Shed electrics.

Colin Stamp · 2012-09-07T11:41:14+00:00

Hi all,I'd welcome any comments on my plan to get power to my forthcoming shed.The shed itself will wooden, on a concrete slab and 3.6m X 6.6m. It's around 20m from the house, with around a 35m cable-run from the house CU to the shed CU. Initially it'll just be for storage but it'll get used as a workshop/office later on.I have a 17th edition CU in the house with some spare non-RCD ways, so I'll feed the sub-main with an MCB in one of them. I'm hoping to squeeze a 40A sub-main out of 10mm SWA, but that doesn't leave much voltage drop for the final lighting circuit in the shed, so I may have to come down to 32A, which should be plenty anyway. I'll be trying to take the SWA all the way from CU to CU, but I'm guessing it's going to be about as flexible as a concrete lintel, so I may have to use T&E in earthed conduit for the bit inside the house.The SWA will be directly buried 600mm deep under a slabbed path to the shed, alongside a 63mm duct for data cables. I'll put warning tape just under the slabs. Do I need any further down too?The house is TN-C-S. After reading the regs and trawling the web, I'm a bit unsure about equipotential bonding. On the face of it there doesn't seem to be anything to bond, but the concrete slab is a bit of an unknown. Ideally, I'd like to use 2 core SWA with the armour as the CPC and no bonding conductor, but I'm not sure if that's acceptable with a bare slab. Would covering the slab with OSB help? Or would I need to embed a grid in the concrete and bond that?If I do need a bonding conductor, I guess I can use 3-core 10mm SWA with the 3rd core as the bonding conductor? I'd really like to avoid TTing the shed if possible.I'm sure I've managed to be overly anal and recklessly negligent both at the same time, so any comments to get me a sensible setup would be very welcome.Cheers,Colin.

Shed electrics.

Sep 07, 2012 23 Replies

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John Rumm 13 years ago

It probably varies with local soil conditions. 10m would probably make certain. However in the past I have done a pair around 4 to 5m apart, and saw the expected halving in Ze.

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Robin 13 years ago

Ah, so. I recall thinking that looked better than some places I'd lived :)

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Colin Stamp 13 years ago

I guess I'll find out in a while. The slab is in - just need to wait for it to dry out a bit. I suppose I really must design the shed...

Cheers,

Colin.

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Colin Stamp 13 years ago

It may come to that...

Cheers,

Colin.

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