Three Phase AC Phase Conductor Colours - Mandatory?

I am not sure what you mean. Provided that the brown input is connected to the brown outputs, etc. how can the phase sequence be "different"?

Hi Chris - thanks for responding. In this case the power panel is wired L1=Grey, L2=Black and L3=Brown. The colours therefore 'change' between the incomer cable (L1=Brown, L2=Black, L3=Grey) to a different scheme within the panel! This is definitely not desirable, but it's a moot point whether it really contravenes any standard ... ?

It looks like David Latimer is the UK guru on this topic. Here's an article that implies that the phase assignments are defined by, in the UK, BS 7671 ... https://electrical.theiet.org/wiring-matters/years/2021/84-march-2021/the-history-of-colour-identification-of-conductors/ 

So how are the terminals identified please? L1/L2/L3, brown/black/grey, or something else?

So how are the terminals identified please? L1/L2/L3, brown/black/grey, or something else?

Hi Chris - thanks again. The conductors (and terminals) have been reasonably well labelled so the wiring is traceable. The residual issue, which I did not mention, is that the 'as built' conductor colours (Grey, Black, Brown) are not i.a.w. the drawing (Brown, Black, Grey) so that's an immediate problem. I see that gkenyon has provided a very useful response below. The problem I'm presented with is whether to demand a 're-wiring' corrective action on multiple panels ($$$) or seek an update to the drawings and improvements to labelling. I suspect our end-client will have a view!

The point of my last question really was how do you know which incomer is L1? It can only be because it is labelled L1 or has brown insulation or identifying mark. So if you have grey cable linking all the L1 parts, that is unhelpful because it may lead to confusion, but GK has covered that and I note your reply to his last point.

I am not clear how the drawing and switchgear as built differ.

If the drawing has terminals labelled "L1" and brown lines joining them, but the manufacturer has used grey cable, again that is unhelpful. However, if say the drawing shows a row of terminals being L1, L2, L3 running from left to right, but the manufacturer has them running from right to left, IMHO that is not as big an issue provided that the terminals and cables are clearly identified.

From the sound of it, changing the drawings would be easier than changing the switchgear. As GK says, it is a matter of contract, but even then, the colours may not be a fundamental issue.

Hi Chris - hey thanks for persevering with this thread ... the photographs we have show a transition on the incoming circuit breaker of each panel where the arriving cable has conductors marked L1=Brown, L2=Black & L3=Grey and on the other side of the circuit breaker, internal to the panel, they become L1=Grey, L2=Black & L3=Brown. The 'N' is always on the right-hand side of these, looking from the front. So at least the labelling is clear; L1 connects to L1, L2 connects to L2, etc. It's just the colour that's changing. Unusually for a panel schematic, it uses Brown, Black and Grey lines for the phases, which is useful for a maintainer - of at least it would be if the schematic matched the as-built situation! If there is no applicable National standard in the CENELEC country that this installation is in, then I'd be OK with the schematic being updated to match the as-built situation. But if there is a National standard (like our BS 7671) that specifies the mapping, the panels will probably need re-wiring to match the schematic (ouch) #sadface - thanks again - Fraser

Fraser, thank you for bearing with me. Now I understand your problem.

I have had a look at BS EN IEC 60445:2021 and at 6.2.3 it lists the phase colours as, "BLACK, BROWN, or GREY" on the basis that the sequence is in alphabetical order in the English language, "... and does not indicate any preferred phasing or direction of rotation."

It seems to me that a maintainer could very easily have difficulty identifying the phases. If they are marked L1, L2, L3, and the terminals possibly U, V and W, all well and good. However, if colour of the insulation is the only means of identification, a maintainer would be perfectly entitled to refer to the wiring diagram(s) and that's where you have a problem.

I would imagine that H&S legislation would require this. A discrepancy between the article and its diagrams hardly leads to a safe system of working.

Thanks Chris. In our case the labelling is actually very good, so there should be no difficulty identifying the phases. The phases are identified using clear labels L1, L2, L3, N. I think the answer here is get the schematics updated to match the 'as built' situation and also add a clear guidance notification on each schematic. Thanks again!