Garage Socket

[elementps]

Hello all,

Have had a request from customer to supply garage with 1 x double socket and 1 x single strip light.

Garage is detached building 40m's from rear of house. Unfortunately consumer unit is at front of house and the cable route to garage from there is not possible. So, am looking to take a fused spur from the downstairs ring, out of house and burried (swa) to garage, double socket then fused conection unit to light.

Made a call to NIC tech line, they seem fairly happy (obviously new circuit from board would have been preferred), referenced me to p.362 of regs.

I am just trying to do cable cals and after some help with how you rate a single double socket, is it 100% of 13A +40% of 13A = 18.2A? If so, how can this be done from a 13A fcu? Bit stuck here, if anyone could advise would be much appreciated.

 

[Adam W]

I'd rate it at 13A because it would be coming off a 13A FCU from the ring.
If there's no rcd at the cu it would need to be rcd'd separately.

 

[elementps]

So, heres what im getting:

with correction factors applied 13/.75 = 17.3A.

1.5 and 2.5 would have voltage drop of 20.07 and 12.46 over 40m's, too high.
4mm would have volt drop of 7.61, so acceptable.

resistance of 4mm is 9.22 @ 20degrees so resistance of the additional spur would be (9.22x40)/1000 = 0.37.

Now to check this can i assume that if zs at ring plus 0.37 is less than 1.15 (32A type B MCB) im ok?

RCD protection is in place.

 

[malcolmsanford]

I would be advising my customer this, OK you only want for now a socket and a light, but what about the future who knows you might want some pretty gardens lights, or perhaps even want to do some DIY in the garage and want more power.

So if we are going to dig a 40 metre trench let's lay some serious SWA in it and fit 6mm perhaps 10mm if you want as there isn't that much of a difference price wise and you can terminate the SWA into 2 adaptable boxes each end then do your small install from there.

 

[elementps]

That is true, however this supply is coming as a spur off the grd fl ring, so really wouldn't be able to add more points. Have advised the customer that I would prefer running a distribution circuit from board to garage. However consumer unit is at front of house and the route to garage would be across other people property etc.

 

[malcolmsanford]

That is true, however this supply is coming as a spur off the grd fl ring, so really wouldn't be able to add more points. Have advised the customer that I would prefer running a distribution circuit from board to garage. However consumer unit is at front of house and the route to garage would be across other people property etc.

True and there is nothing to stop you for now spurring of that ring, but instead of using a small 4mm SWA you will be using the 6/10mm, future proofing.

The same as a customer buys a small 2kw oven which can be plugged in, if I was wiring a new circuit for it I would advise the customer to fit 6mm cable, as you never know 3 yrs down the line they may want to get a larger oven. same scenario here, but instead of a few meters run for that cooker circuit in the house, you have 40 metres buried cable.

 

[elementps]

I completely agree with what your saying. Would you suggest this even though the new spur is from a ring, any future addition would most probably have to be on it's own circuit from board (opposite end of house). So would you still lay heavier cable so that if an addition is made they only have to run from board to existing spur?

 

[malcolmsanford]

Yes that is exactly right. Your protecting a 6mm with a 13amp BS 1362 fuse so it's not going to cause a problem. As said at this time the customer only wants to utilise 1 x socket and 1 x light but who knows what he might want 3 or 5 yrs down the road. How long have people been using induction hobs, I bet 5 yrs before their inception no one would have given a thought of them, but now they are becoming more and more in vogue.

The bottom line is you can only advise the client. If he says no then you do your original design and leave as if. I always think that it show's a professional approach to advise of perhaps something they have not thought of.