Called at my friend's house where he is looking to run CAT6 underground today and he was telling me about his RCD tripping problem.
Virtually every day his RCD trips. Single phase overhead TT supply. Single 30mA RCD in Consumer Unit.
The problem started soon after a new oil fired CH boiler was fitted.
Putting a clamp meter around the meter tails, from 21 to 0mA unbalance step by step as the single pole MCBs were opened one by one.
Rather upsetting to find that with all MCBs in and 21mA unbalance there was only 2mA in the earth lead, could not find either the cable connection or the rod outside.
Hoping to find a convenient place on the boiler where I could access the L & N to check unbalance looked inside and nothing accessible within the time I had. Anyway out of "devilment" you could say, put the clamp meter around one of the CH pipes from the boiler and 21 mA flowing through the 22mm pipe! I'm guessing that assuming the cable and rod are ok, the earth leakage current will flow inversely proportional to the respective resistances.
He has been trying to get an Electrician in to sort out.
Besides ensuring a decent earth rod and cable to the MET I think the ideal would be a new Consumer Unit (metal of course) and Cobs.
To try and confirm the boiler being the main cause, since the CH system runs from a nearby 13a socket, have considered a short extension lead where the L, N & E are separated out for easy application of a clamp meter.
Any other checks to try before his Electrician gets in heavy style?
Clive
