finding an earth break on a ring if in a JB?

[HappyHippyDad]

Morning all..

I have a bugger of a ring problem to solve on monday. All the following faults are on the one ring.

It has a N-E IR fault which I have almost found.
It has an intermittant tripping 32A MCB which looks like an overloaded circuit (one ring for whole house) and...
It has a broken CPC.

This house is absolutely jam packed with clutter.

I can find the broken CPC by doing the following:

1. Split CPC at any socket
2. Test at CU which side has broken CPC (wander lead or R1+R2)
3. Connect line and CPC of good side of ring in CU.
4. R1+R2 all sockets - those with continuity are ok and eliminated.
5. Reconnect at broken socket and break CPC at one of the suspect sockets.
6. Go to 2 above and repeat.

However, I have a feeling from spending a little time there that the fault will be in JB. The above method will find the fault if in a socket but not if its in an unreachable JB. How can I narrow it down to between 2 sockets? (i.e the ones either side of the faulty JB). I have to say I dont like the EFLI method, I dont find it accurate enough and it leaves you even more confused.

Is it just a case of slowly working out the layout of the ring and getting an idea of where the fault might be during all the testing or is there a better way?

 

[HappyHippyDad]

Why not give a high quote and see if the customer wants to go for it ....

sounds like you don't want it!

Well picked up Murdoch!
I guess i'm a bit embarrassed that its going to take quite a while to find these faults. Im used to finding broken rings and poor IR results in 1-3 hours. This has already taken a day tracking down the poor IR results and still not found (although nearly) and there is still the broken ring to contend with. Not my fault I know but still costing them quite a bit!
Id like to rewire the sockets due to all the problems with it.
1. Poor IR results
2. Broken CPC
3. Tripping MCB
4. Imperial cable.
5. 1 ring for whole house.
6. Many spurs.
7. Wall JB's feeding more spurs.

but they would never move out and its literally floor to ceiling in some rooms with junk.... so its a couple of days fault finding I guess to patch up an old system.

I think I just need to slow down and accept Im not going to get this one in a mornings work! I need to slowly go through the house and get a clear idea of the layout of the ring and go from there.
I remember quite a few of your threads saying something along these lines.

 

[Octopus]

Why are you on site? Sounds far too much hassle .................

 

[Dave OCD]

Sometimes you just end up with these jobs for various reasons and take responsibility, if we all avoided such things all the time a lot more people would have dodgy and/or unsafe electrics.

 

[static zap]

Is the attic just as bad ?
(new upstairs ring fed from above ! -oversized-)

 

[buzzlightyear]

what you could need is a good craw bar and a good axe
if all else fails .

 

[HappyHippyDad]

Man that was a tough day!

It needs a rewire!!!

Sockets off the lighting circuit.
Spurs off spurs (ring).
Shed spurred from a socket with multiple sockets in it and then to another shed!
And thats all in addition to the IR issues and broken CPC.

However one thing I could do with some help on is the following..

Broke the ring at the CU and the boiler FCU (on ring).
Leg A shows 1.1Mohm N-E
Leg B shows 20Mohm
Cable going into boiler shows 0.9Mohm

When I connect the cables in the boiler FCU back together I get 0.6Mohm N-E (with the boiler switch off) and 0.4Mohm with the boiler switch on??

 

[marconi]

Time is money. Knowing more now about the state of the installation do you think it time to do some sums on what it is going to cost to make the current installation safer/safe and a rewire; the customer can then decide on the best course of action. If they balk at the cost suggest taking out a loan.

This situation sounds similar to my friend's ward of court's home - the more you investigate the more you find wrong. This chap, Jim, is an adult and can live in his own home but he needs help with anything beyond cooking, cleaning and shopping because he gets confused. He is deaf too. After an EICR ( brittle rubber cables, increasing incidents of fuses blowing) my friend decided a rewire was necessary but Jim had no way of paying. So my friend arranged a small bank loan which Jim paid back over 2 years. The bank, HSBC, had no issues lending him the money.

 

[Deleted account]

We can advise customers on there electrical installations, but financial advise I personally wouldn't get involved in. If the customer was vulnerable I would contact there closest relative, age concern or whoever was best placed to give the client appropriate help.

In your case Marconi it was a friends ward of court, so appropriate advice in that case maybe, but not with everyday customers who you don't know.

 

[buzzlightyear]

this is what I would do ,get me snips out. cut the cable in the c/u for the circuits in question tell them that the installation is unsafe.
and wait for their decision .

 

[Lucien Nunes]

Broke the ring at the CU and the boiler FCU (on ring).
Leg A shows 1.1Mohm N-E
Leg B shows 20Mohm
Cable going into boiler shows 0.9Mohm

When I connect the cables in the boiler FCU back together I get 0.6Mohm N-E (with the boiler switch off) and 0.4Mohm with the boiler switch on??

My hunch is that various things are separately leaking to true earth, so when you parallel the two legs there are various other leakage pathways such as L (A) to CPC (B) in parallel with the 1.1 and 20MΩ readings you have. If you were to repeat the tests with the CPCs commoned in the bar but the L's split, you will probably find the numbers behave more like resistors in parallel. The behaviour with the boiler FCU switch is what I would expect because 0.9MΩ in parallel with 0.6MΩ gives 0.36MΩ.

 

[HappyHippyDad]

That all makes perfect sense Lucien, thankyou.

One last thing.. should the boiler have a result like this? I.e 0.9Mohm N-E. I dont know enough about the internal workings of a boiler to know if this could just be normal for a boiler. I dont think so as I'd get much lower results on other installations.
This particular boiler was only installed one year ago.

 

[buzzlightyear]

This particular boiler was only installed one year ago.

what megg ohm did you use ,having a boiler on the circuit!

 

[Dave OCD]

That all makes perfect sense Lucien, thankyou.

One last thing.. should the boiler have a result like this? I.e 0.9Mohm N-E. I dont know enough about the internal workings of a boiler to know if this could just be normal for a boiler. I dont think so as I'd get much lower results on other installations.
This particular boiler was only installed one year ago.

I'd say that the boiler N-E is very low and ought to be up in the hundreds of Megohms range but again it might be something to do with parallel earth paths through the boiler pipework.

 

[Lucien Nunes]

Not unless they're in parallel with the L & N!

Be careful when IR testing the boiler - it's an electronic appliance. Only do L+N together to E like a PAT IR, and probably only at 250V. If you were testing at 500V and it has MOV surge arrestors, that is likely where your 0.9MΩ came from and it will come up much higher at 250V. If you were doing the whole heating system with pump, valves etc then it could be anything.

 

[Dave OCD]

Re my last post Lucian, sorry it's been a long hard day and my brain has had enough.