RCD keeps tripping on socket circuit

GPack · Jan 20, 2012

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

tony mc · Jan 23, 2012

Switch your meter over to Ohms after the IR test and find out what it is reading.

The RCD will detect a earth neutral imbalance but if the ohms reading is over 7666 ohms the RCD will most likely hold.

230/0.03 = 7660.

Now when you find what it is reading you will have to start spliting the cct to find the problem as its well under 1Meg from your IR test !

ezzzekiel · Jan 23, 2012

common for n/e fault not to trip rcd until load applied, ir the ring and break it down till fault located

GPack · Jan 23, 2012

Thanks for your help. The answer to my question is pretty obvious now you mention it. Sincerely appreciated.

Deleted member 26818 · Jan 23, 2012

Another thing to remember, is that with TN-C-S, the earth and neutral are connected at the head.
Only way to see if there is continuity between the earth and neutral in the installation, is to ensure the neutral is disconnected.
You need the main switch off, not just the MCB.