garden wiring - type + depth?


Postby mortarboard » Thu Jul 24, 2008 1:26 pm

I need to lay a cable across my garden for power sockets in the shed and garden lights. I want to make provision for this with some conduit before I concrete a driveway. Can anyone tell me what type of wire I need and how deep it should be to be legal? Many thanks
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Postby sparx » Thu Jul 24, 2008 6:54 pm

Hi, presuming you know this to be covered under bldg regs part p and you are just making provision for a leckie to do the work or you have notified L.A.Bldg Control, then:
use 32mm plastic water pipe under path at 18" /450mm deep.
The cable to use will be steel wire armoured, probably 4mm2- 3 core to connect to a so called 'garage unit' which is a small consumer unit with RCD, 6A & 16A mcb's fitted which can be connected at the house end to a variety of places depending upon layout of house electrics.
the cable should be buried at a similar depth to tube, back filled to 6" / 300mm from surface, then yellow 'Danger electric cable below' marker tape laid and finally topped up to level.
regards SPARX
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Postby mortarboard » Fri Jul 25, 2008 7:00 am

Thanks sparx - that's really useful info.

Yes, this is just provision for a pro. I'll be getting someone in to wire the extension I am building to the satisfaction of Building Control so I will get the garden bit done and certified at the same time.

I'll bury a 32mm pipe at 450mm in my drainage trench before I backfill.
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Postby sparx » Sat Jul 26, 2008 9:52 am

Hi again, 32 mm will be fine for short run under pathway but unless very straight run with draw string inserted through as pipe laid it will be very difficult to pull cable in afterwards. Better to get cable installed before back filling trench then only needs pipe under path rest can go direct in ground. Talk to intended sparks and agree route and method, most will be happy to let you do the 'donkey work' in layimg cable, I certainly would under such circumstances, a quick evening look-see shouldn't add much to the bill but could save a lot in labour charges (mine £35/hr & rising)
regards SPARX
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Postby TOPSPARK » Sat Jul 26, 2008 7:00 pm

Hi mortarboard
This is topspark i concur with what sparx says the only other piece of info i should add is supply the shed off the mains board in the house with a 40 amp mcb but in your supply cable to your shed DO NOT CONNECT THE EARTH TO THE MAIN EARTHING TERMINAL. Install a 2 way garage consumer unit in the shed and from the main earth terminal of this consumer unit take a 10mm earth outside the shed and put an earth rod in the ground outside the shed. This is defined in the current 17th edition wiring regs about outbuildings.
all the best
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Postby mortarboard » Mon Jul 28, 2008 1:41 pm

Thanks topspark and sparx

I'll put a cable in when I put the pipe in. I want to be able to swtich 2 sets of garden lights from the house so I assume I will need 2 cables to the shed (one 3 core for power points and one 4 core for the 2 house switches). Will that work with this "garage unit"?
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Postby ericmark » Mon Jul 28, 2008 4:57 pm

From your original post I thought you intended to control the lights from within the shed or with sensor.
To switch the lights from the house there are many ways it could be wired but normally one would power them from house rather than shed.
Both myself and Sparx gave some advice which has been removed so only advice I can give is to ask the spark who is doing the work.
Eric
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Postby TOPSPARK » Mon Jul 28, 2008 5:38 pm

When you take your supply cable from the house make provision to take a 1.5mm 3 core and earth cable through your ductway into the shed to a 1gang 2 way switch tis is between the house and shed feed the shed light from the consumer unit in the shed and then you will be able to switch the light on from in the house.Also set the supply to the shed up as i outlined in my earlier reply
all the best
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Postby mortarboard » Mon Jul 28, 2008 8:41 pm

I don't have an electrician on my project yet - wiring seems quite a long way off while I'm still below the damp course. It's just this conduit opportunity in my drain trench that has forced the issue. I'd be interested to know if there is something I am missing If not, I'll just put a bigger pipe in with a pull string and wait for the cavalry!
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Postby TOPSPARK » Mon Jul 28, 2008 10:20 pm

Hi mortarboard
A 42mm wastepipe is big enough with draw wire for your cables to go through so no need to panic as you have the information to put the ductway in and run the cables yourselfto the shed.
all the best
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Postby ericmark » Mon Jul 28, 2008 10:59 pm

I am loathed to give sizes of cable and any specific recommendations as there are so many variables and it would be so easy to give wrong advice. I would normally feed with 6mm SWA as being big enough for most scenarios but this could be reduced to 1.5mm for 20 amp supply and short cable but 16mm where it is a very long run and 30 plus amp supply is required.
In theory before an electrician signs off the installation certificate he should be responsible for design and installation. In practice if he can see enough to be satisfied its OK he may still sign the paperwork. I would not want to take chance and I would get an electrician to agree what he will allow you to do in preparation before you back fill anything.
All best Eric
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Postby mortarboard » Thu Aug 07, 2008 8:51 pm

Thanks everyone for help with this. I think I've got an idea of my options now. I have installed a piece of flexi ducting in the drain trenches with warning tape above so hopefully my electrician will be happy to certify me inside with options to fix the outside stuff later... M
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