The document provides guidance on preparing cable schedules for connecting devices in a power plant to distributed control system (DCS) panels. It describes the various plant equipment, instruments, and panels that require cables, such as operator workstations, switchgear panels, variable frequency drive panels, and junction boxes. It also outlines the types of signals carried by different cable types and provides examples of typical cable schedules needed between devices and the DCS panels. Key considerations for the cable schedules include cable tagging, ferrule numbering, spare cores, and separating power, control and signal cables.

1. 1
PREPARATION OF C&ICABLE SCHEDULES FOR DCS PANELS
What is meantby Cable Schedule?
It is nothing but a schedule prepared giving the specification and the termination details of both end
connections of the cable for each function i.e. control function, feed back function and out going
commands from the DCS panels after analysis based on the predetermined logic defined and
incorporated for a particular system or equipment to operate satisfactorily for the smooth running of
the PowerPlantor System.
Cable schedulesare tobe preparedforboth for PowerCablesandControl Cables.
Panels,equipmentandinstrumentsthat will be comingin to the purviewof cable schedules:
 Operators work Station where fromall the operationsof the PowerPlantare carriedout.
 DCS Panels where the commands received from the OWS and Feed Backs received from the
field equipment or from any logic circuits are processed and the desired signals are
communicated to either to the switchgear panels in case of operation of any motor or to the
pneumatic control equipment for operation of any control damper or valve to maintain the
system conditions desired for that particular operating conditions of the equipment or system to
ensure safe operationof the PowerPlant.
 Switchgear Panels where from the power supply will be extended for operation of any valve,
damper or for starting of any equipment when command is issued from the Operator’s Work
Station in the Centralized Control Room. (Drive Motors of valves, dampers, and all auxiliaries of
the PowerPlant.)
 VFD Panelsinrespectof fewboilerauxiliaries.
 Local instruments like gauges, transmitters, thermocouples, level switches, pressure switches
sensors andanalyzers.
 Pneumatically operatedValvesand dampersof varioussystems.
 Annunciation System to alert the operators and also to indicate the status of the operating
systems.
 Local Control Panels/PLCC Panels: where from any particular equipment can be operated if
desired manually and also from where the status of the system or equipment will be conveyed
to the DCS panels.

2. 2
 Junction Boxes - The enclosures containing terminal blocks and provided with a vermin proof
door with lock and key arrangement, where in the cables of the nearby instruments are brought
into it and wired into the terminals of the terminal blocks and wherefrom the other end of the
terminals are connected to the DCS Panels through the appropriate cables for different kinds of
signalsorfeedbacksbasedon the inputsfromthe field instruments.
 AVR Panels where from the generator terminal voltage is controlled in auto for all operating
conditionsof the unit.
 Turbo Supervisory Panels where the turbine expansions, TG set bearing vibrations and
governing functional logic control systems are installed and the total behavior of the turbine is
supervisedforsafe andefficientoperationof the unit.
 Unit Synchronizing Panel where the auto synchronizer is installed for which all the required
feedbacksshall be providedfor safe synchronizationof the unitwiththe grid.
 GeneratorRelay Panels.
 UPS System.
How to decide the numberof cables requiredto be laid for a particular purpose?
We have to decide the operational requirement of any valve or equipment i.e. whether full open/full
close or regulating valve with position feed back and ON/OFF feed back requirements of each valve or
systemtodecide the numberof cablesrequiredtobe laidtothe DCS Panels.
The various kinds of signals that will be communicated between the field instruments/equipment and
DCS Panelsare as detailedbelow:
1. AI (AnalogInput) toDCSPanels:4-20 mille ampswill be receivedfromthe fieldinstruments.
Example: Signal received from the field transmitters like Pressure Transmitter, Flow Transmitter,
Level Transmitter,Differential Pressure Transmitter,Temperature transmitteretc.
2. AO (Analog Output) from DCS Panels: 4-20 mille amps (command signals) are supplied to the
fieldinstrumentsthroughI/Pconvertor.
3. DI (Digital Input): Source is supplied from the DCS panels. The source is returned back to DCS
systemas in put through the fieldinstrumentslike limitswitchetc.
4. DO (Digital Output) External source will come to DCS and will go to field through the DCS
contacts.

3. 3
5. From RTDs (Resistance Temperature Detector): The RTD is a high precision wire wound resistor
whose resistance varies with temperature. By measuring the resistance of the metal, its
temperature canbe determined.
6. From Thermo Couples: (T/C): A thermocouple consists of two pieces of two dissimilar metals
with their ends joined together (by twisting, soldering or welding). When heat is applied to the
junction,avoltage inthe range of mille voltsisgenerated.
Cablesrequiredto be laid from the MCC Panel to the DCS Panels for operationof a motor:
Function Type of signal
1. Motor Start command DO
2. Motor Stop command DO
3. Motor ON FeedBack DI
4. MCC Disturbance /Trip DI
5. Lower/Raise (L/R) DI
6. SpeedIndication AI
7. KW Indication AI
8. Current Indication AI
Cables required to be laid between the MCC Panels to the DCS panel for operation of a Motorized
Valve:
Function Type of Signal
1. Valve OpenCommand DO
2. Valve Close command DO
3. Valve OperationStopCommand DO
4. Valve OpenFeedBack DI
5. Valve Close FeedBack DI
6. Valve MCCDisturbance /Trip DI
7. Local/Remote Selection DI

4. 4
Cablesrequiredto be laidfrom DCSs Panels for operationof a Pneumatic Valve:
Function Type of Signal
1. Valve OpenCommand DO
2. Valve Close command DO
3. Valve OperationStopCommand DO
4. Valve OpenFeedBack DI
5. Valve Close FeedBack DI
6. Local/Remote Selection DI
Cablesrequiredto be laidfrom DCS Panelsfor operationof a SolenoidValve:
Function Type of Signal
1. Valve OpenCommand DO
2. Valve Close Command DO
3. Valve OpenFeedBack DI
4. Valve Close FeedBack DI
General listof cable schedulesto be prepared for the DCS systemin a Thermal Power Plant:
1. BoilerJunction BoxestoDCSPanels.
2. BoilerMCC PanelstoDCS Panels.
3. BoilerMCC Panels –PRDS ValvestoDCS Panels.
4. BoilerVFDPanelstoDCS Panels.
5. Turbine JunctionBoxestoDCSPanels.
6. TG MCC PanelstoDCS Panels.
7. InterPanel Cable Schedulesi.e.TSSPanel,AVRPanel andGeneratorRelayPaneltoDCSPanels.
8. CommonDrivesMCC to DCS Panels.
9. BFP Motors SwitchgearPanelstoDCSPanels.
10. BFP RTDs to DCS Panels.
11. BOP MCC to DCS Panels.
12. BOP Junction BoxestoDCSPanels.
13. PLCC Panelsof BOPLocations.
14. ESP Control RomSwitchgearPanelstoDCSPanels.
15. ESP ElectronicControllerPanelstoDCSPanels

5. 5
 DI and DO cables can be called as control cables (which will carry power supply) through which
the equipment start/stop operations or open/close operations of valves and dampers are
initiated as per the logic circuits established and installed in the DCS, taking into consideration
of the Protection & Interlocks of various equipment and systems for all unit operating
conditions.
 AI cables can be called as feed back signal cables from the field instruments to the DCS panels
which will always carry very low current of the order of 4-20 mille amps given by the I/P
convertors of the control equipment like Regulating Valves and Regulating Dampers of various
systems like Water, Steam, Air, Flue Gas etc through their respective Transmitters like PT, FT, LT,
DPT and TT etc. The Controllers of the DCS Panels will always analyze the process status based
on the feed back signals and rectify the process deviations if any by giving out the required AO/
DO command and initiate the valve/ damper operating mechanism either pneumatic or
electrical till the specified operating parameters are achieved and the system/unit is stabilized
as per the logiccircuits forall unitoperatingconditions.
 AO cables can be called as command signal cables for the field equipment to operate as per the
processrequirement.
 Separate JunctionBoxesshall be usedforconnectingthe control cablesandsignal cables.
 Furtherthe DI and DO cablesshall be connectedtodifferentJunctionBoxes.
 All AIcablesshall be connectedto AIJunction Boxes.
 All AOcablesshall be connectedto AOJunction Boxes.
BoilerJunction Boxesto DCS Panels:
 The Junction Boxes are the housings of terminal blocks, where from the feed back received
from the field instruments or equipment like valves and dampers is communicated to the
DCS panels throughthe appropriate cables.
 All the Junction Boxes at different locations and elevations of boiler area from shall be
identified fromthe drawingssuppliedbythe boilermanufacturer.
 The BoilerJunctionBoxeswillbe suppliedbythe boilermanufacturer only.
 The locations and the number of Junction Boxes required will be decided by the boiler
supplieronly.
 Thus the cable schedules from the boiler instruments and boiler equipment to the Junction
Boxes will be suppliedbythe boilermanufacturer.

6. 6
 Similarly the Boiler MCC supplier will furnish his cable schedules (Terminal Details) from the
MCC panelstothe DCS panels also.
General informationneededtobe familiarwith for C&Ierectionworks:
 Each unitwill have separate setof panelscontainingI/Omodulesin the DCSroom.
 The DCS supplier will specify the DCS panels related to Boiler, Turbine and Generator of
each unitandalso thatof the BOP equipment.
 The termination details in the DCS panels for connecting the cables from the different
JunctionBoxesandMCCs of the Plantwill be suppliedbythe DCSmanufacturer.
 The cable schedules supplied by the different agencies i.e. manufacturers of boiler, turbine,
Switchgear Panels, AVR panels and turbovisory panels shall be reviewed and common cable
schedules coordinating the terminations in the Junction Boxes, Switchgear panels etc and in
the DCS panels , shall be prepared for facilitating the cable laying and executing the
terminations.
 The cables with input signals shall be connected to the Input cords/modules and the cables
related to the out put signals from the DCS panels shall be connected to the output cords or
modulesof the DCSpanels.
 All cables shall be provided with tag plates containing the cable tag details as per the cable
schedules. The cable tag description will indicate the starting point i.e. either Junction Box
Number or the MCC feeder number etc and the DCS panel number in which it is to be
connected.
 Ferrule numbers shall be provided for each core of each cable at both ends of each core
containing the details of the equipment/instrument, JB/Panel number and the terminal
numberwhere itisto be connected.
 Each wire shall be provided with suitable lug and crimpled before it is connected in the
terminal.
 Spring washers and flat washers shall be used to have a tight connection in the Terminal
Blocks.
 All cable sheathsshall be earthedtothe earthstripmade available inthe control panels.
 The DCS Panels system earth and body earth shall be connected to separate electronic earth
pits. Bare copper of the designedcrosssectionshall be usedforconnectingtoearthpits.

7. 7
 All spikes of the electronic earth pits shall be paralleled through sufficient size copper strip
underground.
 Sleevesshallbe provided forthe bare portionof eachwire before terminatingit.
 All wiring inside the control panels shall be dressed properly using plastic bands. No metallic
wire shall be usedfordressingthe cables.
 Insulation of the unused cores shall not be peeled off and all spare cores not used shall be
bunchedproperlyandtiedwithplasticbandsandthen dressedalongwithothercables.
 All DCSpanelswill be providedwithUPSsupplyfromthe UPSpanels.
 LAN cables will be run between the DCS panels and the OWS and from the Engineering
Console tothe OWS.
 Large Video screens will be installed in the control room which will be working in parallel
withthe OWS.
The followingdetailsare requiredfor preparing the cable schedules:
 Cable schedules from the field instruments to the Junction Boxes with description of the
instrument, the type of signal i.e. AI/AO/DI/DO the cable will carry along with the terminal
numbers in the Junction Box and the designated number of the Junction Box. Single pair 1.5 sq.
mm cable will be sufficientforconnectingthe instrumenttothe JunctionBox.
 About ten instruments will be connected to each Junction Box. Hence multi core cables with
some 30 percentof extrapairs of cablesshall be laidfromthe JunctionBoxestothe DCS Panels.
 The Cables thus going to be laid shall be given a Tag Number as per the standard practice for
identifyingthe cable atbothends.
 Ferrule numbersshall be givenforeachcore of the cable at both endsbefore termination.
 The Cable Schedule shall containthe followingdetails:
 Cable Tag Number.
 Numberof cores.
 Size (Sq.MM.) and type of cable.
 Lengthof the cable inMeters.
 From whichlocationtowhichpanel of the DCS system.
 Inter connection chart containing the details of JB/MCC details and the Panel number of DCS
systemwithcorrespondingI/Omodule number.
 Functional detailsof eachpair of cablesconnected.

8. 8
For deciding the length of the cables, the lay out drawings with the positioning of the plant equipment
shall be available. The cable routing shall be decided such that the route will not foul with any of the
pipe lines are equipment to be erected after erection of the cable trays. The cable routing includes the
elevations also at which the cable trays are to be laid in the plant locations. Then the number of cables
coming from different locations of the plant shall be decided. Number and size of the cable trays
required to contain and carry all the cables shall be decided. Number of layers of the cables that can be
put in each cable tray also shall be decided. The requirement of cable trays of different sizes shall be
arrived at after a comprehensive collection of data on the requirement of different cables. Then the
lengthof eachcable shall be computedfromthe final layoutdrawings.
Note:The powercable trays,control cable trays andthe signal cable traysshall be separate.
Detailsof cables requiredto be laid from the SwitchgearPanels/MCCPanelsto the DCS Panels:
For motors:
For Control: Two pairs Start /StopCommand.
For Indication: Three pairs Remote Selection/ On/OFFFeed Back/MCCdisturbance.
For Motor Operated RegulatingValves:
For Control: Three pairs Open/Close/Stopcommand.
For indication: Two pairs Remote Selection/Tripped.
For Motor Operated-- Full Open/Full Close Valves:
For Control: Two pairs Open/CloseCommand.
For indication: Two pairs Remote Selection/MCCDisturbance.
For motors with VFD Panels:From VFD Panelsto DCS Panels:
For Control: Four pairs Start/Stop Command/Speed input/Speed
Reference.
For indication: Three pairs ON FB/Local/Remoteselection/VFDDisturbance

9. 9
Important note to be consideredwhile preparingthe cable schedules:
 About 30% of spare cores /pairs shall be available in each multi core cable laid from the field to
the DCS Panels to take care of the future needs and also for using as a spare when needed in
case of any faultdevelopedinthe existingwiring.
 Similarly the DCS panels shall be ordered with at least 30% extra I/O cords or modules for future
requirements.
Types ofcables to be usedfrom fieldto DCS Panels:
For DI and DO Communication: Multi core 0.5 sq.mmarmoredcables.
For AIand AO Signals: Multi pair0.5 sq.mm armoredcables.
For Thermocouple Signals: Multi pair 1.0 sq. mm. compensating armored
cables.
For RTD Signals: 2x6P, 1.5 sq.mm. Triadarmoredcables.
For Solenoidcoils operationforoperationof
PowerCylinders: Multi core 0.5 sq.mm. armoredcable.
From Switchgear Panelsi.e.MCC Panelsto DCS Panels:
For all Motor Drives : Multi core 0.5 sq.mm. armoredcables
For MOVs intendedforfullopen/closeoperation: 2x1 pair, 1.5 sq.mm. armoredcables
From VFD Panelsto DCS Panels:
For Start/stopCommand,speed referenceandspeedinput: 4P, 0.5 sq.mm armoredcables.
For ON FB/Local/Remote Selection/VFDDisturbance: Multi core 0.5 sq.mm.Armouredcable

10. 10
Inter Panel cable Schedule:
1. Cables betweenTSSandDCS Panel: Paircablesof 0.5 sq.mm (armored)
2. GeneratorRTDs to DCS panels:
For bearingtempRTDs: Pair cablesof 0.5 sq. mm (armored)
For GeneratorWindingTemperature RTDs: 6 Triad,0.5sq.mm armoredcable.
3. Turbine Gauge Board to DCS panels: Paircablesof 0.5 sq.mm (armored)
4. AVRpanel to DCSPanels: Pair and multi core cables of 0.5 sq. mm
(armored)
5. RMP Panel to DCS Panel:Formeters: Paircablesof 0.5 sq.mm (armored)
For Relays: Multi core 0.5 sq.mm armoredcables.
6. UPS to DCS Panels: Single pair1.5 sq. mmarmoredcables
7. BOP PlantPLCCto DCS Panels: Multi core 0.5 sq.mm armoredcable.
8. ESP control room to DCSPanels: Multi core 0.5 sq.mm armoredcable.
Note: From all instruments to their Junction Box 1P, 1.5sq.mm armored cable shall be used. From the
JunctionBoxestothe DCS Panelsmulti core cablesof differentcategoryasperthe signal shall be laid.