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

 

[Risteard]

As I suggested - a loose connection in a socket-outlet meaning continuity was lost.

 

[Kuba]

It’s hard for me to do any testing in my house recently as my wife is working from home and can’t disconnect the power for too long ?‍

Couple of days ago I checked IR on each circuit and I had 30M ohms on each ring and light circuit separately, smokes were >299M ohms (I only have four circuits).

I did notice in the past that some cables been chewed by rodents so this could be the reason. Rewire is unfortunately not gonna happen as we just finish decorating the whole flat ?

I have no rcd protection on anything and I want to add an rcd or ideally change the whole board with rcbos. Do you think it’ll just trip out my board?

 

[pc1966]

I have no rcd protection on anything and I want to add an rcd or ideally change the whole board with rcbos. Do you think it’ll just trip out my board?

A 500V test giving 30M won't trip anything out, that is perfectly reasonable.

Given how cheap RCBO boards are now you really ought to go for that, and SPD, and have pretty good protection of things. RCD also provide a bit more protection against future rodent-damage possibly starting a fire, etc, as an leaking current on T&E is likely to end up on the unsheathed E and so tripping the RCD side of things.

 

[Kuba]

A 500V test giving 30M won't trip anything out, that is perfectly reasonable.

Given how cheap RCBO boards are now you really ought to go for that, and SPD, and have pretty good protection of things. RCD also provide a bit more protection against future rodent-damage possibly starting a fire, etc, as an leaking current on T&E is likely to end up on the unsheathed E and so tripping the RCD side of things.

I would have changed the board if I could but that would mean I’d have to interrupt my neighbours supply (cut out has two separate lines but both neutrals go into same enclosure) so pulling out both fuses at once to do it safely would have been the way? Not to keen on bothering them (they’re both teachers and school online so need power on)... and I could just add an rcd and put a lock on my main switch, quick and easy hopefully ?

 

[freddo]

Is it just me or does the wiring all look newer than the CU? Didn't expect it to be all harmonised cable colours.

 

[pc1966]

Well harmonised fixed wiring starts 2006-era (from memory) so it might overlap, but interesting point.

 

[freddo]

2004 it began, just after I started work.

 

[Kuba]

How old do you think this CU is? I have put new earth sleeving on each cpc but yeah wiring seem post 2006 (except for one room where they kept the old switched line to a pendant).

 

[littlespark]

I would have changed the board if I could but that would mean I’d have to interrupt my neighbours supply (cut out has two separate lines but both neutrals go into same enclosure) so pulling out both fuses at once to do it safely would have been the way? Not to keen on bothering them (they’re both teachers and school online so need power on)... and I could just add an rcd and put a lock on my main switch, quick and easy hopefully ?

Why would pulling your fuse disrupt next door?
Anyway, that’s a job for the fairies.

As implied earlier, you have to be careful working anywhere near a live board... remember, you’ll only get a serious belt once in a lifetime!

 

[Kuba]

Why would pulling your fuse disrupt next door?
Anyway, that’s a job for the fairies.

As implied earlier, you have to be careful working anywhere near a live board... remember, you’ll only get a serious belt once in a lifetime!

Thanks for the warning. I’m aware of the danger and always try to work safe and isolate where I can.

When you look at the picture you can see that both neutrals come from the same enclosure. If a fairy came and pulled my fuse, there would still be a potential risk of current on a neutral in my main switch through parallel paths?

Ps my supply is the brown cable and my neighbours fuse blocks the enclosure from opening where the neutral is.

 

[Kuba]

If anyone reading is interested, I added a rcd to the board. Did tests and everything came out satisfactory. Just need new labels. Ideally I would have changed the whole board but will wait with this until after pandemic when I can work in an empty house and not be distracted. Happy days ?

 

[westward10]

Why didn't you just replace the main switch with the rcd instead of doctoring one in.

 

[Kuba]

Why didn't you just replace the main switch with the rcd instead of doctoring one in.

I have read about rcd being used as a main switch and seen mixed opinions, being against/ok with regs, bad practise etc etc so decided to keep it in case.

 

[Risteard]

I have read about rcd being used as a main switch and seen mixed opinions, being against/ok with regs, bad practise etc etc so decided to keep it in case.

An RCCB can be used as the main switch. Not sure how it could be considered bad practice.

 

[static zap]

An RCCB can be used as the main switch. Not sure how it could be considered bad practice.

Does get me worried about , IR tests for rest of installation !

 

[Risteard]

Does get me worried about , IR tests for rest of installation !

I'm not following you. There is double pole disconnection with either a switch disconnector or an RCCB.

 

[static zap]

Does get me worried about , IR tests for rest of installation !

Was more thinking ,of a reluctance to have an " RCD" type Master switch.
( any defects getting ignored - Must admit I am guilty of skimming thread...
my brain solving other issues at moment )
as I took RCCB on just 1 circuit ! (and not IR test- risks to RCCB)

 

[telectrix]

Why didn't you just replace the main switch with the rcd instead of doctoring one in.

i'd think he did it that way or he would have had to work live or diss, tail/s from meter. ( assuming no up front isolator. ).

 

[kropaske]

I added a rcd to the board.

You don't have any selectivity now between rcd and downstream mcb's, an earth fault will likely trip your rcd which means you will loose whole installation. IMHO better option would be to install individual rcbo's

 

[telectrix]

You don't have any selectivity now between rcd and downstream mcb's, an earth fault will likely trip your rcd which means you will loose whole installation. IMHO better option would be to install individual rcbo's

think OP has done it temporary till he can get round to replacing CU.

 

[Kuba]

think OP has done it temporary till he can get round to replacing CU.

Exactly, yes. And I agree ? will be swapping it for a new CU eventually.

All points regarding rcd as a main switch taken on board, every day is a learning day ?‍

Ps as I said earlier, isolating the board by pulling the main fuse doesn’t make it 100% safe because neutral shares same enclosure with my neighbours installation. Please tell me if I’m wrong? I posted some pictures earlier in the thread for you to see what I’m on about ?
The only way to look inside is to pull my neighbours fuse because it blocks the lid where neutrals are terminated and I want to avoid doing that.

 

[telectrix]

pull the tails out of the meter in that case.

 

[brianmoooore]

You've posted a pic. of your CU with two grey tails going into it, and you've posted a pic of your service head with a blue, red, and brown tail leading from it. Could you post a pic of where these tails meet, please.
Should be a meter somewhere.

 

[Strima]

On a TNC-S theoretically the neutral and earth should be at the same potential as they're linked at the supply head.

On a TN-S theoretically the earth and neutral could be at the same potential as they're linked at the transformer but there may be resistance differences on the cables and sheath causing a potential difference.

On a TT neutral and earth potentials could be significantly different.

TBH with a shared supply I'd take the much safer option of dropping the tails out of the consumer side of the meter, technically these belong to the consumer so they have the legal right to do this although breaking the seals on the meter could be classed as criminal damage as they belong to the supplier... ??

If possible I would add a main isolator switch to avoid this in the future and make additions/alterations much easier and safer.

As for having an RCD main switch I try to avoid them as one fault will effect the whole installation.

 

[Kuba]

You've posted a pic. of your CU with two grey tails going into it, and you've posted a pic of your service head with a blue, red, and brown tail leading from it. Could you post a pic of where these tails meet, please.
Should be a meter somewhere.

Here’s a pic of the whole thing. TNS system. Quite tight for space if I added an isolator before the CU. I had to pull up my cables from the board as I had no space inside and kept the slack for future when I upgrade it. I will be using some fire rated glands. Ps, yes, my neighbours have their rcd as a mains switch I know ?