Swa for garage

[pippo]

Hi all,

I am about to get a concrete base laid and as its a concrete sectional garage going on top i need to run the electrics through the base as the panels cant be drilled on the garage. So I want to get the cable run now.

My intention is to run the cable for the garage then have an electrician connect it up when Its ready. I will leave the trench open and there is plenty room under the floor boards (4ft) so the electrician can check the run if he wants. The total run from meter cupboard to garage is 15m, 4m of it is under ground.

I have a few questions:

1) When I asked about this before on this forum I was advised that 10mm swa 3 core would be fine for this run, would there be any harm in doing it in 16mm? I dont mind paying extra if it gives more options in future. For example I may build a shed behind the garage that would need power.

2) Is the required depth 18" for the trench ?

3) What protection should the cable be in underground? A friend told me that 100mm waste pipe would do but he is not an electrician, does it need to be more substantial than that? and is there a particular colour?

4) What should I use to protect the cable inside the concrete? Some kind of conduit?

Many thanks in advance for your advice.

Pippo

 

[Steve]

1. No harm. But a little wasteful. I dont think you'll need 63 amps down there. But then again, the wife might want a jacuzzi one day.

2. Yes.

3. None. Go to B&Q and select a piece of guttering. Put it on the ground and stike it with a spade. Now tell me if this would protect a piece of steel armoured cable. No additional protection is needed. But many people choose to run their cables in soil pipe for ease of replacement at a later date, not for protection. A piece of electrical warning tape should be in the ground somewhere above the cable run.

4. Again, no protection is needed, but soil pipe can be used here also for ease of pulling through.

 

[ColJack]

to save time and make your life easire for the future, don't put the cable in, put a duct in.. ( the 100mm drain pipe idea.. )
that way the sparky can be sure the cable is ok ( he might be able to get under the floor of the house, but there's still the burried 4m and the bit embeded in concrete that he can't see.. )

if you put in a decent sized duct ( or a couple of them ) it allows for future proofing also.
You never know if you might want a ethernet cable out there, or a coax for a tv or even a cctv camera maybe.., or water ( 2 ducts.. min.. can't run water with power.. ) etc...

 

[pippo]

Thats sound thanks Steve.

Good advice too coljack

I will go for 10mm since its unlikely I'll need more.

I have 2 last questions

1) Roughly whats the external diameter of 3core 10mm swa ? (there will be blockwork around the base acting as formwork and I need to allow a gap between the blocks for the cable).

2) Have I got any option other than piercing the damp proof membrane to get the cable through the concrete base ?

Cheers

Pippo

 

[ColJack]

you can seal the DPM round the duct..

see here for a good example of how to leave space for services and sealiing the DPM..

 

[Steve]

You altered your original post! Where it says "100mm waste pipe" it said "guttering" hence my "gutter-bashing" post which succeeded it.



Are you aware this is notifiable work? Not sure if you will have notified the garage already. But the electrics definitely need notifying to building control.

 

[pippo]

thanks for the link coljack.

Steve
I did edit my initial post, I done it before i read your reply as I realised that I had spare waste pipe from the bathroom so though id say that instead. I think what you said still applies, it could probably be easy enough broken by a spade.

Pippo

 

[holmslaw]

..

 

[Steve]

2) Have I got any option other than piercing the damp proof membrane to get the cable through the concrete base ?

Do not pierce the dpm, bring the cable up the external structure and then drill through to the inside, well above the dpm.

I think the reason he wants to come through the base is because the walls are prefab slabs.

 

[pippo]

2) Have I got any option other than piercing the damp proof membrane to get the cable through the concrete base ?

Do not pierce the dpm, bring the cable up the external structure and then drill through to the inside, well above the dpm.

I think the reason he wants to come through the base is because the walls are prefab slabs.

Thats correct, the concrete panels are reinforced and crack easy and drilling voids the warranty so I wont be doing that.

Just noticed the bit about notification Steve, I phoned the local authority months ago before I started, as its replacing an old timber garage which had planning permission they said to go ahead, all they said about the electrics was to get a compatent person to do it. Are they more lenient up here in Scotland ? Currently there are 2 cables running out from the house consumer unit direct to where the old garage used to be (one 16A one 6A 2.5mm and 1.5mm, which i terminated in a block,taped and bagged when I demolished the timber garage), these used to go straight to lighting and 1 socket in the old garage without going to any CU. I didnt think this was right and when I asked on here about it I was advised to get a pro in to fit henley blocks and run 10mm to the garage with its own dedicated CU and get it tested etc so this is what I plan on doing. I will also get him to disconnect the 2 cables currently on the house CU.

EDIT: Currently its 20A and 6A

 

[Steve]

Ooooh didnt realise you were in Scotland. No part p up there. Dont need to notify.

 

[squarenut9]

Hi all,

I am about to get a concrete base laid and as its a concrete sectional garage going on top i need to run the electrics through the base as the panels cant be drilled on the garage. So I want to get the cable run now.

My intention is to run the cable for the garage then have an electrician connect it up when Its ready. I will leave the trench open and there is plenty room under the floor boards (4ft) so the electrician can check the run if he wants. The total run from meter cupboard to garage is 15m, 4m of it is under ground.

I have a few questions:

1) When I asked about this before on this forum I was advised that 10mm swa 3 core would be fine for this run, would there be any harm in doing it in 16mm? I dont mind paying extra if it gives more options in future. For example I may build a shed behind the garage that would need power.

2) Is the required depth 18" for the trench ?

3) What protection should the cable be in underground? A friend told me that 100mm waste pipe would do but he is not an electrician, does it need to be more substantial than that? and is there a particular colour?

4) What should I use to protect the cable inside the concrete? Some kind of conduit?

Many thanks in advance for your advice.

Pippo

1) 10mm is fine and 16mm is even better, its a diameter of approx 18mm and the mimimum bending radius of both will be ok if you use a 4" duct depending which 4" bends you use of course, there are sweeping bends and the sharp 90 degree bends. If you lay just the duct let your electrician worry about the cable size. Technically if its PME then you only need a 2 core. You don't take your earth conductor outside the house. Thats why you need an earth stake at the garage/ shed end with an RCD in the consumer unit. Dont forget to seal both ends of the duct to prevent rodents running beteen your house and garage.

2) Your chosen trench depth is fine. In a perfect world you will cover the duct with sand and lay a yellow marker tape over it and it will be marked on your property plan. Like anybody bothers with that.

3) There actually is proper duct for electric cables, Jewson sell it in 50mt rolls but unless you know anybody who has an odd bit enough for what you want I should stick to the ducting previously mentioned.

4) The pipe should stop just above the finished floor level (FFL) and when the garage is complete it can be cut to suit. If you use the 4" stuff there are various types of end stops which plug the hole and just cut the correct size hole in it to suit the cable.

 

[pippo]

Ok Ill buy some 2 core. Will this stuff do? Ill get 20m so theres plenty at each end

http://www.tlc-direct.co.uk/Main_Index/Cable_Index/Armoured_SWA/index.html

Will this earth stake require ducting also then to get it into the garage? remember I cant drill the walls.

Pippo

 

[ColJack]

yes and no..

you can either use a bit of flexible conduit or something similar ( blue water pipe etc.. or you can bury it in the concrete.. ..

you'll need an inspection pit outside and an earth rod.. best your sparky gives you the details.. liasing with him now before the build starts is a good idea to see what he wants done..

 

[pippo]

Right,

On second thoughts, If I just put in enough 100mm ducting with a 90 deg sweeping bend to go from outside of blockwork to finished floor height and put in a pull string, will that be plenty for the electrician to get all he needs in? I can still dig the trench ready for him and clip the cable under the floor in the house.

Pippo