive heat and gases are encountered; also, spaces where they are exposed to damage, such as
exposed sides of deckhouses. Cables are not to be installed in the bilge area unless protected from
bilge water. Cables are not to be installed in water tanks, oil tanks, cargo tanks, ballast tanks or
any liquid tanks except to supply equipment and instrumentations specifically designed for such
locations and whose functions require it to be installed in the tank.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 186
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

5.1.5 Means of Drainage from Cable Enclosures

Where cables are installed in a cable draw box and horizontal pipes or the equivalent is used for
cable protection, means of drainage are to be provided.

5.1.6 High Voltage Cables

Cables serving systems above 1 kV are not to be bunched with cables serving systems of 1 kV and
below.

5.1.7 Cable Installation above High Voltage Switchgear and Control-Gear

Where a pressure relief flap is provided for high voltage switchgear and high voltage control-gear,
the cables are not to be installed near and above this equipment to prevent the damage of cables
from the flare/flame released from the relief flap upon occurrence of short circuit in this
equipment.

5.1.8 Ultraviolet (UV) Light Protection for Wiring Insulation within Fluorescent Light Fixtures
Where the supply cable’s outer sheathing or covering is removed once the cable enters a
fluorescent light fixture to facilitate routing and/or connection, the insulation on the individual
conductors is to be protected against the possible detrimental effects of UV light exposure by one
of the following:

i) The insulation is to be manufactured with additives that protect the insulation from UV
light damage and a test report is to be submitted to ABS.
ii) Adequate shielding arrangements are to be provided inside the fixture for the entire length
of the exposed insulation within the fixture.
iii) UV protective sleeves are to be installed on the full length of the exposed conductors
inside the fixture during the installation.
5.1.9 Protection of Cables in Tanks
Where cables are installed in liquid tanks, the following arrangements are to be complied with:

i) Cables are to be installed in steel pipes with at least extra-heavy wall thickness with all
joints welded and with corrosion-resistant coating.
ii) Cable gland with gastight packing is to be provided for the cable at both ends of the cable
conduit pipe.
iii) Cable inside of the vertical cable conduit pipe is to be suitably supported (e.g., by sand-
filling or by strapping to a support-wire). Alternatively, the cable inside of the vertical
conduit pipe is acceptable without provided support if the mechanical strength of the
cable is sufficient to prevent cable damage due to the cable weight within the conduit pipe
under continuous mechanical load. Supporting documentation is to be submitted to verify
the mechanical strength of the cable with respect to the cable weight inside of the conduit.
iv) For cables terminating inside the tank, special type cable can be considered without
protection provided supporting documents are appropriately reviewed.

5.3 Insulation Resistance for New Installation

For insulation resistance test of each power and each light circuit, refer to 7A-1-5/5.3.

5.5 Protection for Electromagnetic Induction

5.5.1 Multiple Conductor Cables
All phase conductors of alternating-current cables are to be contained within the same sheath in
order to avoid overheating due to induction by use of multiple conductor cables.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 187
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

5.5.2 Single Conductor Cables

AC installations are to be carried out, as far as possible, in twin or multi-conductor cables.
However, when it is necessary to use single conductor cables in circuits rated in excess of 20 A,
the following arrangements are to be complied with:

5.5.2(a) Cables are supported on non-fragile insulators;

5.5.2(b) There are to be no magnetic materials between cables of a group; and

5.5.2(c) Where single conductor cables are run in bunches, each group of cables is to comprise
360 electrical degrees. To this end, in three-phase circuits, single conductor cable runs of 30 m
(100 ft) or longer and having a cross-sectional area of 185 mm2 (365,005 circ. Mils) or more are to
be transposed throughout the length at intervals not exceeding 15 m (50 ft) in order to equalize to
some degree the impedance of the three phase circuits. Alternatively, such cables can be installed
in trefoil formation. See 4-3-4/7.1.5 for armor.

5.5.3 Non-shielded Signal Cables

Except for fiber optic cables, non-shielded signal cables for automation and control systems
essential for the safe operation of the unit which can be affected by electromagnetic interference
are not to be run in the same bunch with power or lighting cables.

5.7 Joints and Sealing

Cables not having a moisture-resistant insulation are to be sealed against the admission of moisture by
methods such as taping in combination with insulating compound or sealing devices. Cables are to be
installed in such a manner that stresses on the cable are not transmitted to the conductors. Terminations and
joints in all conductors are to be so made as to retain the original electrical, flame retarding and, where
necessary, fire resisting properties of the cable. Terminal boxes are to be secured in place and the moisture-
resistant jacket is to extend through the cable clamp. Enclosures for outlets, switches and similar fittings
are to be flame- and moisture-resistant and of adequate mechanical strength and rigidity to protect the
contents and to prevent distortion under all likely conditions of service. See also 4-3-3/5.17.1 and
4-3-3/5.21.

5.9 Support and Bending

5.9.1 Support and Fixing
For support and fixing of cables, refer to 7A-1-5/5.9.1.

5.9.2 Bending Radius

For bending radius requirements, see 7A-1-5/TABLE 1.

5.9.3 Plastic Cable Trays and Protective Casings

5.9.3(a) Installations.
Cable trays and protective casings made of plastic materials are to be flame retardant (see
Appendix 4-8-4-A1 of the Marine Vessel Rules). Where plastic cable trays and protective casings
are used on open deck, they are additionally to be protected against UV light by such as anti-UV
coating or equivalent. Refer to 7A-1-5/5.9.3 for additional installation details.

Note:

"Plastic" means both thermoplastic and thermosetting plastic materials with or without reinforcement, such as PVC
and fiber reinforced plastics (FRP). "Protective casing" means a closed cover in the form of a pipe or other closed
ducts of non-circular shape.

5.9.3(b) Safe Working Load.

The load on the cable trays and protective casings is to be within the Safe Working Load (SWL).
The support spacing is to be not greater than the manufacturer’s recommendation nor in excess of

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 188
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

the spacing at the SWL test (see Appendix 4-8-4-A1 of the Marine Vessel Rules. In general, the
spacing is not to exceed 2 meters.

Notes:

The selection and spacing of cable tray and protective casing supports are to take into account:

● Dimensions of the cable trays and the protective casings;

● Mechanical and physical properties of their material;
● Mass of the cable trays/protective casings;
● Loads due to weight of cables, external forces, thrust forces and vibrations;
● Maximum accelerations to which the system may be subjected;
● Combination of loads.

5.9.3(c) Hazardous areas

Cable trays and protective casings passing through hazardous areas are to be electrically
conductive (see Appendix 4-8-4-A1 of the Marine Vessel Rules).

5.9.3(d) Type Testing.

Cable trays and protective casings made of plastic materials are to be type tested in accordance
with Appendix 4-8-4-A1 of the Marine Vessel Rules. Alternate test procedures for impact
resistance test, safe working load test, flame retardant test, smoke and toxicity tests and/or
resistivity test from an international or national standard can be considered instead of the test
specified in Appendix 4-8-4-A1 of the Marine Vessel Rules. The type test reports are to be
submitted for review.

Commentary:

Requirements in 4-3-3/5.9 are based on IACS (UR) E16 “Cable trays/protective casings made of plastic materials”
and IACS Recommendation no. 73 “Type approval procedure for cable trays/protective casings made of plastic
materials”.

End of Commentary

5.11 Cable Run in Bunches

5.11.1 Reduction of Current Rating
Where cables which are expected to operate simultaneously are laid close together in a cable
bunch in such a way that there is an absence of free air circulation around them, the following
reduction factor is to be applied to the current rating obtained from 4-3-4/ TABLE 2.

Number of Cables in One Bunch Reduction Factor

One to six 1.00

Seven to twelve 0.85

Bunches of more than twelve cables are subject to special consideration based on the type and
service of the various cables in the bunch.

5.11.2 Clearance and Segregation

A clearance is to be maintained between any two cable bunches of at least the diameter of the
largest cable in either bunch. Otherwise, for the purpose of determining the number of cables in
the bunch, the total number of cables on both sides of the clearance are to be used.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 189
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

5.11.3 Cable of Lower Conductor Temperature

The current rating of each cable in a bunch is to be determined based on the lowest conductor
temperature rating of any cable in the bunch.

5.13 Deck and Bulkhead Penetrations

5.13.1 General
Where cables pass through watertight, firetight, or smoke-tight bulkheads or decks, the
penetrations are to be made through the use of approved stuffing tubes, transit devices or pourable
materials installed in accordance with manufacturer’s installation procedures to maintain the
watertight integrity or fire-rating of the bulkheads or decks. These devices or pourable materials
are not to damage the cable physically or through chemical action or through heat build-up, and
are to be examined and tested as specified in 7A-1-2/19.5 and 7A-1-2/TABLE 2.

Where cable conduit pipe or equivalent is carried through decks or bulkheads, arrangements are to
be made to maintain the integrity of the water or gas tightness of the structure.

5.13.1(a) New Construction

A Cable Transit Seal Systems Register (Register) is to be provided by the shipbuilder for all
watertight cable transits fitted to the unit. The Register can be in either a hard copy or digitized
media. It is to include a marking / identification system, documentation referencing manufacturer
manual(s) for each type of cable transit installed, the Type Approval certification for each type of
transit system, applicable installation drawings, and a recording of each installed transit
documenting the as built condition after final inspection in the shipyard. It is to include sections to
record any inspection, modification, repair and maintenance.

The Register is to be reviewed by the attending Surveyor to confirm it contains a list of the
watertight cable transits, applicable cable transit information and sections to maintain in-service
maintenance and survey records.

For manned unit, the Register is to be held on board the unit. For unmanned units, if a suitable
storage location does not exist on board, the Register may be held ashore. The Register is to be
readily available to the attending Surveyor.

5.13.1(b) Units in service

The owner or operator is to maintain the Register to record any disruption (repair, modification or
opening out and closing) to a cable transit or to record the installation of a new cable transit.

Commentary:

The requirements in 4-3-3/5.13.1 are based on IACS Unified Requirement (UR) Z28 “Surveys of Watertight Cable
Transits”

End of Commentary

5.13.2 Non-watertight Penetrations

When cables pass through non-watertight bulkheads where the bearing surface is less than 6.4 mm
(0.25 in.), the holes are to be fitted with bushings having rounded edges and a bearing surface for
the cable of at least 6.4 mm (0.25 in.) in length. Where cables pass through deck beams or similar
structural parts, all burrs are to be removed in way of the holes and care is to be taken to eliminate
sharp edges.

5.13.3 Collision Bulkhead

Cables are not to pass through a collision bulkhead.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 190
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

5.15 Mechanical Protection

5.15.1 Metallic Armor
Electric cables installed in locations liable to damage during normal operation of the unit are to be
provided with braided metallic armor and otherwise suitably protected from mechanical injury as
appropriate for the location.

5.15.2 Conduit Pipe or Structural Shapes

Where cables are installed in locations in way of hatches, tank tops, open decks subject to seas,
and where passing through decks, they are to be protected by substantial metal shields, structural
shapes, pipe or other equivalent means. All such coverings are to be of sufficient strength to
provide effective protection to the cables. Where cables are installed in metal piping or in a metal
conduit system, such piping and systems are to be earthed and are to be mechanically and
electrically continuous across all joints.

5.17 Emergency and Essential Feeders

5.17.1 Location
As far as practicable, cables and wiring for emergency and essential services, including those
listed in 4-3-3/3.29, are not to pass through high fire risk areas (see 4-3-3/3.31). For Emergency
Fire Pumps, see requirements in 4-3-3/5.17.3.

5.17.2 Services Necessary Under a Fire Condition

Where cables for services required to be operable under a fire condition (see 4-3-3/3.29) including
their power supplies pass through high fire risk areas (see 4-3-3/3.31) other than those which they
serve, they are to be so arranged that a fire in any of these areas does not affect the operation of
the service in any other area. For Emergency Fire Pumps, see requirements in 4-3-3/5.17.3. This
can be achieved by any of the following measures:

5.17.2(a) Fire resistant cables in accordance with 4-3-4/7.1.3 are installed and run continuous to
keep the fire integrity within the high fire risk area. See 4-3-3/5.17 FIGURE 2.

5.17.2(b) At least two loops/radial distributions run as widely apart as is practicable and so
arranged that in the event of damage by fire at least one of the loops/radial distributions remains
operational.

Systems that are self monitoring, fail safe or duplicated with cable runs separated as widely as
practicable, may be exempted from the requirements in 4-3-3/5.17.2(a) and 4-3-3/5.17.2(b).

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 191
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

FIGURE 2
Cables within High Fire Risk Areas

5.17.3 Electrical Cables For The Emergency Fire Pump

The electrical cables to the emergency fire pump are not to pass through the machinery spaces
containing the main fire pumps and their sources of power and prime movers. They are to be of a
fire resistant type, in accordance with 4-3-4/7.1.3, where they pass through other high fire risk
areas.

5.17.4 Requirements by the Governmental Authority

Attention is directed to the requirements of the governmental authority of the country whose flag
the unit flies, for the installation of emergency circuits required in various types of units.

5.19 Battery Room

Where cables enter battery rooms, the holes are to be bushed as required for watertight bulkheads in
4-3-3/5.13. All connections within battery rooms are to be resistant to the electrolyte. Cables are to be
sealed to resist the entrance of electrolyte by spray or creepage. The size of the connecting cable is to be
based on current-carrying capacities given in 4-3-4/TABLE 2 and the starting rate of charge or maximum
discharge rate, whichever is the greater, is to be taken into consideration in determining the cable size.

5.21 Splicing of Electrical Cables

5.21.1 Basis of Approval
Replacement insulation is to be fireresistant or flame retardant and is to be equivalent in electrical
and thermal properties to the original insulation. The replacement jacket is to be at least equivalent
to the original impervious sheath and is to assure a watertight splice. Splices are to be made using
an approved splice kit which contains the following:

● Connector of correct size and number

● Replacement insulation
● Replacement jacket
● Instructions for use

In addition, prior to approval of a splicing kit, it is required that completed splices be tested for
fire resistance, watertightness, dielectric strength, etc. to the satisfaction of the Surveyor. This

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 192
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

requirement may be modified for splice kits which have had such tests conducted and reported on
by an independent agency acceptable to ABS.

5.23 Splicing of Fiber Optic Cables

Splicing of fiber optic cables is to be made by means of approved mechanical or fusion methods.

5.25 Cable Junction Box

Except for propulsion cables, junction boxes may be used in the installation of electric cables aboard the
unit, provided the plans required by 4-3-3/1.3 for junction boxes are submitted and the following
requirements are complied with:

5.25.1
The design and construction of the junction boxes are to comply with 6-1-7/13.7, as well as
4-3-3/5.25.2 below.

5.25.2
The junction boxes are to be suitable for the environment in which they are installed (i.e.,
explosion-proof in hazardous areas, watertight or weathertight on deck, etc.).

5.25.3
Separate* junction boxes are to be used for feeders and circuits of each of the following rated
voltage levels:

Note:

*A physical barrier may be used in lieu of two separate junction boxes for circuits having rated voltage levels
corresponding to those in either 4-3-3/5.25.3(a) or 4-3-3/5.25.3(b).

5.25.3(a) Rated voltage levels not exceeding those specified in 4-3-3/7.1.i

5.25.3(b) Rated voltage levels exceeding those in 4-3-3/5.25.3(a), up to and including 1 kV. A
physical barrier is to be used within the junction box to separate distribution systems of different
rated voltages, such as 480 V, 600 V and 750 V.

5.25.3(c) Rated voltage levels exceeding 1 kV. Separate junction boxes are to be used for each of
the rated voltage levels exceeding 1 kV.

Each junction box and the compartment in the junction box separated by a physical barrier are to
be appropriately identified as regards the rated voltage of the feeders and circuits it contains.

5.25.4
The junction boxes for emergency feeders and circuits are to be separate from those used for
normal unit main service feeders and circuits.

In addition to the above, the applicable requirements in 4-3-3/5 and 4-3-4/7 regarding cable installation
and application details are to be complied with.

7 Earthing

7.1 General
Exposed metal parts of electrical machines or equipment which are not intended to be live but which are
liable under fault conditions to become live are to be earthed unless the machines or equipment are:

i) Supplied at a voltage not exceeding 50 volts DC or 50 volts AC rms between conductors; auto-
transformers are not to be used for the purpose of achieving this voltage; or

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 193
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

ii) Supplied at a voltage not exceeding 250 V AC rms by safety isolating transformers supplying only
one consuming device; or
iii) Constructed in accordance with the principle of double insulation.

7.3 Permanent Equipment

The metal frames or cases of all permanently installed generators, motors, controllers, instruments and
similar equipment are to be permanently earthed through metallic contact with the unit’s structure.

Alternatively, they are to be connected to the hull by a separate conductor in accordance with 4-3-3/7.5.
Where outlets, switches and similar fittings are of nonmetallic construction, all exposed metal parts are to
be earthed.

7.5 Connections
7.5.1 General
All earthing conductors are to be of copper or other corrosion-resistant material and are to be
protected against damage. The nominal cross-sectional area of every copper earthing conductor is
to be not less than that required by 4-3-3/9.7.3 TABLE 2.

7.5.2 Earthed Distribution System

Earthing conductors in an earthed distribution system are to comply with 4-3-3/7.5.1, except that
the earthing conductor in line C4 of 4-3-3/7 TABLE 2 is to be A/2.

7.5.3 Connection to Hull Structure

All connections of an earth-continuity conductor or earthing lead to the unit’s structure are to be
made in accessible positions and are to be secured by a screw of brass or other corrosion-resistant
material having a cross-sectional area equivalent to the earth-continuity conductor or earthing
lead, but not less than 4 mm (0.16 in.) in diameter. The earth connection screw is to be used for
this purpose only. See 4-2-1/11.31 for control of static electricity.

TABLE 2
Size of Earth-continuity Conductors and Earthing Connections
[See 4-3-3/7.5]

Type of Earthing Connection Cross-sectional Area, A , of Minimum Cross-sectional

Associated Current Area of Copper Earthing
Carrying Conductor Connection

A1 A ≤ 16 mm2 A
Earth-continuity conductor
2 2
in flexible cable or flexible A2 16 mm < A ≤ 32 mm 16 mm2
cord
A3 A > 32 mm2 A/2

For cables having an insulated earth-continuity conductor

B1a A ≤ 1.5 mm2 1.5 mm2

B1b 1.5 mm2 < A ≤ 16 mm2 A

2 2
B1c 16 mm < A ≤ 32 mm 16 mm2
Earth-continuity conductor
incorporated in fixed cable B1d A > 32 mm2 A2

For cables with bare earth wire in direct contact with the lead sheath

B2a A ≤ 2.5 mm2 1 mm2

B2b 2.5 mm2 < A ≤ 6 mm2 1.5 mm2

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 194
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

Type of Earthing Connection Cross-sectional Area, A , of Minimum Cross-sectional

Associated Current Area of Copper Earthing
Carrying Conductor Connection

C1a Stranded earthing

connection:
1.5 mm2 for A ≤ 1.5 mm2
A ≤ 3 mm2 A for A > 1.5 mm2

C1b Unstranded earthing

Separate fixed earthing connection:
conductor 3 mm2

C2 3 mm2 < A ≤ 6 mm2 3 mm2

C3 6 mm2 < A ≤ 125 mm2 A2

C4 A > 125 mm2 64 mm2 (see Note (1))

Notes:

1 For earthed distribution systems, the size of earthing conductor is not to be less than A/2.

2 Conversion Table for mm2 to circular mils:

mm2 circ. mils mm2 circ. mils mm2 circ. mils mm2 circ. mils

1 1,973 2.5 4,933 6 11,841 70 138,147

1.5 2,960 4 7,894 16 31,576 120 236,823

7.7 Portable Cords

Receptacle outlets operating at 50 volts DC or 50 volts AC rms or more are to have an earthing pole.

7.9 Cable Metallic Covering

All metal sheaths, armor of cable and mineral-insulated, metal-sheathed cable are to be electrically
continuous and are to be earthed to the metal hull at each end of the run, except that final subcircuits may
be earthed at the supply end only. All metallic coverings of power and lighting cables passing through
hazardous area or connected to equipment in such an area are to be earthed at least at each end.

9 Equipment and Installation in Hazardous Area

9.1 General Consideration

9.1.1 General
Electrical equipment and wiring are not to be installed in a hazardous area unless essential for
operational purposes. Where the installation of electrical equipment in such location is necessary,
the selection and installation of equipment and cables in hazardous areas is to be in accordance
with IEC Publication 61892-7, or other recognized standards. Electrical equipment certified for
use in hazardous areas in accordance with the IEC 60079 series is considered suitable for use in
temperatures from -20°C to 40°C (-4°F to 104°F). Account is to be taken of the temperature at the
point of installation when selecting electrical equipment for installation in hazardous areas.

Consideration is to be given to:

i) The zone in which the apparatus are used;

ii) The sensitivity to ignition of the gases or vapors likely to be present, expressed as a gas
group; and

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 195
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

iii) The sensitivity of the gases and vapors likely to be present to ignition by hot surfaces,
expressed as a temperature classification.

Hazardous areas are defined in Section 4-3-6. For certified safe-type equipment, see 4-3-3/9.3.

Fans used for the ventilation of the hazardous areas are to be of non-sparking construction in
accordance with 4-3-3/9.7.

9.1.2 Electrical Equipment

Electrical equipment used in hazardous areas is to be manufactured, tested, marked and installed
in accordance with IEC Publication 60079 series, or other recognized standards, and certified by
an independent testing laboratory acceptable to ABS.

The following equipment and cables are acceptable for installation in hazardous locations:

9.1.2(a) Zone 0 Areas.

Only certified intrinsically-safe circuits or equipment (type "ia") and associated wiring are
permitted in Zone 0 areas.

9.1.2(b) Zone 1 Areas.

Equipment and cables permitted in Zone 1 areas are to be:

i) Certified intrinsically-safe circuits or equipment (type "ia" or "ib") and associated wiring
ii) Certified flameproof (explosion proof) equipment (type "d")
iii) Certified increased safety equipment (type "e"); for increased safety motors, consideration
is to be given to the protection against overcurrent
iv) Certified pressurized enclosure type equipment (type "p") (see 4-3-3/9.3.3).
v) Permanently installed cables with:

● metallic armor, or
● of mineral-insulated, metallic-sheathed type, or
● installed in metallic conduit with explosion-proof gas-tight fittings, or
vi) Flexible cables, where necessary, provided they are of heavy duty type.

Other suitable types of electrical equipment may be specially considered for installation in Zone 1
areas.

9.1.2(c) Zone 2 Areas.

Equipment and cables permitted in Zone 2 areas are to be:

i) All equipment approved for Zone 1 areas

ii) The following equipment, provided the operating temperature does not exceed 315°C
(600°F) and provided any brushes, switching mechanisms or similar arc-producing
devices are approved for Zone 1 areas:

● Enclosed squirrel-cage induction motors

● Fixed lighting fixtures protected from mechanical damage
● Transformers, solenoids or impedance coils in general purpose enclosures
● Cables with moisture-resistant jacket (impervious-sheathed) and protected from
mechanical damage.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 196
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

Other suitable types of electrical equipment may be specially considered for installation in Zone 2
areas.

9.1.2(d)
Simple electrical apparatus and components of simple construction with well-defined electrical
parameters which are compatible with the intrinsic safety of the circuit in which they are used
(e.g., passive components such as switches, junction boxes, resistors and simple semiconductor
devices; sources of stored energy consisting of single components in simple circuits with well
defined parameters, for example capacitors or inductors, whose values shall be considered when
determining the overall safety of the system; sources of generated energy, for example
thermocouples and photocells, which do not generate more than 1.5 V, 100 mA and 25 mW. Refer
to IEC Publications 60079-11 and 60079-14).

9.1.3 Grouping and Temperature Class

ISO/IEC 80079-20-1 Groups IIA, IIB or IIC are to be selected for intrinsically-safe or flameproof
(explosion proof) equipment dependent on the gas/vapor group of the gases and vapors likely to
be present. Other types of certified equipment are to be Group II.

Electrical equipment is to be so selected that its maximum surface temperature will not reach the
ignition temperature of any gas/vapor likely to be present in the hazardous areas in which the
electrical equipment is located. Temperature classes are to be selected in accordance with ISO/IEC
80079-20-1 or 61892-7.

Electrical equipment located in hazardous drilling well areas and active mud processing areas is to
meet at least Group IIA and temperature class T3.

9.1.4 Cables Installation

Cables in hazardous areas are to be armored or mineral-insulated metal-sheathed where required
by 4-3-3/9.1.2, except for cables of intrinsically safe circuits subject to the requirements of
4-3-3/5.15. Where cables pass through hazardous area boundaries, they are to be run through
gastight fittings. No splices are allowed in hazardous areas, except in intrinsically-safe circuits.
Where it is necessary to join cables in hazardous areas (e.g., flexible cable connections to non-
flexible cables), the joints are to be made in approved junction boxes.

9.1.5 Lighting Circuits

All switches and protective devices for lighting fixtures in hazardous areas are to interrupt all
poles or phases and are to be located in a non-hazardous area. However, a switch may be located
in a hazardous area if the switch is of a certified-safe type for the hazardous location in which it is
to be installed. On solidly grounded distribution systems, the switches need not open the grounded
conductor.

9.3 Certified-safe Type and Pressurized Equipment and Systems

9.3.1 Installation Approval
Electrical equipment in hazardous areas is to be of a type suitable for such locations. Where
permitted by the Rules, electrical equipment of certified-safe type will be approved for
installation, provided such equipment has been type-tested and certified by a competent
independent testing laboratory as suitable for hazardous areas and provided that there is no
departure in the production equipment from the design so tested and approved.

9.3.2 Intrinsically-safe System

9.3.2(a) Separation
Intrinsically-safe systems are to be completely separated and independent of all other electric
systems. Intrinsically-safe cables are to have shielded conductors or to be installed a minimum of

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 197
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

50 mm (2 in.) from other electric cables and are not to occupy an enclosure (such as a junction box
or terminal cabinet) with non-intrinsically-safe circuits.

For separation distances of different (separate) intrinsically safe circuits in terminal boxes, the
requirements in IEC 60079-14 , and IEC 60079-11, Clause 6.21, are to be complied with.

The segregation between the intrinsically safe wiring terminals and between bare conducting parts
of connection facilities are to comply with IEC 60079.

9.3.2(b) Physical Barrier

When intrinsically-safe components are located by necessity within enclosures that contain non-
intrinsically-safe systems, such as control consoles and motor starters, such components are to be
effectively isolated in a sub-compartment by physical barriers having a cover or panel secured by
bolts, locks, allen screws or other approved methods. The physical barrier is not intended to apply
to the source of power for the intrinsically-safe circuit interface.

9.3.2(c) Replacement
Unless specifically approved, replacement equipment for intrinsically-safe circuits is to be
identical to the original equipment.

9.3.3 Pressurized Equipment

Pressurized equipment is to consist of separately ventilated enclosures supplied with positive-
pressure ventilation from a closed-loop system or from a source outside of the hazardous areas,
and provision is to be made such that the equipment cannot be energized until the enclosure has
been purged with a minimum of ten air changes and required pressure is obtained. Ventilating
pipes are to have a minimum wall thickness of 3 mm (0.12 in. or 11 gauge). In the case of loss of
pressurization, power is to be automatically removed from the equipment, unless this would result
in a condition more hazardous than that created by failure to de-energize the equipment. In this
case, in lieu of removal of power, an audible and visual alarm is to be provided at a normally
manned control station.

Pressurized equipment in compliance with IEC Publication 60079-2, NFPA 496 or other
recognized standard will also be acceptable.

9.5 Paint Stores

9.5.1 General
Electrical equipment in paint stores and in ventilation ducts serving such spaces as permitted in
4-3-3/9.1 is to comply with the requirements for group IIB class T3 in ISO/IEC Publication
60079-20-1 series.

The following type of equipment will be acceptable for such spaces:

i) Intrinsically-safe defined by 4-3-1/3.13

ii) Explosion-proof defined by 4-3-1/3.7
iii) Pressurized defined by 4-3-1/3.33
iv) Increased safety defined by 4-3-1/3.15
v) Other equipment with special protection, recognized as safe for use in explosive gas
atmospheres by a national or other appropriate authority
9.5.2 Open Area Near Ventilation Openings
In the areas on open deck within 1 m (3.3 ft) of ventilation inlet or within 1 m (3.3 ft) (if natural)
or 3 m (10 ft) (if mechanical) of exhaust outlet, the installation of electrical equipment and cables
is to be in accordance with 4-3-3/9.1.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 198
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

9.5.3 Enclosed Access Spaces

The enclosed spaces giving access to the paint store may be considered as non-hazardous,
provided that:

i) The door to the paint store is gastight with self-closing devices without holding back
arrangements.
Commentary:

A watertight door may be considered as being gastight.

End of Commentary

ii) The paint store is provided with an acceptable, independent, natural ventilation system
ventilated from a safe area, and
iii) Warning notices are fitted adjacent to the paint store entrance stating that the store
contains flammable liquids.

9.7 Non-sparking Fans

A fan is considered as non-sparking if in either normal or abnormal conditions it is unlikely to produce
sparks.

9.7.1 Design Criteria

9.7.1(a) Air Gap.
The air gap between the impeller and the casing is to be not less than 10% of the shaft diameter in
way of the impeller bearing, but not less than 2 mm (0.08 in.). It need not be more than 13 mm
(0.5 in.).

9.7.1(b) Protection Screen.

Protection screens of not more than 13 mm (0.5 in.) square mesh are to be fitted in the inlet and
outlet of ventilation openings on the open deck to prevent the entrance of objects into the fan
casing.

9.7.2 Materials
9.7.2(a) Impeller and its Housing.
Except as indicated in 4-3-3/9.7.2(c) below, the impeller and the housing in way of the impeller
are to be made of alloys which are recognized as being spark proof by appropriate test.

9.7.2(b) Electrostatic Charges.

Electrostatic charges both in the rotating body and the casing are to be prevented by the use of
antistatic materials. Furthermore, the installation onboard of the ventilation units is to be such as
to provide the safe bonding to the hull of the units themselves.

9.7.2(c) Acceptable Combination of Materials.

Tests referred to in 4-3-3/9.7.2(a) above are not required for fans having the following
combinations:

i) Impellers and/or housings of nonmetallic material, due regard being paid to the
elimination of static electricity;
ii) Impellers and housings of nonferrous materials;
iii) Impellers of aluminum alloys or magnesium alloys and a ferrous (including austenitic
stainless steel) housing on which a ring of suitable thickness of nonferrous materials is
fitted in way of the impeller;
iv) Any combination of ferrous (including austenitic stainless steel) impellers and housings
with not less than 13 mm (0.5 in.) tip design clearance.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 199
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 3 Onboard Installation 4-3-3

9.7.2(d) Unacceptable Combination of Materials.

The following impellers and housings are considered as sparking-producing and are not permitted:

i) Impellers of an aluminum alloy or magnesium alloy and a ferrous housing, regardless of

tip clearance;
ii) Housing made of an aluminum alloy or a magnesium alloy and a ferrous impeller,
regardless of tip clearance;
iii) Any combination of ferrous impeller and housing with less than 13 mm (0.5 in.) design
tip clearance.
9.7.3 Type Test
Type tests on the finished product are to be carried out using an acceptable national or
international standard. Such type test reports are to be made available when requested by the
Surveyor.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 200
 PART 4
CHAPTER 3
Electrical Installations

SECTION 4
Machinery and Equipment

1 Objective

1.1 Goals
The electrical installations covered in this section are to be designed, constructed, operated, and maintained
to:
Goal No. Goal

POW 1 provide safe and reliable storage and supply of fuel/energy/power.

POW 2 provide power to enable the machinery/equipment/electrical installation to perform its required
functions necessary for the safe operation of the unit.

POW 3 enable all electrical services necessary for maintaining the unit in normal operational and
habitable conditions to be available without recourse to the emergency source of power.

FIR 1 prevent the occurrence of fire and explosion.

FIR 3 reduce the risk of damage caused by fire to the unit, its cargo and the environment.

Materials are to be suitable for the intended application in accordance with the following goals and support
the Tier 1 goals as listed above.

Goal No. Goal

MAT 1 The selected materials’ physical, mechanical and chemical properties are to meet the design
requirements appropriate for the application, operating conditions and environment.

The goals in the cross-referenced Rules/Standards are also to be met.

1.2 Functional Requirement

In order to achieve the above stated goals, the design, construction, installation and maintenance of the
electrical installations are to be in accordance with the following functional requirements:

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 201
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 4 Machinery and Equipment 4-3-4

Functional Functional Requirements

Requirement No.

Power Generation & Distribution (POW)

POW-FR1 Battery systems and UPS are to be designed to maintain continuity of load power for essential and
emergency electrical power consumers for time specified and for all modes of operations.

POW-FR2 UPS units are to be suitably arranged with high level of integrity and availability for use during an
emergency.

POW-FR3 Provide sufficient stored power and redundancies for propulsion and auxiliary engine starting

POW-FR4 Provide cables with sufficient current carrying capacity to support connected loads and their
overload protection.

Materials (MAT)

MAT-FR1 Be constructed of materials that are able to withstand the marine and operating environment,
maximum design ambient temperature and stresses without deterioration.

Fire Safety (FIR)

FIR-FR1 Cables serving essential or emergency services are to be able to reduce the propagation of fire and to
allow essential and emergency services to continue to operate in a fire condition.

FIR-FR2 Provide adequate ventilation to maintain the flammable gases within the UPS locations to a level
below the lower explosive limit.

The functional requirements in the cross-referenced Rules/Standards are also to be met

1.3 Compliance
A unit is considered to comply with the goals and functional requirements when the prescriptive
requirements are complied with or when an alternative arrangement has been approved. Refer to Part 1D,
Chapter 2.

2 Certification of Electrical Machinery and Equipment

Electrical machinery and equipment required to be certified by ABS are covered under Section 6-1-7.

3 Battery Systems and Uninterruptible Power Systems (UPS)

For certification of accumulator batteries, refer to 6-1-7/9.17.

3.1 References
3.1.1 Emergency Services
For requirements covering emergency services and transitional source of power, see 4-3-2/5.5.3
and 4-3-2/5.7, respectively.

3.1.2 Protection of Batteries

For requirements covering protection of batteries, see 4-3-2/9.9.

3.1.3 Battery Installation

For requirements covering battery installation, ventilation of the battery location and protection
from corrosion, see 4-3-3/3.7.

3.1.4 Cable Installation

For requirements covering cable installation in the battery room, see 4-3-3/5.19.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 202
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 4 Machinery and Equipment 4-3-4

3.3 Engine-starting Battery

Battery systems for engine-starting purposes may be of the one-wire type and the earth lead is to be carried
to the engine frame. See also 4-8-2/11.11 of the Marine Vessel Rules and 4-3-2/5.15 of this Chapter for
main engine starting and the starting arrangement of the emergency generator, respectively.

3.5 Location
3.5.1 Location
The UPS unit is to be suitably located for use in an emergency. The UPS unit is to be located as
near as practical to the equipment being supplied, provided the arrangements comply with all
other Rules, such as 4-3-3/3.7, 4-3-3/3.9, 4-3-3/3.11, and 4-3-3/3.13 for location of electrical
equipment.

3.5.2 Ventilation
UPS units utilizing valve regulated sealed batteries can be located in compartments with normal
electrical equipment, provided the ventilation arrangements are in accordance with the
requirements of 4-3-3/3.7. Since valve regulated sealed batteries are considered low-hydrogen-
emission batteries, calculations are to be submitted in accordance with 4-3-3/3.7.2(d) to establish
the gas emission performance of the valve regulated batteries compared to the standard lead acid
batteries. Arrangements are to be provided to allow any possible gas emission to be led to the
weather, unless the gas emission performance of the valve regulated batteries does not exceed that
of standard lead acid batteries connected to a charging device of 0.2 kW.

3.5.3 Battery Installation

For battery installation arrangements, see 4-3-3/3.7.

3.7 Performance
3.7.1 Duration
The output power is to be maintained for the duration required for the connected equipment as
stated in 4-3-2/5.3 for emergency services and 4-3-2/5.7 of transitional source of power, as
applicable.

3.7.2 Battery Capacity

No additional circuits are to be connected to the battery charger unit or UPS unit without
verification that the batteries have adequate capacity. The battery capacity is, at all times, to be
capable of supplying the designated loads for the time specified in 4-3-4/3.7.1.

3.7.3 Recharging
On restoration of the input power, the rating of the charging facilities are to be sufficient to
recharge the batteries while maintaining the output supply to the load equipment. See also
6-1-7/9.17.2.

5 Computer-Based System (CBS)

A programmable electronic device, or interoperable set of programmable electronic devices, is organized
to achieve one or more specified purposes such as collection, processing, maintenance, use, sharing,
dissemination, or disposition of information. CBSs onboard include IT and OT systems. A CBS may be a
combination of subsystems connected via network. Onboard CBSs may be connected directly or via public
means of communications (e.g. Internet) to ashore CBSs, other vessels’ CBSs and/or other facilities.

CBSs are to meet the requirements of Section 4-9-3 of the Marine Vessel Rules, even when the unit will
not be assigned with ACC or ACCU notations.

CBSs associated with remote propulsion control, are also to comply with 4-3-5/3.11.2.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 203
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 4 Machinery and Equipment 4-3-4

6 Cyber Resilience
Cyber resilience is the capability to reduce the occurrence and mitigating the effects of incidents arising
from the disruption or impairment of operational technology (OT) used for the safe operation of a unit,
which potentially lead to dangerous situations for human safety, safety of the unit and/or threat to the
environment.

A unit that complies with the requirements in Sections 4-9-13 and 4-9-14 of the Marine Vessel Rules is
eligible to be assigned the CR notation. CR notation is mandatory for self-propelled Mobile Offshore
Units, Mobile Offshore Units with DPS notation and Mobile Offshore Drilling Units.

7 Cables and Wires

7.1 Cable Construction

7.1.1 General
Electric cables are to have conductors, insulation and moisture-resistant jackets in accordance with
IEC Publication 60092-350, 60092-352, 60092-353, 60092-354, 60092-360, 60092-370,
60092-376, IEEE Std-45. Other recognized marine standards of an equivalent or higher safety
level, are acceptable to ABS. The tests may be carried out by the manufacturer whose certificate
of tests are acceptable and is to be submitted upon request from ABS. Network cables are to
comply with a recognized industry standard. Cables such as flexible cable, fiber-optic cable, etc.,
used for special purposes are acceptable provided they are manufactured and tested in accordance
with recognized standards accepted by ABS. Conductors are to be of copper and stranded in all
sizes. Conductors are not to be less than the following in cross sectional size:

● 1.0 mm2 (1,973.5 circ. mils) for power and lighting,

● 0.5 mm2 (986.8 circ. mils) for control cables,
● 0.5 mm2 (986.8 circ. mils) for essential or emergency signaling and communications cables,
except for those assembled by the equipment manufacturer, and
● 0.35 mm2 (690.8 circ. mils) for telephone cables for nonessential communication services,
except for those assembled by the equipment manufacturer.

See 4-3-4/7 TABLE 2 for current carrying capacity for insulated copper wires and cables.

For electric cables in hazardous areas, the electric cable construction and the cable glands are to
achieve the appropriate seal, such that gas cannot migrate through the cable.

Note:

See clause 3.16 and clause 4.6 of IEC 60092-350 concerning the provision of an extruded impervious inner sheath
that will prevent the migration of gas through the cable.

7.1.2 Flame Retardant Property

7.1.2(a) Standards.
All electric cables are to be at least of a flame-retardant type complying with the following:

i) Depending on the intended installation, cables constructed to IEC Publication 60092

standards are to comply with the flammability criteria of IEC Publication 60332-3-22 or
60332-3-21, Category A or A F/R, or
ii) Cables constructed to IEEE Std. 45 are to comply with the flammability criteria of that
standard, or
iii) Cables constructed to another recognized marine standard, where specially approved, are
to comply with the flammability criteria of IEC Publication 60332-3-22 or 60332-3-21,

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 204
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 4 Machinery and Equipment 4-3-4

Category A or A F/R (depending on the intended installation) or other acceptable

standards.

Special types of cables, such as radio frequency cable, which do not comply with the above
requirements are subject to ABS technical assessment and approval.

7.1.2(b) Alternative Arrangement.

Flame retardant marine cables, including network cables, which have not passed the above-
mentioned bunched cable flammability criteria may be considered, provided that the cable is
treated with approved flame-retardant material, or the installation is provided with approved fire
stop arrangements. Special consideration may be given to the flame retardancy of special types of
cables, such as radio frequency cables. When specifically approved, bus duct can be used in lieu
of cable.

7.1.3 Fire Resistant Property

When electric cables are required to be fire-resistant, they are to comply with the requirements of
IEC Standard 60331-1 for cables greater than 20 mm overall in diameter, otherwise they are to
comply with the IEC Standard 60331-2 for cable diameters 20 mm or less. For special cables,
requirements in the following standards can be used:

● IEC Standard 60331-23: Procedures and requirements – Electric data cables

● IEC Standard 60331-25: Procedures and requirements – Optical fiber cables

Cables complying with alternative national standards suitable for use in a marine environment can
be considered. Fire resistant type cables are to be easily distinguishable. See also 4-3-3/3.31 and
4-3-3/5.17.

7.1.4 Insulation Material

All electrical cables for power, lighting, communication, control and electronic circuits are to have
insulation suitable for a conductor temperature of not less than 60°C (140°F). See 4-3-4/7 TABLE
1 for types of cable insulation.

7.1.5 Armor for Single-conductor Cables

The armor is to be nonmagnetic for single-conductor alternating-current cables.

7.1.6 Fiber Optic Cables

Fiber optic cables are to be constructed and tested to a recognized fiber optic cable construction
standard acceptable to ABS. The requirements of flame retardancy for the electrical cables are
applicable to the fiber optic cables. The construction of the fiber optic cable which may pass
through or enter a hazardous area is to be such that escape of gases to a safe area is not possible
through the cable.

TABLE 1
Types of Cable Insulation [See 4-3-4/7.1.4]

Insulation Type Designation Insulation Materials Maximum Conductor Temperature

V75, PVC Polyvinyl Chloride – Heat resisting 75°C (167°F) *

R85, XLPE Cross-linked Polyethylene 85°C (185°F) *

E85, EPR Ethylene Propylene Rubber 85°C (185°F) *

R90, XLPE Cross-linked Polyethylene 90°C (194°F) *

E90, EPR Ethylene Propylene Rubber 90°C (194°F) *

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 205
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 4 Machinery and Equipment 4-3-4

Insulation Type Designation Insulation Materials Maximum Conductor Temperature

M95 Mineral (MI) 95°C (203°F) *

S95 Silicone Rubber 95°C (203°F) *

* A maximum conductor temperature of 250°C (482°F) is permissible for special applications and standard end
fittings may be used, provided the temperature does not exceed 85°C (185°F) at the end of fittings. However, when
the temperature at the end of the fittings is higher than 85°C (185°F), special consideration will be given to an
appropriate end fitting.

7.3 Portable and Flexing Electric Cables

Unless otherwise required in the Rules, cables for portable equipment and cables subject to flexing service
need not be armored.

7.5 Mineral-insulated, Metal-sheathed Cable

Mineral-insulated cable provided with approved fittings for terminating and connecting to boxes, outlets
and other equipment may be used for any service up to 600 volts and may be used for feeders and branch
circuits in both exposed and concealed work, in dry or wet locations. The moisture-resisting jacket (sheath)
of mineral-insulated, metal-sheathed cable exposed to corrosive conditions is to be made of or protected by
materials suitable for those conditions.

TABLE 2
Maximum Current Carrying Capacity for Cables

Conductor Size Maximum Current in Amperes (see 4-3-4/7.1.1)

45°C (113°F) Ambient, 750 V and Less, AC or DC; see Notes

1-core 2-core 3- or 4-core

3
10 R85 R90 R85 R90 R85 R90
mm2 circ XLPE XLPE M95 XLPE XLPE M95 XLPE XLPE M95
mils V75 V75 V75
E85 E90 S95 E85 E90 S95 E85 E90 S95
EPR EPR EPR EPR EPR EPR

1.0 13 16 20 11 14 17 9 11 14

1.25 15 18 23 13 15 20 11 13 16

1.5 17 21 23 26 14 18 20 22 12 15 16 18

4.11 21 25 32 18 21 27 15 18 22

2.5 24 28 30 32 20 24 26 27 17 20 21 22

6.53 28 34 38 24 29 32 20 24 27

4 32 38 40 43 27 32 34 37 22 27 28 30

10.4 38 45 51 32 38 43 27 32 36

6 41 49 52 55 35 42 44 47 29 34 36 39

16.5 51 60 68 43 51 58 36 42 48

10 57 67 72 76 48 57 61 65 40 47 50 53

20.8 59 70 78 50 60 66 41 49 55

26.3 68 81 91 58 69 77 48 57 64

16 76 91 96 102 65 77 82 87 53 64 67 71

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 206
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 4 Machinery and Equipment 4-3-4

Conductor Size Maximum Current in Amperes (see 4-3-4/7.1.1)

45°C (113°F) Ambient, 750 V and Less, AC or DC; see Notes

1-core 2-core 3- or 4-core

3
10 R85 R90 R85 R90 R85 R90
mm2 circ XLPE XLPE M95 XLPE XLPE M95 XLPE XLPE M95
mils V75 V75 V75
E85 E90 S95 E85 E90 S95 E85 E90 S95
EPR EPR EPR EPR EPR EPR

33.1 79 93 105 67 79 89 55 65 74

41.7 91 108 121 77 92 103 64 76 85

25 101 120 127 135 86 102 108 115 71 84 89 95

52.6 105 124 140 89 105 119 74 87 98

66.4 121 144 162 103 122 138 85 101 113

35 125 148 157 166 106 126 133 141 88 104 110 116

83.7 140 166 187 119 141 159 98 116 131

50 156 184 196 208 133 156 167 177 109 129 137 146

106 163 193 217 139 164 184 114 135 152

133 188 222 250 160 189 213 132 155 175

70 192 228 242 256 163 194 206 218 134 160 169 179

168 217 257 289 184 218 246 152 180 202

95 232 276 293 310 197 235 249 264 162 193 205 217

212 251 297 335 213 252 285 176 208 235

120 269 319 339 359 229 271 288 305 188 223 237 251

250 278 330 371 236 281 315 195 231 260

150 309 367 389 412 263 312 331 350 216 257 272 288

300 312 370 416 265 315 354 218 259 291

350 343 407 458 292 346 389 240 285 321

185 353 418 444 470 300 355 377 400 247 293 311 329

400 373 442 498 317 376 423 261 309 349

450 402 476 536 342 405 456 281 333 375

240 415 492 522 553 353 418 444 470 291 344 365 387

500 429 509 572 365 433 486 300 356 400

550 455 540 607 387 459 516 319 378 425

300 477 565 601 636 405 480 511 541 334 396 421 445

600 481 570 641 409 485 545 337 399 449

650 506 599 674 430 509 573 354 419 472

700 529 628 706 450 534 600 370 440 494

750 553 655 737 470 557 626 387 459 516

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 207
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 4 Machinery and Equipment 4-3-4

Conductor Size Maximum Current in Amperes (see 4-3-4/7.1.1)

45°C (113°F) Ambient, 750 V and Less, AC or DC; see Notes

1-core 2-core 3- or 4-core

3
10 R85 R90 R85 R90 R85 R90
mm2 circ XLPE XLPE M95 XLPE XLPE M95 XLPE XLPE M95
mils V75 V75 V75
E85 E90 S95 E85 E90 S95 E85 E90 S95
EPR EPR EPR EPR EPR EPR

400 571 677 690 761 485 575 587 647 400 474 483 533

800 576 682 767 490 580 652 403 477 540

850 598 709 797 508 603 677 419 496 558

900 620 734 826 527 624 702 434 514 578

950 641 760 854 545 646 726 449 532 598

500 656 778 780 875 558 661 663 744 459 545 546 613

1000 662 784 882 563 666 750 463 549 617

600 736 872 981 626 741 834 515 610 687

625 755 894 1006 642 760 855 529 626 704

Notes:

1 The values given above have been calculated for an ambient of 45°C (113°F) and assume that a conductor
temperature equal to the maximum rated temperature of the insulation is reached and maintained continuously
in the case of a group of four cables bunched together and laid in free air.

2 The current rating values given in 4-3-4/7 TABLE 2 (and those derived therefrom) may be considered
applicable, without correction factors, for cables double-banked on cable trays, in cable conduits or cable
pipes, except as noted in Note 3.

3 For bunched cables, see 4-3-3/5.11.1.

4 These current ratings are applicable for both armored and unarmored cables.

5 If ambient temperature differs from 45°C (113°F), the values in 4-3-4/7 TABLE 2 are to be multiplied by the
following factors. (See below table.)

Maximum Ambient Correction Factor

Conductor
40°C (104°F) 50°C (122°F) 55°C (131°F) 60°C (140°F) 65°C (149°F) 70°C (158°F)
Temperature

75°C (167°F) 1.08 0.91 0.82 0.71 0.58 —

85°C (185°F) 1.06 0.94 0.87 0.79 0.71 0.61

95°C (203°F) 1.05 0.94 0.88 0.82 0.74 0.67

95°C (203°F) 1.05 0.95 0.89 0.84 0.77 0.71

6 Where the number of conductors in a cable exceeds four, as in control cables, the maximum current carrying
capacity of each conductor is to be reduced as in the following table:

No. of Conductors % of 3– 4/C TYPE Values in 4-3-4/7.5 TABLE 2

5–6 80

7 – 24 70

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 208
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 4 Machinery and Equipment 4-3-4

25 – 42 60

43 and above 50

7 When a mineral-insulated cable is installed in such a location that its copper sheath is liable to be touched
when in service, the current rating is to be multiplied by the correction factor 0.80 in order that the sheath
temperature does not exceed 70°C (158°F).

8 Cables being accepted based on approved alternate standard may have current carrying capacity of that
standard, provided the cables are in full compliance with that standard.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 209
 PART 4
CHAPTER 3
Electrical Installations

SECTION 5
Specialized Installations

1 Objective

1.1 Goals
The electrical installations covered in this section is to be designed, constructed, operated, and maintained
to:

Goal No. Goal

PROP 1 provide sufficient thrust/power to move or maneuver the Unit when required.

PROP 2 provide redundancy and/or reliability to maintain propulsion.

PROP-SG 9 maintain the vessel/unit on station in the open waters.

POW 2 provide power to enable the machinery/equipment/electrical installation to perform its required
functions necessary for the safe operation of the unit.

POW 3 enable all electrical services necessary for maintaining the unit in normal operational and
habitable conditions to be available without recourse to the emergency source of power.
POW 5 enable supply/power for essential services to be restored after malfunction.

FIR 1 prevent the occurrence of fire and explosion.

SAFE 1.1 minimize danger to persons on board, the unit, and surrounding equipment / installations from
hazards associated with machinery and systems.

MGMT 5.1 design and construct unit, machinery, and electrical systems to facilitate safe access, ease of
inspection, survey, and maintenance.

AUTO 1 perform its functions as intended and in a safe manner.

AUTO 2 indicate the system operational status and alert operators of any essential machinery/systems
deviate from its defined design/operating conditions or intended performance.

AUTO 3 have an alternative means to enable safe operation in the event of an emergency or failure of
remote control.

Materials are to be suitable for the intended application in accordance with the following goals and support
the Tier 1 goals as listed above.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 210
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

Goal No. Goal

MAT 1 The selected materials’ physical, mechanical and chemical properties are to meet the design
requirements appropriate for the application, operating conditions and environment.

The goals in the cross-referenced Rules/Standards are also to be met.

1.2 Functional Requirements

In order to achieve the above-stated goals, the design, construction, installation and maintenance of the
electrical installations to which this Section applies are to be in accordance with the following functional
requirements:

Functional Functional Requirements

Requirement No.

Propulsion, Maneuvering, Station Keeping (PROP)

PROP-FR1 (POW) Have suitable arrangements to maintain the integrity/continuity of supplies to services required for
propulsion and steering as well as the safety of the unit.

PROP-FR2 (POW) Provide independence of and redundancy for electrical equipment forming part of the electric
propulsion drive train such that a single failure will not completely disable the propulsion of the
unit.

PROP-FR3 (AUTO) Provide means for controlling the prime mover speed at the control assembly for safe operation.

PROP-FR4 Provide means to prevent unintentional loss of propulsion systems in the event of the need to access
control system components or leakage of control system fluids.

PROP-FR5 The design of propulsion control system is to prevent a dangerous situation due to a control failure
or switching of control location.

PROP-FR6 (POW) Provide protection measures to prevent voltage variations and over speeding of the propulsion
system due to regenerative power.

PROP-FR7 Drilling and production units are to be able to keep station in the open waters and keep the integrity
of the well while shutdown logic is activated.

Power Generation and Distribution (POW)

POW-FR1 Provide winding connection methods for high voltage transformers to achieve redundancy of power
supply upon a single failure.

POW-FR2 (PROP) The capacity of the main source of power is to be such that in the event of any one power source
being stopped it will still be possible to supply services necessary to provide normal operational
conditions of propulsion, minimum habitability, and safety.

POW-FR3 Provide means of storing energy for the safe operation of high voltage circuit breakers and switches.

POW-FR4 Provide means to distribute loads such that blackouts are avoided, and power is always maintained
to essential services and propulsion loads.

POW-FR5 (PROP) Provide means to shut down the propulsion machinery in case of emergency operation.

POW-FR6 Circuit disconnecting devices used for generators and motors are to be designed to operate at full
load conditions and are to be constructed to prevent flammability due to any damage.

POW-FR7 Provide means to absorb the excessive regenerated energy.

Materials (MAT)

MAT-FR1 Circuit disconnecting devices are to be constructed to withstand vibration or shock encountered
during normal marine environmental conditions and avoid deterioration. Fire Safety (FIR)

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 211
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

Functional Functional Requirements

Requirement No.

Fire Safety (FIR)

FIR-FR1 For drilling units, units operating next to drilling units or units producing hydrocarbons, means to
initiate a shutdown of electrical equipment or complete shutdown are to be provided to take
protective measures against flammable and explosive hazards.

FIR-FR2 (SAFE) The sequence of emergency shutdowns and associated recovery and restoration operations are to be
predetermined in different levels to minimize the risk in emergency scenarios.

FIR-FR3 The equipment is to be suitable for the environment (gas group and temperature classification) in
which they operate.

Safety of Personnel (SAFE)

SAFE-FR1 Provide designs and arrangements that allow for the safe use of hull return and earthing systems.

SAFE-FR2 Provide means to monitor and alarm the earth fault in the high voltage electric power systems.

SAFE-FR3 Provide protection to prevent accidental contact with live parts of the assembly.

SAFE-FR4 Provide measures to prevent hazards and injuries due to high voltage cables in the accommodation
spaces.

SAFE-FR5 Provide segregation for high voltage cables and equipment to avoid potential electric hazard and
injuries.

SAFE-FR6 Provide means of effective electrical bonding to earth for safe operation of high voltage cables.

SAFE-FR7 Provide working space for high voltage equipment to prevent potential severe injuries to personnel
performing maintenance activities.

SAFE-FR8 Provide measures to avoid exposure of high voltage equipment to damaging environments.

SAFE-FR9 HV electrical system is to be designed such that the crew can safely isolate any damaged distribution
equipment and switch to alternative supplies without the need to open the HV equipment.

SAFE-FR10 Provide neutral earthing methods of three-wire dual-voltage direct-current systems at the generator
switchboards for protection against electrical shock.

SAFE-FR11 Provide protection for DC propulsion circuits to avoid a damaging flashover.

SAFE-FR12 Emergency shutdown (ESD) stations are to be arranged at normally manned locations and are to be
protected from unauthorized operations.

SAFE-FR13 (POW) Provide critical emergency services required for operation after an emergency shutdown.

Safety Management (MGMT)

MGMT-FR1 Provide accessibility to all the parts of the equipment requiring inspection or adjustment or
replacement.

MGMT-FR2 Cables are to be constructed to withstand marine environment and support connected loads and their
(AUTO/POW) overload protection.

MGMT-FR3 Provide means to seal the propulsion cables to prevent admission of moisture or air.

MGMT-FR4 Provide means of disconnecting the electrical equipment from power source for maintenance.

MGMT-FR5 Provide suitable marking for high voltage cables, equipment and spaces containing them for ready
(SAFE) identification of danger.

MGMT-FR6 Provide consolidated information regarding design, operations, tools, permissions, maintenance, and
(SAFE) other considerations to be taken involving high voltage equipment.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 212
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

Functional Functional Requirements

Requirement No.

MGMT-FR7 (POW/ To provide instructions to recover normal operations after emergency shutdown.
PROP)

Automation (Control, Monitoring and Safety systems) (AUTO)

AUTO-FR1 (POW) Provide protection against overload, short circuit, earth-fault and overvoltage conditions and other
hazards to prevent damage to equipment and maintain continuity of power to remaining circuits.

AUTO-FR2 Provide protection against loss of excitation to avoid dangerous operation.

AUTO-FR3 Provide safety measures and alarms to protect the electrical distribution system from harmonics and
failure of power management system.

AUTO-FR4 Provide means to prevent reversal of generator rotation upon failure of the driving power of its
prime mover.

AUTO-FR5 Interlock arrangements are to be provided for propulsion control levers to avoid improper operation.

AUTO-FR6 The control station is to be provided with means to monitor the parameters and status of propulsion
system for normal operation of propulsion machinery.

The functional requirements covered in the cross-referenced Rules/Standards are also to be met.

1.3 Compliance
A unit is considered to comply with the goals and functional requirements when the applicable prescriptive
requirements are complied with or when an alternative arrangement has been approved. Refer to Part 1D,
Chapter 2.

2 High Voltage Systems

2.1 General
2.1.1 Application
The following requirements in this Subsection are applicable to AC systems with nominal voltage
(phase to phase) exceeding 1 kV. Unless stated otherwise, high voltage equipment and systems are
to comply with the other parts in Part 4, Chapter 3 for low voltage equipment and systems, as
well.

2.1.2 Standard Voltages

The nominal standard voltage is not to exceed 15 kV. Systems with nominal voltage over 15kV
will be reviewed on a case-by-case basis in accordance with applicable industry standards and this
section.

2.1.3 Air Clearance and Creepage Distance

2.1.3(a) Air Clearance.
Phase-to-phase air clearances and phase-to-earth air clearances between non-insulated parts are to
be not less than the minimum as specified below.

Nominal Voltage in kV Minimum air clearance in mm (in.)

3 – 3.3 55 (2.2)

6 – 6.6 90 (3.6)

10 – 11 120 (4.8)

15 160 (6.3)

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 213
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

Where intermediate values of nominal voltages are accepted, the next higher air clearance is to be
observed. In the case of smaller distances, an appropriate voltage impulse test is to be applied.

2.1.3(b) Reduction.
Alternatively, reduced clearance distances may be used provided:

i) The equipment is not installed in ‘Machinery Spaces of Category A’ or in areas affected

by a Local Fixed Pressure Water-spraying or Local Water-mist Fire Extinguishing
System.
ii) The equipment is subject to an impulse voltage test with test voltage values shown in
Table below. Where intermediate values of rated operational voltage are used, the next
higher rated impulse withstand test voltage is to be used. The impulse voltage test reports
are to be submitted to ABS for review.
Rated Voltage Rated Impulse Withstand Voltage
kV kV (peak value)

3.6 40

7.2 60

12 75

15 95

2.1.3(c) Insulating Material.

Any insulating material that is used to cover live parts of equipment used to comply with
clearance distance requirements is to be suitable for the application. The equipment manufacturer
is to submit documentation which demonstrates the suitability of such insulation material.

2.1.3(d) Creepage Distance

i) The minimum creepage distances for main switchboards and generators are given in the
Table below:
Nominal Voltage Minimum Creepage Distance for Proof Tracking Index
V mm (in.)

300V 375V 500V > 600V

(1) (1) (1)
1000-1100 26 (1.02) 24 (0.94) 22 (0.87) 20 (0.79)(1)

< 3300 63 (2.48) 59 (2.32) 53 (2.09) 48 (1.89)

< 6600 113 (4.45) 108 (4.25) 99 (3.9) 90 (3.54)

(2)
≤ 11000 183 (7.20) 175 (6.89) 162 (6.38) 150 (5.91)

Notes:
1 A distance of 35 mm is required for busbars and other bare conductors in main switchboards.
2 Creepage distances for equipment with nominal voltage above 11 kV are subject to
consideration.

ii) The minimum creepage distances for equipment other than main switchboards and
generators are given in the Table below:
Nominal Voltage Minimum Creepage Distance for Proof Tracking Index mm (in.)
V
300V 375V 500V > 600V
1000-1100 18 (0.71) 17 (0.67) 15 (0.59) 14 (0.55)
< 3300 42 (1.65) 41 (1.61) 38 (1.50) 26 (1.02)

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 214
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

Nominal Voltage Minimum Creepage Distance for Proof Tracking Index mm (in.)
V
300V 375V 500V > 600V
<6600 83 (3.27) 80 (3.15) 75 (2.95) 70 (2.76)
≤ 11000* 146 (5.75) 140 (5.51) 130 (5.11) 120 (4.72)

Note:
* Creepage distances for equipment with nominal voltage above 11 kV are subject to consideration.

iii) Creepage distances between live parts and between live parts and earthed metal parts are
to be in accordance with IEC 60092-503 for the nominal voltage of the system, the nature
of the insulation material, and the transient overvoltage developed by switch and fault
conditions.

2.3 System Design

2.3.1 Selective Coordination
Selective coordination is to be in accordance with 4-3-2/9.1.5, regardless of the system neutral
earthing arrangement.

2.3.2 Earthed Neutral Systems

2.3.2(a) Neutral Earthing.
The current in the earth fault condition is to be not in excess of full load current of the largest
generator on the switchboard or relevant switchboard section and in no case less than three times
the minimum current required for operation of any device in the earth fault condition.

At least one source neutral to ground connection is to be available whenever the system is in the
energized mode.

2.3.2(b) Equipment.

Electrical equipment in directly earthed neutral or other neutral earthed systems is to be able to
withstand the current due to a single phase fault against earth for a period necessary to trip the
protection device.

2.3.3 Neutral Disconnection

Each generator neutral is to be provided with means for disconnection.

2.3.4 Hull Connection of Earthing Impedance

All earthing impedances are to be connected to the hull. The connection to the hull is to be so
arranged that any circulating currents in the earth connections will not interfere with radio, radar,
communication and control equipment circuits. In systems with neutral earthed, connection of the
neutral to the hull is to be provided for each generator switchboard section.

2.3.5 Earth Fault Detection and Indication

An earth fault is to be indicated by visual and audible means. In low impedance or direct earthed
systems, provision is to be made to automatically disconnect the faulty circuits. In high impedance
earthed systems where outgoing feeders will not be isolated in case of an earth fault, the insulation
of the equipment is to be designed for the phase to phase voltage.

i) In unearthed or high impedance earthed systems, an earth fault is to be indicated by visual

and audible means at the centralized control system.
ii) In low impedance or direct earthed systems, provision is to be made to automatically
disconnect the faulty circuits. Audible and visual indication is to be provided at the
centralized control station to indicate that a ground fault had occurred and has been

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 215
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

cleared by ground fault protection. An audible alarm is to be provided if the ground fault
was not successfully cleared.
iii) In high impedance earthed systems where outgoing feeders will not be isolated in case of
an earth fault, the insulation of the equipment is to be designed for the phase to phase
voltage.
2.3.6 Number and Capacity of Transformers
Requirements for the number and capacity of transformers are given in 4-3-2/7.1.6(a).

For transformers with a high voltage winding over 1000 V, the following would not be accepted as
complying with the above requirement:

i) The provision of a spare single phase transformer to substitute a failed transformer.

ii) The operation of two single phase transformers in an open delta (V-V) connection.

2.5 Circuit Breakers and Switches – Auxiliary Circuit Power Supply Systems for
Operating Energy
2.5.1 Source and Capacity of Power Supply
Where electrical energy or mechanical energy is required for the operation of circuit breakers and
switches, a means of storing such energy is to be provided with a capacity at least sufficient for
two on/off operation cycles of all of the components. However, the tripping due to overload or
short-circuit, and under-voltage is to be independent of any stored electrical energy sources. This
does not preclude the use of stored energy for shunt tripping, provided alarms are activated upon
loss of continuity in the release circuits and power supply failures. The stored energy may be
supplied from within the circuit in which the circuit breakers or switches are located.

2.5.2 Number of External Sources of Stored Energy

Where the stored energy is supplied from a source external to the circuit, such supply is to be from
at least two sources so arranged that a failure or loss of one source will not cause the loss of more
than one set of generators and/or essential services. Where it will be necessary to have the source
of supply available for dead ship startup, the source of supply is to be provided from the
emergency source of electrical power.

2.7 Circuit Protection

2.7.1 Protection of Generator
Protection against phase-to-phase fault in the cables connecting the generators to the switchboard
and against interwinding faults within the generator is to be provided. This is to trip the generator
circuit breaker and automatically de-excite the generator. In distribution systems with a low-
impedance earthed neutral, phase to earth faults are to be likewise treated.

2.7.2 Protection of Power Transformers

Power transformers are to be provided with overload and short circuit protection. Each high-
voltage transformer intended to supply power to the low-voltage unit main service switchboard is
to be protected in accordance with 4-3-2/9.15. In addition, the following means for protecting the
transformers or the electric distribution system are to be provided:

2.7.2(a) Coordinated Trips of Protective Devices.

Discriminative tripping is to be provided for the following. See 4-3-2/9.1.5.

i) Between the primary side protective device of the transformer and the feeder protective
devices on the low-voltage unit main service switchboard, or
ii) Between the secondary side protective device of the transformer, if fitted, and the feeder
protective devices on the low-voltage unit main service switchboard.
2.7.2(b) Load Shedding Arrangement.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 216
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

Where the power is supplied through a single set of three-phase transformers to a low-voltage unit
main service switchboard, automatic load shedding arrangements are to be provided when the total
load connected to the low voltage unit main service switchboard exceeds the rated capacity of the
transformer. See 4-3-2/1.7 and 4-3-2/9.3.3.

2.7.2(c) Protection from Electrical Disturbance.

Means or arrangements are to be provided for protecting the transformers from voltage transients
generated within the system due to circuit conditions, such as high-frequency current interruption
and current suppression (chopping) as the result of switching, vacuum cartridge circuit breaker
operation, or thyristor-switching.

An analysis or data for the estimated voltage transients is to be submitted to show that the
insulation of the transformer is capable of withstanding the estimated voltage transients. See
6-1-7/15.3.3(b).

2.7.2(d) Protection from Earth-Faults.

Where a Y-neutral of three-phase transformer windings is earthed, means for detecting an earth-
fault are to be provided. The detection of the earth fault is to activate an alarm at the manned
control station or to automatically disconnect the transformer from the high-voltage power
distribution network.

2.7.2(e) Transformers Arranged in Parallel.

Refer to 4-3-2/9.5.2 for requirements.

2.7.3 Voltage Transformers for Control and Instrumentation

Voltage transformers are to be provided with overload and short circuit protection on the
secondary side.

2.7.4 Fuses
Fuses are not to be used for overload protection.

2.7.5 Over Voltage Protection

Lower voltage systems supplied through transformers from high voltage systems are to be
protected against overvoltages. This can be achieved by:

i) Direct earthing of the lower voltage system,

ii) Appropriate neutral voltage limiters, or
iii) Earthed screen between primary and secondary winding of transformers

2.9 Equipment Installation and Arrangement

2.9.1 Degree of Protection
The degree of equipment protection is to be in accordance with 4-3-5/2 TABLE 1.

2.9.2 Protective Arrangements

2.9.2(a) Interlocking Arrangements.
Where high-voltage equipment is not contained in an enclosure, but a room forms the enclosure of
the equipment, the access doors are to be so interlocked that they cannot be opened until the
supply is isolated and the equipment earthed down.

2.9.2(b) Warning Plate.

At the entrance of such spaces, a suitable marking is to be placed which indicates danger of high-
voltage and the maximum voltage inside of the space. For high-voltage electrical equipment

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 217
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

installed outside of these spaces, a similar marking is to be provided. An adequate, unobstructed

working space is to be left in the vicinity of high voltage equipment for preventing potential
severe injuries to personnel performing maintenance activities. In addition, the clearance between
the switchboard and the overhead/deckhead above is to meet the requirements of the Internal Arc
Classification according to IEC 62271-200.

2.9.2(c) Spaces Containing High Voltage Equipment.

All entrances to spaces containing high voltage equipment are to have suitable marking indicating
the danger of high voltage and the maximum voltage inside the space. Where the spaces contain
high voltage switchgear the marking at the entrances is also to include marking indicating that the
space is only accessible to authorized personnel only.

2.9.2(d) Exposure of HV Equipment to Damaging Environments.

The arrangements of the installation are to be designed to avoid exposure of high voltage
equipment to contaminants, such as oil or dust, as might be found in machinery spaces or close to
ventilation air inlets to the space, or to water spray from water-mist systems and local fire hose
connections.

2.9.3 Cables
2.9.3(a) Runs of Cables.
In accommodation spaces, high voltage cables are to be run in enclosed cable transit systems.

2.9.3(b) Segregation.
High voltage cables of different voltage ratings are not to be installed in the same cable bunch,
duct, pipe or box. Where high voltage cables of different voltage ratings are installed on the same
cable tray, the air clearance between cables is not to be less than the minimum air clearance for the
higher voltage side in 4-3-5/2.1.3(a). However, high voltage cables are not to be installed on the
same cable tray for the cables operating at the nominal system voltage of 1 kV or less.

Higher voltage equipment is not to be combined with lower voltage equipment in the same
enclosure unless segregation or other suitable measures are taken to ensure safe access to lower
voltage equipment

2.9.3(c) Installation Arrangements.

High voltage cables are to be installed on cable trays or equivalent when they are provided with a
continuous metallic sheath or armor which is effectively bonded to earth. Otherwise, they are to be
installed for their entire length in metallic casings effectively bonded to earth.

2.9.3(d) Termination and Splices.

Terminations in all conductors of high voltage cables are to be, as far as practicable, effectively
covered with suitable insulating material. In terminal boxes, if conductors are not insulated, phases
are to be separated from earth and from each other by substantial barriers of suitable insulating
materials. High voltage cables of the radial field type, i.e., having a conductive layer to control the
electric field within the insulation, are to have terminations which provide electric stress control.

Terminations are to be of a type compatible with the insulation and jacket material of the cable
and are to be provided with means to ground all metallic shielding components (i.e., tapes, wires
etc.).

Splices and joints are not permitted in propulsion cables. For purposes of this Rule, propulsion
cables are those cables whose service is related only to propulsion.

2.9.3(e) Cable Rating

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 218
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

The rated phase to earth voltage (Uo) of high voltage cables is not to be less than shown in the
Table below:

Nominal System Voltage Highest System Voltage Minimum Rated Voltage of Cable (Uo /U )
(Un ) (Um ) (kV)
(kV) (kV)
Systems with Automatic Systems without
Disconnection Upon Automatic Disconnection
Detection of an Earth Upon Detection of an
Fault Earth Fault

3.0/3.3 3.6 1.8/3.0 3.6/6.0

6.0/6.6 7.2 3.6/6.0 6.0/10.0

10.0/11.0 12.0 6.0/10.0 8.7/15.0

15.0/16.5 17.5 8.7/15.0 12.0/20.0

20.0/22.0 24.0 12.0/20.0 18.0/30.0

30.0/33.0 36.0 18.0/30.0 ---

Notes:
1 Nominal System Voltage (Un) in 50 Hz and 60 Hz.

2 Cables being accepted based on approved alternate standard may have voltage ratings of that standard
provided the cables are in full compliance with that standard.

2.9.3(f) Cable Current Carrying Capacities

The maximum current carrying capacity of high voltage cables is to be in accordance with 4-3-4/7
TABLE 2.

2.9.3(g) Marking.
High voltage cables are to be readily identifiable by suitable marking.

2.9.3(h) Test after Installation.

A voltage withstand test is to be carried out on each completed cable and its accessories before a
new high voltage installation, including additions to an existing installation, is put into service.

An insulation resistance test is to be carried out prior to the voltage withstand test being
conducted.

For cables with rated voltage (Uo /U) above 1.8/3 kV (Um = 3 . 6 kV) an AC voltage withstand
test may be carried out upon advice from high voltage cable manufacturer. One of the following
test methods to be used:

i) An AC test voltage for 5 min with the phase‐to‐phase voltage of the system applied
between the conductor and the metallic screen/sheath.
ii) An AC voltage test for 24 h with the normal operating voltage of the system.
iii) A DC test voltage equal to 4Uo may be applied for 15 minutes.

For cables with rated voltage (Uo /U) up to 1.8/3 kV (Um = 3 . 6kV), a DC voltage equal to 4Uo is
to be applied for 15 minutes.

After completion of the test, the conductors are to be connected to earth for a sufficient period in
order to remove any trapped electric charge.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 219
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

The insulation resistance test is then repeated.

Alternatively, an AC voltage withstand test may be carried out upon advice from the high voltage
cable manufacturer at a voltage not less than the normal operating voltage of the cable, and it is to
be maintained for a minimum of 24 hours.

Note: Tests in accordance with IEC Publication 60502 are also acceptable.

The above tests are for newly installed cables. If due to repairs or modifications, cables which
have been in use are to be tested, lower voltages and shorter durations are to be considered.

2.9.4 High Voltage Shore Connection

Where arrangements are made for the supply of electricity at high voltage from onshore, and
designed to allow the shipboard generators to be shut down while in port, the requirements given
in Part 6, Chapter 4 of the Marine Vessel Rules are to be complied with.

2.11 Cable Construction

Cables are to be constructed to IEC Publication 60092-353, 60092-354, or other equivalent recognized
standard. See also 4-3-4/7.1.

2.13 Design Operating Philosophy

2.13.1 Objective
While this section covers the specific ABS requirements for High Voltage (HV) systems, it is
recognized that system design and equipment construction are only parts of an overall approach
that are required to allow HV systems to be operated safely. Other aspects that contribute towards
HV safety include maintenance procedures, unit and equipment operating procedures, permit to
work procedures, company safety policy, personal protective equipment (PPE) and training, most
of which are beyond the role of Classification. However, in order to assist ABS in its review of the
design and construction of the unit and its equipment it is necessary for ABS to be assured that the
design is part of a larger overall approach or plan.

The High Voltage Design Principles document is to outline the concepts that are the basis of the
design. It is to identify risks and document the strategies that are used to mitigate each of the risks
(e.g., remote switching, arc flash energy reduction equipment).

2.13.2 HV System Failures

The design is to take into account each reasonably foreseeable failure type and address what
actions will be expected of the crew for each failure. Due to the limited availability of specialist
tools, equipment and spare parts on board and recognizing the additional dangers associated with
space limitations, the remoteness of specialized medical help and facilities in the event of
emergencies, it is desirable that, as far as practicable, the crew is not exposed to dangers that could
be avoided. For these reasons it is preferable that the unit’s HV electrical system be designed such
that the crew can safely isolate any damaged distribution equipment and switch to alternative
supplies without the need to open the HV equipment.

2.13.3 Activities
For all HV switchboards and distribution boards, each type of operation or activity is to be
identified and the means of undertaking the operation or activity safely is to be established. The
operations and activities to be considered are to include the following:

i) Taking readings
ii) Normal operational switching
iii) Isolation and making safe

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 220
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

iv) Maintenance
v) Fault finding
vi) Inspection
vii) Class Surveys

Where switchgear design calls for circuit breakers to be inspected prior to being put back into
service following operation on overcurrent, this is also to be covered.

2.13.4 Accessibility
An adequate, unobstructed working space of at least 2 m (6 ft) is to be left in the vicinity of high
voltage equipment for preventing potential severe injuries to personal performing maintenance
activities. Where the clear space around a location where activity is taking place is less than 2 m
(6 ft), then the activities are to be covered in sufficient detail to take into account the work
involved and the possible need to have clear and safe access for emergency medical evacuation.
Where recommended by the switchgear manufacturer, the working space may be reduced to a
minimum of 1.5 m (5 feet) at the front/side and 1 m (3.3 ft) at the rear due to special
considerations such as the use of arc resistant switchgear.

Activities that do not require operation at the switchboard (e.g., telephones or manual call
points)are not to require the operator to be within 2 m (6 ft) of the switchboard.

2.13.5 Modifications
No modifications are to be made to HV switchgear without the plans being approved and the
drawings being made available to the ABS Surveyor in advance of the work taking place. Testing
of approved modifications is to be conducted in the presence of the ABS Surveyor. Temporary
repairs are to be in full compliance with the requirements of these Rules.

2.13.6 HV Systems with Enhanced Operating Redundancy

Where the HV electrical system is designed with sufficient redundancy to allow switching and
isolation along the principles in 4-3-5/2.13.2 and still meet the requirements of 4-3-2/3.1.2 with
one generator in reserve, then the activity associated with that failure is not required to be
included.

2.15 Preliminary Operations Manual

2.15.1 Objective
The preliminary operations manual contains the shipyard’s description of operations affecting the
unit’s HV equipment. The description ‘preliminary’ is used to capture the fact that it may not be
the final document used by the unit’s Owner.

The manual is to be complete and sufficiently detailed to capture each piece of HV equipment and
how the activities associated with that equipment can be achieved consistently with the Design
Operating Philosophy. This manual is to be made available to the Owner by the shipyard.

The Owner will need the information contained in the preliminary operations manual to
understand how the shipyard designed the HV equipment to be operated safely. It is likely that the
Owner will modify some aspects of the manual to bring it in line with their own company policies,
organizational responsibilities and legal duties.

The preliminary operations manual is to include for each piece of HV equipment:

i) Details of the tasks (operations and activities) associated with that piece of equipment
ii) Details of the Authorization needed to perform each of the tasks
iii) Details of the tools required to perform each of the tasks

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 221
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

iv) Details of PPE and safety equipment (locks, barriers, tags, rescue hooks, etc.)
v) Identify the tasks for which a ‘permit to work’ system is to be used.
2.15.2 Details of Authorization
For each operation or task involving HV switchgear and for access to the HV switchgear rooms,
the appropriate authorizations are to be determined before delivery.

2.15.3 Training Requirements for Authorization

Part of the basis of establishing any level of authorization is training. It is not expected that the
shipyard will stipulate what training qualifications are required. However, a description of the
subjects that would need to be covered in the training for each level of authorization should be
included.

The Owner can be guided by the above information in making decisions regarding the crew
training requirements.

2.15.4 Test, Maintenance Tools and PPE

Where tasks require the use of PPE, the required protection clothing rating are to be identifiable in
the preliminary operations manual and on a label on the HV equipment where that task will take
place. The level of protection offered by the PPE is to be readily identified on the PPE itself in the
same terms or units as used on the labels.

Some PPE for general use is not suitable for High Voltage or arc flash hazards, mostly through
inappropriate fire performance; such PPE is to be excluded from high voltage switchgear rooms.
Information alerting the crew of the need to be able to recognize and use the right PPE is to be
included in the manual.

2.15.5 Inspection and Maintenance of Test Equipment Tools and PPE

Where PPE or test equipment is provided by the shipyard the means for its proper use, inspection,
calibration and maintenance is to be made available. The instructions or directions regarding
where they are kept are to be contained in the Preliminary Operations Manual.

Where the PPE is not provided by the shipyard a description or specification regarding the
required tools and PPE are to be provided in the Preliminary Operations Manual.

TABLE 1
High Voltage Equipment Locations and Minimum Degree of Protection

Switchboards, Distribution Boards, Motor Control

Centers and Controllers

Generators
Example Condition
of of Motors
Location Location
Transformers, Converters

Junction/
Connection Boxes

Dry control rooms Danger of touching live parts IP32 N/A N/A IP23 IP44
Authorized Personnel Only only

Dry control rooms IP42 N/A N/A IP44 IP44

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 222
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

Control rooms Danger of dripping liquid IP32 N/A N/A IP23 IP44
Authorized Personnel Only and/or moderate mechanical
damage
Control Rooms IP42 N/A N/A IP44 IP44

Above floor plates in machinery IP32 IP23 IP23 IP23 IP44

spaces
Authorized Personnel Only (1)

Above floor plates in machinery IP42 IP23 IP43 IP44 IP44

spaces

Emergency machinery rooms IP32 IP23 IP23 IP23 IP44

Authorized Personnel Only

Emergency machinery rooms IP42 IP23 IP43 IP44 IP44

Below floor plates in machinery Increased danger of liquid N/A N/A * * IP44
spaces and/or mechanical damage
Authorized Personnel Only

Below floor plates in machinery N/A N/A * N/A IP44

spaces

Ballast pump rooms Increased danger of liquid IP44 N/A IP44 IP44 IP44
Authorized Personnel Only and mechanical damage

Ballast pump rooms IP44 N/A IP44 IP44 IP44

Holds for general cargo Danger of liquid spray * * * * IP55

presence of cargo dust,
serious mechanical damage,
and/or aggressive fumes

Open decks (2) Not exposed to seas N/A IP56 IP56 IP56 IP56
(2)
Open decks Exposed to seas N/A N/A * * *

“*” indicates that equipment in excess of 1000V is not normally permitted in these locations

Notes:

1 See 4-3-3/3.1.1 where the equipment is located within areas affected by local fixed pressure water-spraying or
water-mist fire extinguishing systems

2 For High Voltage Shore Connections (HVSC) see the requirements in Part 6, Chapter 4 of the Marine Vessel
Rules
.
3 Where the IP rating of the high voltage electrical equipment has been selected on the basis that it is only
accessible to authorized personnel, the entrance doors to the spaces in which such equipment is located, are to
be marked accordingly.

3 Electric Propulsion System

3.1 General
3.1.1 Application
The following requirements in this Subsection are applicable to the electric propulsion system.
Electric propulsion systems complying with other recognized standards will also be considered,
provided it can be shown, through either satisfactory service experience or a systematic analysis
based on sound engineering principles, to meet the overall safety standards of these Rules. Unless

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 223
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

stated otherwise, electric propulsion equipment and systems are to comply with the applicable
requirements in other parts of Part 4, Chapter 3, as well.

3.1.2 Plans and Data to be Submitted

In addition to the plans and data to be submitted in accordance with 4-3-2/1, 4-3-3/1, and 6-1-7/3,
the following plans and data are to be submitted for review.

● One line diagrams of propulsion control system for power supply, circuit protection, alarm,
monitoring, safety and emergency shutdown systems, including list of alarm and monitoring
points.
● Plans showing the location of propulsion controls and its monitoring stations.
● Arrangements and details of the propulsion control console or panel including schematic
diagram of the system therein.
● Arrangements and details of electric coupling.
● Arrangements and details of the semiconductor converters enclosure for propulsion system
including data for semiconductor converter, cooling system with its interlocking arrangement.

3.3 System Design

3.3.1 General
For the purposes of the electric propulsion system requirements, an electric propulsion system is
one in which the main propulsion of the unit is provided by at least one electric motor. A unit may
have more than one electrical propulsion system.

An integrated electric propulsion system is a system where a common set of generators supply
power to the unit service loads as well as the propulsion loads.

In the case of an integrated electrical propulsion system the electrical drive train is considered to
consist of the equipment connected to the electrical network such as a drive (frequency converter)
and the propulsion motor(s).

All electrical equipment that is part of the electric propulsion drive train is to be built with
redundancy such that a single failure will not completely disable the propulsion of the unit. Where
electric motors are to provide the sole means of propulsion for a unit, a single propulsion motor
with dual windings does not meet this requirement.

3.3.2 Generating Capacity

For units with an integrated electric propulsion system, under normal sea-going conditions, when
one generator is out of service, the remaining generator capacity is to be sufficient to carry all of
the loads for unit services (essential services, normal services and for minimum comfortable
conditions of habitability) and the propulsion loads to provide for a speed of not less than 7 knots
or one half of the design speed, whichever is the lesser.

3.3.3 Power Management System

For unit with an integrated electric propulsion system, a power management system is to be
provided. The power management system is to be designed to control load sharing between
generators, prevent blackouts, maintain power to the essential service loads and maintain power to
the propulsion loads.

The system is to account for the following operating scenarios.

● All generators in operation, then the loss of one generator

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 224
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

● When at least one generator is not in operation and there is an increase in the propulsion
loads, or a loss of one of the generators, that would result in the need to start a generator that
was not in operation.
● Upon failure of the power management system, there is to be no change in the available
electrical power. Failure of the power management system is to be alarmed at a manned
control station.

Further, the system is to prevent overloading the generators, by reducing the propulsion load or
load shedding of non-essential loads. The system is to limit power to the propulsion loads to
maintain power to the vessel’s essential service loads. However, the system is to shed non-
essential loads to maintain power to the propulsion loads.

An audible and visible alarm is to be installed at each propulsion control location and is to be
activated when the system is limiting the propulsion power in order to maintain power to the other
essential service loads.

3.3.4 Regenerative Power

For systems where regenerative power may be developed, the regenerative power is not to cause
overspeeding of the prime mover or in the system voltage and frequency which exceeds the limits
of 4-3-1/9. See also 6-1-3/3.7.1 and 6-1-3/3.7.5.

3.3.5 Harmonics
A harmonic distortion calculation is to be submitted for review for all unit with electric
propulsion. The calculation is to indicate that the harmonic distortion levels at all locations
throughout the power distribution system (main generation switchboard, downstream power
distribution switchboards, etc.) are within the limits of 4-3-2/7.9. The harmonic distortion levels at
dedicated propulsion buses are also to be within the limits of 4-3-2/7.9, otherwise documentation
from the manufacturer is to be submitted indicating that the equipment is designed for operation at
a higher level of distortion.

Where higher values of harmonic distortion are expected, any other possible effects, such as
additional heat losses in machines, network resonances, errors in control and monitoring systems
are to be considered.

Means of monitoring voltage harmonic distortion are to be provided, including alarms at the main
generation switchboard and at continuously manned stations when to notify of an increase in total
or individual harmonic distortion levels above the maximum allowable levels.

Harmonic filters, if used, are to comply with requirements mentioned in 4-3-2/9.19.

3.5 Propulsion Power Supply Systems

3.5.1 Propulsion Generators
3.5.1(a) Power Supply.
The power for the propulsion equipment may be derived from a single generator. If a unit main
service generator is also used for propulsion purposes other than for boosting the propulsion
power, such generator and power supply circuits to propulsion systems are also to comply with the
applicable requirements in this subsection. See also 4-3-2/3.1.4.

3.5.1(b) Single System.

If a propulsion system contains only one generator and one motor and cannot be connected to
another propulsion system, more than one exciter set is to be provided for each machine.
However, this is not necessary for self-excited generators or for multi-propeller propulsion units
where any additional exciter set may be common for the unit.

3.5.1(c) Multiple Systems.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 225
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

Systems having two or more propulsion generators, two or more semiconductor converters, or two
or more motors on one propeller shaft are to be so arranged that any unit may be taken out of
service and disconnected electrically without preventing the operation of the remaining units.

3.5.1(d) Excitation Systems.

Arrangements for electric propulsion generators are to be such that propulsion can be maintained
in case of failure of an excitation system or failure of a power supply for an excitation system.
Propulsion may be at reduced power under such conditions where two or more propulsion
generators are installed, provided such reduced power is sufficient to provide for a speed of not
less than 7 knots or 1/2 of the design speed, whichever is the lesser.

3.5.1(e) Features for Other Services.

If the propulsion generator is used for purposes other than for propulsion, such as dredging, cargo
oil pumps and other special services, overload protection in the auxiliary circuit and means for
making voltage adjustments are to be provided at the control board. When propulsion alternating-
current generators are used for other services for operation in port, the port excitation control is to
be provided with a device that is to operate just below normal idling speed of the generator to
remove excitation automatically.

3.5.2 Propulsion Excitation

3.5.2(a) Excitation Circuits.
Every exciter set is to be supplied by a separate feeder. Excitation circuits are not to be fitted with
overload circuit-interrupting devices, except those intended to function in connection with the
protection for the propulsion generator. In such cases, the field circuit breaker is to be provided
with a discharge resistor, unless a permanent discharge resistor is provided.

3.5.2(b) Field Circuits.

Field circuits are to be provided with means for suppressing voltage rise when a field switch is
opened. Where fuses are used for excitation circuit protection, they are not to interrupt the field
discharge resistor circuit upon rupturing.

3.5.2(c) Unit’s Service Generator Connection.

Where the excitation supply is obtained from the unit’s service generators, the connection is to be
made to the generator side of the generator circuit breaker with the excitation supply passing
through the overload current device of the breaker.

3.7 Circuit Protection

3.7.1 Setting
Overcurrent protective devices, if any, in the main circuits are to be set sufficiently high so as not
to operate on overcurrents caused by maneuvering or normal operation in heavy seas or in floating
broken ice.

3.7.2 Direct-current (DC) Propulsion Circuits

3.7.2(a) Circuit Protection.
Direct-current propulsion circuits are not to have fuses. Each circuit is to be protected by overload
relays to open the field circuits or by remote-controlled main-circuit interrupting devices.
Provision is to be made for closing circuit breakers promptly after opening.

3.7.2(b) Protection for Reversal of the Rotation.

Where separately driven DC generators are connected electrically in series, means are to be
provided to prevent reversal of the rotation of a generator upon failure of the driving power of its
prime mover.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 226
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

3.7.3 Excitation Circuits

An overload protection is not to be provided for opening of the excitation circuit.

3.7.4 Reduction of Magnetic Fluxes

Means are to be provided for selective tripping or rapid reduction of the magnetic fluxes of the
generators and motors so that overcurrent does not reach values which may endanger the plant.

3.7.5 Direct-current (DC) Propulsion Motors Supplied by Semiconductor Converters

The protection features of the semiconductor converters are to be arranged to avoid a damaging
flashover in the DC propulsion motor. A possible cause of a damaging flashover is the removal of
the field current. The protection features of the semiconductor converters are to take into account
the increase in armature current created by the removal of the field current, due to accidental loss
of the field, or activation of a protection feature intended to protect the field.

To verify compliance with the above, the maximum time-current characteristics that can be
commutated by the motor as well as the time-current characteristics of the protective features of
the semiconductor converters are to be submitted for review. To avoid a damaging flashover, the
maximum time-current characteristics of the motor is to be provided by the motor manufacturer
and is to be used by the semiconductor converter manufacturer to determine the appropriate set
points for the protection features of the semiconductor converters.

3.9 Protection for Earth Leakage

3.9.1 Main Propulsion Circuits
Means for earth leakage detection are to be provided for the main propulsion circuit and be
arranged to operate an alarm upon the occurrence of an earth fault. When the fault current flowing
is liable to cause damage, arrangements for opening the main propulsion circuit are also to be
provided.

3.9.2 Excitation Circuits

Means are to be provided for earth leakage detection in excitation circuits of propulsion machines
rated 500 kW or more, other than in circuits of brushless excitation systems.

3.9.3 Alternating-current (AC) Systems

Alternating-current propulsion circuits are to be provided with an earthing detector alarm or
indicator. If the neutral is earthed for this purpose, the current at full-rated voltage is not to exceed
20 amperes upon a fault to earth in the propulsion system. An unbalance relay is to be provided
which is to open the generator and motor-field circuits upon detection of an unbalanced fault.

3.9.4 Direct-current (DC) Systems

The earthing detector may consist of a voltmeter or lights. Provision is to be made for protection
against severe overloads, excessive currents and electrical faults likely to result in damage to the
plant. Protective equipment is to be capable of being so set as not to operate on the overloads or
overcurrents experienced in a heavy seaway or when maneuvering.

3.11 Electric Propulsion Control

3.11.1 General
Failure of a control signal is not to cause an excessive increase in propeller speed. The reference
value transmitters in the control stations and the control equipment are to be so designed that any
defect in the desired value transmitters or in the cables between the control station and the
propulsion system will not cause a substantial increase in the propeller speed.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 227
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

3.11.2 Automatic and Remote Control Systems

Where two or more control stations are provided outside of the engine room, or where automatic
control of the propulsion machinery is provided, Part 4, Chapter 9 of the Marine Vessel Rules, as
applicable, are to be complied with. See 4-9-1/3 of the Marine Vessel Rules for propulsion class
symbols.

3.11.3 Initiation of Control

The control of the propulsion system can be activated only when the delegated control lever is in
zero position and the system is ready for operation.

3.11.4 Emergency Stop

Each control station is to have an emergency stop device which is independent of the control lever.

3.11.5 Prime Mover Control

Where required by the system of control, means are to be provided at the control assembly for
controlling the prime mover speed and for mechanically tripping the throttle valve.

3.11.6 Control Power Failure

If failure of the power supply occurs in systems with power-aided control (e.g., with electric,
pneumatic or hydraulic aid), it is to be possible to restore control in a short time.

3.11.7 Protection
Arrangements are to be made so that opening of the control system assemblies or compartments
will not cause inadvertent or automatic loss of propulsion. Where steam and oil gauges are
mounted on the main-control assembly, provision is to be made so that the oil will not come in
contact with the energized parts in case of leakage.

3.11.8 Interlocks
All levers for operating contactors, line switches, field switches and similar devices are to be
interlocked to prevent their improper operation. Interlocks are to be provided with the field lever
to prevent the opening of any main circuits without first reducing the field excitation to zero,
except that when the generators simultaneously supply power to an auxiliary load apart from the
propulsion, the field excitation need only be reduced to a low value.

3.13 Instrumentation at the Control Station

3.13.1 Indication, Display and Alarms
Instruments to continuously indicate existing conditions are to be provided and mounted on the
control panel convenient to the operating levers and switches. Instruments and other devices
mounted on the switchboard are to be labeled and the instruments provided with a distinguishing
mark to indicate full-load conditions. Metallic cases of all permanently installed instruments are to
be permanently earthed. The following instruments, where applicable, are to be provided.

3.13.1(a) For AC Systems.

Ammeter, voltmeter, indicating wattmeter, and field ammeter* for each propulsion generator and
for each synchronous motor.

3.13.1(b) For DC Systems.

An ammeter for each main circuit and one or more voltmeters with selector switches for reading
voltage on each propulsion generator and motor.

3.13.1(c) For Electric Slip Couplings.

An ammeter for the coupling excitation circuit.

* Field ammeter is not required for brushless generators.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 228
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

3.13.2 Indication of Propulsion System Status

The control stations of the propulsion systems are to have at least the following indications for
each propeller.

3.13.2(a) "Ready for Operation".

Power circuits and necessary auxiliaries are in operation.

3.13.2(b) "Faulty".
Propeller is not controllable.

3.13.2(c) "Power Limitation".

In case of disturbance, for example, in the ventilators for propulsion motors, in the converters,
cooling water supply or load limitation of the generators.

3.15 Equipment Installation and Arrangement

3.15.1 General
The arrangement of bus bars and wiring on the back of propulsion-control assemblies is to be such
that all parts, including the connections, are accessible. All nuts and connections are to be fitted
with locking devices to prevent loosening due to vibration. Clearance and creepage distance are to
be provided between parts of opposite polarity and between live parts and earth to prevent arcing.
See 4-3-1/19, 6-1-7/9.9.6 and 6-1-7/15.3.2(b).

3.15.2 Accessibility and Facilities for Repairs

3.15.2(a) Facility for Supporting.
Facilities are to be provided for supporting the shaft to permit inspection and withdrawal of
bearings.

3.15.2(b) Slip-couplings.
Slip-couplings are to be designed to permit removal as a unit without axial displacement of the
driving and driven shaft, and without removing the poles.

3.15.3 Propulsion Cables

Propulsion cables are not to have splices or joints, except terminal joints, and all cable terminals
are to be sealed against the admission of moisture or air. Similar precautions are to be taken during
installation by sealing all cable ends until the terminals are permanently attached. Cable supports
are to be designed to withstand short-circuited conditions. They are to be spaced less than 915 mm
(36 in.) apart and are to be arranged to prevent chafing of the cable. See 7A-1-5/5.9.1.

3.17 Machinery and Equipment

3.17.1 Certification
For certification requirements of machinery and equipment related to electric propulsion system,
see 6-1-7/17.

3.17.2 Switches
3.17.2(a) General Design.
All switches are to be arranged for manual operation and so designed that they will not open under
ordinary shock or vibration. Contactors, however, may be operated pneumatically, by solenoids or
other means in addition to the manual method which is to be provided, unless otherwise approved.

3.17.2(b) Generator and Motor Switches.

Switches for generators and motors are preferably to be of the air-break type, but for alternating-
current systems where they are to be designed to open full-load current at full voltage, oil-break
switches using nonflammable liquid may be used if provided with leak-proof, non-spilling tanks.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 229
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

3.17.2(c) Field Switches.

Where necessary, field switches are to be arranged for discharge resistors unless discharge
resistors are permanently connected across the field. For alternating-current systems, means are to
be provided for de-energizing the excitation circuits by the unbalance relay and earth relay.

3.17.3 Cooling Systems for Machinery and Equipment

3.17.3(a) Air Coolers.
For requirements covering air cooling systems of propulsion generators and motors, see
6-1-7/17.3.1(c).

3.17.3(b) Forced Cooling.

For requirements covering forced ventilation or forced water cooling of semiconductor converters,
see 6-1-7/12.5.8.

5 Three-wire Dual-voltage DC System

5.1 Three-wire DC Unit’s Generators

Separate circuit-breaker poles are to be provided for the positive, negative, neutral and also for the
equalizer leads unless protection is provided by the main poles. When equalizer poles are provided for the
three-wire generators, the overload trips are to be of the algebraic type. No overload trip is to be provided
for the neutral pole, but it is to operate simultaneously with the main poles. A neutral overcurrent relay and
alarm system is to be provided and set to function at a current value equal to the neutral rating.

5.3 Neutral Earthing

5.3.1 Main Switchboard
The neutral of three-wire dual-voltage direct-current systems is to be solidly earthed at the
generator switchboard with a zero-center ammeter in the earthing connection. The zero-center
ammeter is to have a full-scale reading of 150% of the neutral-current rating of the largest
generator and be marked to indicate the polarity of earth. The earth connection is to be made in
such a manner that it will not prevent checking the insulation resistance of the generator to earth
before the generator is connected to the bus. The neutrals of three-wire DC emergency power
systems are to be earthed at all times when they are supplied from the emergency generator or
storage battery. The earthed neutral conductor of a three-wire feeder is to be provided with a
means for disconnecting and is to be arranged so that the earthed conductor cannot be opened
without simultaneously opening the unearthed conductors.

5.3.2 Emergency Switchboard

No direct earth connection is to be provided at the emergency switchboard. The neutral bus or
buses are to be solidly and permanently connected to the neutral bus of the main switchboard. No
interrupting device is to be provided in the neutral conductor of the bus-tie feeder connecting the
two switchboards.

5.5 Size of Neutral Conductor

The capacity of the neutral conductor of a dual-voltage feeder is to be 100% of the capacity of the
unearthed conductors.

7 Emergency Shutdown Arrangements

The following requirements are applicable to drilling units, or units operating next to drilling units or units
producing hydrocarbons.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 230
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

7.1 Emergency Shutdown Facilities

Arrangements are to be provided for the disconnection or shutdown, either selectively or simultaneously,
of all electrical equipment and devices, including the emergency generator, except for the services listed
under 4-3-5/7.1.4 from the emergency control station (see 8-2-1/17.5). Initiating of the above shutdowns
may vary according to the nature of the emergency. A recommended sequence of shut-downs is to be
provided in the unit’s operating manual.

Risks associated with technical faults and inadvertent operations of the emergency shutdown. Each unit is
to develop a detailed plan for recovery and restoration of operation after operation of each level of ESD.

ESD Stations that can enable a total unit shutdown are to be located at normally manned locations under
normal operations except in the backup DP Control Station. Where ESD stations are provided at the
lifeboat stations or other unmanned locations, the total unit ESD (complete shutdown) is to be protected
from unauthorized personnel or not available at these unmanned locations.

7.1.1 Functional Design Basis Document (FDS)

The ESD FDS Operation Manual is to define the ESD levels and provide a list of equipment or
areas that are affected by the different ESD levels. Also, this is to indicate which ESD levels are
available at each ESD station. Further, the manual is to provide instructions on to reset the affected
systems after each ESD.

The ESD FDS is to provide guidance describing the typical scenarios that the ESD levels are to be
used and who has access to use them.

The ESD FDS is to be included or referenced in the unit’s operating manual.

7.1.2 Gas Detection / ESD System Cause and Effect Chart

Where shutdown groups are initiated automatically upon gas detection, a Gas Detection / ESD
System Cause and Effect Chart is to relate gas detection sensors to ESD shutdown groups of
equipment and areas on the unit.

7.1.3 Machinery Associated with Dynamic Positioning System

In the case of units using dynamic positioning systems, disconnection or shutdown of machinery
and equipment necessary for maintaining the operability of the dynamic positioning system is to
be based on a shutdown logic system designed to preserve the capability to maintain operational
control over the integrity of the well and station keeping capability. Shutdown of generators and
related power supply equipment needed for the operation of the dynamic positioning system is to
be divided into independent groups to allow response to gas detection alarms while maintaining
position keeping and protecting the integrity of the well. Also, please see 10/3.9 of the ABS Guide
for Dynamic Positioning Systems for additional requirements.

7.1.4 Operation After Shutdown

The following services are to be operable after an emergency shutdown:

i) Emergency lighting for locations listed in 4-3-2/5.3.1 for half an hour

ii) General alarm
iii) Blow-out preventer control system
iv) Public address system
v) Distress and safety radiocommunications

All equipment in exterior locations which is capable of operation after shutdown is to be suitable
for installation in Zone 2 locations.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 231
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 5 Specialized Installations 4-3-5

9 Energy Storage Systems

9.1 Lithium-ion Batteries

For units provided with lithium-ion batteries, see the requirements in the ABS Requirements for Use of
Lithium-ion Batteries in the Marine and Offshore Industries.

9.3 Supercapacitors
For units provided with supercapacitors, see the requirements in the ABS Requirements for
Supercapacitors in the Marine and Offshore Industries.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 232
 PART 4
CHAPTER 3
Electrical Installations

SECTION 6
Hazardous Areas

1 Objective

1.1 Goals
The electrical equipment covered in this section is to be designed, constructed, operated, and maintained
to:

Goal No. Goal

FIR 1 prevent the occurrence of fire and explosion.

FIR 2 reduce the risk to life caused by fire.

FIR 3 reduce the risk of damage caused by fire to the Unit, its cargo and the environment.

SAFE 1.1 minimize danger to persons on board, the Unit, and surrounding equipment/installations from
hazards associated with machinery and systems.

Materials are to be suitable for the intended application in accordance with the following goals and support
the Tier 1 goals as listed above.

Goal No. Goal

MAT 1 The selected materials’ physical, mechanical and chemical properties are to meet the design
requirements appropriate for the application, operating conditions and environment.

The goals in the cross-referenced Rules/Standards are also to be met.

1.2 Functional Requirements

In order to achieve the above-stated goals, the design, construction, and maintenance of electrical
installations to which this Section applies are to be in accordance with the following functional
requirements:

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 233
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 6 Hazardous Areas 4-3-6

Functional Functonal Requirements

Requirement No.

Materials (MAT)

MAT-FR1 (FIR) Electrical equipment and cables installed in hazardous areas are to be suitable for the environment
(gas group and temperature classification) in which they operate.

Fire Safety (FIR)

FIR-FR1 Classification of hazardous areas according to the likelihood of the presence of an explosive gas
atmosphere to prevent explosions and maintain safe operation of the unit.

FIR-FR2 Provide arrangements to allow an enclosed space to be classified as a less hazardous zone or non-
hazardous area with corresponding electrical equipment or ignition sources, where the enclosed
space is designed with direct access to a more hazardous zone location due to operational reasons.

FIR-FR3 For spaces protected by pressurization, protective measures are to be provided in the event of the
loss of pressurization to prevent fire and explosion risks..

FIR-FR4 Provide means to maintain the gastight integrity of hazardous area boundaries to prevent spread of
flammable gas or vapor.

FIR-FR5 Provide protective measures to prevent the cross-contamination of flammable gases or vapor
through ventilation systems.

FIR-FR6 Ignition sources are to be separated from combustible materials and flammable liquids or vapors.

Safety of Personnel (SAFE)

SAFE-FR1 (FIR) Electrical and machinery installations in hazardous areas are to be restricted to minimize the
potential risks that may affect the safety of the ship, persons on board and equipment.

The functional requirements covered in the cross-referenced Rules/Standards are also to be met.

1.3 Compliance
A unit is considered to comply with the Goals and Functional requirements when the applicable
prescriptive requirements are complied with or when an alternative arrangement has been approved, refer
to Part 1D, Chapter 2.

2 Definitions

2.1 Hazardous Areas

Hazardous areas are all those areas where a flammable atmosphere may be expected to exist continuously
or intermittently. See IEC Publication 60079-10-1. Such flammable atmospheres may arise from drilling or
well test operations, other operations such as use and storage of flammable liquids, paint and acetylene, or
any such operation pertinent to the particular service of the unit. Hazardous areas are subdivided into
Zones 0, 1, 2, defined as follows:

● Zone 0 A zone in which ignitable concentrations of flammable gases or vapors are continuously
present or present for long periods.

● Zone 1 A zone in which ignitable concentrations of flammable gases or vapors are likely to occur
in normal operating conditions.

● Zone 2 A zone in which ignitable concentrations of flammable gases or vapors are not likely to
occur, and if it occurs, it will exist only for a short time.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 234
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 6 Hazardous Areas 4-3-6

2.3 Enclosed Space

An enclosed space is considered to be a space bounded by decks and bulkheads which may or may not
have doors, windows or other similar openings.

2.5 Semi-Enclosed Location

A semi-enclosed location is considered to be a location where natural conditions of ventilation are notably
different from those on open decks due to the presence of structure such as roofs, windbreaks and
bulkheads and which are arranged so that the dispersion of gas may not occur.

2.7 Outdoor Location

An outdoor location is considered to be a location substantially free of structures (or other obstructions)
where natural ventilation is not impeded and causes the rapid dispersion (dilution) of gases and vapors, and
stagnant areas are not present.

3 Plans and Data to be Submitted

The following plans and data are to generally be submitted electronically to ABS for review.

● Arrangement plans clearly indicating the hazardous areas

● A description of the ventilating system for all hazardous areas
● Complete particulars of the ventilating system including capacities of fans, number of complete
changes of air per minute, air flows, areas subject to positive and negative pressure, and location and
direction of opening of self-closing doors

5 Classification of Areas (Non-Drilling and Production Related)

The following hazardous areas are defined for offshore units. In addition, hazardous area classifications for
specific unit types and operations are defined in Part 8, e.g. 8-2-1/9 for classification of area associated
with drilling activities.

5.1 Hazardous Areas Zone 0 Include:

i) Internal spaces of closed tanks and piping or oil [closed-cup flash point below 60°C (140°F)] or
flammable gas and vapor.
ii) Outdoor location within 0.5 m (1.65 ft) from an opening to the hazardous areas defined in
4-3-6/5.1.i, such as a tank vent.

5.3 Hazardous Areas Zone 1 Include:

i) Enclosed spaces containing tanks and pipes described in 4-3-6/5.1.i;
ii) Enclosed spaces containing liquid or solid substances that are likely to emit flammable gases or
vapors;
iii) An enclosed space or semi-enclosed location:

● Having a direct access or opening into the hazardous areas defined in 4-3-6/5.3.i or
4-3-6/5.3.ii or other Zone 1 areas, through a door, a ventilation opening, etc.;
● Immediately adjacent to the closed tanks defined in 4-3-6/5.1.i; or
● Containing pumps or piping used for conveying liquid described in 4-3-6/5.1.i, except for all-
welded or continuous closed piping systems without valves, flanges or similar devices;
iv) Outdoor location within 1 m (3.3 ft) beyond the Zone 0 area defined in 4-3-6/5.1.ii;
v) Outdoor location within 1.5 m (5 ft) from an opening to the hazardous areas defined in 4-3-6/5.3.i,
4-3-6/5.3.ii. or 4-3-6/5.3.iii., such as a door, a ventilation opening, a tank vent, etc.;

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 235
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 6 Hazardous Areas 4-3-6

vi) Outdoor or semi-enclosed locations within 1.5 m (5 ft) from any equipment, container, etc.,
stowed in a designated open deck area, that are likely to emit flammable gases or vapors. An area
of open deck may be a designated Zone 1 hazardous area for the future stowage of this type of
products with a height of 1.5 m (5 ft) above the estimated maximum height of the equipment,
container, etc. to be stowed. Equipment, containers, etc., that can generate a Zone 1 hazardous
area, may be located within the designated Zone 1 hazardous area;

5.5 Hazardous Areas Zone 2 Include:

i) Outdoor location within 3 m (10 ft) from the boundaries of the closed tanks defined in 4-3-6/5.1.i;
ii) Outdoor location within 1.5 m (5 ft) from pumps or piping used for conveying liquid described in
4-3-6/5.1.i, except for all-welded or continuous closed piping systems without valves, flanges or
similar devices;
iii) Outdoor location within 1.5 m (5 ft) beyond the Zone 1 areas defined in 4-3-6/5.3.iv and
4-3-6/5.3.v.;
iv) Outdoor or semi-enclosed location within 1.5 m (5 ft) beyond the Zone 1 areas defined in
4-3-6/5.3.vi. An area of the open deck may be a designated Zone 2 hazardous area. Equipment,
containers, etc. that can generate a Zone 2 hazardous area, may be located within the designated
Zone 2 hazardous area;
v) Air lock spaces between Zone 1 and non-hazardous space, in accordance with 4-3-6/7.5.1.i

6 Classification of Miscellaneous Areas

6.1 Paint Stores

i) Hazardous Areas Zone 1:

● The interior of the paint store;

● Outdoor or semi-enclosed locations within 0.5 m (1.65 ft) from the boundaries of the
ventilation inlet and natural ventilation outlet;
● Outdoor or semi-enclosed locations within 1.5 m (5 ft) from the boundaries of the power
ventilation outlet.
ii) Hazardous Areas Zone 2:

● Outdoor or semi-enclosed locations within 0.5 m (1.65 ft) beyond the Zone 1 area from the
ventilation inlet and natural ventilation outlet;
● Outdoor or semi-enclosed locations within 1.5 m (5 ft) beyond the Zone 1 area from the
power ventilation outlet.

See also 4-3-3/9.5.

6.3 Battery Rooms

i) Hazardous Areas Zone 1:

● The interior of the battery room;

● Outdoor or semi-enclosed locations within 0.5 m (1.65 ft) from the boundaries of the natural
ventilation outlet;
● Outdoor or semi-enclosed locations within 1.5 m (5 ft) from the boundaries of the power
ventilation outlet.
ii) Hazardous Areas Zone 2:

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 236
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 6 Hazardous Areas 4-3-6

● Outdoor or semi-enclosed locations within 0.5 m (1.65 ft) beyond the Zone 1 area from the
natural ventilation outlet;
● Outdoor or semi-enclosed locations within 1.5 m (5 ft) beyond the Zone 1 area from the
power ventilation outlet.

See also 4-3-3/3.7.

6.5 Helicopter Refueling Facilities

i) Hazardous Areas Zone 1:

● Enclosed space containing components of the refueling pump/equipment;

● Outdoor or semi-enclosed locations within 1.5 m (5 ft) from the boundaries of the ventilation
outlet of enclosed space containing refueling pump/equipment;
● Outdoor or semi-enclosed locations within 1.5 m (5 ft) from the boundaries of the tank vent
outlet;
● Outdoor or semi-enclosed locations within 1.5 m (5 ft) from the boundaries of the refueling
pump/equipment.
ii) Hazardous Areas Zone 2:

● Outdoor or semi-enclosed locations within 1.5 m (5 ft) beyond the Zone 1 area from the
ventilation outlet of enclosed space containing refueling pump/equipment;
● Outdoor or semi-enclosed locations within 1.5 m (5 ft) beyond the Zone 1 area from the tank
vent outlet;
● Outdoor or semi-enclosed locations within 1.5 m (5 ft) beyond the Zone 1 area from the
refueling pump/equipment.

See also 4-2-6/7.1.2.

6.7 Oxygen-acetylene Storage Rooms

i) Hazardous Areas Zone 1:

● The interior of the storage room;

● Outdoor or semi-enclosed locations within 0.5 m (1.65 ft) from the boundaries of natural
ventilation outlet;
● Outdoor and semi-enclosed locations within 1.5 m (5 ft) from the boundaries of power
ventilation outlet.
ii) Hazardous Areas Zone 2:

● Outdoor or semi-enclosed locations within 0.5 m (1.65 ft) beyond the Zone 1 area from the
natural ventilation outlet;
● Outdoor or semi-enclosed locations within 1.5 m (5 ft) beyond the Zone 1 area from the
power ventilation outlet.

See also 4-2-6/5.3.

7 Openings, Access, and Ventilation Conditions Affecting the Extent

of Hazardous Zones
Except for operational reasons, access doors or other openings are not to be provided between a non-
hazardous space and a hazardous zone, nor between a Zone 2 space and a Zone 1 space.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 237
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 6 Hazardous Areas 4-3-6

Where such access doors or other openings are provided, any enclosed pace not referred to under 4-3-6/5.3
or 4-3-6/5.5 and having a direct access to any Zone 1 location or Zone 2 location becomes the same zone
as the location, except that:

7.1 Enclosed Space with Direct Access to any Zone 1 Location

An enclosed space with direct access to any Zone 1 location is considered as Zone 2, provided: (see also
4-3-6/7 FIGURE 1):

i) The access is fitted with a self-closing gas-tight door opening into the Zone 2 space,
ii) Ventilation is such that the air flow with the door open is from the Zone 2 space into the Zone 1
location, and
iii) Loss of ventilation is alarmed at a normally manned station;

FIGURE 1
Hazardous Zones

7.3 Enclosed Space with Direct Access to any Zone 2 Location

An enclosed space with direct access to any Zone 2 location is not considered hazardous, provided (see
also 4-3-6/7 FIGURE 2):

i) The access is fitted with self-closing gas-tight door that opens into the non-hazardous space,

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 238
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 6 Hazardous Areas 4-3-6

ii) Ventilation is such that the air flow with the door open is from the non-hazardous space into the
Zone 2 locations, and
iii) Loss of ventilation is alarmed at a normally manned station.

FIGURE 2
Hazardous Zones

7.5 Enclosed Space with Access to any Zone 1 Location

An enclosed space with access to any Zone 1 location is not considered hazardous, provided the access is
through either arrangement described below (see also 4-3-6/7 FIGURE 3):

7.5.1 Air Lock

i) The access is fitted with two self-closing doors forming an air lock, which open toward
the non-hazardous space and has no hold-back devices,
ii) The doors are to be spaced apart at least a distance that prevents an individual from
opening both doors simultaneously. A notice is to be affixed to each side of each door to
the effect that only one door is to be open at a time.
iii) An audible and visual alarm system to give a warning on both sides of the air lock is
provided to indicate if more than one door is moved from the closed position,
iv) Ventilation is such that the non-hazardous space has ventilation overpressure greater than
25 Pa (0.25 mbar) in relation to the Zone 1 location,

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 239
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 6 Hazardous Areas 4-3-6

v) The air lock space has independent mechanical ventilation from a gas-safe area such that,
with any of the air lock doors open, the air flow is from the less hazardous space to the
more hazardous space or area,
vi) The air lock space is fitted with gas detection, and
vii) Loss of ventilation overpressure is alarmed at a normally manned station.
7.5.2 Single Door
i) The access is fitted with a single self-closing, gas-tight door which opens toward the
nonhazardous space and has no hold-back device,
ii) Ventilation is such that the air flow with the door open is from the non-hazardous space
into the Zone 1 location with over-pressure greater than 25 Pa (i.e., non-hazardous space
has ventilation overpressure greater than 25 Pa (0.25 mbar) in relation to the Zone 1
location), and
iii) Loss of ventilation overpressure is alarmed at a normally manned station.

FIGURE 3
Hazardous Zones

7.7 Ventilation Alarms

The alarms to indicate failure of the mechanical ventilation as required by 4-3-6/7.1.iii and 4-3-6/7.3.iii are
to provide audible and visual signals at the designated normally manned station. The initiation of these
alarms by a fan motor running or fan rotation monitoring device is not acceptable.

The alarms to indicate loss of ventilation overpressure as required by 4-3-6/7.5.1.vii and 4-3-6/7.5.2.iii are
to be set to a minimum overpressure of 25 Pa (0.25 mbar) with respect to the adjacent Zone 1 location. A
differential pressure monitoring device or a flow monitoring device may be used for the initiation of the
alarm. When a flow monitoring device is used and a single self-closing gas-tight door is fitted, the
minimum overpressure is to be maintained with the door fully open without setting off the alarm, or
alternatively, an alarm is to be given if the door is not closed. The initiation by a fan motor running or fan
rotation monitoring device is not acceptable.

7.9 Hold-back Devices

Hold-back devices are not to be used on self-closing gas-tight doors forming hazardous area boundaries.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 240
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 6 Hazardous Areas 4-3-6

9 Ventilation

9.1 General
Attention is to be given to ventilation inlet and outlet locations and airflow in order to minimize the
possibility of cross contamination. Ventilation inlets are to be located in non-hazardous areas and as far as
practicable from the boundaries of any hazardous area, but to a distance not less than 1.5 m (5 ft).
Ventilation for hazardous areas is to be completely separate from that for non-hazardous areas.

9.3 Ventilation of Hazardous Areas

Enclosed hazardous spaces are to be provided with adequate ventilation so as to dilute a possible release of
flammable gas or vapor in them and to maintain them at a lower pressure than adjacent less hazardous
spaces or areas. Refer to 4-3-6/7 for adjacent spaces not separated by gastight boundaries. The arrangement
of ventilation inlet and outlet openings in the space is to be such that the entire space is efficiently
ventilated, giving special consideration to location of equipment which may release gas and to spaces
where gas may accumulate.

The outlet air from Zone 0, Zone 1 and Zone 2 spaces is to be led in separate ducts to outdoor locations
which in the absence of the considered outlet are of the same or lesser hazard than the ventilated space.
The internal spaces of such ducts are the same Zone as the inlet space. Ventilation ducts for hazardous
areas are to be at under pressure in relation to less hazardous areas and at overpressure in relation to more
hazardous areas, when passing through such areas, and are to be rigidly constructed to avoid air leaks.

Fans are to be of non-sparking construction, in accordance with 4-3-3/9.7.

9.5 Ventilation of Non-hazardous Areas

Enclosed non-hazardous spaces adjacent to hazardous spaces or areas are to be provided with adequate
ventilation so as to maintain them at a higher pressure than adjacent hazardous spaces or areas. Refer to
4-3-6/7 for adjacent spaces not separated by gastight boundaries. Ventilation inlets and outlets for non-
hazardous spaces are to be located in non-hazardous areas. See 4-3-6/9.1. Where passing through
hazardous areas, ducts are to have overpressure in relation to the hazardous area.

11 Machinery Installations in Hazardous Areas

Electrical equipment and wiring in hazardous areas are to be in accordance with 4-3-3/9.

Internal combustion engines are not to be installed in Zone 0 hazardous areas. When essential for
operational purposes, internal combustion engines may be installed in Zone 1 and 2 hazardous areas. Such
installations are subject to ABS technical assessment and approval.

The installation of steam generators/boilers may be permitted in zone 2 hazardous areas, provided that
sufficient precaution has been taken against the risk of dangerous ignition.

● The steam generator/boiler is to be installed in a suitable enclosure and has ventilation overpressure in
relation to the Zone 2 location during operation. The pressurization of the enclosure is to be monitored
by a pressure differential switch.
● The pressurization fan is to meet requirements of 4-3-3/9.3.3.
● The inlet and outlets of the enclosure are to be provided with gas tight dampers.
● The enclosure is to be provided with self-closing gas tight doors. Hold-back devices are not to be used.

The loss of ventilation overpressure is to be alarmed at a normally manned station and is to initiate
automatic shutdown of the equipment, pressurization fans and closing of gas tight dampers.

Exhaust outlets of internal combustion engines and boilers are to discharge outside of all hazardous areas.
Air intakes are to be not less than 3 m (10 ft) from hazardous areas. Exhaust outlets of internal combustion

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 241
Part 4 Machinery and Systems
Chapter 3 Electrical Installations
Section 6 Hazardous Areas 4-3-6

engines are to be fitted with suitable spark-arresting devices, and exhaust piping insulation is to be
protected against possible oil absorption in areas or spaces where the exhausting piping is exposed to oil or
oil vapors.

ABS RULES FOR BUILDING AND CLASSING OFFSHORE UNITS • 2025 242