Outdoor Sockets & Power


18 Jun 2004
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United Kingdom
Hello Folks
I wanting to install outdoor power for:
A single Socket
Switches for water feature pump, and
for Low voltage lighting via transformer.

I can run a supply from the kitchen, which is protected by RCD.
I was thinking of an external junction box, leading to the socket, and then to a three point external switch further up the garden, with transformers housed in an external weatherproof box.
?? Do I need additional RCD protection??

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No, multiple RCDs daisy chained perform no useful purpose, unless one of them is a slow acting type, other than to cause confusion as to which one has tripped.
But it would be better to take a feed from a non-RCD circuit breaker and then have a separate RCD for the outdoor stuff. Otherwise an earth fault on the outside circuits will also remove kitchen power -fridge or freezer off ?
However, if you decide can live with the risk of a nuisance trip, then what you propose will work OK. Depending on the current rating of the circuit from which you propose to spur, you may also need a switched/fused spur box, the switch so you can independently isolate the outdoor circuits from indoors, and the fuse to keep the thickness of cable to a manageable level (as it has to be rated as if for the maximum current available.)
What were you going to take a feed from ?
regards M.
How will you get your cable to those switches "further up the garden"? Can you go along a wall (NOT a fence) in conduit or will you have to go underground? If you can't use wall mounted conduit I'd be inclined to put the switches and transformers INSIDE the house. I would also aim to bring the mains wire out straight into the back of that socket.

With this method you don't need any waterproof boxes or switches , you can turn your lights/pump on and off from inside and, since the outside wires will all be low voltage, you can get away with almost anything. You will want a fused connection unit to connect those light switches into your ring main and you can put the outdoor socket on this as well.

The only drawback to running low voltage lights at the other end of the garden is the voltage drop you'll get along their wires. Halogen lights should not be run undervoltage because their internal tungsten recycling system doesn't work if they aren't up to temperature. Ordinary lights will simply run dim and actually last longer. You'll have to do some voltage drop calculations. Example: a 12 volt 20 watt lamp will take a little under two amps. If you put this at the end of a modest 10 metres of 1mm cable you will lose almost a whole volt. The answer of course is simple; use thicker cable.
Thanks folks.
I was going (still musing) to take the feed from the kitchen. I have a socket on top of some units that the cooker hood is plugged into. Was thinking take this feed, thro the wall, and down some sort of conduit to some sort of external box - and put in an external socket.
I take Felix's point about outdoor power, but the socket is necessary.

Also - having thought about it, having switches at the wrong end of the garden is not necessarily good - but its only 15metres.

The kind of switch I was using is:
and this will power LV lights and pump. As its at the end of the garden(?) then I should get less of a power drop.
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You're right about the voltage drop. That's why the national grid runs at such a high voltage. If it was all 240 volts those overhead power lines would have to be several metres thick - and that's a lot of copper!

You can or course still have your switches at the house end - inside or outside - and run mains voltage down the garden to remote transformers. Just out of interest, what sized lights are you thinking of putting in?
The Idea was to have a simple set of 5 or 6 garden lights (LV). I was thinking halogen spots or similar. And then some LED decklights that sit facing up on the deck(deck is in the corner and transformers can sit underneath) Finally, power to a water feature.
The fence up the garden has a concrete base, so I think im ok to run a mains up the concrete, but will need to bury the armoured cable.
Im usually quite handy with internal electrics, but will get a spark if it gets too complicated. I thought a series of boxes and switches should be OK.
OK, five or six LV halogen spots will need a lot of current; ten amps for six 20 watt lamps - and 25 amps for fifties! If you put those at the end of a 1mm cable you won't get much light out of them. In this case, and if you don't mind the complexities of outdoor wiring, you'ld be better off with a remote transformer.
thanks for all the help!

One more concern - Building regs for outdoor sockets? Necessary or not?
If they are then a spark is needed. I seem to get conflicting info from the sites Ive visited

Building control or a spark who is an approved scheme member should be involved for new circuits, or modifications other than a like for like replacement of a broken fitting or a single cable outdoors. This applies to all work started or agreed to start, after Jan 1st.
Otherwise jobs already agreed / started have a 3 month grace period to finish.
Thats the official line.

However, I suspect many people will "forget" to notify, as the fees are a significant part of the job cost, as many do now when changing a sink or toilet pan, for example. In practice it is very hard to say after a few years exactly what was done when, and so long as it is all according to regs, and no-one gets hurt, then it is unlikely to be made an issue if the paper trail is lacking. However, that said it would be most unwise of me to suggest breaking a law, but one may ask when did you start planning this job ?

regards M.

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