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electrical discharges.
2. Several earthing circuits shall be provided as follows:
a. Dirty Earth: this is the circuit ensuring safety in the alternating current distribution
network; all cable armor, instrument housing and electrical equipment support must
be connected to the primary earth ground by means of a suitable cable, bus bar or
earth conductor.
b. Clear Earth: this is the reference point for all electronic signals. All commons (in the
case of a DC supply with a polarity to earth), all instrument cable shields shall be
connected to this earth via the electronic earth circuit. Instruments shields shall be
earthed only at one point.
3. The “Clear Earth” circuitry shall be a dedicated and isolated from the “Dirty Earth” in
order to avoid electronic noise and provided with high frequency chokes.
2.07 INSTRUMENT CABLES, WIRING AND JUNCTION BOXES
A. Instrument cables
1. Cable Requirements
a. The following cables shall be fire resistant cable to meet IEC 60331
i. Cables to Fire Pumps.
ii. Cables for/to Fire Fighting Equipment such as Clean Agent System.
iii. Fire Detection and Notification circuits.
iv. Cables for safety evacuation lighting or electrical signs.
v. Public address systems.
vi. Cables for Gas detection and Gas shutdown system.
b. All other instrument signal and control cables should be flame retardant cables to
meet IEC 60332.
c. Foundation Fieldbus cable shall be in accordance with the requirements for Type A
cable as defined by IEC 61158-2.
d. System Cables should as per manufacturer’s recommendation.
e. Network Cables should be UTP Cat 6 cable as minimum.
f. Fiber optical cables should refer to Section 40 66 33 - Metallic and Fiber-Optic
Communication Cabling and Connectors.
g. Cables shall have design temperature range limits of -30C to +90C.
h. Instrument cables shall have a rated voltage of 300V, low voltage power supply and
control cables a rated voltage of 500V.
i. Isolation materials for Instrument cables can be PVC, Polyethylene or XLPE or as
per manufacturer’s recommendation.
j. Insulation materials shall be resistant to termites and fungus growth.
k. Instrument 230VAC power feeder cables should refer to SECTION 26 05 19.
l. Direct buried cables should be only applicable for Irrigation Water Solenoid Valves,
and should not be permitted with all other applications.
m. For Irrigation System, cables should as per following below:
i. Direct buried, unarmoured, shielded single core irrigation cable are normally
used for irrigation solenoid valves line connection, another separate direct
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buried, unarmoured, single core shielded cables to be used as common
neutrals for all solenoid valves, in this application the neutral cable size should
be minimum 2.5mm and for the line connection, distance between RTU and
solenoid valve less than 600m, 1.5 mm cable will be used. For distance
between RTU and solenoid valve more than 600m, 2.5 mm cable will be used.
ii. Direct buried, unarmoured, shielded pair cores irrigation cable for solenoid
valve will be also acceptable.
iii. Direct buried, armoured, shielded, pair core cables shall be used for other
instruments connections such as electromagnetic flow meter or pressure
transmitters or analyzers etc.
n. Armored cables should be used for directly buried underground routing, otherwise
the Instrument cables must be protected by conduits, duct, cable trays or cable
trenches.
o. Multi-core cables shall be provided with at least 20 percent spare cores.
p. The manufacturer shall provide certificates for tests carried out on cables. Tests
shall be those listed in the relevant standard specification and any additionally
specified within the purchase order.
q. Design / selection of instrument cables should be modulated to standard cores, only
1PR / 2PR / 5PR / 10PR / 20PR / 40PR etc. should be used.
2. Cable Construction
a. The conductor shall be of minimum 0.8 Sq.mm size, high conductivity, multi-
stranded copper tinned as per ASTM B33 & B8 for all types of instrumentation
cables except the thermocouple extension cables which shall be 1.31 mm Sq. solid
alloy type.
b. The cable shall be embossed with marking including:
i. manufacturer's name.
ii. insulation material.
iii. conductor size.
iv. No. of pairs.
v. voltage ratings.
vi. type of cable etc.
vii. Progressive sequential marking of the length of the cable at every one meter &
progressive markings to read FRLS at every 5 Meters.
c. The Instrument cables shall be provided on the outer sheath of all instrumentation
cables. Pairs of cables shall be identified by color coding & color banding.
d. Fillers in multiple conductor cables shall be flame retardant and moisture resistant.
Cable accessories such as harnessing components, markers, bedding, cable
jointer, binding tape etc. shall also have flame retardant quality.
e. The color of outer sheath shall be a unique color so that C&I cables are easily
distinguished from other cables.
f. All instrumentation cables shall be provided with overall shielding. However multi-
pair cables carrying 4-20mA analogue signals shall be provided with individual pair
shielding in addition to overall shielding. Separate drain wires for individual pair
shield (wherever applicable) as well as overall shield shall be provided.
g. For binary signals carry free contact or 24VDC, only overall shielding with drain wire
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is required.
h. Drain wire shall be of seven (7) strand 0.5 Sq.mm tin coated copper conductor.
i. All instrumentation cables shall be suitable for continuous operation at 90 C.
except for high temperature resistant Teflon insulated cables which shall be suitable
for continuous operation at 205 C. The cables shall be suitable for laying in wet or
dry locations in trays, conduits, ducts, trenches and underground buried
installations.
j. Teflon Cable (205 C /600 V)
i. All cables near high temperature zone like generator engine metal
temperature, RTDs on motor bearings and casing etc. shall be high temp.
cables (205 C /600),which shall be terminated at a junction box in the normal
temperature location.
k. Identification of the cores & pairs shall be done with suitable colour coding & band
marking as well as by numbering of cores/ pairs as per RC guidelines. The details
of color coding etc. shall be as approved by the RC during detailed stage.
3. Cable Installation
a. Instrument cable shall be separate from power cables by following distances:
i. For 6.6 KV to 33KV above - 1000mm
ii. For 380V to 415V - 600mm
iii. For 120V ~ 240V - 300mm
iv. The above figures apply to parallel runs of cable. For crossover a minimum of
300 mm separation distance will be permitted on all applications.
b. Cable trays, duct, trench or conduits dimensions shall be adequate to
accommodate 30% spare cables.
c. Cable armour shall be continuous between field and home run cables at the
junction box.
d. Cable screens and drain wires shall be open at the field end with continuity between
field and home run cables being provided by screen terminals, or insulated earth
bars.
e. Screens and drain wires shall be earthed at the control panel or outstation by
means of an earth bar. The earth bar shall be isolated from the panel or outstation
and connected to the instrument “Clean earth” system.
f. All connections and terminations shall be made on terminals. Splicing of cables is
not permitted.
g. All instrument cables and wiring shall be provided with core identification ferrules.
All cables shall have plasticized PVC cable label /marker securely fitted.
h. Cables shall be clearly numbered at each end, on both sides of a transit point, and
when entering a panel, junction box or gland plate.
i. IS circuits and non IS circuits shall be run in separate cables.
j. Cables shall be drummed in maximum continuous lengths on non-returnable
wooden drums. The manufacturer shall guarantee that drums are of sufficient
strength to protect cable during shipping and handling.
k. Seal all conduit and cable entries passing through outside walls of buildings,
through partition walls separating electrical rooms from other areas, through fire
separations, and through floors above grade.
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l. Seal openings after all wiring entries have been completed.
m. Sealing material shall be fire resistant and not contain any compounds which will
chemically affect the wiring jacket or insulating material. Cable penetrations
through fire separations, if required, are to be sealed. Acceptable methods are
Canstrut "Fire Stop", Electrovert "Multi-Cable Transit" or Dow Corning RTV Silicone
Foam.
n. Cable transit blocks (with knock out blocks) are also acceptable as long as they
have capability to be sealed.
o. Sleeves
i. Provide sleeves of galvanized steel pipe with machine cut ends of ample size to
accommodate conduits passing through walls, partitions, ceilings, floors, etc.
ii. For wall, partitions and ceilings the sleeve ends are to be flush with the finish on
both sides. For floors the ends shall extend 100mm above finished floor level.
iii. Fill the space between the sleeve and the conduit with fire stop material and
caulked around the top and bottom with approved permanently resilient, non-
flammable and weatherproof silicone base compound. Ensure that the seal is
compatible with the floor and ceiling finishes.
iv. Locate the sleeves and position exactly prior to construction of the walls and
floors.
v. Failure to comply with the above requirements shall be remedied at the
Contractor's expense.
B. Wiring and terminals
1. All terminal should be spring loaded type and suitable for Screw, Push-in. Spring-cage
or Fast Connection technologies.
2. Terminal Rails to be provided with Group Marker at top of each rail in junction boxes.
3. Provide knife disconnect terminals in the control panels for all devices or control system
input/outputs sourced from the panel.
4. Provide knife fused terminals for 24 VDC or 230 VAC power control loops, such as
solenoid Valves, Actuators, Electrical MCC interfaces etc.
5. Where circuit isolation is required, terminals shall including a built in circuit isolator.
6. One terminal shall be provided for each incoming and connecting wire. Only one wire
may terminate on each side of a terminal. Where more than one wire is to be connected
on one side of a terminal for looping purposes, a pre-formed link jumper between
adjacent terminals shall be used.
7. Prior to the connection of signal wiring to process control and instrumentation devices,
check the device voltage rating and polarity for compatibility with the corresponding loop
and/or schematic diagram. Where device and circuit characteristics are found to be
incompatible, the connections are not to be made. Report the condition immediately to
the responsible engineer.
8. All control wiring diagrams illustrate typical control circuits applicable to the type of
equipment specified. Control circuits may vary with different manufacturer’s equipment.
Verify all control circuits with the suppliers of the equipment and make any corrections
to the control wiring diagrams that may be required.
C. Junction Boxes
1. Junction boxes protection class should as per IEC 60529 with minimum IP65 for
outdoor installations.
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