Discuss tt and rcd problems in the Industrial Electricians' Talk area at ElectriciansForums.net

B

bigal

Ahha I've found where to start a thread.
Hello everyone I'm newly registered and a bit green in finding my way around this site, but i'll do my best.
Here goes with my phenomenon.
Been working on a TT system, Just finished rewire of a house to 17th. Installation required a supply to an out building. Here my problem started.
I wanted to protect the cable going out of the house on a 30ma rcd (it was necessary). I Installed a garage board in the out building that also had a 30ma rcd as a main switch, so to avoid nuisance tripping I disconnected the outgoing cpc (the one from the main board in the house) at the garage board end and added another stake to give it it's own earth supply.
All seemed ok until I tested the rcd at the garage board end. It tests fine on x1 but when I test on x5 it trips the rcd at the house. This should not be possible because the outbuilding supply has not got a direct path back to the house because it is disconnected inside the garage board and relies solely on the nearby stake. earth electrode reading at the house (main earth was 20 ohm (loop test) and reading at outbuilding end 18.5 ohm. Any suggestions?
NICEIC technical say it's not possible. However, I've taken everything apart and checked for cross connections etc and put it all back together again. Still the same happens.
Help please. Bigal.
 

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