Fuses

Selective Coordination

The Association of Electrical Equipment and Medical Imaging Manufacturers

 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Scope
This presentation provides information
for proper application of fuses when
selective coordination is either desired
for design or required by code

2
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Goals
• Understand key terms related to selective coordination

• Understand where selective coordination is required by Code and

where it can be a design goal

• Discern the difference between a “selectively coordinated” system

and a “coordinated” system

• Understand the impact of fault current to selective coordination

• Determine how to achieve selective coordination with fuses

3
Selective Coordination
A Design Goal

The Association of Electrical Equipment and Medical Imaging Manufacturers

 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Benefits of selective coordination

• Minimize risk of power loss to life safety systems, such as
emergency lighting, fire detection, elevators, and others.

• Minimize risk of costly downtime, such as is necessary for

IT equipment or continuous process manufacturing
operations.

• Faster location and resolution of fault on the system due to

isolation (closes OCPD to the fault opens)

5
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Life Safety Requirements

• Power is Important For Life Safety
• Lights
• Fire Pumps
• HVAC
• Security
• Communications
• Visual and Audible Signaling

Reliable Power Systems Are Important For Life Safety

6
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Continuity of Service
• Power is Important For Continuity of Service
▪ Computers
▪ Manufacturing Equipment
▪ Data Storage Systems
▪ Office General Lighting
▪ Broadcast Equipment
▪ Meeting Room Essentials

Reliable Power Systems Are Important

For Business Profitability
7
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

The Design Goal

Reliability in Refining and Petrochem facilities

• Unplanned outages can cost $M in lost production, lost

productivity, damaged equipment.
▪ Average downtime cost $704,000 USD per hour.

A 100 MW petro-chemical plant produces approximately $2 billion per year in revenues

– or $228,000 per hour. With an average of 8 hours of downtime per year, an average
100 MW plant will lose over $1.8 million in revenue annually to electrical system
outages
8
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Grocery Store Value Proposition

• Florida's largest supermarket chain has created its own initiative to
make sure its stores can open after a hurricane. Publix is spending
$100 million to install 500 kilowatt generators at every store in
hurricane prone areas.

• In 2004 alone, Publix lost $60 million from groceries that went bad
after hurricanes knocked out power to its stores.

9
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Grocery Store Value Proposition

• More than 100 South Florida supermarkets now are equipped with
stationary generators large enough to restore them to business as
usual, fresh and frozen food aisles included, during power
outages. Most were installed after Hurricane Wilma hit in 2005.
The storm left residents frustrated by long lines and limited food
selections when dozens of grocery stores had no power for days.

10
 Definitions

The Association of Electrical Equipment and Medical Imaging Manufacturers

 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Definitions
• Fault Current
• Fault Current, Available
• Coordination, Selective (Selective
Coordination)

12
 Definitions
Fault Current

The Association of Electrical Equipment and Medical Imaging Manufacturers

Article 100 Fault Current
• New definition in Article 100 for NEC 2020
• Part of a Correlating Committee taskforce to
address correlation with NFPA 70E recent
changes
• Aligns the use of the terms Short-Circuit
current and available fault current
Article 100 Fault Current
Fault Current
The current delivered at a point on the system
during a short-circuit condition. (CMP-10)
 Definitions
Fault Current, Available
(Available Fault Current)

The Association of Electrical Equipment and Medical Imaging Manufacturers

 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Fault Current, Available (Available Fault Current)

• New definition for NEC 2020
• Replaces “maximum available short-
circuit current” where used in the NEC
• Aligns with NFPA 70E recent changes in
use of the same term
17
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

100 Fault Current, Available

The largest amount of current capable of being
delivered at a point on the system during a
short-circuit condition. (CMP-10)
Informational note: A short-circuit can occur
during abnormal conditions such as a fault
between circuit conductors or a ground-fault.
See Informational Note Figure 100.1
18
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Fault Current, Available (Available Fault Current)

Ac or dc supply source
Source New Diagram
Available fault current
OCPD with an
Available fault current Equipment
Interrupting Rating

OCPD
Available fault current

Equipment with a SCCR

Load
19
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Available Fault Current

• Maximum current is used to evaluate:
▪ Interrupting ratings of OCPDs
▪ SCCR ratings of equipment
▪ Selective Coordination of OCPDs

20
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Available Fault Current

• Rarely occur in power distribution systems
• Commonly associated with first startup
after installation or maintenance activities
▪ Forgetting to remove shipping straps
▪ Forgetting to remove intentional grounding for
maintenance
21
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

110.9 Interrupting Rating

• NEC Requires:
▪ OCPDs interrupt fault current and must have an
interrupting rating, at nominal circuit voltage, equal to
or greater than the current that is available at the line
terminals of the equipment
• Installers and inspectors must ensure the
interrupting rating of the OCPD is greater than
or equal to the available fault current
22
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Fuse applications
• Fuses are capable of 200kA and higher
interrupting ratings
• For systems not capable of delivering
200kA, applying 200kA fuses removes
the need for detailed fault current
calculations for the purpose of
interrupting rating evaluation 23
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

110.10 Circuit Impedance, Short-Circuit Current

Ratings, and Other Characteristics
• NEC Requires:
▪ Equipment must have a short-circuit current
rating (SCCR) equal to or greater than the
current that is available at the line terminals
of the equipment

24
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Short-Circuit Current Rating (SCCR)

• The ability of equipment to withstand magnetic
forces and thermal heating of high fault
currents passing through the equipment until
an OCPD clears the fault
• This is NOT an interrupting rating
• SCCR must be greater than or equal to
maximum fault current
25
 Definitions
Coordination, Selective
(Selective Coordination)

The Association of Electrical Equipment and Medical Imaging Manufacturers

 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination Normal

• Selective coordination has been Source
in the vocabulary of the power
systems engineer for decades
• Goal is to minimize system
outages & increase reliability
• Minimizes system down time
• Fault location on system is more Panel

efficient Closed OCPD

Opened OCPD
De-Energized
27
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Coordination, Selective (Selective Coordination)

“Localization of an overcurrent condition to restrict
outages to the circuit or equipment affected, accomplished
by the selection and installation of overcurrent protective
devices and their ratings or settings for the full range of
available overcurrents, from overload to the maximum
available fault current, and for the full range of overcurrent
protective device opening times associated with those
overcurrents.”

2020 Version NFPA 70, National Electrical Code, Article 100 Definitions
28
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Coordination, Selective (Selective Coordination)

Normal
“Localization of an overcurrent condition Source
to restrict outages to the circuit or
equipment affected. . .”

• The OCPD Closest To The Fault

Opens

• Branch Circuit Fault Opens The

Closest Branch Circuit OCPD Closed OCPD Panel

Opened OCPD
De-Energized 29
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Coordination, Selective (Selective Coordination)

Normal
“Localization of an overcurrent condition Source
to restrict outages to the circuit or
equipment affected. . .”
• The OCPD closest to the fault opens
• Faulted feeder opens the first feeder
OCPD
• Outage to downstream equipment
only Closed OCPD Panel

Opened OCPD
De-Energized 30
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

A lack of selective coordination

Normal
“Localization of an overcurrent condition Source
to restrict outages to the circuit or
equipment affected. . .”

• Multiple OCPDs Open Due To

The Fault

• Wide Spread System Outage Is

Caused Closed OCPD Panel
Opened OCPD
De-Energized 31
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

A lack of selective coordination

• Main OCPD Opens Due To The Normal
Fault Source

• Wide Spread System Outage Is

Caused

• Main OCPDs Have Been Known

To Open Because of A Lack Of
Selective Coordination
Closed OCPD Panel
Opened OCPD
De-Energized 32
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination – Article 100

“Localization of an overcurrent condition to restrict
outages to the circuit or equipment affected, accomplished
by the selection and installation of overcurrent protective
devices and their ratings or settings for the full range of
available overcurrents, from overload to the maximum
available fault current, and for the full range of overcurrent
protective device opening times associated with those
overcurrents.”

2017 Version NFPA 70, National Electrical Code, Article 100 Definitions
33
“As selectivity and maximum safety to personnel are critical, engineers should
always perform a total short-circuit, coordination, and component protection
study for a project. This study first determines the available short-circuit
currents at each major component throughout the system. Then it will include
time vs. current coordination curves to be drawn and to coordinate time
intervals to determine if the overcurrent devices are selectively coordinated at
the various available fault currents. Then the study will examine the component
withstand ratings to ensure that the device can actually protect the components
at the fault current levels that may be present during a fault.”

IEEE Std. 602-2007, “Electric Systems in Health Care Facilities” Page 113

Selective Coordination At Various Available Fault Currents Should Be

Achieved – Life Safety
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

The TCC curve

• The TCC plots time versus
current

Time (Seconds)
• Log-log paper to enable
plotting of trip
characteristics

Current (Amps) 35
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

The TCC curve

• The TCC curve provides
information as to how the fuse
will respond to current 8

• 4,000A flowing through this fuse 2

will open it anywhere between

2 & 8 seconds
4,000 Amps
• Be aware of the scale (Current
in amps X 10)
36
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination A Class J 60A Class J 100A B

• The TCC curve provides information as Isc
B
to how the fuse will respond to current

• 700A flowing through both fuses A

▪ Fuse A maximum clearing time is 0.23 3.0
seconds
▪ Fuse B Minimum melt time is
3.0 seconds 0.23

• These devices are selectively

coordinated at 700A 700A

37
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

TCC curve A Class J 60A Class J 100A B

• 4000A flowing through both Isc

B
fuses
▪ Based on the TCC selective A
coordination is NOT achieved
▪ Fuse ratio tables provide tested data
to determine selectivity

4000A

38
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

TCC curve A Class J 60A Class J 100A B

• Class J fuses must maintain a Isc

B
ratio of 2:1 for selectivity
▪ Ratio of upstream to downstream fuses
A
• This example ratio = 100/60 < 2:1 so
selective coordination is NOT achieved

• Upstream fuse must be 120A or

greater to selectively coordinate for 4000A
ALL fault currents up to 200kA

39
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination - Fuse

• Example system – two Class J fuses
Isc 600A
that must selectively coordinate Class J
300 Amps

Class J
600 Amps
• Fuse curves MAY be plotted
300A

• Maintaining a ratio of 2:1 for these

fuses ensures selective coordination
for all currents up to 200kA
“. . . from overload to the maximum Isc = Amps All
available fault current, and for the full Currents
range of overcurrent protective device
opening times . . .”
40
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination - Fuse

800A
Maintain a 2:1 Ratio for
these Class fuses
400A

100A
800/400 = 2:1 only 2:1 needed
Selective Coordination achieved
Overloads or faults of any level 400/100= 4:1 only 2:1 needed
up to
200,000A Selective Coordination achieved
between these two fuses 41
41
Selective Coordination
NEC Requirements

The Association of Electrical Equipment and Medical Imaging Manufacturers

 The Association of Electrical and
Medical Imaging Equipment Manufacturers

National Electrical Code Requirements

Art Title NEC
100 Definitions 2005

1975 GF
517 Healthcare Facilities 2005 “Selective”
2014 “Coordination”

Elevators, Dumbwaiters, Escalators, Moving Walks, Wheel Chair Lifts, and Stairway Chair
620 1993
Lifts

645 Information Technology Equipment 2014

695 Fire Pumps 2011

700 Emergency Systems 2005

701 Legally Required Standby Systems 2005

708 Critical Operations Power Systems (COPS) 2008 43

 The Association of Electrical and
Medical Imaging Equipment Manufacturers

NFPA 70 NEC 2017 Requirements

Article 517 Health Care Facilities Article 700 Emergency Systems
517.17 Ground-Fault Protection 700.32 Selective Coordination

Article 620 Elevators, Dumbwaiters, Article 701 Legally Required Standby

Escalators, Moving Walks, Platform Lifts, and Systems
Stairway Chairlifts
620.62 Selective Coordination 701.27 Selective Coordination

Article 645 Information Technology Article 708 Critical Operations Power

Equipment Systems (COPS)
645.27 Selective Coordination 708.52 Ground-Fault Protection of Equipment
708.54 Selective Coordination

Article 695 Fire Pumps

695.3 Power Source(s) for Electric Motor-Driven
Fire Pumps.
44
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Article 517 – Health Care Facilities

517.17 Ground-Fault Protection.

(C) Selectivity. Ground-fault protection for operation of the service and feeder
disconnecting means shall be fully selective such that the feeder device, but not the
service device, shall open on ground faults on the load side of the feeder device.
Separation of ground-fault protection time-current characteristics shall conform to
manufacturer’s recommendations and shall consider all required tolerances and
disconnect operating time to achieve 100 percent selectivity.

45
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Article 620 – Elevators, Dumbwaiters, Escalators,

Moving Walks, Platform & Stairway Chairlifts
620.62 Selective Coordination. Where more than one driving machine disconnecting
means is supplied by a single feeder, the overcurrent protective devices in each
disconnecting means shall be selectively coordinated with any other supply side
overcurrent protective devices.

Selective coordination shall be selected by a licensed professional engineer or other

qualified person engaged primarily in the design, installation, or maintenance of
electrical systems. The selection shall be documented and made available to those
authorized to design, install, inspect, maintain, and operate the system.

46
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Article 645 – Modular Data Centers

645.27 Selective Coordination. Critical operations data system(s) overcurrent protective
devices shall be selectively coordinated with all supply-side overcurrent protective
devices.

47
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Article 695 – Fire Pumps

695.3 Power Source(s) for Electric Motor-Driven Fire Pumps. Electric motor-driven fire pumps shall
have a reliable source of power.

(A) Individual Sources. . . .

(B) Multiple Sources. . . .
(C) Multibuilding Campus-Style Complexes.

If the sources in 695.3(A) are not practicable and the installation is part of a multibuilding campus-
style complex, feeder sources shall be permitted if approved by the authority having jurisdiction and
installed in accordance with either (C)(1) and (C)(3) or (C)(2) and (C)(3).
(1) Feeder Sources. . . .
(2) Feeder and Alternate Source. . . .
(3) Selective Coordination. The overcurrent protective device(s) in each disconnecting
means shall be selectively coordinated with any other supply-side overcurrent protective
device(s).
48
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Article 700 – Emergency Systems

700.32 Selective Coordination.

Emergency system(s) overcurrent devices shall be selectively coordinated with all

supply-side overcurrent protective devices.

Selective coordination shall be selected by a licensed professional engineer or other

qualified persons engaged primarily in the design, installation, or maintenance of
electrical systems. The selection shall be documented and made available to those
authorized to design, install, inspect, maintain, and operate the system.

Exception: Selective coordination shall not be required between two overcurrent

devices located in series if no loads are connected in parallel with the downstream
device.

49
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Article 701 – Legally Required Standby Systems

701.27 Selective Coordination.

Legally required standby system(s) overcurrent devices shall be selectively coordinated

with all supply-side overcurrent protective devices.

Selective coordination shall be selected by a licensed professional engineer or other

qualified persons engaged primarily in the design, installation, or maintenance of
electrical systems. The selection shall be documented and made available to those
authorized to design, install, inspect, maintain, and operate the system.

Exception: Selective coordination shall not be required between two overcurrent devices
located in series if no loads are connected in parallel with the downstream device.

50
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Article 708 – Critical Operations Power Systems

708.54 Selective Coordination.

Critical operations power system(s) overcurrent devices shall be selectively coordinated

with all supply-side overcurrent protective devices.

Selective coordination shall be selected by a licensed professional engineer or other

qualified persons engaged primarily in the design, installation, or maintenance of
electrical systems. The selection shall be documented and made available to those
authorized to design, install, inspect, maintain, and operate the system.

Exception: Selective coordination shall not be required between two overcurrent

devices located in series if no loads are connected in parallel with the downstream
device.

51
Selective Coordination
Exceptions

The Association of Electrical Equipment and Medical Imaging Manufacturers

 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination Requirements

“Exception: Selective
coordination shall not be
required between two
A

overcurrent devices located

in series if no loads are B

connected in parallel with

the downstream device.”
53
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination Requirements

Branch devices “A” must
selectively coordinate with
devices “B” and “C”.
C

A
54
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination Requirements

“Exception: Selective
coordination shall not be
required between two
C

overcurrent devices located

in series if no loads are
B
connected in parallel with
the downstream device.” A
55
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

All supply-side overcurrent devices

NEC requirements are consistent in all areas of
the NEC mandating selective coordination that
devices must selectively coordinate with all
supply-side overcurrent protective devices.
NEC 2020 added an informational note to 700.32,
701.32, and 708.54 to clarify what devices must
selectively coordinate
56
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Utility
Selective Coordination
G
Requirements
• 700, 701 and 708 power A E

system overcurrent B F
devices
• OCPDs on Emergency
side of transfer switch C

D
57
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Utility

Selective Coordination G
Requirements
A E

• 700, 701 and 708 power B F

system overcurrent devices

• Devices On The Normal

Power Supply System C

D
58
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination
Utility

G
Requirements
A E
• 700, 701, and 708 OCPDs must selectively
coordinate with all upstream overcurrent
B F
protective devices:
• D must Selectively Coordinate with C,
F, E, B and A
• C must Selectively Coordinate with F,
E, B and A C
• F must selectively Coordinate with E
• OCPDs A and B do not have to selectively
coordinate with each other D
59
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination Utility

G
Requirements
A E
• 700, 701, and 708 OCPDs must selectively
coordinate with all upstream overcurrent
B F
protective devices:
• D must Selectively Coordinate with C,
F, E, B and A
• C must Selectively Coordinate with F,
E, B and A C
• F must selectively Coordinate with E
• OCPDs A and B do not have to selectively
D
coordinate with each other
60
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination Utility

G
Requirements
A E
• 700, 701, and 708 OCPDs must selectively
coordinate with all upstream overcurrent
B
protective devices: F
• D must Selectively Coordinate with C,
F, E, B and A
• C must Selectively Coordinate with F,
E, B and A C
• F must selectively Coordinate with E
• OCPDs A and B do not have to selectively
coordinate with each other D
61
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Selective Coordination Utility

G
Requirements
A
• 700, 701, and 708 OCPDs must selectively E
coordinate with all upstream overcurrent
protective devices: B F
• D must Selectively Coordinate with C,
F, E, B and A
• C must Selectively Coordinate with F,
E, B and A C
• F must selectively Coordinate with E
• OCPDs A and B do not have to selectively
coordinate with each other D
62
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Coordination vs. Selective Coordination

• Selective coordination is not the same as
coordination as required in 517.30(G)

63
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

NEC Article 517 - Coordination

517.30(G) Coordination. Overcurrent protective devices serving the essential electrical system
shall be coordinated for the period of time that a fault’s duration extends beyond 0.1 second.

Exception No. 1: Between transformer primary and secondary overcurrent protective devices,
where only one overcurrent protective device or set of overcurrent protective devices exists on
the transformer secondary.

Exception No. 2: Between overcurrent protective devices of the same size (ampere rating) in
series.

Informational Note: The terms coordination and coordinated as used in this section do not cover
the full range of overcurrent conditions.

64
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Coordination Definition - NEMA

Localization of an overcurrent condition to minimize outages to the
circuit or equipment affected, accomplished by the selection and
installation of overcurrent protective devices and their ratings or
settings, ensuring separation of their time current curves beyond a
specified time period without regard to fault current magnitude or below
a specified level of fault current less than the maximum available fault
current.
https://www.nema.org/Standards/Pages/Selective-Coordination-of-Low-Voltage-Circuit-Breakers.aspx#download

65
Article 517 Coordination

The Association of Electrical Equipment and Medical Imaging Manufacturers

 The Association of Electrical and
Medical Imaging Equipment Manufacturers

NEC Article 517 -

2 1
Coordination
Isc

This TCC Curve 1

Shows A Pair Of fuses

That Both See 2

4,000Amps of Fault
Current 4000A
1 Class J 100A

2 Class RK5 50A

67
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

NEC Article 517 - 2 1

Coordination Isc
“. . . Separation of their time 1
current curves ..”
2
• Separation of time current
curves looks for space
between curves
4000A

• Overlap in this example 1 Class J 100A

illustrates no separation 2 Class RK5 50A

68
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

NEC Article 517 - 2 1

Coordination Isc

“. . . separation of their time current 1

curves beyond a specified time period . .
.”
2

• Separation of curves for times > 0.1

seconds
4000A
• Overlaps for times < 0.1 seconds are
ignored
0.1 Second Tool

69
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

NEC Article 517 -

2 1
Coordination
Isc
“. . . separation of their time current 1
curves beyond a specified time period Coordinated
without regard to fault current magnitude”
2
• Disregard Calculated Maximum Isc
Current

• “Informational Note: The terms 4000A

coordination and coordinated as used

in this section do not cover the full 0.1 Second Tool
range of overcurrent conditions.”
(NEC 2014 change) 70
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

NEC Article 517 -

2 1
Coordination
517.31(G) Coordination. Overcurrent protective devices serving the Isc
essential electrical system shall be coordinated for the period of time 1
that a fault’s duration extends beyond 0.1 second. Coordinated
Exception No. 1: Between transformer primary and secondary
overcurrent protective devices, where only one overcurrent protective 2
device or set of overcurrent protective devices exists on the
transformer secondary.

Exception No. 2: Between overcurrent protective devices of the same

size (ampere rating) in series.
4000A
Informational Note: The terms coordination and coordinated
as used in this section do not cover the full range of
overcurrent conditions. 0.1 Second Tool

71
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

NEC Article 517 - Coordination

• Selectively Coordinated fuses Will exceed
coordination requirements found in Article 517
(0.1 Seconds)
• Coordinated fuses May Not Selectively Coordinate
to maximum available fault current
• Fuses that achieve selective coordination exceed
the performance of a coordinated system
72
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Typical Selective Coordination Process

• Short circuit study

• Equipment Evaluation

• Selective Coordination
Evaluation

73
Selective Coordination -
Specifications

The Association of Electrical Equipment and Medical Imaging Manufacturers

 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Clarity in specifications is important for all involved

• Consultant creates a specification

• Contractors work with distributors and manufacturers

to quote the system seeking value engineering
opportunities that could jeopardize selectivity
• Series rated solutions may selected which
compromises selective coordination goals

Specifications must be clear and specific to ensure what the

consultant expects is what is quoted
75
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Examples of Selective Coordination Spec

Language
A Nationally used specification service

260573 - OVERCURRENT PROTECTIVE DEVICE COORDINATION STUDY

Graphic illustration may or may not provide enough information for selective
coordination.

Need for clear specification language

76
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Examples of Selective Coordination

Spec Language
A Nationally used specification service

Does 0.01 mean “Selective Coordination”? Does this meet NEC definition of selective
coordination? Does this meet design goals?

Need for clear specification language

77
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Examples of Selective Coordination

Spec Language
A Nationally used specification service

Terms 0.1 and “Selective Coordination” contradict one another. More

information is needed to determine if this is an Article 700, 701, 708 or other
type of system requiring selective coordination.

Need for clear specification language

78
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Suggested Specification Language – Selective

Coordination
• Those portions of this design that specify selective coordination, or are
required by the National Electrical Code to selectively coordinate, are
intended to localize the impact of an overcurrent condition thus restricting
outages to the circuit or equipment affected and shall meet the following:

• a. Overcurrent protective devices must selectively coordinate for the full

range of available overcurrents, from overload to the maximum available
fault current, and for the full range of overcurrent protective device
opening times associated with those overcurrents.

• b. A preliminary short-circuit study with available fault currents at each

bus is available from << design engineer firm name here>>
79
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Suggested Specification Language – Selective

Coordination
• Those portions of this design that specify selective coordination, or are
required by the National Electrical Code to selectively coordinate, are
intended to localize the impact of an overcurrent condition thus restricting
outages to the circuit or equipment affected and shall meet the following:

• c. Overcurrent devices shall selectively coordinate with all supply-side

overcurrent protective devices up through the normal source (i.e. utility)
and alternate sources (i.e. generator).
▪ 1. OCPD devices on the emergency side (secondary) of a transfer switch shall selectively
coordinate with all line side OCPD devices up through the normal source.
▪ 2. Standard exceptions identified in the National Electrical Code apply

80
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Suggested Specification Language – Selective

Coordination
• Those portions of this design that specify selective coordination, or are required by the National
Electrical Code to selectively coordinate, are intended to localize the impact of an overcurrent
condition thus restricting outages to the circuit or equipment affected and shall meet the
following:

• d. The OCPD devices on the “Normal” side of the emergency system transfer switch:

• <<SELECT ONLY ONE OF THE FOLLOWING>>

• Are not required to selectively coordinate for this design

(Meets NEC Requirement)
• Ensure separation of trip curves for all times greater than 0.1
seconds and beyond (Exceeds NEC Requirements)
• Selectively coordinate (Exceeds NEC Requirements)
81
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Suggested Specification Language – Selective

Coordination
• Those portions of this design that specify selective coordination, or are
required by the National Electrical Code to selectively coordinate, are
intended to localize the impact of an overcurrent condition thus restricting
outages to the circuit or equipment affected and shall meet the following:

• e. Documentation shall be included in the forms of manufacturer selective

coordination tables and/or Time Current Characteristic (TCC) Curves that
demonstrate selective coordination has been achieved.

• f. The selective coordination study shall be performed by a licensed

professional engineer or other qualified persons engaged primarily in the
design, installation, or maintenance of electrical systems
82
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Achievements – Now we . . .
• Understand key terms related to selective coordination

• Understand where selective coordination is required by Code and

where it can be a design goal

• Discern the difference between a “selectively coordinated” system

and a “coordinated” system

• Understand the impact of fault current to selective coordination

• Determine how to achieve selective coordination with fuses

83
 The Association of Electrical and
Medical Imaging Equipment Manufacturers

Closing Remarks
• Selective Coordination is important for system reliability

• When TCC curves are used plotting fault current is

critical to determining selectivity

• Leverage the fuse ratio tables to ensure selectivity

without impact of changing fault current levels

• Ensure a qualified individual and/or a Professional

Engineer performs the study
84
The Association of Electrical and
Medical Imaging Equipment Manufacturers

Thank you!

Questions?
SOUTHERN REGION MIDWEST REGION
Bryan Holland Tim McClintock
130 Duxbury Ave. 11813 Township Road 516
Port Charlotte, FL 33952 Shreve, OH 44676
Office: (941) 613-6803 Office: (330) 749-9782
Mobile: (972) 358-0543
bryan.holland@nema.org tim.mcclintock@nema.org

NORTHEAST REGION WESTERN REGION

Jack Lyons Mike Stone
12 Ireland St. 676 Robinson Rd.
West Chesterfield, MA 01084 Sebastopol, CA 95472
Office: (413) 296-4399 Office: (707) 878-0042
Mobile: (413) 695-2869 Mobile: (831) 229-0056
jack.lyons@nema.org mike.stone@nema.org 85