Shed electrics

[Skinnersplace]

Hi All, I have a question about wiring up garden shed for power.

I want to fit a metal Garage consumer unit to power 2 double sockets a 100W lighting circuit and the possibility of a 500w flood light.
The shed is to be fed by a armoured cable suspended from a catenary wire (methord 13).

Looking at the standard parts available, A 40A breaker in my main cu, feeding a 4mm armoured cable (41A) feeding the second consumer unit fitted with a 32A (30ma) RCD feeding a 20A MCB for the sockets and a 6A MCB for the lighting should be sufficient.

However when I look at the diversity of the load (600W/240)*1.8 for the lighting + 13A for the sockets I get a load of 17.5A. Is there a better set up than the one I have set out above ? Perhaps utilising a thinner cable ?

Any suggestion would be much appreciated.

[Steve]

I wouldn't suspend armoured cable using a catenary - its very heavy. Consider split concentric cable for this method. Its structure is a bit like co-axial, with the live core in the middle and neutral and earth surrounding it forming the protective sheath.

[Skinnersplace]

Thanks Crafty,

I have also considered using 2.5mm Artic cable (rated to 20A), which is ok for my diversified load. However what size breakers should I use with that ? (can the RCD / MCB rating be less than the cable rating)

[Steve]

Distance is all important here.

For a start, 4mm cable of any variety is not to be used on a 40 amp breaker, as it would only be suitable for this for about 5 metres with no derating factors. 4mm generally goes on a 32A MCB max.

Not sure if arctic is suitable for suspension, perhaps someone else can respond here. It is more widely available. Is burial not an option?

Not sure if you're aware of this, but this job comes under part p of the building regs, it is therefore notifiable to your local building control. Look in the wiki for information.

[Skinnersplace]

Thanks Carafty,

Yeah, I am aware of part p - just trying to gauge the severity of the job at this point.

The shed is about 5 m from the house but on a concrete terrace, so difficult to bury.

Any one have any advice on a suitable set up for supplying twin double sockets and possible 600W lighting load in a shed ? Specifically What size wire to use / What size breakers are acceptable.

Skinner

[luminaire]

I would have thought 4mm T & E cable would be ample, afterall we use 2.5mm on 32A circuit.

Using a catenary is ok but not with swa cable.

You can then use 2.5mm for your 20A circuit and 1.5mm for your 6A circuit. No need for artic cable.

[davelx]

luminaire wrote:

I would have thought 4mm T & E cable would be ample, afterall we use 2.5mm on 32A circuit. Using a catenary is ok but not with swa cable. .

In a ring, don't forget - 2.5 is no good for a 32A radial.

Hi-Tuf is a good choice for catenary. But difficult to find >2.5mm.

Can anyone point to a suppier for split-con - I can't find one anywhere near me (S. London)

[Skinnersplace]

Thanks Luminaiure,

The internal wiring is no problem, it is the wire between the house and the shed, I am not familiar with.

I was hoping for advice on what that cable should be for the job, and what size MCB it should be fed from and what size the RCD in the shed should be because of it ?

Regards

Skinner

[ricicle]

Crafty wrote:

I wouldn't suspend armoured cable using a catenary - its very heavy. Consider split concentric cable for this method. Its structure is a bit like co-axial, with the live core in the middle and neutral and earth surrounding it forming the protective sheath.

WTF are you on Crafty

[Skinnersplace]

Can any one give me examples of what they have used to provide power to an out building ?