Neutral from neighbour?

[n180]

Only the one ring circuit in whole house. Small 2 bed terraced house.

Doing an EICR, and the socket ring circuit is working perfectly fine with all neutrals at CU disonnected (led up to all neutrals being disconnected). Getting 242v at socket outlets without neutral .

In case one of the earth's got mixed up as neutral somewhere, I tested with all earth's disconnected. Still getting 242v at socket outlets.

Switch the breaker off at the CU and power to sockets goes off.

Where could the neutral at the sockets be coming from, is it neighbours possibly?

 

[Strima]

Any FCU's spurred off for lighting etc? Could be linked to another circuit, quite possibly bathroom extractor fan?

 

[HappyHippyDad]

Are you saying you are get 240V L-N when the neutrals are disconnected, or 240V L-E when the neutrals are disconnected.

Are ALL the neutrals disconnected or just the ones to the ring?

Is there any continuity between the ring neutrals and any of the other neutrals?

What's the IR between N and E, perhaps they are touching? This would only be possible if there is no RCD though otherwise it would be tripping.

 

[n180]

No FCU off the ring.

All neutrals on all circuits in CU are disconnected, and still getting 242v L-N. I can actually plug in something like a drill and it actually still works.

IR between N and E is 78.3 so not great but no RCD anyway.

 

[HappyHippyDad]

No FCU off the ring.

All neutrals on all circuits in CU are disconnected, and still getting 242v L-N. I can actually plug in something like a drill and it actually still works.

IR between N and E is 78.3 so not great but no RCD anyway.

Is that 78.3Ω or 78.3MΩ?

 

[HappyHippyDad]

If it's 78Ω then you have a N-E fault and the voltage is finding a pathway from the neutral you are testing back through earth.

The earth will then be connected to the supply neutral as I'm taking it it must be TNCS or TNS if there is no RCD?

 

[n180]

78.3MΩ

 

[n180]

That's what I thought also hhdad, but I disconnected all the earth's from cu for a quick test also. Sockets still work.

So with all neutrals and earth's of every circuit disconnected I can only think that somehow there's a borrowed neutral from next door. Can't think of anything else it could be.

 

[HappyHippyDad]

Perhaps try an IR between the neutrals of the ring and the bonding conductors. The bonding conductors may be connected to next doors, which wouldn't be unusual. Unless of course you did a global IR which will already have ruled this out.

 

[Cid]

Split the ring into two radials and see if you can narrow down which socket the neutral is coming in from.

Also check the loft to see if it's a shared loft.

 

[westward10]

If you have 70 plus Meg between neutral and earth it is not likely to be a borrowed neutral. If it were you are likely to get zero Meg where the borrowed neutral is still at earth potential

 

[HappyHippyDad]

If you have 70 plus Meg between neutral and earth it is not likely to be a borrowed neutral. If it were you are likely to get zero Meg where the borrowed neutral is still at earth potential

Deleted before anyone could quote

 

[Lucien Nunes]

All functioning neutrals are near earth potential, that's what makes them neutrals. The IR would read near zero resistance too, it must be no more than a few ohms if it can pass enough current to operate an appliance.

I would say it's much more likely to be down to something earthy nearby rather than someone else's neutral. I can imagine a screw going through the N in the cable and hitting a metal water pipe, but not going all the way into next door's cable!

Was your IR test done with all the CPCs connected to earth? I.e. have you tested from the RFC neutral to the MET or just to the CPCs?

I can think of a few quick troubleshooting strategies but someone's at the door...

 

[snowhead]

It could be something as simple as a nail through a socket Neutral in the floor, touching a copper water pipe.
Or squashed cable with only the Neutral touching a pipe.

 

[Deleted member 26818]

I have had this where someone has taken power to an interconnected smoke alarm from a socket circuit, with others taken from lighting circuits.

 

[Wilko]

Hi - I vote for a N-E fault too. You could also be using neighbour's bonding to complete the circuit.

 

[Andrew B]

With all equipment disconnected on the circuit, incoming supply off and circuit N disconnected at the CU measure IR from circuit N to the supply N.

If there is a borrowed neutral from neighbours or other circuits, or an earth crossover you'll see low resistance.

Then it's a case of elimination, one by one remove circuit neutrals and check IR until you get a high reading. If it stays low move onto circuit CPCs and bonding conductors one by one.
If you've removed all circuit CPC and N and still get a low Resistance from circuit N to supply N then it must be bypassing the CU somehow

 

[Toneyz]

When you are doing an insulation resistance test is all the cpc's bonding and the main earthing conductor connected?