Lighting and the dreaded borrowed neutrals !!!

[tuckermot]

Hi all

In the board changes i have done i have never come across a borrowed neutral on a lighting circuit,how common is this and between what years was this practice done .

Richard

 

[Dunc]

In my experience very common if the house was built in the 60s or 70s. If it's wired in double insulated singles expect there to be a borrowed neutral.

 

[tuckermot]

Hi dunc
how do you get round it bud apart from puting both circuits on same side of rcd and whats the best test to show if borrowed neutrals are present ??

 

[SirKit Breaker]

As Dunc says extremely common. I find that almost all houses wired in singles have shared neutrals. A good give away is in the CU or old fuse board. You will have 2 or 3 lighting circuits all on different fuses, but once you start to test you will quickly find out that there is only one neutral. They used to wire loop in and out Live at the switches on the ground floor from the CU, same upstairs, and sometimes the landing 2 way would also be wired on its own, so you get the impression of 3 lighting circuits, but then they just ran one neutral around the whole lot. I suppose they didn't know that sometime in the future the RCD was going to be invented,

Cheers.........Howard

 

[sparks_114]

I done a commercial board change a couple of months ago, it had 2 borrowed neutrals. In another board there was a borrowed line and so both the 3036 fuses had to be pulled for the circuit to die as one of the line conductors was intermittent in its workings.

 

[tuckermot]

when you discover borowedneutral on 2way lighting what do youdo to get round it and still fit the board with out tripping on 2 way switching ??

 

[tony mc]

Remedial work should be done to eliminate the issue!!
But if the customer won't have it
Place them both on the same RCD and in the same MCB and document it on the EIC.

 

[tuckermot]

are you saying that the 2way would need rewiring again ??

 

[telectrix]

in a word... yes.

 

[ian]

i tend to find out before the CU change, then pull another neutral and feed to service the most convenient circuit. it is very common, especially for houses wired in the 60,70 & early 80s.

ian

 

[SirKit Breaker]

I usually shove them on the same RCD but into separate MCB's, at least if they pop a lamp it normally takes the MCB out just for that circuit and doesn't plunge them into total darkness.

 

[tony mc]

Here is a old post re the subject.

Still unsure about testing for borrowed neutrals.

 

[tuckermot]

explain please

 

[tuckermot]

thank you tony for the posting

 

[Dunc]

I'd always prefer to fix the problem using a single neutral and earth (6241Y) from the downstairs circuit. I have fitted a RCBO before and noted on the certificate but i still don't like the idea that one fault will take out all the lights, just doesn't seem safe to me.

 

[tony mc]

It was just a post with different opinions re placing either in seperate mcb;s or placed into one mcb.

 

[ezzzekiel]

a single core will be in the upstairs light (switched live) disconect all the cables and put in junction box above ceiling except the single core which is your live from downstairs, run a twin earth from downstairs lighting or fusebox upto the light (cut back the live as its not required) you will end up with a switch live and new neutral and earth at the upstairs lighting point.

 

[telectrix]

i prefer to remove the live feed from the downstairs and run 3 core between the switches , if practicable, bearing in mind the damage to decor. obviously, each job would need it's own assessment of the best way to go with minimal disruption to decoration etc.

 

[steve447]

The last one i saw took me a while to suss it out, but with the help from this place i got it sorted, by as mentioned above running T&E from a JB on the downstairs lighting to the landing light and putting the rest in a JB in the loft. However it was whilst doing this i realised there was one too many wires in the loop in of the ceiling rose, a bit of head scratching and then getting the meter out confirmed that whoever done this had dropped the switched live down to the switch (using the black cable, no sleeving in sight) but had also connected a red to the loop in but just left it cut back (live at the switch). The switches were out of the bloody ark and once i got the switch plate off and found there was no back box but only a lump of wood which the switch plate was screwed into and the the live from the ceiling rose loop had made a nice scorch mark and was a rather burnt black colour at the end. Must of been that way for over 30yrs according the owners.

 

[Chr!s]

I usually shove them on the same RCD but into separate MCB's, at least if they pop a lamp it normally takes the MCB out just for that circuit and doesn't plunge them into total darkness.

Id be a little concerned about seperate mcb's, makes more sense if loading permits to make one radial circuit.

Chris