Temp fix to 'borrowed neutral'

[clowes_ian]

Whilst swapping a light fitting at the w/e I came across what I think is termed 'borrowed neutral' on our landing light.

The fitting was a standard loop-in rose, with the switched live coming from a 2+E to the landing light via the red. The black was left cut (but unstripped) and unconnected in the switch and also the rose.

The neutral was being drawn from a spur on the upstairs lighting. I believe this is bad but, having Googled and tried/failed to digest old Bob Mannix and Mungo postings, don't fully understand why.

The dangerous aspect (to my mind) was that the borrowed netural's line counterpart had been 'parked' in the central block of the loop-in terminals.

Although this may be obvious, there was still an amount of spare connection space in the rose as it wasn't being looped out of for other lamps. Just to recap: lamp line plus switched line in normal slots; lamp neutral plus borrowed neutral in two of the three slots normally used for neutral; and one lonely line from the upstairs circuit sitting in the middle block.

I'll look into pulling 3+E through at some point to sort all this out. In the short term am I right thinking it would be safer to disconnect the unused line at the other end of the spur, or is there some good reason for leaving it as is?

IanC

[Christian McArdle]

I take it that the unswitched live to the switch was not looped through at the rose?

In which case, provided that the neutral and the switched live are from the same circuit, it shouldn't matter excessively.

It seems that someone has looped through neutral at the rose and live at the switch, but using T&E, with one conductor unused. This used to be a common way of wiring up lighting circuits, but is now deprecated.

The reason not to do this is that it sets up an induction loop, which can interfere with hearing aids.

Provided neutral and live are from the same circuit, I would leave it until rewiring anyway.

Christian.

[clowes_ian]

through at

Although I haven't looked, I'm guessing the unswitched live is obtained from the 2-gang plate on the ground floor by linking the COM of one switch to the permanant live of the other switch on the plate, which is for the hallway light. The L1 and L2 terminals of the former are then fed using 2+E to the 1G plate on the landing, which then has this switched live fed to the landing light by the red core of the cable with the unused black.

I'm perhaps being dim, but isn't the switched live the same as the unswitched live, except on opposite sides of the switch(es)? The live that eventually makes its way to the light is from the downstairs circuit. The neutral in use there is from the upstairs circuit. The live that goes with the neutral is completely unused, and is parked as the only connector in one bank of the rose's connector blocks.

Nothing is looped through at the rose. It's the end of the run. What you're describing there sounds a bit like what I was trying to describe at the ground floor switch.

Better fix it soon then, the way my hearing seems to be going...

But I don't think they are. I suspect your terminology and conceptualisation of the circuit is a little ahead of mine. I'd obviously be happy not to have to do anything, but wouldn't want to mislead myself into this state.

To recap one more time (as I've probably confused you all now), at the rose there's a live (from downstairs, via switches) and a neutral (from upstairs) feeding the lamp, plus the unused live, plus the cut but unterminated neutral that has a matching twin in the switch.

I'm not sure I explained what I actually found the dangerous bit: It's that if you turn off the downstairs circuit and open up the rose then the 'parked' live from the upstairs circuit is still at 240V. To fix this in the short term it seems sensible to disconnect it at wherever it spurs from.

IanC

[Christian McArdle]

Well, if you're sure you've identified the conductors, then there is a simple fix.

Connect the live from upstairs to the centre terminal (where it already is). Connect the switch red to this. Sleeve the switch black with red sleeving.

At the switch end, disconnect the downstairs live and use only the upstairs live and switched live coming down the cable.

You still have 2 circuits sharing a box, but this is common in 2 way switched circuits, so competent people would know that throwing the MCB for downstairs doesn't deenergise the upstairs circuit in the downstairs switch.

Christian.

[Christian McArdle]

And connect to lamp live, of course...

Christian.

[bigcat]

Lethal. You could die from just walking underneath it.

Being serious,

1. a label on the CU would alert anyone to the potential for confusion.
2. Your stairs are 1000 times more dangerous.
3. So if you want to improve your safety, youre wasting your time on this one.

NT