I installed a new split load CU today. RCCB tripped and the fault was traced to the downstairs ring main. A test with a multimeter showed no continuity across the neutrals at the CU end, however the circuit worked when installed on the non RCCB side of the CU. I can only presume that the fault has existed for some time and has been brought to light by the new install. Does anyone have any suggestions as to how I can go about locating the fault. I've removed some of the socket fronts in the kitchen and checked the wiring there. If I remove all the others on the downstairs ring main and find no problem is my only course of action to start lifting the floor? Any assistance most gratefully appreciated.
Ring main problem
- Thread starter hilfe
- Start date
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What are the IR values for the ring?
Is there continuity on r1 and r2 ?
I will stick my neck on the line, and guess you have a N - E fault, possibly caused by one of the O/C neutrals shorting out somewhere.
Easiest thing to do is split the ring in the middle. You will have to estimate where the middle socket is and split the ring there. Then connect your testers on the continuity setting between N - E on each leg of the ring. This should show you the fault on one of the legs. work out which half of the split ring it is on, and split this half again. If the fault clears (at the mains) then the fault lies between the two sockets you have split. If not it is between the mains and the second socket you removed.
Continue doing this until you track it down to 1 socket / cable.
This should clear the N - E fault, and should be verified with an IR test once continuity has been re-established.
There may be more than one fault, so if you find one fault do not assume 'oh its cured then'
Test to make sure everything is right.
Is there continuity on r1 and r2 ?
I will stick my neck on the line, and guess you have a N - E fault, possibly caused by one of the O/C neutrals shorting out somewhere.
Easiest thing to do is split the ring in the middle. You will have to estimate where the middle socket is and split the ring there. Then connect your testers on the continuity setting between N - E on each leg of the ring. This should show you the fault on one of the legs. work out which half of the split ring it is on, and split this half again. If the fault clears (at the mains) then the fault lies between the two sockets you have split. If not it is between the mains and the second socket you removed.
Continue doing this until you track it down to 1 socket / cable.
This should clear the N - E fault, and should be verified with an IR test once continuity has been re-established.
There may be more than one fault, so if you find one fault do not assume 'oh its cured then'
Test to make sure everything is right.
Thanks to RF for the in-depth reply. I think I should point out that this is a diy install and IR values, r1 and r2 just went whooshing straight over my head. I was looking for some magical test that would save the work you describe. Looks like tomorrow is going to be a long day. Thanks for taking the time. If I sort it I'll post back.
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Someone may have 'borrowed' a neutral connection to a circuit on the non-RCD side, that would cause the RCD to trip too.
In any even you need to sort out your lack of continuity on the ring final neutrals, (this should not cause the RCD to trip).
In any even you need to sort out your lack of continuity on the ring final neutrals, (this should not cause the RCD to trip).
Oh sugar....I definitely thought that solving the continuity problem would be the answer. You mean that there could be something else???. I feel that it's unlikely that it's a borrowed neutral. The affected ring main runs down from the CU and both lighting circuits go up over. It would have to be a hell of a long neutral. As I said earlier....tomorrow is going to be a long day.
DIYers are not not not exempt from having to know how to do things properly.hilfe said:
//www.diynot.com/forums/viewtopic.php?p=75416#75416
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Just thought I'd give an update. I did indeed find a disconnected neutral at the back of one of the kitchen sockets. This restored the continuity in the neutral circuit. Problem solved, NOT. Connected into RCCB side again and it tripped. I now appear to have continuity between the neutral and earth conductors of this ring main circuit. Looks as if a little bit more investigation is called for.
At least you have a consistent fault to track. Better that than one that happens twice a day, sometimes...
Didnt the neutral/earth fault and broken ring show up when you did a PIR on the installation before you changed the CU? Ah guessed not, you didnt test it, right?
OK first possible is that a neutral has been trapped by one of the screws holding on a socket plate. Go whip out all the screws and pull out the sockets. If that doesnt fix it you'll need to follow RF Lighting's advice re splitting the ring and then use some detective work to narrow it down.
Good luck
Didnt the neutral/earth fault and broken ring show up when you did a PIR on the installation before you changed the CU? Ah guessed not, you didnt test it, right?
OK first possible is that a neutral has been trapped by one of the screws holding on a socket plate. Go whip out all the screws and pull out the sockets. If that doesnt fix it you'll need to follow RF Lighting's advice re splitting the ring and then use some detective work to narrow it down.
Good luck
Just thought I'd update. Fault was located in the last socket that I really wanted to look at, low down behind built in oven. Neutral insulation had been nicked and the core was either touching the metal box or the unsleeved earth conductor adjacent to it. All wired into the RCCB side now and working fine.
Why do you have unsleeved earth wires. This is very bad practice!!hilfe said:
The house is approx forty years old. All the stranded earths I came acroos in my investigations were unsleeved. I remedied that as I went along. The kitchen was re-modelled and extra sockets added about six years ago by a guy who I later found out had rather dubious qualifications. Had I not changed the consumer unit I would not have found his errors as the ring main appeared to operate correctly with the old re-wireable fuses.
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