New Consumer unit RCD problems

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Hi all,

My problem is this :

I have just changed my consumer unit from a 4 fuse unit to an MK MCB type consumer unit. The incoming supply feeds 6 MCB's and an RCD. The RCD then supplies 4 MCBs, which I have run my mains power onto.

As far as I can tell, my entire house is powered from one ring. I can not find the riser for the first floor anywhere. I have run the old cable from the "Power" fuse to a 32A MCB. When I make the main isolation switch and then the RCD, the RCD trips, even when the power MCB isn't made. If I remove the wiring for the power, the RCD doesn't trip.

What would cause the RCD to trip? I have checked my earth connection and that is good. I have also checked (as far as I can) the ring main and it appears good.

I'm not fully conversant with the workings of an RCD and can't work out why it keeps tripping. There's obviously a fault on the ringmain, but I don't know where to start.

Any help would be much appreciated.
 
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in a split load board, there are 2 neutral bars. 1 for the RCD and 1 for the non-RCD. make sure all neutral are in the correct neutral bar. if they are, it could be a N-E fault. test the insulation with a insulation tester
 
The way I have tested this so far is to disconnect all the neutrals ( both bars) and reconnect individually. All of the non-RCD circuits are good.

As soon as I put the power circuit neutral onto the neutral rail (with no other neutrals connected), make the main insolation switch and then the RCD, the RCD trips instantly.

I have also put the power circuit to an MCB on the non-RCD side of the board, and it works fine.
 
I've just removed the wires for the power and tested them to earth. There is a good circuit between live and neutral to earth.

Have just found 1 riser to the 1st floor, but don't fancy ripping up a load of floorboards to find where the other is :)

What's the easiest way to chase an earth ?
 
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DanE said:
I've just removed the wires for the power and tested them to earth. There is a good circuit between live and neutral to earth.

did you disconned all appliance before testing? there should be a hig resistance between the conductors, at least 0.5 M ohm. did you use an insulation tester to do this?
DanE said:
Also, when I switched the main isolator back on, there was a pop.

What's the easiest way to chase an earth ?

pop on what? did the RCD or MCB trip? have you done any DIY lately what could have damaged a cable? and what do you mean by 'chase an earth'? if there is a direct short between neutral and earth, expect it to be in a backbox or something where the screw has went thru the neutral. if it is old cable with bad insulation, youll have to replace the cab;e
 
I removed all the wires (L,N+E) from the CU, with the exception of the power circuit. When I turned the MCB on, there was a popping sound from the main isolation switch, although I haven't had it since.

I have not done any DIY recently so I don't think there are any cables damaged in that way. I'm not sure if the earth wasn't there before I started as I didn't test it.

I have found a single cable which goes upstairs to the first floor, but can't find the other cable which I presume comes straight from a socket somewhere. I haven't seen any obvious candidates yet.

On the previous CU, there were 3 wires being fed from the power fuse (which I thought was strange). I have all 3 wires in a TB and am now in the process of chasing the ground floor power circuit under the floorboards.
 

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