Garage supply

[oldbutnotdead]

Morning all, apologies if this one has been done but I can't find it and I can't get hold of my electrician at the moment.

Situation- digger man coming a week early to dig out the driveway. While he's here I want him to dig me a trench for SWA to the garage. Question- how much current capacity should I provide for the garage (6m x 9m)

I'll need lighting- either fluorescent or similar with a PIR flood outside (that'll be LED or something low energy)

I'll need power- 32A ring was the plan, heaviest power consumption at the moment is the MIG, there will be other stuff but no really high draw items.

Doncaster Cables volt drop calculator thing tells me 10mm 2 core SWA will go up to 32 amps (garage is 56 metres from meter in house), more than that I'll need 16mm. Supply arrangement to house is TN-S as far as I can tell.

Is 32A adequate for a 4 way CU with 1 x 5A (lighting) and 1 x 32A (ring main) backed by (presumably) 32A MCB a the CU in the house or do I need to go the next step- 45A MCB in the house and 16mm SWA to the CU in the garage.

Cheers

PS Before anyone asks, I'm not planning on wiring the thing myself- all I need to know right now is what size supply cable to bury under the driveway (at about 400 in sand with marker tape and a lot of old bricks above the 150mm clean fill above the cable). And is 2 core SWA still acceptable (using the armour for ground) or do I have to use 3 core? )

 

[diyer56]

Is 32A adequate for a 4 way CU with 1 x 5A (lighting) and 1 x 32A (ring main) backed by (presumably) 32A MCB a the CU in the house

The 32A cannot supply a 32A and a 5A

You would either need a higher rated MCB at the house (and therefore larger cable) or consider reducing the 32A at the garage. What tools/equipment will you be running in the garage?

PS Before anyone asks, I'm not planning on wiring the thing myself- all I need to know right now is what size supply cable to bury under the driveway

You may be better off installing a duct and draw string. Your electrician could then install the correct cable.

 

[bernardgreen]

Install two ducts,

One for the 230 volt SWA and one for ELV circuits ( phones, alarms, and other services )

 

[ban-all-sheds]

This sort of product:

http://www.drainageonline.co.uk/Ducting/Black-Twinwall-Duct-x-50m-coil.htm

(other suppliers are available)

Twin-wall, smooth inside for ease of pulling cables through, ribbed outside for strength. Comes with a draw-cord installed so no messing about with a vacuum cleaner (or a hungry ferret and a piece of chicken ). The drawcord is a bit pathetic though - might be a good idea before you bury it to use the supplied one to pull some stronger rope through.

Do make sure that the bends are swept enough for cable to be pulled through or you'll have to dig up the new drive. Make sure you prepare the trench properly, that it's deep enough and that you put warning tape down. And take photos at stages if you want an electrician to use it.

 

[oldbutnotdead]

Thanks all. Duct is not a bad plan as it goes- was pondering whether to put one in anyway for alarm, LAN etc, not sure about drawing SWA through a duct but that scheme has its merits......

Another wee thorn in the ointment is at the house end- wasn't planning on digging out the shabby concrete (underneath which are some shabby but serviceable drains which are on the replacement list) just yet but will have to if I go the duct route.

Good point regarding the photos and trench route- since the garden is not terrifically ornamental at the moment and there are a load of variables on the job and baby diggers aren't expensive for a day I'm going to bin the cable burying off for the moment- driveway is only road planings rather than concrete so once I've got the definitive answers from electrician (and I decide whether I really need ELV services at the garage) I'll dig a trench and plant the goodies while sparks is available to certify depth and route are acceptable. Will mean crossing the driveway but that's not a massive trauma.

Many thanks again for responses.

 

[winston1]

You don't need a consumer unit in the garage. 32amp MCB in the house feeding garage ring, and lights fed off this ring via a switched fused connection unit is all you need.

You should not use 2 core SWA. Use 3 core.

 

[JohnW2]

You don't need a consumer unit in the garage. 32amp MCB in the house feeding garage ring, and lights fed off this ring via a switched fused connection unit is all you need.

Unless you're talking about a 'lollipop' circuit (which would probably stimulate some discussion), to run a ring in the garage from an MCB in the house would require at least 5-core (some would say at least 4-core) SWA. Far better to have a 4mm² radial sockets circuit in the garage, I would have thought (that is, if the OP really needs anything like 32A).

Kind Regards, John

 

[winston1]

You don't need a consumer unit in the garage. 32amp MCB in the house feeding garage ring, and lights fed off this ring via a switched fused connection unit is all you need.

Unless you're talking about a 'lollipop' circuit (which would probably stimulate some discussion),
Kind Regards, John

I was, suppose I should have said so.

 

[oldbutnotdead]

Ta again for responses.

Right now I could get away with 16A supply- 3 A for lighting and 13A for power- after all I can only use one tool at a time, the biggest draw (and the one that is sensitive to volt drop) is the MIG welder- only 200A domestic type thing but still tugs a fair bit through a 13A fuse.

Reason for going for greater capacity- allows more flexibility in the future (if, for instance, I should fancy going into hydroponics ) or more realistically baking spray paint, running a bead blaster, stuff like that.

And 3 core SWA looks like the easy way to compliance- with copper equivalence of armour being 8 to 1 on a good day the effective cross section would be about 3mm on a 10mm SWA. For the extra £50 it'll cost I'll put it in.....