SOLVED: Suspected borrowed neutral

[mfarrow]

As the outside lights live feed comes from the switch, it's likely that the two extra neutrals in the rose are for these, or another downstairs fitting.

You really need to lift that loft carpet and get a neutral up there. Any redundant circuits floating around? Old shower cable for instance?

 

[Iggifer]

no unfortunately no redundant circuits anywhere.

I think I could fairly easily take a neutral from a bedroom supply though if this would solve it, push some conduit under the floorboards (they dont go all the way to the end of the loft) and then feed some T+E or conduit cable through and then just cut an access panel above the rose

 

[Taylortwocities]

If one of those is really a borrowed neutral (and you still do not really know)

Take all three neutrals out and reconnect them one at a time, when the RCD trips, there's your culprit.

EDIT & PS You wont find this problem with a Megger (insulation tester)

 

[RMS]

My advice would be to put both lighting circuits on the same RCD.

This is obviously the next best thing to rewiring. It clearly fails to comply with regulation 314.1.

There must have been plenty of electricians experiencing this problem when the seventeenth edition came into effect and RCD protection was required to protect all lighting circuits for the majority of domestic installations.

A method of testing for a borrowed neutral is to remove the neutrals for the lighting circuits at the consumer unit and carry out a continuity test between them. You need to ensure there is a tungsten filament lamp in the light(s) and operate the light switches in all positions. Your meter will show a dead short between the neutrals if there is a borrowed neutral.

 

[ericmark]

If and remember it's only a guess the two wire instead of three wire link between the two 2 way switches is the problem then only when the two switches are in one configuration will one detect the borrowed neutral.

To put both MCB's on the same RCD will stop it tripping, but will NOT comply with regulations. To comply with regulations you need to put all the lights on the same MCB.

It is a common fault. As I have said before with so called energy saving lamps today 6A for all lighting should be ample.

 

[17thman]

JonnW and myself are proponents of leaving lamps in and switches closed and checking for continuity between live and neutral for opposing up and down circuits and down and up circuits respectively. This will prove borrowed neatral.

If other dead tests are ok, change the cu for your proposed rcbo on each circuit set up with up and down lights on the same rcbo and put non maintained emergency lighting units next to cu and/or ground floor and one on landing, this should satisfy regulations if you wish to enterpret them in that way

EDITED rcbo and up and down lights on same rcbo

 

[Taylortwocities]

JonnW and myself are proponents of leaving lamps in and switches closed and checking for continuity between live and neutral for opposing up and down circuits and down and up circuits respectively. This will prove borrowed neatral.

I think this only works if you are using tungsten lamps, you'll need a lowish resistance through the lamp(s) to prove the connection. If CFL's etc are in place it wont work.
-unless I have misunderstood your method.

 

[Iggifer]

thanks for all the responses guys. thinking I will start by finding out the purpose of the extra neutral in the hallway rose, I suspect it's nothing

I will then go with 17thman and JohnW's testing adivce, and I especially like 17thman's suggestion for a non-maintained light to light the c/u, hadn't even thought of this.

Will let you know how I get on

 

[ericmark]

JonnW and myself are proponents of leaving lamps in and switches closed and checking for continuity between live and neutral for opposing up and down circuits and down and up circuits respectively. This will prove borrowed neatral.

If other dead tests are ok, change the cu for your proposed rcbo on each circuit set up with up and down lights on the same rcbo and put non maintained emergency lighting units next to cu and/or ground floor and one on landing, this should satisfy regulations if you wish to enterpret them in that way

EDITED rcbo and up and down lights on same rcbo

To test all combinations of the two way switch have to be tested. This is the problem although lights are on with one combination they will test as OK.

With RCBO there is not a problem but with MCB's I have found where instead of combining both circuits together using one MCB they have been only combined to use one RCD. So with two MCB's you still have a borrowed neutral even if it does not trip the RCD.

It is this image

which makes me think only two wires instead of three go between the two switches. The link is common in those cases and the link can clearly be seen here.

Of course it could be something completely different. But that picture rung alarm bells for me as soon as I saw it.

 

[Iggifer]

It is this image

which makes me think only two wires instead of three go between the two switches. The link is common in those cases and the link can clearly be seen here.

Of course it could be something completely different. But that picture rung alarm bells for me as soon as I saw it.

having re-looked at that photo, I might show a certain level of ignorance with two way lighting circuits, but hey, that's what I'm here for

The link wire between the middle and left switch is a live link no?

The switches run from left to right

Outside Light (D/S) Landing Light (U/S) Hall Light (D/S)

so linking middle to left is borrowing a live no? If I replaced this with a link from the far right switch to the far left, this would at least remove one instance of borrowing?

 

[Iggifer]

and worth mentioning I think that the Outside light is the one that takes the single, so I suspect this has been added, and they've skimped on taking T+E from the O/S light to the switch and just used a single and taken a Neutral from the nearest ceiling rose/fitting

 

[EFLImpudence]

The link wire between the middle and left switch is a live link no?

Yes

so linking middle to left is borrowing a live no? If I replaced this with a link from the far right switch to the far left, this would at least remove one instance of borrowing?

Only if the live comes from upstairs and not CU.

 

[Iggifer]

without proper checking, isolating the U/S MCB disables the U/S light, so fingers crossed the live is from the U/S circuit.

Having said that, the rightmost T+E is going into both an U/S and D/S commons

 

[EFLImpudence]

Is the outside light switched off by the upstairs MCB?

If so your suggestion re the link could be right

 

[Iggifer]

YES. The outside light goes off when I knock off the U/S light MCB.