Any Standard or Guidelines for Spare Cores in Instrument Cables


Thread Starter


We are setting up a power plant and in the design phase at the moment. We are discussing spare cores for control and instrumentation cables and not having an agreement with EPC contractor.

Our EPC contractor is Chinese and they are designing the spare cores inside the cables according to the Chinese standard. According to their standard they are designing spare cores only for control cables which have 7 or more cores. For 7 or lesser cores, there will be no spare core. Similarly, for Digital Input, Analog Input and Thermocouple Input, there will be no spare core for 1X2X1 and 2X2X1 and at least one spare core for 5X2X1 or 7X2X1.

For reliable and safe operation of plant (considering it 30 year life) and considering cable laying as a one time activity, we the owners want a spare core in each and every cable.

We want to know any specific code or standards that highlights the spare cores for the control and AI,DI, RTD and TC cables to be left inside the cables.

Any help in this regard will be highly appreciated.
I am unable to translate the description of the core requirements into plain English. I do not know of any US standard that specifies spares. That is up to your engineering specifications provided to your EPC contractor.

When I was designing instrument & control wiring in the petrochemical industry for a user company, I designed for 25% spare and required contractors to provide them if it was contracted out. The plant will need those spares in the future. EPC firms did not like to provide that because they typically lump sum bid the project and spares cost them profits and some project managers also because it raises project cost but I always looked at the lifecycle cost not strictly project costs.

William (Bill) L. Mostia, Jr. PE
ISA Fellow
WLM Engineering Co.

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