Ok. Not come across this before, so I'd appreciate some feedback please. I have a dual rcd board, 10 circuits all protected, evenly split. On the 'A' side I have a kitchen socket circuit. On the 'B' side I have a house socket circuit. If both McB's are made active, the Kitchen circuit mcb trips the 'B' side RCD, not it's own RCD. The only way I can get the Kitchen socket circuit to stay active is to ensure the mcb on the other side of the board stays off. I've checked neutrals/earths on the CU are in the right bars. So - what is likely to be the issue? Somewhere in the wiring has a spur been made where a live is taken from the Kitchen circuit and a neutral from somewhere else? Perhaps a messed up junction box? Is the best WYoming to test this to carry out an IR test on the house socket circuit and split it until I find an issue? Any thougts/comments are welcome Cheers.
Hello everyone. I've not carried out testing yet. Made sure everything was safe before I finished today. Back down there tomorrow. Just want to make sure that IR testing the mcb on the RCD trip side is the correct approach. It seems from comments above that it is. Thank You.
The dead tests should be carried out before its energised otherwise how do you know its safe to do so? If it was done prior to energising there is a good chance you would of picked the fault up.
My bets are that you have a neutral earth fault somewhere on one of the circuits. The RCD is tripping as the neutral current is diverting via the N-E fault, the impedance of the fault determines the proportion of the current which diverts and so the amount of load required to cause a trip hence when tripping when kitchen circuit is turned on as usually have higher current using equipment plugged in like a fridge freezer for example. Any current in use on the installation can cause this because the current can flow from the main switch common neutral back vie the RCD neutral on the faulty side through the NE fault and to earth.The current flowing through the neutral does not have a corresponding live current and so the RCD trips.
This does need a proper test, dead test. An insulation test is a must but and i presume the kitchen sockets and house sockets are ring finals need to be tested for correct polarity and a figure of 8 dead test done. Sounds to me like either you have one leg of the ring final from the kitchen mixed up with the ring final from the house, or polarity is the wrong way round in one of the sockets as in the Neutral in the Line and the Line in the Neutral kind of thing. All this is picked up by a simple ohm meter test which is done before you do your insulation test. As many have said above, you should always do these tests before you apply power to the board without fail.Very bad practice not to. Ok you can sometimes push your luck with an insulation test but NOT the continuity and polarity testing and to be 100% sure the ring final is actually a ring and not broken somewhere. At a guess that is what i am thinking it is. If you have it powered on and you have one of these: http://www.screwfix.com/p/kewtech-loopcheck-107-advanced-plug-in-socket-tester/4670j Plug it in and test it.
Thanks fire, JP - I did use a socket/polarity tester when trying to identify which sockets were on which circuit earlier in the job. All appeared to have the correct polarity but ..... it's possible I missed some (behind cupboards etc.. you know the deal). For a bit of background.... The house is very old 1860's and I'd guess the sockets most pendants are 30 years old, maybe older. The fusebox had cermaic type casings, 4 pin push in metal fuses. The Kitchen does "appear" to be on it's own rfc from the socket tests, but of course this isn't definitive as yet. The issue is in the rest of the house. There are two other 'socket' circuits, but they aren't divided at all logically east/west or upstairs/downstairs etc.. I've come across three sockets in one room on two different circuits, some upstairs/down rear of house/front etc.. I'm about to leave for the job. I'll let you know how I get on.