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

[RandomGrinch]

Personally, I put unused cores into a connector block or wago at each end.

Over on the plumbing forum, posters who have new builds often want to change their 'stats to smart 'stats.
The second heating zone may have a simple battery powered, two wire 'stat installed, but the wiring behind it is 3 core + earth.
Several times, the poster has simply taken the spare core (usually grey), connected it to the N of their new mains powered stat and wondered why it doesn't work.
(Equally as common, is when a poster has taken the live return to the zone valve and connected this to the N!).

Of the posts I have helped with, only one has had the spare core connected to the earth terminals in the wiring centre - the rest were terminated separately in Wagos, spare terminals, or just wrapped in tape!

In terms of helping posters wire up stats, I would prefer the spare core to be terminated separately - if it were connected to earth, with a standby power of less than 4W, some of these cheap wired smart stats might actually power up.

 

[pete01]

Unused cores of multicore cables - Snag 22

It is advisable to properly terminate unused cores of a multicore cable.

www.voltimum.co.uk

 

[SUNRAY]

I presume he means that, as he wrote, if someone subsequently finds a conductor (particularly an insulated one) which is not identified by G/Y insulation or sleeving connected to an earth terminal, they might wonder (and perhaps 'have to investigate') whether it is performing some 'earthing function' for something.

IF earthing a spare condctor may be deemed to confuse, one could fit a label.

 

[FrodoOne]

In the USA, a Neutral is now required to be "available" at the switch for all new work.

 

[JohnW2]

IF earthing a spare condctor may be deemed to confuse, one could fit a label.

One could, just as one could with any of the other methods of dealing with an unused conductor.

'Confused' is probably not really the right word - "make one wonder" might perhaps be more appropriate.

However, I would personally not lose any sleep, nor comment, over anyone's choice between the various methods, with or without labels - and I definitely would not want to potentially (really!) confuse/mislead people by telling them that that the "should" or "must" earth unused conductors.

 

[JohnW2]

In the USA, a Neutral is now required to be "available" at the switch for all new work.

As has been said, in the UK the regs now say that that "should be considered" ... which is perhaps slightly odd, in a set of regulations that are primarily about safety, rather than 'convenience'!

 

[veedee]

At Toolstation, 100m of 1mm², the 3-core+E is 41.75% dearer than T&E.

2 Core & Earth - £38.99

3 Core & Earth - £55.27

The cost to call a spark (or DIY the job) would far exceed £16.28

In my location, sparkies are charging a minimum of £70 just to step foot in your house. Also, if walls/ceilings are chopped and chased, your likely to need a plasterer, decorator, not to mention cost of materials.

Again this would far exceed the £16.28 price difference

Not to mention the potential inconvenience, mess etc caused by the various tradesmen.

We didn't know the future.

@EFLImpudence I understand that the average sparky isn't clairvoyant, this is why i posed the below question

Given the benefits, why isn't the use of 3-core and earth the norm in modern electrical work?

By modern, I am referring to new installations). Apologies, I probably wasn't clear.

 

[veedee]

We see it on this forum - a core connected to the earths - all of a sudden, alarm bells start ringing, and people demand to know what the hell is going on.

Then there's always the fear that someone will come along, see an used core connected to the earth terminal, and then question whether that core is actually providing an earth for something, somewhere.

To me, connected unused cores to earth just complicates things for the next man.

Took the words right out of mouth.

Personally, it doesn't feel right to connect an unused core to earth connector block.

I know what's going on.. but in a few years time, I may forget, or the next person may not have a clue what's going on.

At the moment, the core is sleeved with earth sleeving and placed in the earth connector blocks.

However, if I were to place the unused core in a separate connector block, how would you label this, or inform the next person that it's unused?

 

[JohnW2]

Personally, it doesn't feel right to connect an unused core to earth connector block.

As has been mentioned, there certainly are (minor) potential downsides.

At the moment, the core is sleeved with earth sleeving and placed in the earth connector blocks.

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.

However, if I were to place the unused core in a separate connector block, how would you label this, or inform the next person that it's unused?

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?

 

[sparkwright]

I don't see any need to label unused cores that have been terminated in connector blocks.

If there is only one wire in the connector block, it's fairly obvious it's spare - or at least, 'not doing anything'.

 

[EFLImpudence]

Now we know why 3-core&E isn't used when it's not needed - because it's not needed, costs more and what to do with the spare core causes too many arguments and confusion.

 

[JohnW2]

I don't see any need to label unused cores that have been terminated in connector blocks.

I must say that that is what I would do, and probably wouldn't even dream of any 'labelling' However ....

If there is only one wire in the connector block, it's fairly obvious it's spare - or at least, 'not doing anything'.

.. it will certainly be obvious that it's currently 'not being used for anything' - but that doesn't neceesarily preclude the possibility that it is 'live' - and some might feel that there should be some label/whatever 'warning about that.

The first example which comes to mind is the situation if, for whatever reason, a timer fan is replaced by a non-timer one. Since the new fan wouldn't require a 'permanent live', it's that which would end up in a bit of connector block (or Wago/whatever), and might well still be 'live'.

 

[JohnW2]

Now we know why 3-core&E isn't used when it's not needed - because it's not needed, costs more and what to do with the spare core causes too many arguments and confusion.

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.

 

[EFLImpudence]

Yes, but there is no point discussing it.

 

[JohnW2]

Yes, but there is no point discussing it.

I would say that discussion is worthwhile, and potentially beneficial, in relation to almost any issue which requires a decision to be made - unless, of course,the person who has to make the decision is so arrogant as to believe that no views other than their own are worth listening to or considering.