Three Phase AC Phase Conductor Colours - Mandatory?

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

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.

Please realise that the L1,L2,L3 is arbitary

Agreed. As far as I've been able to tell there's not even a standard as to the rotation of R/Y/B (or L1/L2/L3) coming in from the street - each area seems to have own historical convention. I understand that there's one area around York for example that has the reverse rotation compared with surrounding areas - and it's not easily standardized without taking a huge risk with all the existing 3-phase motors.

   - Andy,

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.

Thanks Andy - I mentioned above that we have some air-supported structures that use blowers (fans) to keep them inflated - phase rotation is very important to us! We really don't want air being sucked out rather than pushed in ... cheers!

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.

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.

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.

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 ?

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!