Tripping Query

[alanaac]

I changed a couple of sockets at a property I am working on and put my plug tester in to check and it tripped the rcd. Tried a couple of times then took sockets off to check them - all ok. Tried to do loop test with my kew 63 tester - tripped again. Tried a few other sockets in property and all tripped out. Plugged Dyson into same sockets and it worked fine. Consumer unit is 30 year old split load unit with 100mA rcd main switch and 30mA secondary rcd. Can test ok on 100mA rcd side but trips on testing secondary side. Connections ok inside. Has anyone come across this type of fault before. I seem to recall it happening before on another consumer unit which I changed. I believe it was an MK unit as is the one I am writing about now.

 

[Mike Johnson]

Sounds like a borrowed/misplaced neutral.

 

[alanaac]

Sounds like a borrowed/misplaced neutral.

quite possible why does only my tester set it off but anything else thats plugged is fine

 

[Mike Johnson]

If the neutral is in the wrong bar in the CU it can't find a complete circuit.

 

[telectrix]

If the neutral is in the wrong bar in the CU it can't find a complete circuit.

but then the dyson would trip it.

@ OP. have you tested the RCD inc. ramp test?

 

[Rockingit]

Puzzled as to why there's a 100mA RCD on one side of the board and a 30mA on the other - what's the supply type? Or do you actually mean a 100A main switch, not an RCD??

 

[alanaac]

Puzzled as to why there's a 100mA RCD on one side of the board and a 30mA on the other - what's the supply type? Or do you actually mean a 100A main switch, not an RCD??

there is 100A rcd main switch ( TT system ) with lighting circuits on that rail and a 2nd rail with 30mA rcd on it powering sockets. I cannot do any tests on 30mA rcd side because it trips as soon as I plug in my socket tester or kew 63 meter. It is 30 years old and I am changing it. I am fairly confident that the rcd is faulty - there is no other possibility. Thanks for the input.