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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.

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  • 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.

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  • 0 in reply to Fraser Donachie
    Fraser Donachie said:
    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.

    Make sure that, if a "colour code" is used on the schematics, it complies with the colour code specified in BS EN IEC 60757 and BS EN IEC 60445, to avoid confusion, i.e. brown indicated by "BN", black by "BK", grey by "GY", blue by "BU" and green-and-yellow by "GNYE".

    These colour codes were presented in the Draft for Public Comment of Amendment 2 to BS 7671:2018, because they've actually been harmonized (HD 457 S1) for around 30 years or more, yet this is not widely known in the industry, and we see a huge mix of colour code abbreviation variations - which, on control and switchgear panels can be a nightmare if someone gets it wrong! I guess that's why the IEC 60757 colour code was also included in BS EN IEC 60445 in 2017.

  • 0 in reply to gkenyon

    Many thanks Graham ... all noted! Best regards - Fraser

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