SWA Sizes for outside shed

[jord35davies]

Need a bit of advice on this one,
I need to supply a 4 way consumer unit in a block shed from the main consumer unit in the house.

The supply from the four way db will be powering 10 double sockets, 2 lights and 3 outside lights.

What size SWA would I need to use and if I install a ring in the block shed would it be ok to use a 32 amp breaker as the supply to the shed will be running on a 20 amp breaker iin the house?

 

[tony.towa]

Just posted a reply to this on your outside light problem thread. Hope it helps.

 

[wattsup]

Depends what all the sockets are for. If the sockets are for small power tools and the like. I would use 10mm on a 45a breaker with rcd protection, I would cut the tails and have a stand alone dis board dedicated to outbuilding, unless the existing dis board is modern with several spare ways. I'm assuming the shed isn't miles up the garden.

 

[tony.towa]

First thing I would say is that if you are installing ten double sockets there must be a reason in which case a twenty amp supply is not likely to be adequate.
As for a 32amp breaker downstream of a 20 amp, this will not give you any discrimination and the 20amp will trip at the source before the local 32amp in the building.
If the building is outside the equipotential zone, which it sounds like it is, you will also need RCD protection.
My advice is to establish the maximum load, ensure a suitable supply is available and then work out what parts and cable you need.
Take it steady

 

[jord35davies]

the shed is a good 20m up the garden. would I get away with 6mm using a bit of diversity.the extra sockets are for band equipment, subs and amplifiers etc. what about the ring in the shed is it ok?

 

[wattsup]

would I get away with 6mm, yeah but then use 32a main breaker, put the ring main on a 20/25a breaker. Some amps can surge and knock a 16a breaker off. (I know cos done it) So I suppose there is a possibility the 20a could trip, if you use a 6mm you cannot upgrade the 32a main breaker, well I suppose you could maybe get away with a 40a..but I'm not saying you should

Really though price difference between 10mm and 6mm swa is not that great, especially if only 20mtrs or so, you then have no worries.
For some obscure reason I bought 4-core 16mm swa when I only needed 3-core, cheaper. Because I only wanted 15 mtrs, end of drum 4-core just 15mtrs! £10 quid cheaper..well these wholesellers know what they are doing I suppose...just get rid of it