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/ 

HD 308 S2 applies to the colours of insulation over conductors for multicore cables for LV use.

It does not specify which phase is connected to that core.

The harmonized standard for identification is BS EN IEC 60445 - it is these days identical to IEC 60445, and has the same statement regarding assignment of BN, BK or GY to particular phases L1, L2 and L3.

Only BS 7671 specifies the colour assignment for the phases (BN for L1, BK for L2 and GY for L3), in Table 51.

The LV Switchgear and Controlgear Assemblies standard, BS EN 61439-1, only points to IEC 60445 - which as you say permits an option, so if it's not tied down in a Purchase Order or Contract or Specification, the manufacturer is able to comply with the standard with a different phase assignment to BS 7671.

It may very well not break any rule, but in someways it would be better if they were all brown, and then at least folk would check

Actually deliberately cycling phases is common, to balance the load, as single phase lamps and controls nearly always seem to be on phase 1 (let's call it brown) when machines are built.

Cylcling 1>2>3  or 2>3>1 or 3>1>2   all go the same way.

Reversing the sense of circulation so 1>2>3>  becomes 3>2>1 is less desirable, as that way machines go the wrong way, and cooling fans suck when they should blow and so on.

I suggest that some extremely clear labeling or over-sleeves  wil be needed of brown goes in and comes out grey  but black is black..

M

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!

Hello - thank you so much for your response, which is illuminating! In my case the installation and panel manufacturer reside in a CENELEC country but not the UK, making things tricky as BS 7671 will not apply there. But I understand the gist of your response - the IEC / CENELEC standards don't mandate the assignment between cores (L1, L2, L3) and colours - that's why the Internet tells me that the assignments L1=Brown, L2=Black & L3-Grey are "preferred" from an IEC viewpoint and only a National standard such as BS 7671 may make such an assignment mandatory. In our case, the labelling of cores is good / reasonable / unambiguous, however the 'as built' installation (Grey, Black, Brown) differs from the designers' drawing (Brown, Black, Grey) which is an immediate problem. I have the unenviable challenge of determining the best way forward ... which could be to seek re-wiring on all panels ($$$) or to get the 'as built' drawings changed. My gut feel, from a through-life safety and human factors viewpoint, is to demand the former ... but impact will be most unwelcome ... thanks again.

Hi there - many thanks. Yes, we have some air-supported structures that use 'blowers' (fans) to keep them up, so phase sequence is definitely important to us!! In our case, the labelling of conductors is good - but I take your point that to tolerate any departure from the "preferred" colour seqeuncing (Brown, Black, Grey) demands excellent labelling. Cheers.

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.