RCD tripping

20 Jan 2014
Reaction score
United Kingdom
As I am building an extension I replaced the Mk 8 way consumer unit with a 16 way Hager split load 17th edition as I wanted to get some plasterboards skimmed in the same room. The MK board never tripped, the rings and cooker spurs were on the RCD side.
The CU is on a board above the meter.
On this new CU Only one of the RCDss had the busbar fitted and only four existing circuits were wired to their respective MCB

Existing cooker spur feeding a hob and cooker.
Existing kitchen ring.
Existing rest of house ring
existing lights.
Theses circuits worked ok.

I then wired the mcb for the loft lights on the RCD. The lights worked, but switching on a kettle on the kitchen ring tripped the rcd .
Trying to reset the rcd was difficult. I switched on the cooker socket and turned the hob up to max with no problem but it tripped when the oven was on. I repeated this 15 minutes later after trying other permuations and then rcd tripped whenn the hob was turned to lowest heat. Then a circuit tripped when a socket with no appliance was on. Switch the socket off and the circuit can be switched on without the rcd tripping, but plug anything in andd it tripped. Mostly the lights would work. I switched all of them on and the cooker extractor fan and the rcd did not trip.
So seems to be a build up of current in the circuits from the loft lights circuits. I switched the whole system off for three hours and then switched it on and it and the four circuits worked ok.
The new rcds have the same rating as the old one, 30mA.
Earth is pme four wires going into the CU, same as the old CU. One from earth rod, water pipes and boiler oil supply pipe
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What happened to all the testing that you should have done before energising the circuits?

Given your description of the things you did after you found this problem it doesn't look as if you have anywhere near enough competence to be installing wiring and a new CU.

Who is going to sign this declaration?

I being the person responsible for the design, construction, inspection & testing of the electrical installation (as indicated by my signature below), particulars of which are described above, having exercised reasonable skill and care when carrying out the design, construction, inspection & testing hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge and belief in accordance with BS 7671:2008, amended to 2015 except for the departures, if any, detailed as follows:

When you applied for Building Regulations approval, what did you tell Building Control, or by default allow them to assume, would be your route to compliance with Part P?

Please get an electrician to do the electrical work for you.
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