I have had a problem with a very random tripping of the RCD on my CU. I have isolated all the appliances over time and can't narrow it down. There is no pattern to the tripping, it can happen in the day, in the night, with appliances running or turned off, rain, dry, etc etc.. can't tie it down to a specific pattern. So I called an electrician. He said the wiring checked out and that the RCD needs changing at a cost of £140. The RCD is a 80A with a 30mA differential. I asked what it was tripping at when he did his ramp check and he said 23mA which he said is low. My understanding is they should trip before the 30mA so first question, is this 23mA low and should I get the RCD replaced?I wasn't totally satisfied with his price so I decided to take the cover off the CU and have a look for a part number of the RCD just to price it up. I noticed one of the earths for the downstairs lights MCB loose so I tightened it up. I know the RCD will trip when there is a difference in current between the Live and the Neutral but could the loose earth on a MCB cause the RCD to trip without the MCB tripping?Any help would be greatly appreciated..

Lectrician wrote on Mar 22^nd, 2012, 3:49pm:


Thanks for your reply. The RCD is a Legrand 086 31, 80A 30mA. The chap who tested the RCD and wiring was a Part P registered Electricrian.

Just because he's Part P registered means nothing.

Borrowed neutral?

Mice nibbled part way through a cable...we've had that..a right pain to sort out and identify.