New RCD tripping

[Mell]

Hello everyone just a quick one and any advice is welcome, just fitted new consumer unit Schneider split board single phase in a house done all my verification tests all ok and passed but then come to do RCD ramp test as soon as I touch the test button on my metrel it trips so I tried a test plug with an RCD test button and it tripped before I pressed the button so I tried a basic test plug with no RCD button and showed everything was wired ok I opened the socket all ok db board wired ok I even tried an electric multi tool and switched it on and it worked fine no tripping so I tried my metrel again and it tripped, tried the lighting circuit and it instantly tripped again but lights come on no problem. Now this is happening on the upstairs circuit I've already done the down stairs RCD test and passed does anyone have any ideas before I start opening up all the sockets which is 13 of them or have I a faulty rcd. 

 

[poni]

Have you tried with all circuits disconnected on that side 

Remove all cables and then test the RCD then put them back one at a time to see what happens

The fault could be a neutral brorred on the lights

 

[Murdoch]

Have you got the metrel in RCD setting?

IR tests?

Your house?

 

[Mell]

Hi no I haven't tried disconnecting the other circuits but I know what you mean and will try and as for the metrel I have it on the RCD test and set to 30ma which is what the RCD is and my IR readings came out satisfactory.

Thanks 

 

[poni]

What about your R2 results?

 

[Murdoch]

This is a good example of why most sparks don't supply and fit dual RCD boards anymore ................

Are you saying 1 RCD is OK?

 

[Mell]

Yes the first RCD which I've made all downstairs works fine on the RCD test its just the upstairs that instantly trips on anything what tests an RCD, put anything with a plug in the sockets and it operates fine without tripping.

The r2 results are fine did my 3 step ring main test along with Ze and all falls within the regs.

 

[Murdoch]

Yes the first RCD which I've made all downstairs works fine on the RCD test its just the upstairs that instantly trips on anything what tests an RCD, put anything with a plug in the sockets and it operates fine without tripping.

not ideal - you should split so not all downstairs is lost at the same time - i.e. down sockets and up lights on 1 RCD, up sockets and down lights on the other RCD ....

You obviously have a fault or borrowed neutral

Your house or customers?

 

[Mell]

Its a customers house, so you think it could be a borrowed neutral on the lighting circuit 

 

[poni]

 You won't know until you do more tests 

What happens when you trun on the lights ?

You could try 

Disconnecting all cables on that side and test the RCD

Then check all live conductors to each other and to the good side to see if you have any crossed over 

 

[Mell]

The lights work perfectly fine, I think I'll disconnect all the circuits on that RCD and test only the sockets see if it trips if it doesn't then add a circuit one at a time see if it trips at a certain circuit.

 

[Murdoch]

You need to IR the circuits on the RCD affected by the trip.

And don't do them together, do them individually, disconnecting each live and neutral but leaving the cpc connected. 

Then look at the results for each circuit

how many circuits?

 

[Mell]

Yes I did my IR individually took live neutral and CPC out and tested all came out as pass mainly greater than 1000 or not far from it. There is 4 circuits the sockets the lights, combi boiler and shower I disconnected boiler fuse switch and shower pull cord before IR test, I have got the bathroom fan connected to an isolator which is then connected to the lighting loop and recently found out the fan is faulty I wonder if that's causing a fault.

 

[Murdoch]

The cpc should always be connected to the earth bar with all the other cpcs to give an accurate result.

What about L to cpc ?

 

[Mell]

I haven't got the paperwork at the moment and I've always been taught to measure with the CPC out unless doing a global test but I'm willing to give it a try as I don't class myself as experienced as most in fault finding.

 

[Mell]

Back at the house now and removed all circuits except sockets and did a RCD ramp test and this time tripped on the last test half the load which it should not. Then I have added each circuit in turn and did not trip straight away but only on the last test, half the load, any ideas please 

 

[Murdoch]

I haven't got the paperwork at the moment and I've always been taught to measure with the CPC out unless doing a global test but I'm willing to give it a try as I don't class myself as experienced as most in fault finding.

What paperwork?

Fault finding is a huge part of this job and unless you understand the necessity to do the right thing in the right order you won't make any progress.

Go back to basics - have you confirmed continuity of all the circuits on the "bad" side of the fuseboard?

Have you IR'ed each in turn, with the CPC's connected to the earth bar?

Are ALL the loads disconnected?

What are the IR readings for L-N, L-E and N-E for each circuit?

Remember with fixed loads such as boilers to turn them off at the local isolation switches .. and that is why isolation switches should always be fitted

Tripping on 1/2 test suggests you have a fault

 

[poni]

Why did you not remove all circuits? 

All this has told you is that nothing's  changed 

You could still have actually RCD or a fault on a circuit

 

[poni]

Faulty not 

actually

 

[kerching]

What "paperwork" and why did you disconnect the CPCs?

just curious and confused