New Outside Socket and Security Light

[homehome16]

Hi I am looking for some advice in installing an outside plug socket and security light in the garden. This is what I though I would do:

1.Take a spur from the downstairs main ring. 2.Connect the spur to a RCD. 3.Connect a cable from the RCD to a junction box 4.Connect 2.5mm armoured cable (about 12 meters) to the junction box and lay under the lawn 5.Connect to a waterproof socket 6.From the waterproof socket spur to a 150W security light.

Does this sound expectable? Also I'm not to sure what size RCD I should install. The only things that would be connected to the outside sockets would be garden tools, or maybe a radio. (not forgetting the

150W light)

Could I use 1.5mm cable? or should I stick with 2.5 to reduce the voltage drop?

Also I read somewhere that I may need to install an extra earth in the garden near the socket. Is this correct. My supply is a TN-S.

Thanks

John

[Owain]

You may not need an RCD, if your socket ring is already RCD protected. Cascading two RCDs in series will not usually provide discrimination (ie either may trip in the event of a fault).

You can get Fused Connection Units with inbuilt RCD. You will need to fuse the spur at 13A as you are supplying two points, and an unfused spur on a ring can only supply one point.

With some 'buried cable below' tape between the surface and the cable.

You may need to fuse down to 3A for the light (assuming the spur from the ring is fused at 13A).

I would stick with 2.5mm - voltage drop /might/ be an issue especially at motor start. More importantly, digging up the lawn is the sort of job you only want to do once, and the marginal cost of the larger cable is insignificant.

Besides, 2.5mm lets you use the George Forman outside :-)

Probably not at 12m with TN-S.

(Part P will apply.)

Owain

[Chip]

On 27 Jun 2005 13:09:50 -0700,it is alleged that [e-mail] spake thusly in uk.d-i-y:

Make sure the spur is *fused* not just a 'normal' unfused spur as if it was another socket on the inside of the house. (

) is probably what you'd be after on this count.

Your solution of using a junction box outside to terminate the SWA sounds reasonable, although you'd have to ensure a good seal around the (presumably) T&E feeding the box, TLC supply glands for this purpose for NotMuchMoney:-)

The light should be protected by the fuse recommended by the manufacturer which is *probably* 5-6 amp maximum, which would not be ok for the socket, given high loading of some garden tools.

I have thought of various ways round this without excessive expense, the simplest (if clunky) solution is a double outside socket, of the type with the in-use covers that can be occupied when wet, with the light plugged into this using a 3-5amp fuse in the plug, outside FCUs are available from TLC but the price made me go 'ouch'.

(see points 1-2)

Over 12m, volt drop shouldn't be a major issue at 13 amps or below, but 2.5 is not much more expensive than 1.5 and it's less fragile.

To my knowledge, a TN-S supply is not the one that requires extra earthing, you run into issues with TN-C-S (aka PME) when feeding outbuildings/external equipment but I have never heard of requiring it with a TN-S supply, although I am sure to be corrected if wrong .

• Heavy disclaimer: Please, if you're not confident, and/or concerned about complying with part P if not in Scotland, don't do this. If you are confident etc, HTH:-) *

Also, I have no affiliation with TLC, they are just generally good guys, and my closest wholesaler, and the one I am familiar with. Other suppliers undoubtedly have the same things maybe at lower prices.

[homehome16]

Thanks for you help guys