Rcd tripping but cannot find fault

jh3141 · 24 Dec 2013

Had a bit of a flood due to last night's heavy rain, and woke up to find the rcd thst protects my downstairs ring main had tripped. Verified that it was that circuit causing the problem by switching it off at the mcb and leaving the others active at which point the rcd stopped tripping.

I then disassembled a socket on that ring to test insulation between the conductors, but all are reading >2M ohm. As they're all connected, I assumed I would be able to detect the fault at any socket, but this one is testing as fine. Any ideas what else might be going wrong here?

PrenticeBoyofDerry · 24 Dec 2013

jh3141 said:
Any ideas what else might be going wrong here?

If you take all the load of the sockets ie unplug everything and close any double pole switches to fixed appliances. Does the circuit trip when being reenergized?

EFLImpudence · 24 Dec 2013

jh3141 said:
I then disassembled a socket on that ring to test insulation between the conductors, but all are reading >2M ohm.

What are you using to measure it?

PrenticeBoyofDerry · 24 Dec 2013

jh3141 said:
I then disassembled a socket on that ring to test insulation between the conductors, but all are reading >2M ohm.

Did you also disconnect any conductors at the board?
And are sure it is ring final circuit? If so how did you come to this conclusion?

jh3141 · 24 Dec 2013

EFLImpudence said:
jh3141 said:

I then disassembled a socket on that ring to test insulation between the conductors, but all are reading >2M ohm.

Click to expand...

What are you using to measure it?

A fairly standard cheap digital multimeter.

jh3141 · 24 Dec 2013

PrenticeBoyofDerry said:
jh3141 said:

Any ideas what else might be going wrong here?

Click to expand...

If you take all the load of the sockets ie unplug everything and close any double pole switches to fixed appliances. Does the circuit trip when being reenergized?

Yes.

jh3141 · 24 Dec 2013

PrenticeBoyofDerry said:
jh3141 said:

I then disassembled a socket on that ring to test insulation between the conductors, but all are reading >2M ohm.

Click to expand...

Did you also disconnect any conductors at the board?

No, have merely switched off at the switch between meter and consumer unit.

And are sure it is ring final circuit? If so how did you come to this conclusion?

Pretty sure, yes. There are two live conductors at the consumer unit and all of the sockets on the circuit have two cables connected.

EFLImpudence · 24 Dec 2013

You suspect the flood so did any sockets actually get covered?
If so, you may just have to wait until it dries.

Are there outside sockets or lights on the circuit?

jh3141 · 24 Dec 2013

No, the sockets are dry. I assumed initially that the problem was caused by an extension cable that was plugged into the circuit and which did get wet. I'm not really sure why it's still a problem. The circuit is all internal.

jh3141 · 24 Dec 2013

PrenticeBoyofDerry said:
jh3141 said:

I then disassembled a socket on that ring to test insulation between the conductors, but all are reading >2M ohm.

Click to expand...

Did you also disconnect any conductors at the board?
And are sure it is ring final circuit? If so how did you come to this conclusion?

Have now done this, with no change in the results. The two cables coming to the consumer unit tested as continuous,.so it now seems certain that the circuit is a ring.

Stevoon · 24 Dec 2013

Could there be a junction box under the floor?

EFLImpudence · 24 Dec 2013

jh3141 said:
Have now done this, with no change in the results.

You mean it does not trip. ?

For the RCD to trip you must have a 'connection' of less than (around) 8,000Ω either between L & E or N & E.

If you say these are >2MΩ then it would appear to be alright.
Are you sure it's MΩ ?

I don't really know what else to suggest.

flyingsparks · 24 Dec 2013

You need an insulation resistance tester to check this really.

PrenticeBoyofDerry · 24 Dec 2013

Does your multimeter test insulation resistance?

I would suspect a low level junction/connection being flooded with water.

flyingsparks · 24 Dec 2013

PrenticeBoyofDerry said:
Does your multimeter test insulation resistance?

I doubt it as he said it's just a bog standard cheap digital multimeter..

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Rcd tripping but cannot find fault

Similar threads