Why isn't 3-core cable the standard for lighting circuits?

[mattylad]

I don't think there is a regulation, but good practice, any cores not earthed can pick up voltage due to capacitive and inductive linking, but it would depend on cable lenght.

EAWR.
See section 8

The Electricity at Work Regulations 1989

These Regulations impose health and safety requirements with respect to electricity at work.

www.legislation.gov.uk

I always terminate them and if they are an unused conductor then they are identified as such at both ends, earthed at the supply end.

 

[DetlefSchmitz]

Why does that remind me of the 'bond everything metal in sight' 'rule'?

 

[JohnW2]

EAWR. .... See section 8

Rather strange language ...

.... any conductor (other than a circuit conductor) which may reasonably foreseeably become charged as a result of either the use of a system, or a fault in a system, becomes so charged ...

At least they define "circuit conductor' (essentially as a conducting which carries current during normal operation), but what do they mean by "charged" - do they just mean 'live', or what.

In any event, in context, I would not have thought that the 'unused' conductors we have been discussing would qualify as ones which "may reasonably foreseeably become charged", do you ?

 

[mattylad]

I absolutely do John, ANY conductor that is not connected to the circuit can become charged by mutual inductance, I have seen it happen.
Additionally, a fault may be someone screwing into a cable, you are I'm sure aware that it sometimes does not result in a big bang and tripping things, sometimes it gets left for years without someone knowing - this could connect the unused conductor to a live one.
Grounding it causes the protective devices to operate.

So all conductors that are not connected to the circuit should be made safe, the only way of doing that is to terminate them at both ends and ground them, it's not hard to do and is best practice as well as in keeping with the law.

 

[ebee]

Can I suggest that putting a connector at the ends but not sleeving the conductor(s) g/y but at least at the supply end connect to an earthing conductor/c.p.c that actually has a g/y colour?
Ok, potentially you have a conductor or group of conductors at the far end that tests out as E or N and you might not be sure of its intended use unless we invent another colour or label for it.

 

[veedee]

That is surely totally wrong, and non-compliant with BS7671. Whatever else, if the core is not being used as a protective conductor, it must not be identified with G/Y sleeving.

Okay, I will remove the sleeving and just leave the spare, unused core in the earth connector block. Thanks

That's surely not beyond the wit of man? - e.g. a 'tab' made out of a bit of white PVC tape with something written ion it with a Sharpie?

Would a sparky likely have understood if it was labelled 'U' for 'unused?'

Only asking as the Wago 221 2-way connector blocks I have are tiny. I probably wouldn't be able to label and fit 'unused' on it.

I would say that it really depends upon how likely one thinks it is that an extra core might be required (e.g. to provide a neutral at switch positions) in the foreseeable future.

If one feels that such a requirement might arise in the not-too-distant future, then it might well make sense to install 3C+E, since the additional cost (and hardly any additional effort) would undoubtedly be far less than the cost, effort and disruption (maybe including re-decoration etc.) that would arise if a T+E cable had to be subsequently replaced with 3C+E.

Exactly.

There's also the 'time value of money'. Like my teacher used to always say, £1 today is worth more than £1 in the future.

The price difference between the cable is £16-£17 today, but in future money it will worth far less, so you will be paying more.

When you do the job right, you only have to do it once and it's works out cheaper.

 

[JohnW2]

Okay, I will remove the sleeving and just leave the spare, unused core in the earth connector block. Thanks

Yes, you should do that. BS7671 is very clar about this ....

514.4.2 Protective conductor
The bi-colour combination green-and-yellow shall be used exclusively for identification of a protective conductor
and this combination shall not be used for any other purpose.

Would a sparky likely have understood if it was labelled 'U' for 'unused?'

Probably not, but it wouldn't have to be a very big (e.g. white PVC tape) 'tab' for you to write "Unused" on it.

Only asking as the Wago 221 2-way connector blocks I have are tiny. I probably wouldn't be able to label and fit 'unused' on it.

It's quite possible to label a 2-way Wago directly in that way (again, with white PVC tape), per this rough mock-up ...

... but I was actually talking of something more like this ....

... although, as I have implied,I would very rarely contemplate doing anything like that (I might if the conductor in question was 'live'.

Exactly. ... There's also the 'time value of money'. Like my teacher used to always say, £1 today is worth more than £1 in the future. ... The price difference between the cable is £16-£17 today, but in future money it will worth far less, so you will be paying more. .... When you do the job right, you only have to do it once and it's works out cheaper.

Quite so - but, as I said, it really depends upon how likely one thinks it is that the additional 'provision' will ever be needed, at least for a very long time. If one regards it as very unlikley that the extra core would be needed during the remainder of one's occupancy of the house, even a small bit of additional cost would probably not be sensible.

Let's face it, there is no end to what one might install "in case it was conceivable (but unlikley) that it would be needed in the future"!

 

[JohnW2]

I absolutely do John, ANY conductor that is not connected to the circuit can become charged by mutual inductance, I have seen it happen.

Do you really think that they mean "charged" in that sense? Even if you do, I think I would say "So what?". The EAWR reg you mentioned only talks about "to prevent danger", and I really don';t think that any significant "danger" would result from inductive or capacitive coupling to a floating conductor in a domestic environment,can you?

Additionally, a fault may be someone screwing into a cable, you are I'm sure aware that it sometimes does not result in a big bang and tripping things, sometimes it gets left for years without someone knowing - this could connect the unused conductor to a live one. ... Grounding it causes the protective devices to operate.

I can't disagree with what you are saying, but I think you are 'scraping the barrel' in relation to an incredibly improbable occurrence.

In any event, such and incredibly rare occurrence would only present a danger if someone was daft enough to work on any of the cores of the cable whist at least one of the cores was, or might be, 'live'!

However, if despite all that you were concerned, and if you were doing as proposed (installing a 3C+E cable, one core of which was currently unused), if you arranged things such that the unused core was the one on it's own on one side of the CPC in the cable, then it would be next-to-impossible for penetration of the cable to result in the unused core becoming live without there also being contact with the CPC (hence resulting in operation of a protective device.

 

[JohnW2]

Can I suggest that putting a connector at the ends but not sleeving the conductor(s) g/y but at least at the supply end connect to an earthing conductor/c.p.c that actually has a g/y colour?

I think that's what some people (started by eric) have been suggesting.

One thing I do occasionally do, if a whole cable(all its cores) is left in situ although unused, is to join all the cores together with Wago or connector block at both ends. It is then very obvious to anyone that the cable is being used.

Kind Regards, John