Is there a Control Cabinet Wiring Code?

I recently noticed the following Facebook post which I wanted to share. At Rom-Control, we specialize in repairing electronic control systems from all types of industries, so we are familiar with the different coloured wires connecting to similar functions but to an untrained eye, there doesnt appear to be s system or standard. This is not necessarily true.

Originally the question on Facebook was posted by an electrician who recently entered the industrial workforce who typed ”  …….sometimes I see control panels with wires in different colours (orange, white, black, grey, purple, yellow, red). I know they are used for control systems (PLC, sensors…) but I don’t know which colour is used for which circuit. Is there a standard for which colour is supposed to be used?”

The answers were varied and interesting but suggested the majority or respondents did not know the right answer? For example;

Answer 1. “Every company could have a different standard. Most panel shops stick to the NEC standard. The multi-meter won’t lie to you.”

Answer 2. “Orange is coming from outside the current panel. White is neutral, white with blue stripe is com. Red is 120V control power inside the panel, black is providing 120V power, usually to receptacles or circuit breakers. Blue is 24V. That’s the standard everyone should use.”

Answer 3 which was surprising. “actually, I built this control panel 2 yeas ago”. The engineer that planned it doesn’t know why he used that color coding, his comment was “this is how they teach in electrical engineering school so it is what I did”.

The real answer can be found in AS3000:2018 Section 3.8 – Practical Electrical Wiring Standards (click here for preview) which specifies that “internal wiring of equipment is not regarded as installation wiring ……. but certain rules must be observed with certain wiring insulator colours”. It is worth a read though if you are involved in wiring up switchboards or any other control system cabinet to ensure you conform.

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