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Three Phase AC Phase Conductor Colours - Mandatory?

Fraser Donachie

An LV Switchgear manufacturer has correctly used Brown, Black and Grey conductor colours in their panels. But the assignment is not the "preferred" L1=Brown, L2=Black & L3=Grey. Instead, the phase sequence is different. Whilst this is extremely undesirable from a safety and human factors viewpoint, is it 'illegal' or would it mean their DofC is invalid? IEC 60445 does not specify the assignment between L1, L2 & L3 and Brown, Black or Grey. I believe CENELEC HD 308 S2 may specify the "preferred" assignment but I cannot obtain a copy of that. How mandatory is the "preferred" and generally accepted assignment L1=Brown, L2=Black & L3=Grey? THANKS!

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  • 0

    Whilst this may be considered a problem, I am slightly intreged by why. I would probably look on this as a curiosity and cannot see why the L1 seems to be special to you. The only special thing about a multiphase system is the rotation order, unless one intends to parallel up two supplies where the specific phase is important to prevent a big bang! I can see no reason why a terminal marked L1 needs to connect to a Brown wire, although this tends to be the standard method. As Graham has pointed out above, the standards are ambiguous, and BS7671 is only interested in the phase sequence during testing, not which phase is which. (643.9)

    In fact knowing which EHV cable on a pylon is which phase at a consumer is quite complex to check, and really does not matter to a consumer, as we do not usually use the mains phase as an absolute phase timing reference standard. Therefore I suggest that your equipment is fine, but the connections throughout to it should follow the colours and not the L1, L2, L3 labelling. A note on the drawing will clarify this for the future, and everyone should be happy. The phase rotation is unaffected by this change. Please realise that the L1,L2,L3 is arbitary, the colours are not.

  • 0 in reply to David Stone

    Good morning David - thank you for your response - super. My issue is simply about safety and maintainability, as power technicians (even in my non-UK country) will most probably expect L1=Brown, etc whereas the panel, in this case, has something different. But power technicians are trained to be very cautious and plan their task before conducting it. And the conductor labelling is very good. So in this case, I would get the 'as built' schematics updated to very clearly indicate the panel conductor colours in use - a bold notice on the front sheet - or on every sheet perhaps! PS BS 7671 specifies the assignments in Table 51.

  • 0 in reply to David Stone
    David Stone said:
    Please realise that the L1,L2,L3 is arbitary, the colours are not.

    Quite so. Choose whichever you like for L1, but then L2 has to be the one which is 120° behind.

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  • 0 in reply to David Stone
    David Stone said:
    Please realise that the L1,L2,L3 is arbitary, the colours are not.

    Quite so. Choose whichever you like for L1, but then L2 has to be the one which is 120° behind.

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  • 0 in reply to Chris Pearson
    Chris Pearson said:
    David Stone said:
    Please realise that the L1,L2,L3 is arbitary, the colours are not.

    Quite so. Choose whichever you like for L1, but then L2 has to be the one which is 120° behind.

    However, to BS 7671, L1 = brown, L2 = black, L3 = Grey, and I'm guessing what's happened in this particular assembly is more than likely either:

    (a) terminals or conductors labelled, for example, "L1" with conductors terminated in them that are not brown; or
    (b) the assembly has a drive or similar in it, and the phase rotation doesn't go brown, black, grey ?

  • 0 in reply to gkenyon

    Thanks Graham. The installation has been completed and is commissioned now (with no known phase rotation / sequencing issues). I think your hypothesis (a) is the root cause; the panels were incorrectly wired (Grey, Black, Brown) not i.a.w. the designer's schematic (Brown, Black, Grey). As you can imagine, we've asked the panel manufacturer to explain the inconsistency and I await their response! From your responses and my own research, and given the very good conductor labelling, I'm minded to have the schematics updated to match the 'as built' situation rather than have every panel re-wired (!) ... and I would also seek a bold notification on each schematic informing the maintainer of the colour code in use within the panel. Regards - Fraser

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