Borrowed neutral and how to fix

[Spikenaylor]

Got a 2 gang 2way switch on downstairs hall, The switch for the upstairs circuit is fed from the downstairs circuit, lives cables( t& e) go in the wall and up across the finished landing floor and up to the upstairs 2way switch, live (just one) the goes up in wall to rose, borrow a neutral from upstairs circuit and hey presto, it works.

How do I fix this, without running new cables, as client just replastered, painted and layer new flooring.

 

[ezzzekiel]

a neutral needs taking to landing light from downstairs lights/cu

or place all lights on same mcb if loading is ok

 

[Top Cat]

Had the same problem a few days ago when changing c/unit. Had to put both cicuits on 1 mcb. Not ideal but it is clased as 1 circuit then. The only other way would be to disconnect the neutral to landing light and run a cable from down stairs lights to the landing light up the outside of building. Make sure you mark in c/unit that landing light is off downstais light and i would mark in back of landing switch that the switch has 2 circuits in it.

 

[vernam616]

Call an electrician matey

 

[ezzzekiel]

i would mark in back of landing switch that the switch has 2 circuits in it.

no it wont

 

[Top Cat]

You are right! Must have had the brain on backwards at that point. Stupid boy!

 

[SparkyDips]

Call an electrician matey

always amuses me this lol

 

[oldtimer]

House painted customer wants no mess then you cannot fix it ie put them on the same breaker

 

[ackbarthestar]

You have one of those curious old fashioned problems where a rewire wasn't a complete rewire but, most likely a CU change using old cables.
The least you can do without running either a separate feed or neutral to the upstairs landing light is to place both lighting circuits on the same RCD but separate breakers.
This is not a conventional circuit or compliant with BS761. Since you will not achieve isolation by one MCB alone.

I remember once being approached by a right 'Lone Ranger' painter and decorator, who said. "We rule the roost. If we didn't exist then the job would never get finished" It appears he maybe right.....

 

[ezzzekiel]

to place both lighting circuits on the same RCD but separate breakers.

that is bad practice in my opinion, if this method is to be employed then both circuits must share same mcb for isolation purposes.

 

[ackbarthestar]

that is bad practice in my opinion, if this method is to be employed then both circuits must share same mcb for isolation purposes.

It depends what the loading is on each of the circuits and the diversity likely to be applied. Older properties seem to have less lights, newer properties are often loaded to the gills.
I'd agree its not compliant and generates ambiguity, but then, on the other hand the client doesn't want his paint work damaged so that leaves you with no choice but to condemn the circuit, and fight it out in the courts for payment.

If it was a consumer unit change then it would have been up to the sparks to check that the circuit's neutral wasn't shared before the work started.

 

[ringer]

Ackbar, you seem to be missing the point. With two lighting circuits each on their own mcb, and a shared neutral at some point on those circuits, if you isolate one mcb you can get backfeed from the unisolated circuit VIA the shared neutral. It is not about overloading a circuit, but ensuring electrical isolation when required.


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[ackbarthestar]

No, I think I covered the points you have raised
1/ The loading, or lack of it, on each lighting circuit will determine whether or not to put them both on the same MCB
2/ As stated earlier, Isolation will not be achieved by one MCB alone.

It could still be achieved by mechanically linking them together so that there is a single point of isolation and the loading is catered for.

Doesn't it get complicated when:
A/ the sparky does check before doing any work
B/ An intransigent customer who would prefer to have nice paintwork and probably frilly curtains, rather than making sure all electrical systems were safe and compliant.

 

[malcolmsanford]

Taking the argument on further Ack, purely as discussion. what would you do ......remit CU change, borrowed neutral found before change started, client did not want it remedied .............cancel CU change?

 

[ackbarthestar]

Depends on the client's attitude. My first question would be somewhere along the lines of 'Did you plan to have the CU changed and the wiring checked before decoration took place?