No reading N-N end to end on a ring main

[Kuba]

I’m doing some tests on my board at home in order to prepare it for an upgrade. It’s an old plastic GE board with no rcd protection. Doing continuity of ring final circuit on the main ring. When it comes to end to end tests at the consumer unit I’m getting no reading between neutrals. All good between L-L and E-E. Figure of eight and I’m testing L-N on sockets and all readings come good (0.45-0.50 ohms) in every room. What could be the cause of this? ? Neutrals terminated badly at a socket somewhere? Rodents? JB?

Would taking one leg of ring out and looking with a Martin dale be a quick solution to find it before I start looking by splitting the ring?

Insulation resistance was L-N >299Mohms, L-E >299Mohms but N-E only 8Mohms.

 

[Risteard]

No point doing the cross-connections (figure of 8) if you don't have rn continuity. That needs sorted first. Probably loose connection on the neutral in a socket-outlet or screwed onto insulation. So it might be worth checking all connections including the phase and cpc.

I presume you've checked that the neutrals aren't mixed up in the DB?

 

[telectrix]

most likely is that a N has come out of a socket terminal. any case that's the easiest check to do, just by inspecting each outlet. if not, then short 1 end L-N at CU, go round sockets mesuring L-N resistance. this will track the fault location. or you could do N-E.

 

[Kuba]

No point doing the cross-connections (figure of 8) if you don't have rn continuity. That needs sorted first. Probably loose connection on the neutral in a socket-outlet or screwed onto insulation. So it might be worth checking all connections including the phase and cpc.

I presume you've checked that the neutrals aren't mixed up in the DB?

Yes I have tidied up and dressed all cables so I’ve got a pretty clear view of what’s what.

Someone told me that disconnecting one leg and checking each socket with a Martin dale socket tester is an easy and quick search. Should I give this a go? Otherwise I’ll follow what @telectrix suggested ?

 

[kropaske]

You can short LN on one leg and NE on the other and just change lead arrangement at every outlet, it will save you going around twice

 

[Lucien Nunes]

You suggest disconnecting one end of the ring, leaving the other powered, and going round with a Martindale to find the which are live L-N and which are dead. Yes, that will work, however it is a live test and where possible, dead tests with a resistance meter are often safer and possibly easier. If you short N-E at one end in the board and go round testing for continuity, you can open any suspect points immediately to check, without having to isolate, inspect, close up, re-energise and start testing again. The break could be at the last socket with continuity, the first one without, or somewhere between, so it could be a nuisance having to re-energise each time to use the Martindale.

 

[pc1966]

@kropaske suggestion seems the best quick test.

Or do you have a wander lead? A really simple option is to connect it to one of the N (with both isolated) and go round looking for which socket has N continuity or not, where it changes is (at least one) of the fault locations.

 

[telectrix]

main problem with the wander lead method is that :
1. customer's dog chews it
2, customer's cat shats on it
3.customer trips on it and sues you.

 

[pc1966]

The OP is testing in their own home, so I guess any trouble with Gnasher is up to them!

 

[Kuba]

You suggest disconnecting one end of the ring, leaving the other powered, and going round with a Martindale to find the which are live L-N and which are dead. Yes, that will work, however it is a live test and where possible, dead tests with a resistance meter are often safer and possibly easier. If you short N-E at one end in the board and go round testing for continuity, you can open any suspect points immediately to check, without having to isolate, inspect, close up, re-energise and start testing again. The break could be at the last socket with continuity, the first one without, or somewhere between, so it could be a nuisance having to re-energise each time to use the Martindale.

Thank you @Lucien Nunes for the advice ? I found it quite fast too.

 

[telectrix]

well done for finding it. now check every termination as one limp wristed termination may not be all.

 

[pc1966]

Did that also deal with the lower than usual IR for N-E?

 

[kropaske]

It may be good idea to switch off main switch next time, especially when you have nice shiny live busbar exposed like that

 

[telectrix]

It may be good idea to switch off main switch next time, especially when you have nice shiny live busbar exposed like that

where's the fun in that?

 

[cloverman]

Don't know why they had to uncover the Busbar , BUT should have powered off anyhow as good practice.
Always good to get into that routine of safety first