Workshop power

[Lawrence Zarb]

What would the recommended size of amoured cable to use to power a small workshop, about 20 metres from the house?....I was thinking of using

6mm, but maybe this is overkill

[Rob Hamadi]

Depends on the load. There's a handy calculator here:

[Andy Hall]

How long's a piece of string?

One would need projected load to answer that question and to ensure that voltage drop is within the required limits.

SWA cable is cheap. 6mm cable is £1.90 and 4mm cable £1.36 from TLC, so for a 20m length the discussion is about £10.

Digging it up and changing it if needs increase later is a bigger PITA/cost than £10.

[nightjar]

I laid 16mm to my garage, 25m from the house. Too big is always better than too small in this situation.

Colin Bignell

[tony sayer]

In article , Andy Hall writes

Ducting is also quite cheap and that means if you need any other "services"

[Ian_m]

I helped my mate put power into his shed. Put a 2 MCB + RCD CU in his grarage next to main CU. One MCB was 32A for power and other 6A(?) for lights, basically put lights on two way switches (one at house back door and other on shed) so that you could turn lights on when leaving house/shed. Both cables buried at depth recommended in B&Q "outside power leaflet" (0.5m, we made a measuring stick). For the two way light switching you need an underground junction box (or run two cable upto the switch on the house).

The main power cable was 6mm like previously mentioned, not much more cost than 4mm and lighting circuit was 4 core 1.5mm. In shed another CU with 2

16A MCB's one for shed "ring" and other for outside socket.

[Clive Mitchell]

In message , Ian_m writes

Underground junction box.... A device that inevitably fills with water whether through the seals or via the inside of the cable.

Not sure why you needed one. For the house switch you would only have needed three cores and earth straight from the hut to a suitable switch and enclosure.

[Ian Middleton]

I put in two underground junction boxes at parents house (from TLC when they were CEF down our way) about 17 years ago and three are at my current house all still fine, no RCD trips. Mind you not cheap, about =A325 each.

[Lurch]

On Wed, 7 Mar 2007 10:42:04 -0000, "Ian_m" mused:

Not sure why you'd need that.

[Lurch]

On 7 Mar 2007 12:03:01 -0800, "Ian Middleton" mused:

If you're going to join cables underground you really want a resin filled joint, ideally.

[Ian_m]

Because for the switch at the house you need a cable in from CU and cable out ot the shed (and at shed end a cable into switch and cable out to light) and if using MK outdoor switches and suitable SWA glands you can only get one cable entry per side. A MK switch with two SWA's leaving from it looks naff, would never pass an SWMBO inspection and is hard to work with so run single cable from underground junction box to switch, no SWMBO complaints about cabling.

[David Hansen]

On Thu, 8 Mar 2007 09:25:29 -0000 someone who may be "Ian_m" wrote this:-

Feed the light from the shed.

The switch in the shed (or a nearby box) has a cable coming from the consumer unit in the shed, a cable going to the light and a (three core) cable going to the switch at the house end. All of these can be SWA, though presumably the first one will not be SWA in most instances.

If the switch in the shed is small then it is probably best to terminate the SWA in a suitable box, which can be tucked out of the way and so hopefully not be a great problem to SWMBO. If it is try flattery:-) A neat run of round conduit with singles in it takes the appropriate wires to the switch. A terminal strip in the junction box will make the appropriate connections.

The cables to the light and switch at the house end are then continuous unbroken SWA, which can be brought out of the ground at the appropriate places without fuss.

It is far easier to make connections out of the rain in a shed than in the bottom of a hole. However, if you are determined to use joints then they should be polymer encapsulated joints. Remember to join the armour.

[Clive Mitchell]

In message , Ian_m writes

If the light in the shed was powered from there you would only need a single three core and earth cable to the house switch.

[Lurch]

On Thu, 8 Mar 2007 09:25:29 -0000, "Ian_m" mused:

Like I said, not sure why you'd need to do that.

Well, I find 1.5 and 2.5 SWA a breeze to work with, love the stuff tbh. I buy it in 100m drums and use it all over the place.

Personally, I'd have fed the light from the shed and run 1 3 core SWA to the house for the switch. If jointing in the middle then I'd either mount it in the shed, on the side of the house or by the CU. No need for underground joints on a new installation.