workshop power

[paulw]

I'm afraid I have to ask the knowlegable folk here to cover the familiar topic of outside electrics.

I have searched on sheds outside ect already
I have noted BAS's comments
I have considered part P
I considered burying the cable to the right depth
I considered the voltage drop
I have local electricians quote which is very high
I will apply for PP and get an electrician to assist
I promise I won't turn anything on until someone qualified tells me to!

however I still have a question,

I wish to supply power to an outside shed taking a spur from an inside socket which is part of the 13A ring main.

The shed is 12M from the socket and inside the shed I will have a dedicated shed CU with 35amp and 6amp circuits with RCD's, supplying a couple of sockets and a flourescent light. I rarely expect the load to exceed 2000W. Odd drills soldering iron etc.

Between the shed and the house I will use 12m of 2.5mm 3c SWA, cleated and running along the bottom of a brick wall.

However whilst I'm happy at the shed end, I'm not sure what to do at the house end. I've got a ip55 spur unit with RCD and it's rated at 13 AMPS.

I could mount this on the outside wall which would be opposite the intenal socket and use 12 inches of 2.5m twin to feed the spur.

I reckon that this would suffice in power terms, however the wife would like a pond pump and external low voltage lights and I could see the load climbing if I wasn't really careful, or if I needed to run a heater in the winter.

So my question is about the most legal and efficient way to get the maximum power from the ring main socket to the SWA cable.

Could I replace the 13amp external spur with a 20A CU with RCD (maybe even the same type of shed CU I have at the shed end) in an IP55 box for example? I believe the loading would be accepted by the wiring but maybe not by regulations?

My house CU does not have any RCD which is why I need to begin the external wiring with a RCD unit. (so I am told)


The easiest thing of course would be wired to the MAIN CU in the house but that is not possible, as the shed is an after thought following major internal redecoration and the CU is central in the house.

Any thoughts or guidance would me most apprciated.


thanks

Paul.

 

[notb665]

I wish to supply power to an outside shed taking a spur from an inside socket which is part of the 13A ring main.

I'm not a professional but I am pretty darn sure that isn't allowed.

The easiest thing of course would be wired to the MAIN CU in the house but that is not possible, as the shed is an after thought following major internal redecoration and the CU is central in the house.

I think you mean best, not easiest, but as you say yourself, the power must come from a single feed from your Consumer Unit.

I am sure the Shed-Lover or Barcardi-Boy will elaborate.

 

[paulw]

You are right I did mean the best option would be the main CU.

I've been told by part P certified people that I can spur from the socket which is on the ring main.

cheers paul

 

[mapj1]

You can spur from a ring main for any reasonable purpose, but only one 13A worth is allowed at one point, to keep the ring in balance, so one socket point (single or doube socket count as 'one point' for this rule) or one fused spur feeding anything you like.
Sadly if you want more than 13A, then the ring main is not the place to take it from. How about going up the outside wall a bit with the SWA and into the floor ceiling void of the house- in a place where you can thread across to the CU cupboard with bamboo or whatever? Then its a bit like wiring in a cooker radial - you can have a 25A breaker if you like on 2.5mm SWA, so long as it routes in poistions where it can cool itself.
Otherwise, as drawn it is 13a max, which migh be enough to be going on with.

 

[paulw]

Thanks Mapj1, just the information I needed.

The way my house is wired, I know I have two seperate ring mains that I could potentially take spurs from. Using one for the pond and low voltage lighting and the other for my workshop.

however I really would like something neater than sticking an ip55 fused spur rcd unit on the outside wall from which to run the SWA to the shed.

Is is there a product that would do the job from the inside by utilising the existing twin 13amp socket space? i.e I could then drill straight out to the outside from the back of the socket hole and route the SWA straight out of the wall?

thanks,

Paul.

 

[Spark123]

RCD Fused spur unit on the inside wall in a dual knockout box with a blank plate to create room to make terminating the SWA easier.

 

[paulw]

Thanks Sparks,

I wonder why I was told to go for the external RCD, probably because it's more expensive eh

Possibly the last questions now

Wiring this thing I presume I'd chase the 2.4 twin along the wall from the side of the twin 13 amp socket and then cover with metal strip before plastering back over or is it ok to run a few inches of plastic surface connduit?

Does the SWA need to go into the unit via a gland or would that be ok going directly through the wall from behind the unit. I.E no sight of the SWA indoors just the conduit bringing the twin from the spur?

Really appreciate the detailed guidance guys!

Thanks

Paul.

 

[Spark123]

Wiring this thing I presume I'd chase the 2.4 twin along the wall from the side of the twin 13 amp socket and then cover with metal strip before plastering back over or is it ok to run a few inches of plastic surface connduit?

2.5mm² twin + earth?
You could replace the double socket with items on previous post or you can run across the wall in conduit from the socket on the ring to the RCD spur. Although it is OK to run horizontally burried in plaster, I prefer the surface method as you can forget where the burried cables are. You could mount the RCD spur below the double socket if there is enough space.

Does the SWA need to go into the unit via a gland or would that be ok going directly through the wall from behind the unit. I.E no sight of the SWA indoors just the conduit bringing the twin from the spur?

The SWA needs to connect into the back box with a gland. It does't really matter if you cannot see the gland so long as it is in the banjo and sound (and the electrician can see enough of it under the cover for inspection). The back box and banjo on the gland both require earthing.

 

[paulw]

Many thanks Spark123

And thanks to everyone for replying to a new user without making me feel like I was stupid.

Paul.