RCD keeps tripping on socket circuit

[GPack]

Hello
What a day. I have just changed an old rewireable consumer unit for a new shiney twin RCD unit but the sockets are tripping the RCD. When all the appliances are unplugged the RCD stays in. When I plug some appliances in it is okay. When I plug other appliances in it trips. The RCD ramp test indicates it is tripping at 27ma. The ring has continuity on all each of the conductors. I've done an insulation resistance test on 250V on line to earth and have 240Mohms but seem to be getting 0 Mohms on Neutral to Earth. The circuit breaker is staying in.
Really appreciate any ideas as to why this RCD could be tripping.

Thanks

 

[MarkieSparkie]

If your measuring 0 MOhms N-E, then you need do a continuity test on the ring between N-E. You will probably find a resistance of several tens of KOhms or greater, this is causing the N-E leakage path, but the resistance is high enough not to trip the RCD directly, however, as the appliances are connected the leakage increases until a point is reached which trips the RCD.
Once you have identified the problem, further continuity tests around the ring should find the point of the fault.

 

[GPack]

Really Helpful. Thanks a lot.
I'm back there next week. Fingers crossed.

 

[JONOXNAM]

Hello
What a day. I have just changed an old rewireable consumer unit for a new shiney twin RCD unit but the sockets are tripping the RCD. When all the appliances are unplugged the RCD stays in. When I plug some appliances in it is okay. When I plug other appliances in it trips. The RCD ramp test indicates it is tripping at 27ma. The ring has continuity on all each of the conductors. I've done an insulation resistance test on 250V on line to earth and have 240Mohms but seem to be getting 0 Mohms on Neutral to Earth. The circuit breaker is staying in.
Really appreciate any ideas as to why this RCD could be tripping.

Thanks

Eliminate the actual socket accessories, switch them all to the off position, I have a a problem of Low I/R where two sockets caused high resistance problems of 40Meg when the socket was switched on but oc when in the off position. This problem as you can guess can come and go dependent on switch positions. See the photo..



IR should be at 500V but I guess your only running 250V until you clear the fault... and remove the conductors from the consumer unit common bars so you are sure you are only testing your circuit concerned.

Have you done all your dead tests (end to ends to make sure you have a ring etc)?

To trouble shoot find the mid point and do 50/50 split i/r tests to see where the issue is.

 

[telectrix]

a possibility is a crossed N/E at a socket. this will only trip the RCD when a load is applied.

 

[Octopus]

Really Helpful. Thanks a lot.
I'm back there next week. Fingers crossed.

"Back there next week", couldn't you go any sooner???

 

[GPack]

Thanks for all your help.

No sooner unfortunately. I've arranged a work around for them so they're happy enough. The chap has done a fair bit of his own wiring I think so he's being quite reasonable.

 

[oldtimer]

I changed a board and 2weeks later I got a call RCD was tripping sourced it to a faulty iron and the customer said but thats the top of the range and cost me £65 2 years ago I tested on my PAT tester and it failed so in your case you need to pin it down to what appliance or at what socket it is tripping

 

[Amp David]

a possibility is a crossed N/E at a socket. this will only trip the RCD when a load is applied.

Should of identified this though when doing his r1+r2 and r1+rn tests.

Some appliances might be duff too.

 

[SPARTYKUS]

Duff appliance is a common one. Kettles are good to do it.

 

[cablemonkey]

I find a quick pre-inspection when quoting saves loads for problems popping up later. hindsight is a wonderful thing :dozey:

 

[SPARTYKUS]

I find a quick pre-inspection when quoting saves loads for problems popping up later. hindsight is a wonderful thing :dozey:

yeah, been said already (other thread?) only takes minutes to do a global N-E test. Can speak volumes.

 

[GPack]

Just a quick one. Might sound like a silly question but as I'm getting 0 Mohms on a N-E insulation resistance test, why isn't the circuit breaker tripping when the circuit is energised?

 

[SPARTYKUS]

Because Mcbs detect overload between LINE and another conductor.

Not N-E. which is why you can have a neutral shoved in with cpc's & if no RCD present no one will notice. Maybe.

 

[SPARTYKUS]

Ps. NO such thing as a silly question, but understanding when/why a circuit breaker will break is pretty basic. I'm suprised you ask this while in the middle of a CU change!!