RCD tripping on ring main after new CU Install?

**Dave M** · 19th April 2009, 04:29 PM

I have just fitted a new 17th edition Consumer unit as a replacement for an old bs3036 rewireable fuseboard and i have had some problems with the ring main circuit.

The problem is that the RCD (63 Amp - 30ma) keeps tripping, i have found a broken neutral in one of the walls and replaced the faulty wire and can now get continuity on both the neutral and live conductors but as soon as i connect the circuit into the RCD it keeps tripping out. The RCD is working ok with two other circuits so its not faulty.

The load on the ring main is neglible with only the central heating controls drawing any current. (so 5 amps max)

I will do an insulation resistance test on all the conductors next and check the earth continuity.

Does anyone please have any idea what might be causing this tripping?

**grandad** · 20th April 2009, 10:36 AM

sounds like an earth fault,do insulation test.
you should by rights have carried out this test among others before energizing.
you need to test it to issue an installation certificate

**pattester** · 13th May 2009, 05:35 AM

Hi

I think you will find it is either a fridge or a freezer or even the central heating coming on that is causing the RCD to trip these should be in an non RCD protected circuit.

**slybacon** · 13th May 2009, 09:52 PM

i have had this problem in the past when fitting new board and found that someone has used a neutral of a socket to feed a new light but taken live of light switch ,, try disconecting lighting live and neutrals and see if it stops tripping ,

**C. ME** · 24th May 2009, 11:30 PM

Dont forget to check that the neutrals are definatly connected to correct neutral bar for the circuit being protected. It is a very common problem.

**akaboosi** · 5th June 2009, 08:14 PM

Does it trip instantly after switching the MCB on for that circuit or does it stay on for a while.

I've just done a house not long ago and same thing happened. Turned out to be a nail through a 2.5mm twin earth cable. Silly joiners. Semi-skilled tradesmen!!

You could test continuity between earth and live and then earth to neutral. Make sure everything unplugged first.

**cj-sharpy** · 25th July 2009, 12:30 PM

I'm pressuming you carried out all your legally required tests on the installation before energising the new board. If so then you will already know that you circuits are fine. You R1+R2, insulation resistance tests should have proven this.
So given that you should have carried out these tests and have a schedual of test results with your installation cert to prove this then I would say that you must have a faulty aplliance on the ring main.
Or a dodgy light fitting if these were disconnected for testing.
Hope that helps.

**Greg** · 26th July 2009, 08:25 PM

OK switch everything off on the consumer unit, switch on the main isolator and both Main RCD's. They should hold with each MCB turned off, now try the test button on both RCD's chances are one won't trip this is most likely caused by a neutral/earth fault.

**max power** · 4th August 2009, 06:50 PM

i know this sounds stupid but have you put your neutral in the right bar because if you havent it will trip every time .If it was working on the old board chances are you have made a mistake always start by checking the simple things first