PREPARATION OF C&I CABLE SCHEDULES FOR DCS PANELS

PREPARATION OF C&I CABLE SCHEDULES FOR DCS PANElS

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PREPARATION OF C&I CABLE SCHEDULES FOR DCS PANELS
What is meant by 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 Power Plant or System.
Cable schedules are to be prepared for both for Power Cables and Control Cables.
Panels, equipment and instruments that will be coming in to the purview of cable schedules:
 Operators work Station where from all the operations of the Power Plant are carried out.
 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 operation of the Power Plant.
 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 Power Plant.)
 VFD Panels in respect of few boiler auxiliaries.
 Local instruments like gauges, transmitters, thermocouples, level switches, pressure switches
sensors and analyzers.
 Pneumatic ally operated Valves and dampers of various systems.
 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.

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 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
signals or feed backs based on the inputs from the field instruments.
 AVR Panels where from the generator terminal voltage is controlled in auto for all operating
conditions of 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
supervised for safe and efficient operation of the unit.
 Unit Synchronizing Panel where the auto synchronizer is installed for which all the required
feed backs shall be provided for safe synchronization of the unit with the grid.
 Generator Relay Panels.
 UPS System.
How to decide the number of cables required to 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
system to decide the number of cables required to be laid to the DCS Panels.
The various kinds of signals that will be communicated between the field instruments/equipment and
DCS Panels are as detailed below:
1. AI (Analog Input) to DCS Panels: 4-20 mille amps will be received from the field instruments.
Example: Signal received from the field transmitters like Pressure Transmitter, Flow Transmitter,
Level Transmitter, Differential Pressure Transmitter, Temperature transmitter etc.
2. AO (Analog Output) from DCS Panels: 4-20 mille amps (command signals) are supplied to the
field instruments through I/P convertor.
3. DI (Digital Input): Source is supplied from the DCS panels. The source is returned back to DCS
system as in put through the field instruments like limit switch etc.
4. DO (Digital Output) External source will come to DCS and will go to field through the DCS
contacts.

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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 can be 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, a voltage in the range of mille volts is generated.
Cables required to be laid from the MCC Panel to the DCS Panels for operation of a motor:
Function Type of signal
1. Motor Start command DO
2. Motor Stop command DO
3. Motor ON Feed Back DI
4. MCC Disturbance /Trip DI
5. Lower/Raise (L/R) DI
6. Speed Indication 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 Open Command DO
2. Valve Close command DO
3. Valve Operation Stop Command DO
4. Valve Open Feed Back DI
5. Valve Close Feed Back DI
6. Valve MCC Disturbance /Trip DI
7. Local/Remote Selection DI

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Cables required to be laid from DCSs Panels for operation of a Pneumatic Valve:
Function Type of Signal
1. Valve Open Command DO
2. Valve Close command DO
3. Valve Operation Stop Command DO
4. Valve Open Feed Back DI
5. Valve Close Feed Back DI
6. Local/Remote Selection DI
Cables required to be laid from DCS Panels for operation of a Solenoid Valve:
Function Type of Signal
1. Valve Open Command DO
2. Valve Close Command DO
3. Valve Open Feed Back DI
4. Valve Close Feed Back DI
General list of cable schedules to be prepared for the DCS system in a Thermal Power Plant:
1. Boiler Junction Boxes to DCS Panels.
2. Boiler MCC Panels to DCS Panels.
3. Boiler MCC Panels – PRDS Valves to DCS Panels.
4. Boiler VFD Panels to DCS Panels.
5. Turbine Junction Boxes to DCS Panels.
6. TG MCC Panels to DCS Panels.
7. Inter Panel Cable Schedules i.e. TSS Panel, AVR Panel and Generator Relay Panel to DCS Panels.
8. Common Drives MCC to DCS Panels.
9. BFP Motors Switchgear Panels to DCS Panels.
10. BFP RTDs to DCS Panels.
11. BOP MCC to DCS Panels.
12. BOP Junction Boxes to DCS Panels.
13. PLCC Panels of BOP Locations.
14. ESP Control Rom Switchgear Panels to DCS Panels.
15. ESP Electronic Controller Panels to DCS Panels

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 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 logic circuits for all unit operating conditions.
 AO cables can be called as command signal cables for the field equipment to operate as per the
process requirement.
 Separate Junction Boxes shall be used for connecting the control cables and signal cables.
 Further the DI and DO cables shall be connected to different Junction Boxes.
 All AI cables shall be connected to AI Junction Boxes.
 All AO cables shall be connected to AO Junction Boxes.
Boiler Junction Boxes to 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 through the appropriate cables.
 All the Junction Boxes at different locations and elevations of boiler area from shall be
identified from the drawings supplied by the boiler manufacturer.
 The Boiler Junction Boxes will be supplied by the boiler manufacturer only.
 The locations and the number of Junction Boxes required will be decided by the boiler
supplier only.
 Thus the cable schedules from the boiler instruments and boiler equipment to the Junction
Boxes will be supplied by the boiler manufacturer.

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 Similarly the Boiler MCC supplier will furnish his cable schedules (Terminal Details) from the
MCC panels to the DCS panels also.
General information needed to be familiar with for C&I erection works:
 Each unit will have separate set of panels containing I/O modules in the DCS room.
 The DCS supplier will specify the DCS panels related to Boiler, Turbine and Generator of
each unit and also that of the BOP equipment.
 The termination details in the DCS panels for connecting the cables from the different
Junction Boxes and MCCs of the Plant will be supplied by the DCS manufacturer.
 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
modules of the DCS panels.
 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
number where it is to 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 sheaths shall be earthed to the earth strip made available in the control panels.
 The DCS Panels system earth and body earth shall be connected to separate electronic earth
pits. Bare copper of the designed cross section shall be used for connecting to earth pits.

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 All spikes of the electronic earth pits shall be paralleled through sufficient size copper strip
under ground.
 Sleeves shall be provided for the bare portion of each wire before terminating it.
 All wiring inside the control panels shall be dressed properly using plastic bands. No metallic
wire shall be used for dressing the cables.
 Insulation of the unused cores shall not be peeled off and all spare cores not used shall be
bunched properly and tied with plastic bands and then dressed along with other cables.
 All DCS panels will be provided with UPS supply from the UPS panels.
 LAN cables will be run between the DCS panels and the OWS and from the Engineering
Console to the OWS.
 Large Video screens will be installed in the control room which will be working in parallel
with the OWS.
The following details are required for 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 sufficient for connecting the instrument to the Junction Box.
 About ten instruments will be connected to each Junction Box. Hence multi core cables with
some 30 percent of extra pairs of cables shall be laid from the Junction Boxes to the DCS Panels.
 The Cables thus going to be laid shall be given a Tag Number as per the standard practice for
identifying the cable at both ends.
 Ferrule numbers shall be given for each core of the cable at both ends before termination.
 The Cable Schedule shall contain the following details:
 Cable Tag Number.
 Number of cores.
 Size (Sq. MM.) and type of cable.
 Length of the cable in Meters.
 From which location to which panel of the DCS system.
 Inter connection chart containing the details of JB/MCC details and the Panel number of DCS
system with corresponding I/O module number.
 Functional details of each pair of cables connected.

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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
length of each cable shall be computed from the final lay out drawings.
Note: The power cable trays, control cable trays and the signal cable trays shall be separate.
Details of cables required to be laid from the Switchgear Panels/MCC Panels to the DCS Panels:
For motors:
For Control: Two pairs Start /Stop Command.
For Indication: Three pairs Remote Selection/ On/OFF Feed Back /MCC disturbance.
For Motor Operated Regulating Valves:
For Control: Three pairs Open/Close/Stop command.
For indication: Two pairs Remote Selection /Tripped.
For Motor Operated-- Full Open/Full Close Valves:
For Control: Two pairs Open/Close Command.
For indication: Two pairs Remote Selection/MCC Disturbance.
For motors with VFD Panels: From VFD Panels to DCS Panels:
For Control: Four pairs Start/Stop Command/Speed input/Speed
Reference.
For indication: Three pairs ON FB/Local/Remote selection/VFD Disturbance

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Important note to be considered while preparing the 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 fault developed in the existing wiring.
 Similarly the DCS panels shall be ordered with at least 30% extra I/O cords or modules for future
requirements.
Types of cables to be used from field to DCS Panels:
For DI and DO Communication: Multi core 0.5 sq.mm armored cables.
For AI and AO Signals: Multi pair 0.5 sq. mm armored cables.
For Thermocouple Signals: Multi pair 1.0 sq. mm. compensating armored
cables.
For RTD Signals: 2x6P, 1.5 sq. mm. Triad armored cables.
For Solenoid coils operation for operation of
Power Cylinders: Multi core 0.5 sq. mm. armored cable.
From Switchgear Panels i.e. MCC Panels to DCS Panels:
For all Motor Drives : Multi core 0.5 sq. mm. armored cables
For MOVs intended for full open/close operation: 2x1 pair, 1.5 sq. mm. armored cables
From VFD Panels to DCS Panels:
For Start/stop Command, speed reference and speed input: 4P, 0.5 sq. mm armored cables.
For ON FB/Local/Remote Selection/VFD Disturbance: Multi core 0.5 sq.mm. Armoured cable

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Inter Panel cable Schedule:
1. Cables between TSS and DCS Panel: Pair cables of 0.5 sq. mm (armored)
2. Generator RTDs to DCS panels:
For bearing temp RTDs: Pair cables of 0.5 sq. mm (armored)
For Generator Winding Temperature RTDs: 6 Triad, 0.5sq.mm armored cable.
3. Turbine Gauge Board to DCS panels: Pair cables of 0.5 sq. mm (armored)
4. AVR panel to DCS Panels: Pair and multi core cables of 0.5 sq. mm
(armored)
5. RMP Panel to DCS Panel: For meters: Pair cables of 0.5 sq. mm (armored)
For Relays: Multi core 0.5 sq. mm armored cables.
6. UPS to DCS Panels: Single pair 1.5 sq. mm armored cables
7. BOP Plant PLCC to DCS Panels: Multi core 0.5 sq. mm armored cable.
8. ESP control room to DCS Panels: Multi core 0.5 sq. mm armored cable.
Note: From all instruments to their Junction Box 1P, 1.5sq.mm armored cable shall be used. From the
Junction Boxes to the DCS Panels multi core cables of different category as per the signal shall be laid.