Neutral Woes

[Doctor D.]

Wotcha,

Could someone tell me whether it has it EVER been permissible to borrow a neutral on a landing light please?

Last weekend I replaced a consumer unit for a friend, and on pre-commissioning tests I realised that something was amiss. Investigation revealed that that the landing light was running from the downstairs lighting circuit (despite the fact that both switches are one gang) with a neutral borrowed from the upstairs circuit.

The property was built in the mid 1960's and cabling is plastic. Supplying lighting cable is earthed, whilst switch drops are not. Would the borrowed neutral date from the original installation on the property, as it does not appear much has been done to the wiring in that part of the house.

Due to the time of day we discovered this "characteristic" I left it with both lighting circuits connected via the RCD, to be sorted when I have to lift the floorboards on the landing to carry out some more rewiring in the next few weeks. The friend is aware of the problem with his wiring.

I am fully aware of the dangers associated with borrowing neutrals, and would just appreciate knowing it was ever commonplace or acceptable?

Thanks.

[Harry Bloomfield]

It was never acceptable, but is commonplace. It was once common to have just one single lighting circuit for the entire house, the installation of some earths suggests that some rewiring has been done which might have been the time when it was split into two circuits.

[Bob Mannix]

You should worry! I discovered my landing light was fed from the downstairs live circuit and the upstairs live circuit (one in each switch). Merrily I went along, having removed the upstairs circuit fuse, dismantling another upstairs light fitting. SWMBO turns on the landing light from downstairs. By this time I had broken the upstairs neutral circuit and had the wires in my mitt. Landing light glows dimly, due to the fact that I am the neutral circuit, after the neutral has risen in voltage enough to be very noticeable. WTF! Some time later I realise the person who did it obviously wasn't aware of the existence of 3core+E and got a bit stuck having laid in the 2core+E to a 3 gang switch downstairs already operating downstairs lights. "Never mind, there's a live here, that'll do". Grrrrr.

[Lurch]

How do you manage to get two lives in one circuit? Surely you had it that the live was from downstairs and the neutral from upstairs. When some of these installation were, well, installed there would more than likely have only been one lighting circuit so the neutral wasn't borrowed. At some time over the years thick people change the CU's and split the lighting circuit thing "ooh, more convenience etc...", not very often do they think "ooh better check those circuits for electrical safety before altering it". I generally leave lighting as it is when changing CU's for this very reason.

SJW A.C.S. Ltd.

[Bob Mannix]

I did not say there were two lives in one circuit, I said there were two circuits and the two way switch arrangement for one light (the landing light) used both of them. In a normal two way switch arrangement, the live from one circuit and its local switch is fed (via the 3core+E cable) to the remote switch. In my case the remote switch was on the end of a 2 core +E. The live for the remote switch was then borrowed from another switch in the same box, that was on the downstairs circuit. This made the lights worked but also sometimes connected the two lives together and electrified me!

Hope the ASCII art comes out OK

Correct:

L---------------------------------------------------------------------------

----------------

/o----------------------------------------------o | N--------[LIGHT]-------------/ 3-core (and earth) /o-----

o----------------------------------------------o/

SW1 SW2 Incorrect:

L---------------------------------- |

/o----------------------------------------------o N--------[LIGHT]-------------/ 2-core (and earth) /o------------ A different live

o----------------------------------------------o/

The 3-gang switch downstairs was new, so probably postdated the installation of two lighting citcuits, which I believe was done in the 60's.

I suppose that, had it originally been one circuit, such an arrangement would have been OK, but no-one should have ever replaced the switches and left it like that. I believe there did not use to be a landing light switch downstairs. Someone ran a cable down and fitted an extra switch to the box (badly).

Bob

[Lurch]

/o------------ A different live

I think you misunderstand. You did say there were two lives in one circuit, whether you meant to say this or not is a different matter. But, there are not 2 lives, the live is taken from the downstairs lighting, sent upstairs via the 2c+e through the switch on the landing and onto the landing light fitting. There are no other lives in this light, only one, not 2. there might be a red cable coming from the landing light to the landing switch but it's taking power to the light, not from it. So that's one live, not two. The ASCII art didn't survive as you may have noticed. So I'm going on what I managed to reconstruct out of the schrapnel!

SJW A.C.S. Ltd.

[Doctor D.]

Sadly I'm 99% sure that this is all original.

The cable is stranded with shiny plastic insulation, none of the earth wires are sleeved.

The CU was the original (8 way I believe) Wylex unit and appears to have been designed with two lighting circuits as it's quite a big place.

[Bob Mannix]

Sorry the ASCII art confused the issue. There was also mutual misunderstanding (and, as you point out a mistake on my part).

a) By circuit I meant upstairs or downstairs lighting "circuit" not the local circuit for the light (I could have been clearer, sorry) - clearly there is only one live in each of these.

b) Yes, you are right, of course, the two lives were never connected at the same time to the light, my mistake- the ASCII art was correct, I think, I misread it when describing the arrangement in words. The arrangement was as you describe.

Still very wrong as the live supply for the light should come from it to the switch(es) and back not from another lighting circuit, but not quite as bad as I described. The fundamentals that I suspect whoever it was laid in 2 core+e and then started scratching their heads and bodged it, causing me pain, still remains. (I pulled it all out and installed it properly).

Bob

[Harry Bloomfield]

Doctor D. wrote on Friday (23/01/2004) :

Stranded would be pre metrication. No earth wire would mean pre 1965 at a guess. The sleaving came in round about the time of metrication.

The earth back then, was only required if there was a metal fitting to be earthed, otherwise there was no need. That might explain why the switches lack an earth wire.

You might consider rewiring it to bring it up to current standards.

[Lurch]

[..]

Good idea rewiring, although it wasn't classed as a bodge when it was done, if you did have 2 lighting circuits from day 1 it was probably a sparky not quite being up to date with current practices, i.e. borrowing the neutral when splitting the lighting in 2. Then again it was the 60's, apparently hazey for all involved anyway!!

SJW A.C.S. Ltd.