This fault has me confused!

[HappyHippyDad]

I rather foolishly booked in a fault finding job in a 2 hour slot thinking I could solve it quickly, I couldn't!

It has me confused, although I haven't let myself slow down yet and focus so you guys may point out something obvious.

It is an intermittent tripping MCB on a 32A ring ciruit (sometimes the RCD trips) on a dual RCD board. It trips a number of times each day. This has been going on for perhaps a week. Over the last 2 days 5 sockets have actually stopped working completely even with the power on. The ring feeds the whole house.

r1 = 0.14 Mohm (140,000 ohms)
r2 = 28K ohms (28,000 ohms)
rn = 0.7 ohms

With all sockets connected and the ring split in the CU I get :

Leg 1 = L/N - E 0.01Mohms
Leg 2 = I didn't write down the results but they were >1Mohm.

When I split the ring at one socket the IR results were all >1Mohm when tested in the CU, I didn't test at the split socket.

I think I'm getting confused because of the 5 non working sockets. If a ring is broken (as this is) all sockets should still work. Am I right in thinking there HAS to be 2 faults either side of those non working sockets (assuming they are not all spurred from the same socket) or am I missing something?

Usually, in order to find the break I would split the ring. Reconnect the leg that has continuity with the relevant leg in the CU liven them up and eliminate the working ones, but if there are 2 breaks this wont work, i don't think!

Update... the customer has literally just rang saying he removed a socket and just plastered in the cables a while ago and when he bangs that part of the wall it trips! However, this would be just one fault and would still not stop 5 sockets from working!!

 

[HappyHippyDad]

Update....

I returned this morning at 8am. It turns out the customer hadn't hidden a socket in the wall, they had removed a TV wall bracket and plastered over. I cut a hole in the wall (stud wall) where the bracket had been and found this..



I fixed the above which cleared the poor IR results and got the 5 non working sockets working, I then started fault finding the broken ring. I'd already quizzed the customer a number of times about any thing they'd done or anything out of the ordinary. 30 mins into the fault finding they remembered they'd had a spark off a redundant fused spur. I opened it up and found a disconnected line and cpc. Connected them up and the ring tested as intact.

Then.... I tested the RCD (as at the beginning it was not tripping when tested which I thought may be due to the fault(s) as this sometimes stops the RCD from working) with all outgoing terminals disconnected (thanks again DS). It was faulty. I put a new one in, all tested fine!

3 major faults! Bloody ell, never had that before. I am now having a half day off so I can sit contentedly with a superior grin on my face whilst sipping my coffee and telling you all about it ?

 

[Strima]

Happy days, now foot down Friday for a well earned beer.

 

[static zap]

so I can sit contentedly with a superior grin on my face whilst sipping my coffee and telling you all about it ?

You are completely in the zone.
(Or was that the TV bracket !)
Enjoying the happy ending.

 

[Lucien Nunes]

Result. There's nothing better than using skill and strategy to solve a problem that started out so obtuse that it was difficult even to describe to begin with.

 

[Peakyblinder89]

Great work, well done . Enjoy your Friday night take away and pint . ?

 

[littlespark]

I am now having a half day off so I can sit contentedly with a superior gin in my hand

Corrected that for ya

 

[Dave OCD]

Very well done HHD,give yourself tomorrow off as well mate.

 

[Zerax]

Well done and great update... As Hannibal in the A Team used to say... I love it when a plan comes together !

 

[Gary latto]

Well done finding them fella enjoy the beer ?