DIY Doctor

Garage Power Supply

Postby Jake B » Wed Feb 13, 2008 4:49 pm

Hi guys, I'm about to start wiring our garage and I need some advice about the circuit breakers. I plan to have about 5 or 6 double sockets inside the garage, a basic lighting circuit and also an external socket for the pond equipment. I will be using a 20 Amp MCB for the sockets and a 6 Amp MCB for the lighting. These will be both be protected by an RCB. The thing is that the RCB that came with the 2 way consumer unit it rated at 63 Amps. This seemed a little high to me and I was wondering if this would be ok, or whether I should buy a 30 Amp RCB. Am I also right in thinking that the breaker in the main consumer unit should be 30 Amps, fed t the garage y 4mm cable? Any help would be greatly appriciated.
Thanks :)
Jake B
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Simply Build It

Postby ericmark » Wed Feb 13, 2008 5:54 pm

The 63amp on the RCD refers to max amps and using it for a lower current is OK. Your 20amp and 6amp MCB’s seem OK. 30amp with 4mm² is right on the edge. And it would also depend on how far the run is. At 12mV/A/m and since you have lights 3% volt drop gives max length of approx 20 meters. You will need to apply to building controls under Part P unless you live is Scotland and satisfy them you are competent. Then of course complete the electrical installation certificate including your readings for earth loop impedance and test results for tripping time and current for the earth leakage trips etc. With the questions you are asking I somehow think you may have a problem with this. There are links on the projects section to Part P and even if you live is Scotland without the test results you insurance may be void. I would recommend that at least you employ an electrician as Clark of the works and do the work under his guidance and allow him to sign the paper work. He has to be responsible for the work he can’t just sign latter.

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