UK RCD tripping when using loft socket.

archee · Jun 5, 2023

Afternoon all,

I have an issue with the loft socket. When we moved the previous owners had a 2.5mm cable going up from the CU Via FCU however, the wiring was old and did not have earths(they cut them off).

So I decided to completely rip out the old wiring including unnecessary spur and put brand new 2.5mm cable connected to 16A mcb.

However, it trips the RCD but not the MCB. I don’t understand why.

I replaced the McB with the spare one I had laying around, was doing the same thing. Removed the mcb opened it up saw burnt marks on the inside. Ok I thought it might the MCB, so I received a new one today, same thing.

Checked previously:

All the wiring to the socket is correct!
Continuity check all fine!
Checked for Earth leakage with multimeter seems to be fine.

What else could cause this ?

P.S I’m not using it for anything heavy just a 2A NAS server.

Thanks

newfutile · Jun 5, 2023

Usually wrong neutral bar , or wrong Wiring .does it trip before anything plugged in?

Uplight99 · Jun 5, 2023

Have you carried out any IR tests?

You obviously have some sort of earth leak somewhere as this has only started happening since introducing the new cable with a cpc, as they cut it out of the old cable it wouldn’t have been possible to trip the RCD

Have you tried plugging something else into the socket? You might find that you have a fault appliance

archee · Jun 5, 2023

newfutile said:
Usually wrong neutral bar , or wrong Wiring .does it trip before anything plugged in?

No it doesn’t trip anything when nothing is plugged in. I also used the same cable and out it (just to test) on another 20A mcb and it worked fine.

Uplight99 · Jun 5, 2023

No

archee said:
No it doesn’t trip anything when nothing is plugged in. I also used the same cable and out it (just to test) on another 20A mcb and it worked fine.

You misunderstood what I said

Try and plug something else in. Grab your kettle or anything and plug it into this socket. If it doesn’t trip then whatever you are plugging into it is faulty.