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.

Here are some of the accessories that are used.. http://www.tlc-direct.co.uk/Main_Index/Cable_Accessories_Index/Catenary_Wire/index.html

And here is some more information about overhead wiring..
http://www.tlc-direct.co.uk/Book/7.13.1.htm

[This message has been edited by ryanjuk (edited 12-28-2004).]

I would tend toward your system Paul. I don't usually 'pipe-up' the whole internal installation, just the drops, unless it is;
a) Requested, or
b) Easier to fix that way ( steelwork etc ).

I install a dedicated CCU with EP ( metalclad) and run SWA underground - or overhead if required. All bonding, etc, is carried out in the shed as for any other installation.

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? )

Yep, catenary wire, although I haven't done one of those for a long time now.

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.

Stick your neck out all you want John!

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.

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).]

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?.

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.

That actually raises an interesting point.

There is a British Standard which lists the colors to be used for identifying pipes and conduits, and it specifies orange for electrical conduits.

So wouldn't it be sensible if we could obtain orange PVC conduit?

EN 50086-2-4 specifies underground conduit: Red for power, black for communications.

Red seems to be the accepted standard for underground power conduit here in Ireland.

Yellow for gas pipes.

Orange gets used for Public Lighting and Traffic Lights

Telecommunications ducts are a mixture of colours:

Eircom (the former state owned phonecompany) has black ducting for bundles of copper telephone cables.

Fiber optic and coax cables tend to be layed in green duct (for all companies)

Although, sometimes trunk network fiber optic cables are ducted in blue.

Communications companies are now required to print their name along their ducts too as it makes identification easier.

You would think so wouldn't you? I have yet to find it around these parts - and not even the utils use it around here ( although the u/g cables are now sheathed in orange ); they still use black + warning ribbon.

We've always used the Orange conduit here for underground Power services, at least as far back as the 50's.
Mind you, the older (first) form of PVC conduit here was nothing short of rubbish and we are still digging it up today, to find that most of it has collapsed.
Green conduit is used here for Telecom's cabling and Yellow for Gas.
Just as a little note, I once connected up a shed for a guy that pulled the submain cable through 2" Galvanised Steel water pipe.
The cable was 2.5mm2 and he was remarking as to how hard it was to pull it through.
After hearing that I went to get my Megger, it shouldn't be that hard to pull and I suspected cable damage.
The Megger confirmed this and up came the pipe-work!.
4 90 degree elbows.
I dismantled the work and pulled the cable out, to find all 3 cores bare at one part of the cable, the result of a huge burr on one of the pipe threads.
That was lucky!.

There were major road works going on in the city centre here over the past few years and you could see a lot of older duct work some of which would date back almost 100 years. Interesting to see how the very old ducts were fully intact while the 1960s and 70s plastic ducts, particularly ones carrying public lighting cabling had collapsed.

The power and telephone service ducts were huge concrete pipes several inches in diameter. They certainly didn't skimp!

The electrical service cables from the old distribution pillars were all direct burried sheilded cables. They looked like about 2" thick with a layer of coiled metal around the outside. These were replaced with modern multicore shielded equivilants layed in red ducting.


Warning for cable serving a small island off the west coast of ireland.

[This message has been edited by djk (edited 01-04-2005).]

If I were supposed to do it ba German standards I'd definitely bury it by all means. NYY cable is available at every hardware store and can be buried direct.
An overhead service would (according to some German sparkies) have to be NYY or similar strung on steel wire for support. The steel wire would have to be connected to the ground bus via 16mm2 Cu (sic!) and surge diverters would have to be fitted at the house end.
So guess what's easier...

Even if the feeder was, say, only 20A?

For an overhead lemgth of maybe a few tens of feet at most?

Sounds like those German rules are a little excessive.

Vorsprung durch technik!

(Spelling probably upp thu kreeck)

My intention was a 6A feed off an existing 10A circuit, just to power a 60W light bulb and a single receptacle for maybe a table light or a 800W heater in the winter. The 16mm2 were for lightning protection.
The surge diverters weren't required, just strongly recommended. Hearing about the 16mm2 I nearly choked and had to strain hard not to call them crazy.
Besides, there's no way I could attach a 16mm2 wire to the equipotential bonding bus bar in the basement. All screws are rusted shut, except for the part of the bar that has already broken off from rust...
According to new code we would have to drive a 30mm copper ground rod with a length of 4,5m(!).

Good grief, 16mm cable to a rod 14' 9" long for lightning protection on a short suspension wire to a shed!!!!

I think your instincts to go with calling them crazy were right!

Ragnar,
That sounds really silly.
I'm all for good lightning protection and yes the conductors do need to be reasonably heavy, to match the current that they will carry in the event of a strike.
But, how common is lightning where you are?.
Seems rather excessive if the wire will never carry any actual fault current.
And as Paul said, it is only a short eposed run.
Your comments......

We're in an urban area with only underground supplies, and the only lightning strike we've had here in all the years (been living here all my life) hit a phone wire somewhere in the distance and shot our PABX.
The earth rod is not only for lightning protection, it's a general requirement for TN-C-S and TT services.
I'd love to bury NYY, but there's a concrete path butting right up to the house, so no way to get through... anyway, the garden hut probably won't ever be built, so I don't care much.