I have a problem with an underground mains cable that goes from my house to my garage, and was wondering if anyone could assist in working out the fault please. The setup is as follows:
My house has a standard consumer unit, with a 30mA RCD covering all circuits, and individual MCBs. The circuit to the garage is a 2.5mm twin & earth cable going outside under the garden and into the garage. The end coming into the garage is enclosed in a metal pipe, I'm not sure if this extends all the way along though.
Recently, the house RCD has started tripping, and I traced this to the garage circuit. Even with the wire disconnected completely at the garage end, the RCD trips. I tested the cable with it disconnected at both ends and found a 120K resistance between live & neutral, and a
0.4V voltage between earth and neutral and the same between earth & live. Does this sound normal?I can't decide if the cable is faulty, or if it's just the RCD which has become too sensitive (it has been OK for the last 4 years). Would the problem be fixed if I disconnected the earth at the garage end and used a local earth? Or should I try usung a higher rated (100mA) RCD at the house end?
Any suggestions most welcome, many thanks in advance for any help!
Tim