DIYbanter - View Single Post

wrote:
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.

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.

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

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

5.Connect to a waterproof socket
6.From the waterproof socket spur to a 150W security light.

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

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 1.5m m cable? or should I stick with 2.5 to reduce the
voltage drop?

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 :-)

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.

Probably not at 12m with TN-S.

(Part P will apply.)

Owain