RCB in new consumer unit for garage

30 Jul 2003
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United Kingdom
I have installed a new garage consumer unit fitted with an RCB unit and 2 MCB's rated 6a for the lights, and 16a for the sockets. But, when I powered it up and tried the lights and sockets the RCB kept tripping out. I know I have not gone through any cables and all circuits are wired correctly, so I removed the RCB and wired direct to the MCB's and all is well.(The MCB's do not trip), I have already got an RCB fitted to the house from which this unit is fed. Can you fit 2 RCB units in the same circuit?, or do you think the RCB rating should be higher. (Rated at 30ma 40A) same as the house?

I would be grateful for any advice on this problem.) :confused:
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it may be (unlikely) the rcd is faulty.

You have to remember that an rcd is there to save lives if it trips it usually indicates a fault. yes you can have two or more identical rcd's on the same cct.

to test it, first connect nothing to it, and see if it ok. Then connect one circuit back at a time (i know you only have 2)

I would say connect the sockets first. If all is well then it must be the lights.
but do connect each circuit on its own to verify you only have one fault

which ever one is causing it to trip check all the connections. make sure that there are no neutral connections (the black ones) touching any thing metal (socket back boxes?) or other wires.

I would guess that this is probably the case, also when you put the socket fronts on, make sure no screws have "nicked" the neutral insulation as this will cause your rcd to trip.

for more information regarding how an rcd works see this

and you should have posted this in the electrics forum , but welcome aboard
Thanks for the advice, I will try as you stated and hopefully I can trace the problem.
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He's been lying dead on the garage floor for nearly 9 years now, krieghammer, but thank you for your concern.

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