Garage supply

[sambotc]

Quick question,

Need to run a supply to my garage soon to replace the buried 2.5 T&E which is existing

Was planning on a 16a type 2 RCBO on main house CU, 4mtr's of 2.5 T&E joining 8 mtr's of 2.5 SWA inside the house through to the garage. The SWA will be fixed to a wall surface along it's entire length into the garage. From there it'll feed a pair or three double sockets. The sockets will run a 150w light, small freezer, and a radio most of there time, but occasionally other tools and a pressure washer.

I've completed the part P full scope (heating engineer) so have some knoweldge, but not to say the Part P course makes me an electrician.

Does the earth for the SWA only go through the SW, as most cables are 2 core?

Obviously there is RCD protection at the CU, does the incoming supply need any form of local isolation in the garage or fused spur?

Does the above all sound ok?

Cheers, Sam

 

[1john]

if you are planning on using an RCBO to provide earth leakage and over current protection, i would install a 20Amp double pole switch next to the consumer unit if you re choosing a single poled (one module) unit.

That being said, why not run a bigger supply incase you ever want anything more up there?

As you should be aware, inform the LABC before commencing ANY works.

 

[sambotc]

Cheers for the reply.

What is the purpose of the double pole you suggested? To isolate this circuit for maintenance etc rather than flick off the whole CU?

The CU currently consists of 5x rcbo and a 100a main switch.

The garage is only a small prefab so there isn't much else it can be used for. The existing supply has never tripped so assumed the same size would suffice.

With regards to LABC, we are NICEIC registered, my understanding was that this was self notifyable on completion? We have 2 fully qualified electricians, one of them is a very close friend of mine so i'm hoping he'll do it for me while I make the tea and butties

Sam
Cheers, Sam

 

[333rocky333]

Why not do the whole run in swa.
Two core uses the outer steel as earth, this has to be terminated to provide earth up to your last point.
For the slight extra cost 3 core may be more suitable.

 

[1john]

agreed with rocky on the 3 core front. the double pole switch provides complete isolation of all 'live' conductors (line/live/phase and neutra)l, although this isnt exactly neccisary as the new circuit will not be on a shared RCD so it can't cause nuisence tripping.

 

[sambotc]

So if I use 3 core, I can use one core for the earth? Is there a requirement to earth the SW also incase of mechanical damage?

I could you SWA all the way, although it may be more complicated running it through the house from CU to outside without being an eyesore!


Thanks, Sam

 

[ColJack]

personal preference..
6mm² 3 core SWA direct from fuseboard on a 32A MCB on the none RCD side.
in the shed terminate into a "garage CU" with a 20 or 16A RCBO and a 6A RCBO for the lights.. that way you don't end up in the dark holding a still spinning circular saw or drill when you trip out the rcd in the house..

 

[1john]

Always earth the armour.

 

[sambotc]

Thanks for all the replies.

Earthing the armour won't be a problem presuming only the CU side of the SWA gland need's earthing.

Coljack. The suggestion you made is a good one, my only concern was that the SWA would not be RCD protected although being SWA I suppose it isn't an issue?

Certainly having 2 circuits in the garage would be better.

Whats the approx cost per mtr of SWA in 4 or 6 mm? 2.5mm looks to be about 1.20 P/M although haven't priced it through CEF yet only online.

Sam

 

[1john]

wont cost a great deal more and this is the best route to take, the SWA doesn't require RCD protection, you can provide RCD protection to the cricuits at the garage with a 2 way board with an RCD upfront, or you could get posh and have a main switch and 2 RCBO's, or an RCBO for the sockets and an MCB for the lighting if requirments are met.

 

[ColJack]

15m 6.0mm 3 core LSF on TLC for £28.50 ( £1.90/m ) clearance..

or regular 6.0mm 3 core normal for £1.96/m

 

[Paul_C]

personal preference..
6mm² 3 core SWA direct from fuseboard on a 32A MCB on the none RCD side.
in the shed terminate into a "garage CU" with a 20 or 16A RCBO and a 6A RCBO for the lights.. that way you don't end up in the dark holding a still spinning circular saw or drill when you trip out the rcd in the house..

Second that. While you're doing the job anyway, it isn't going to cost much more to run in 30A feed to allow to possible future expansion.

 

[sambotc]

OK seem's like a plan.


How is the SWA gland connected to the CU, directly or do I need to pick up some differant fitting(s).

Is it not just as easy to use 2 core and earth the SW, or am I missing something else? Got plenty of 6mm earth cable in the van anyway.

Once the supply is in, i'll re-wire the garage, was thinking of using pvc conduit to keep it tidy, is it actually a requirement?

They've got a garage unit with RCD and x mcb's on offer at CEF at the mo for £15 +vat

Cheers, Sam

 

[1john]

conduit is a good idea to protect the cables against impact damage. the cable may been to be glanded into a seperate box and then a bit of T&E into the board, really does depend on the board.

 

[ColJack]

an adaptable box ( or even a galv conduit box, through or angle to suit need ) butted up to the CU..

leave the inner insulation of the SWA long and pass it through into the CU and strip back there..
wire direct, no need for T+E and a joint then..