Cable colours for 110v fixed wiring

[Andy Hall]

For convenience of use in the workshop I've added wiring and EN 60309 yellow industrial outlets carrying 110v from a centre tapped site transformer switched on when power is required.

There is a male wall mounted connector near the CU to pick up the outlet from the transformer and the wiring from that runs through the third compartment of the three compartment trunking to a few outlets around the walls. This trunking section is segregated and dedicated to the 110v wiring which is wired in PVC singles.

I need to add some more outlets and am doing some additional 230v wiring as well and while looking at some other issues looked at the identification section 514 of BS7671

I had done the original wiring using red and black for the two 55v cables and green/yellow for the centre tapped earth on the argument of it being a single phase circuit.

However, having thought about it, I rather wonder since one could argue that the two 55v cables are equivalent with neither being at or close to ground potential. There does not seem to be an official colour identification spec. in BS7671 (even in the new colours) to cover this case.

It doesn't seem right to run it with two reds either, although I suppose one could argue that a red and a yellow as being two "phases" would be legitimate. Equally, it could be reasonably argued that two yellows be used, especially since they would be 6mm^2 and quite obvious as well as segregated on the basis that yellow is associated with the 110v transformer and outlets.

I can't see anything that clearly covers this scenario of a split low voltage single phase a.c. circuit.

Thoughts?

.andy

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[Andrew Gabriel]

I've seen it done (once) in two browns, which was a mixure of singles in conduit and T&E. This was before that would become the new colour replacing two reds of course. (These colour T&E have been in use in the Irish Republic for some years, so they probably have been available with some difficulty for long time.) Given the new colours, I would be tempted to go for two yellows now if it's all singles and you aren't using yellow for anything else.

AFAIR, the yellow Arctic flex uses the standard brown/blue/green/yellow.

I guess you remembered to allow for 4 times the power loss due to voltage drop.

[Mike Tomlinson]

In article , Andy Hall writes

My first reaction is that, although you have the 110v and 230v cables segregated in your trunking, it would be sensible to choose different colours for different voltages, purely as an identification aid in case you have a 'senior moment'.

How about running the 110v cct in the American wiring colours - black for live/hot, white for neutral, green/yellow for earth? If you look at the flex wiring for 110v power tools, those are the colours used.

[Andy Hall]

It is all singles.

Table 51A in the blue book only lists yellow as used for the Y phase of a three phase circuit, although of course it is also commonly used as one of the lives in two way lighting. I've used 1mm^2 yellow in the centre compartment of the trunking for that purpose.

Interestingly, table 51 in Amendment 2 allows yellow as a control circuit colour.

Given that the 110v wiring is running in another compartment and is in

6mm^2, it is pretty obvious and yellow does seem reasonable and not missing from existing Table 51A.

Yes it does. I looked at some in an extension.

Oh, yes. Hence the 6mm^2. The lengths are relatively short.

.andy

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[Andy Hall]

I did debate that, although on pulling off the trunking lids it does become obvious because the wiring from the edge compartment drops only into the EN60309 sockets and nowhere else.

I considered that as well, except that American ground connection is green and not green/yellow, and there is potential confusion over black in the new wiring colours anyway.

Added to this, I already have 6mm^2 black and red in the main section of the trunking to carry single phase 230v radial circuits for the machine outlets.

.andy

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[N. Thornton]

If you use the same colours as something else, ie red or yellow/green, mistakes are liable to occur in future. A purpose of colour selcetion is to greatly reduce this chance. This is especially relevant with yellow/green colour, which I certainly would not use for the 0v line, any more than one would use it for 240v neutral.

Regards, NT

[Dave Liquorice]

From the "common sense" stand point the supply is balanced so there is not need to identify the phases (like there is in 3 phase) so the same colour can be used for both. Both are at 55v above earth and yellow is already associated with 110v "safe" supplies it therefore seems logical to use two yellows.

The center tap, is that bonded to local earth or floating? If it is bonded and thus a real protective earth then green/yellow would be logical. If it's floating hum, well...

[Owain]

"N. Thornton" wrote | If you use the same colours as something else, ie red or yellow/green, | mistakes are liable to occur in future. A purpose of colour selcetion | is to greatly reduce this chance. This is especially relevant with | yellow/green colour, which I certainly would not use for the 0v line, | any more than one would use it for 240v neutral.

But in this setting the 55-0-55 centre tap is earth, it's analogous to using red-yellow-blue and green/yellow on a three-phase supply with no neutral.

Owain

[Andy Hall]

It is bonded to earth.

Like you say and Andrew had also suggested, large yellow cables seem sensible. It isn't even as though phase identification is important as it is with three phase. Nevertheless, I'll probably connect it consistently.

.andy

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[Dave Plowman (News)]

Absolutely no help, but I always use yellow for AC other than mains in electronics. Suppose it's because I didn't want to double up on every colour of equipment wire, and have that as one of my 24/0.2 reels.

[Dave Plowman (News)]

I'd certainly *not* use black, given that it's already a designated colour.

[Mike Tomlinson]

In article , Dave Plowman (News) writes

Andy did say that he has used segmented trunking. And if it were me installing the wiring, I'd use cable ties to group cables together to avoid confusion. Perhaps use grey instead of black?

[Christian McArdle]

Personally, I'd use new colours. Blue for neutral (0V) and two phase colours for the 55V, avoiding brown, purely to distinguish from standard 230V live. I would not use green/yellow unless it was used as a protective conductor, in which case green/yellow would be compulsory.

Christian.

[Owain]

"Mike Tomlinson" wrote | Andy did say that he has used segmented trunking. And if it | were me installing the wiring, I'd use cable ties to group | cables together to avoid confusion. Perhaps use grey instead | of black?

Three-wire dc circuits are supposed to be L+ brown, Mid (possibly earthed) Blue, and L- Grey, so brown and grey would be 'consistent'.

However "control circuits, ELV and other applications" phase colour can be Brown, Black, Red, Orange, Yellow, Violet, Grey, White, Pink or Turqoise. Neutral or Mid-wire is Blue. An earthed PELV conductor is blue.

(from Wiring Matters).

I think White is/was Telecomms Functional Earth, which might not be too happy about being mistaken for 55 V ac.

Owain

[Andy Hall]

I did think about that, but then thought that really the 0v is not really a neutral but more of a protective earth since it is connected to the case of the tool if it is not double insulated and through to earth at the transformer. It shouldn't be carrying current either except under fault conditions. Therefore I think that it should be green/yellow.

Then the question is for the two 55v lines This really only leaves grey using the new colours because I would not want to use black.

.andy

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[G&M]

White is often used for both 110v wires in sound and lighting touring equipment to identify it as NOT one fo the three 240v phases or directly connected to it. Up to the 1970s white (line-ish) and black (neutral-ish) were used.

[Dave Plowman (News)]

That certainly makes more sense than yellow, but of course might be much more difficult to obtain.

If it's off an isolating transformer, there's no such thing.

[Andrew Gabriel]

Not to be confused with cream, which is a clean earth.

Those are the US colours, except they're the wrong way round.

[N. Thornton]

I'm a bit unclear what the OP is doing with the 110v CT wiring. I would have expected a power circuit to use N rather than E. 240v neutral is earth too, but theres reason we dont use it for CPC earth. The Americans do.

Without knowing quite what OP is doing with that CT...

Regards, NT

[G&M]

Not quite. B****y valve amps without transformers were the problem. Everything had to be carefully earthed to avoid ground buzz so convention was the black one could be connected to the common earth if needed, the white most definitely couldn't. Nowadays I think all such amps use isolating transformers and in any case all live (as opposed to soon to be dead) guitarists have protective cutouts on their leads.