# Borrowed Neutrals

#### kermitklein

CAlling all experienced sparks........

#is there any reliable test one can carry out at the Consumer Unit to check for borrowed neutral especially in a lighting circuit?

I am tired of finding the problem in old 50's house once I have stuck a dual rcd board in !! lol

Thanks!!

#### Spark123

If you know which two you suspect are borrowing/lending then there's theoretically a couple of things you can do.
You can test between circuits to see if there is a join - switch on all lamps (using normal filament lamps and removing dimmers might be advantageous) and then join phase+neutral from one circuit.
Join phase and neutral from the other and test between the two circuits.
If there is a link you will see the resistance of the lamp between the two circuits.
You could also use a bog standard clamp meter (not one that gives you the result using a single flex), clamp the phase and neutral of each circuit together, as phase and neutral cancel each other out you should see zero amps flowing unless something is amiss.
I don't know how good the 2nd test is tbh, never tried it.

#### ColJack

ok.. meterless testing..
lets call the circuit you suspect is being borrowed FROM, circuit 1.
lets call the circuit you suspect of DOING the borrowing, circuit 2.

turn off the power.

1) take the neutral of circuit 1 out of the bar and place in a terminal block.
restore the power to circuit 2 and see if the lights on it all still work..

2) now put the neutral back and remove the neutral of circuit 2 and restore power to circuit 2 and see if any of the lights still work..

if a light on circuit 2 doesn't work at step 1, then it has a borrowed neutral from circuit 1.
if ANY lights work on circuit 2 at step 2, then they have a borrowed neutral from circuit 1, however this would also happen if you managed to connect both neutrals together somehow, so step 1 is the best indicator..

#### Space cat

ColJack said:
-- however this would also happen if you managed to connect both neutrals together somehow --

This makes step 2 a useful test in its own right.

#### ColJack

indeed.. if one light works then you know you have a borrowed neutral at that light, if they ALL still work then you know you've got your neutrals interlinked..

#### flameport

Another easy check is before even starting the work or quoting a price, look behind the light switches in the hall and upstairs landing. If there are only 2 cores between upstairs and down, its a borrowed neutral for sure.

#### ColJack

that's a wildly speculative leap..
the lights at mothers house are wired that way between switches and a black single and earth runs from the downstairs light to the upstairs light..

#### oharaf

I consider the problem like this.

The borrowed neutral is nearly always between the landing light and the down stairs light circuit, 2 cores behind the switches is a GOOD indicator also.

I generally perform a continuity test between the 2 circuits, if it shows then I inform and price accordingly!!

#### ColJack

I'm not disputing that it's a good indicator that it MAY be a borrowed neutral, but flameport stated it as a surity that it is..

G

#### Goldberg

Is it really that hard?

If you turn off all MCBs and disconnect all neutrals (except one) from the bar, then continuity between any two neutrals implies borrowing.

#### ColJack

no it doesn't
borrowing is not interconnection..
borrowing is using a live from 1 circuit and a neutral from another..
there is no connection between the neutrals of the first and second circuit.

as already said, you would get a readiing from the live of one circuit through a filament lamp to the neutral of the other circuit..

G

#### Goldberg

no it doesn't
borrowing is not interconnection..
Yes it is.

borrowing is using a live from 1 circuit and a neutral from another..
there is no connection between the neutrals of the first and second circuit.
Yes there is...

as already said, you would get a readiing from the live of one circuit through a filament lamp to the neutral of the other circuit..
...and there it is.

#### ColJack

so you're basing your claim on there being filament lamps in, and all the switches being on..

claiming that 2 neutrals are interconnected if they have to go through 2 lamps to do it?

G

#### Goldberg

so you're basing your claim on there being filament lamps in, and all the switches being on..
Of course. Who would want to go to the effort of removing all the lamps just to find out if there's a borrowed neutral?

claiming that 2 neutrals are interconnected if they have to go through 2 lamps to do it?

#### ColJack

Goldberg said:
Who would want to go to the effort of removing all the lamps just to find out if there's a borrowed neutral?

What if there are no filament lamps in the house? mine are all CLF's or FL's.. so are my mothers..
Who wants to go round and switch every single light on?

very handy that..
I missed one word off and sudenly you don't comprehend?
I missed the word "You're" off the front..

You're claiming that 2 neutrals are interconnected if they have to go through 2 lamps to do it?

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