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I'm thinking of running power to my garage, it's about 40 meters away (as the cable flies).

I've been researching and already know the best way to do this would be to run a cable from the house consumer unit to a consumer unit in the garage, and then run a ring of sockets and lighting on appropriate fuses.

My question is, if I ran steel armoured cable from a normal UK plug socket to the garage (no CU) and only run basic lighting and restrict my use of power tools (nothing too high load) would I get away with this simpler setup?

Basically treating this as a large extension cord.

For those interested, the reason I ask is because the solution would be semi-permanent, in that I would be able to remove it in the future. I can't bury the cable and as I don't own the house don't fancy messing with the consumer unit.

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As this is, as you suggest, effectively a long extension cable, as long as you don't exceed the 13A maximum that you can draw from the single plug, there is little to stop you doing what you suggest (though it would be prudent to check that you will have enough "headroom" in your proposed cable in terms of voltage drop and earth loop impedance).

While you could run armoured cable, you might not want to. SWA can be pretty "uncooperative", although this is less of a problem at the cable sizes you are likely to need for a 13A load.

Personally, I'd give serious consideration to using some 2.5mm2 arctic grade flex rather than SWA, as it will be a lot more compliant to get it connected into the plug. (I'm guessing you'll need 2.5mm2 to meet the requirements for voltage drop over that distance and the earth loop impedance). Unless of course, you have particular concerns about damage to the cable.

For protection, it would also be worth making sure that the this is fed via an earth leakage circuit breaker, be it either in the plug, socket, or within your current consumer unit.

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  • Hi John, in the end I went with 2.5mm2 SWA, I really didn't want anything getting through the cable. I ended up earthing the steel outer core all the way along. I've terminated it into a double socket in the garage, of which is plugged into a single socket in the house. So far so go, I only run one thing a time off of it, but it'll be nice to be able to see the load being put on it.
    – Ben Everard
    Jul 25, 2014 at 8:01
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While you might not think you will have a high load now, if you're going to go through the effort of running cable, why not do it right? What if you or a future owner were to ever use the garage as a shop and have some tools that draw more than 13A? If it's not your house, consult the owner, and if you're willing to take on the cost, I can't imagine why they'd have an issue with you having the Garage powered as long as it's done properly. if it were me, I'd consider installing a 40A or greater breaker, and having a sub-panel installed in the Garage to control lighting, outlets, and give the possibility of adding 20A circuits for some more powerful tools.

As for the actual materials, in Canada we use Teck cable, which is rated for direct burial without a conduit. It's basically armored cable with a rubber membrane to weatherproof it. The armored cable I'm thinking of has an exposed metal sheath which is not suitable for underground burial.

As well, your method also leaves a very easy opportunity for overload. You have a 15A circuit, with probably a number of fixtures already installed in the house. Adding a long run with only 15A, then extra lights could put you over the maximum 12 fixtured allowable by code on a 15A circuit.

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  • It's far more usual for UK sockets to be on a 30A circuit, which gives more spare capacity.
    – John
    Jul 18, 2014 at 19:57
  • Thanks for your answer amace, this installation will not exist beyond my living in this house so I don't need to worry too much about future load. As the comment said, the load on the socket should be 30A.
    – Ben Everard
    Jul 19, 2014 at 8:04
  • The UK has very different wiring standards to the US and Canada. So the amperages you state don't really make sense in that context.
    – Brad Gilbert
    Jul 21, 2014 at 11:47
  • I ran this directly from a socket in the end, however I've wired it such that if I want to put it through the consumer unit at a later stage I could do.
    – Ben Everard
    Jul 25, 2014 at 8:02

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