DIY Doctor

Extra Power to the Garage

Postby ByTheCringe » Sat Jan 19, 2008 8:44 am

I have bought a new welder, and rather late have found that I need to supply more current than is available in the garage. Rather than disturb the existing installation in the garage, I would like to run a new underground cable to a new consumer unit. This would contain an RCD, a 32A type C (slow-blow) MCD supplying a 32A industrial socket, and a 32A MCD supplying a ring main with 4 double 13A sockets.

Apart from getting a professional to dig and supply the cable, and connect to the consumer box, I would like to supply and fit the consumer box and the sockets myself, and have the work certified. I am in England, and P Regulations apply.

My questions are:
1. The meter is in an outside box. How can the armoured cable be attached? Does there need to be a new inside box in the house and then the cable goes outside again, and what would need to be in the box, an RCD and main switch, and an MCD? Or can it just connect directly to the meter with extra tails and go out from the meter box?

2. If I want to do some of the work, I understand that I will have to notify the council and get the work tested by them - I cannot get the professional to test and certify my part of the work, correct? Or will it be cheaper to let the professional do everything?

3. Any advice regarding cable sizes would be much appreciated.

Thanks for any help. :)
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Simply Build It

Postby ericmark » Sat Jan 19, 2008 12:22 pm

1. Normally you would take SWA to a steel box and then into existing consumer unit exact way would depend on local conditions.
2. Extra tails normally will not physical fit.
3. You may find an electrician who will let you labour for him. We don’t like hard work and having only to do technical bit often suits.
4. You have realised I see that you will have inrush problem but when using type C or D the requirements for the earth loop impedance also change you may need thicker cable than you first think.
5. You may also need 16 amp blue plugs and sockets for welding machine
6. Have you considered a switched mode welding machine these are lighter and have less problems with inrush allowing 160 amp output for 13 amp plug.

Postby ByTheCringe » Wed Jan 23, 2008 7:10 am

Thanks for your reply, and please excuse the delay before responding; I was waiting to see if there would be any other response.

To provide closure for anyone searching for similar information, here is what I did:

I found an electrical contractor who will provide a main switch box, which will fit in the outside meter box, and fit a 16mm2 SWA cable underground from that switch to a new consumer unit in the garage. He will estimate separately for the consumer unit, the Type C and normal (Type B) 32 amp MCBs and the RCD, a 32-amp blue (industrial) socket and the ring main of 4 double sockets. If I like, he will let me supply and fit those and will certify my work.

The welder had already been purchased, and it is a 200 amp AC/DC Inverter Tig unit, so I really needed a very beefy supply for it. The cable attached to it is 14 mm diameter! I found the contractor by searching yellow pages for someone who did commercial, as well as domestic work, and was Part P-registered.
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