What's your preferred method for providing power to the typical detached garage, shed, or workshop? And what's your favored method of wiring within?
For the feed, I prefer buried SWA wherever possible, as it's relatively easy to do and keeps much of the outdoor wiring out of sight, which seems to be a desirable point with many people these days. (And in a lot of cases, the owner is happy to provide some of the labor for digging the trench ).
I'll generally go with overhead only if it's impractical to route underground (e.g. concrete paths and patios all the way) or if there's some other reason that the owner requests it.
Internally, assuming a block garage or a shed/workshop which won't be dry-walled internally, I prefer to run everything in PVC conduit. Twin-&-earth might be acceptable, but to me conduit just makes the installation look far more planned and better quality.
Maybe years of seeing horrendous shed wiring with T&E just hung on nails with twisted & taped splices has influenced my thinking though. What do you reckon?
Agreed. With a remote shed fed from a TNCS type supply system which may have metallic service pipes, the swa may need to be insulated from earth and a TT system established. Compromise perhaps with TE clipped at wall plate and HG plastic conduit for drops.
Paul, I'd go about a typical Garage or Workshop installation as follows:
Install a 25A RCBO at the Main Switchboard in the house, this circuit would be designated as a Sub-Main.
Run either a 4mm2 2 Core + Neutral-Screened (Buried Direct) or a 4mm2 2 Core + Earth TPS Cable in Orange PVC Conduit under ground.
The cable would feed a Splitter Box in the Garage, which would have a Single Pole Isolator and an MCB for each circuit.
Depending upon the type of building construction, the Sub-circuit wiring would be run in conduit in a concrete block/brick building or neatly clipped on the surface in a timber-framed building, with cable protection added where there is a possibility of it being damaged.
Just a small question Paul, how would an overhead cable be run to a shed in the UK?. I'm thinking thimbles and a Catenary wire, but you guys may have a different way of doing it over there. I try and avoid an over-head installation like the plague these days.
Due to not wanting to attempt to lift a tarmac path, I was forced to route the cable to my garden shed overhead. The distance from the house to the shed is only slightly more than 4 metres, so I simply ran a piece of SWA from the house to the shed, on a piece of catenary wire.
I installed a 32amp MCB in the main consumer unit, then ran a short length of 10mm twin and earth to an adaptable box in the roof space, from their I simply used 3 core SWA cable, running straight into the shed.
At the end of the SWA, I installed a standard metal 8 way consumer unit. In the consumer unit, there was a standard isolator, and three RCBO's, supplying the sockets in the shed, the lights in the shed, and another for the weatherproof socket on the outside of the shed.
All the sockets and light switches in the shed were metal-clad, and the light was a 7 foot Fitzgerald Anti-Corrosive fitting.
Cabling was run in PVC conduit, simply because it looked nicer and more professional than twin and earth, and that it was easier to use than metal conduit.
Mike, we tend to use catenary wire, but sometimes other methods are used.
Understand the "pipe only on the drops" method, but I figure that while I'm installing that I might as well run the whole lot in conduit for what little extra work is involved on the typical install. (Could use some extra ventilation from using the PVC cement in some places though... ).
I like to run a 30A sub-feed to a garage or workshop, unless it's just a small shed, owner on a very tight budget, long run of feeder which could be substantially cheaper on a 20A circuit, etc. Even if the extra capacity isn't needed now, it might be in the future, and as I always try to point out, upgrading to a 30A feed later is going to be much more expensive than the extra it will cost at the outset.
Lyle raises some interesting questions regarding earthing arrangements. About 90% of the homes in my immediate area are TT with a single main RCD. I really don't like taking the sub-feed off the existing panel if I can help it, as I'm not keen on the idea of an earth fault on the garage/workshop taking out power to the whole house, but if space and/or cost constraints mean I can't tap and fit a separate RCD/MCB combination or RCBO for the feed, there's not much choice. (It's no secret around ECN that I don't much care for TT systems anyway, right? )
Just a small question Paul, how would an overhead cable be run to a shed in the UK?
Yep, catenary wire, although I haven't done one of those for a long time now.
the light was a 7 foot Fitzgerald Anti-Corrosive fitting.
My regular supplier carries Fitzgerald, but not the anti-corrosive types, for some reason. I just recently installed a couple of 6 ft. Dexra anti-corrosives, about £22 plus VAT each as I recall, excluding tubes.
I'm sticking my neck out here; pleas keep inmind that I am writing this from an American perspective, and I know your methods may be different.
If I can, I prefer the feed to be in exposed pipe, running along a wall. My second choice is in pipe, prefarable oversized, buried DEEP, with a junction box at either end; that way, you can replace it later. I have had great success passing wire through pipe under paths, pavement, etc. by using water pressure to bore a tunnel, then passing the pipe under through it, without having to disturb the tarmac. Of course, a regular roadway would require a very large access hole on either side, in order for you to work!
Once in the garage, I like to mount a small panel. Quite often, this building later becomes a workshop, apartment, etc., and additional circuits are needed. (With our modern world, perhaps I ought to start running a second pipe for telephone, TV, etc!)
Within the building, and especially where the walls are open, I prefer pipe or MC (metal clad cable). While our code allows using Romex (plastic clad cable), I like a little more protection.
Running along a wall is a good choice, even if only part of the way to save labor. We can do that here, although our code does not allow wiring to be run along a fence.
I have had great success passing wire through pipe under paths, pavement, etc. by using water pressure to bore a tunnel,
Sounds an interesting way of doing it. I've never tried that, although I've gone under narrow paths by driving an off-cut of conduit or water pipe through the ground then pulling the cable through on the end of it.
Buried conduit would also be acceptable here, but I think many of us have gotten so used to using SWA for underground cabling that it just seems like the natural way to do it.
If you're not quite sure what SWA is, it looks like this (available in 2, 3, or 4-core varieties):
[This message has been edited by pauluk (edited 12-31-2004).]
Re: Garage/Shed/Workshop wiring#142281 01/02/0505:22 AM01/02/0505:22 AM
John, Good to see you down here!. Personally I'd never bury any cable (Neutral-Screened or what ever) without Conduit over it. Sure, for an Out-Building, the derating isn't going to make a bit of difference. But, what will is some idiots shovel or spade that never took any notice of the Signal Strip at 300mm below the surface. I'd sooner the PVC conduit(Orange) was seen before the shovel hits the cable. I'm talking purely from a repair point of view here. Besides, all of our PoCo street cables run through 200mm ducts under the footpaths, so who am I to argue?.
But, what will is some idiots shovel or spade that never took any notice of the Signal Strip at 300mm below the surface.
I take your point there Trumps... Really annoying when it happens!
I tend to route cable where they are unlikely to be "dug over"; under paths etc.. The conduits here would be easier to chop through with a spade than the cable - and I haven't seen any bright-coloured ones. We have blue water pipe and yellow gas, but are not permitted to use them for power services. The only orange colour I have seen is for drainage ( both soil and ground ) and their use is prohibited.
If hindsight were foresight, we'd all be millionaires!