Exterior electrics to new workshop(shed)

[Andy Jeffries]

Hi everyone,

I have the following situation currently:

I have a 13A fused spur going in metal conduit for about 2 metres to a brick shed. Within that shed I have a 5A fused connection to a fluorescent light and then three power sockets (computer equipment, low power usage).

What I would like to do is as follows:

Extend the connection from the furthest power point in the brick shed for about 25 metres using SWA cable (how far down does SWA cable need to be dug, AFAIK non-SWA needs 1/2 metre - how about SWA?) to a new wooden shed. Inside that shed have two fluorescent lights and a number of power sockets.

I know I'm going to be limited to 13A total usage for the whole outside (due to the fused spur) which is fine - I'll either be in the woodworking shop or in the "office", not both at the same time.

Any problems aside from this? I need to get an electrician to certify the work, correct (as Part P covers outside electrics)? No problems with the length? Can I actually do the work myself and just have him certify it's connected OK? What would he need to see to certify (can he just check the connection end or will he need to see the wiring to every circuit in the shed)?

Cheers,

Andy

[Andy Wade]

A single 13 A supply from a fused spur does not sound adequate for something described as a "woodworking shop," unless you're only using hand tools or small portable power tools. You didn't say how large the brick shed is but you're likely to need 200+ W of fluorescent lighting, ~2 kW of electric heating in winter, plus any fixed machinery and dust extraction. Even if the total load comes in under 13 A you may find that motor starting currents give problems, blowing the 13 A fuse at the house end, plunging the whole works into darkness and taking your computer equipment off supply.

In fact the fused spur sounds just about OK for your office alone. The workshop, unless very small-scale, really needs its own submain circuit from the meter in the house.

[Andy Jeffries]

OK, I'll give a sort of answer then ask a question...

The current brick shed has the powertools in it or run from an extension from there (to be used outdoors) and the fuse never blows. The powertools aren't industrial things, but small home-workshop type tools. The biggest things are a 1500W saw (peak I'm assuming) and a 1300W router. They are never used simultaneously.

Anyway, on to the question. How much do you think it would cost (ballpark is fine) for a new submain circuit? 25 metre SWA cable run dug by me (but would now need to be 2x cable length for ring, right). Need say 5 electrical sockets, 2 lights at far end. Ring comes from house wich is about 28 metres from the shed (brick shed takes 2 metres, plus 1 metre of metal conduit to house). From that wall there is the kitchen (cables can be run behind cupboards) then the utility room with the consumer unit in it.

I know nobody would give a fixed price over the net for something like this, just after a ballpark. Hundred quid? Couple of hundred quid? A thousand? I'm just after an idea so I know how feasible this is now I've got my heart set on it... :-(

Cheers,

[michaelangelo7]

If I were you I would run 6mm x 3core SWA from the main building to the first outhouse. In this building install a small metalclad consumer unit with rcd protected circuits, as a first step. Then,loop out again to the remote outbuilding in the same type of cable,terminating at a second consumer unit like the other one.I should do all the "donkey work" yourself like digging the trenches and mounting the consumer units on the wall and then employ an electrician to run a main in through the house to connect to your new cable via a suitable main switch. Making off swa glands is not reccomended unless youv'e had previous experience. This will stand you in good stead for any further expansion of the "garden empire" Look on ebay for good deals of swa cable.It needs to be buried 18'' minimum.

[John Rumm]

No, the submain would be a single cable run...

There is no need to take SWA all the way to the CU in the house - you can revert to T&E for the internal run.

Well depends a bit on what you already have on the house CU... If there is a spare way you could populate it with say a 30A HRC fuse in a carrier, run 6mm^2 T&E through the house to a box where you could go to SWA and drop out though the wall and to the shed. Say 70 quid for that lot.

At the shed you could stick in a small CU with a couple of ways with 20A and 6A MCBs for power and lighting circuits, add an earth rod and a RCD so as to make the shed a TT instalation (i.e. not using the house earth). Say another £50 for that lot. Add on the costs of any sockets and lights etc you want in the shed.

So all in you ought to be able to DIY for under £200 in materials (i.e. ignoring the cost of your time and any associated with any part p nonsense)