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]

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 !