Hi,
As paert of the current reworking of my garden I want to prepare for my shed (whcihI am going to rebuild either in a few months or next year) to be 'electrified'. I want to set up a little workshop in there.
So I need to prepare for laying the cables, for whcih I will get an electrician to do all the work on the switchboard/consumer units, etc, and all the connecting, but want to prepare the conduit etc myself.
What are the regulations for burying a cinduit, what conduit can or have I got to use? Does it have to be an armoured one, how deep do I have to bury , it does it depend on the volatgeI expect it to carry, etc.?
Does anyone know?
Thank you very much!
NIk
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Replies
Hi Nik
what you are doing here is regulated under part P of building regs on electrics
best i ca suggest is look at the area you are working along and go over the regulatons as there will be min depth requirments for the trench depending on what cable and the cable will depend on the power you need down there.
to be honest if you work everything to the 32Amp supply this should be ample for a couple of socket points and a basic light set up but if your looking at high power consuming tools and kit going down there then look at the regs for 64Amp supply.
also there is no issue you digging trench however either the sparky will need to see it before infill or building regs will as you will not be able to self cert this if doing everything by the book
An electrician (very professional/qualified) just laid on a power supply to my sons "cabin" at the end of his garden. No "conduit" needed............ just use armoured cable. He left us to bury the cable as we hadn't decided where to run it......... he said there were were no regulations about the depth..... in fact we could just leave it on the surface by the perimeter hedge if we wanted to. I'm not saying he's right here but he's a very experienced professional and he "signed off" (that's what he called it) the installation. He did say though that if the ground was very stoney, it's worth putting sand round the cable when you bury it........ apparently stones can penetrate the waterproof cable casing and cause problems later on.
I am a qualified electrician and can tell you that electricians can tie themselves in knots trying to decide how to wire a garden shed. Without specific details I cannot give you an exact design and you need to really speak to the electrician who will connect it up for you, I’ll give you some pointers for if you’re planning to get on with it over this Bank Holiday weekend.
Just assume that you need to use SWA steel wire armoured cable regardless of if it is in a duct or buried directly into the ground.
The electrical regulations does not give a depth to bury the cable at, regulation 522.8.10 says “sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground” it also says to put a plastic marker tape above it.
In a small garden shed you will want some lights which is less than 1 amp, a 3kW fan heater which is 13 amps and to be able to run a power tool generally of 13 amps or less, a total of around 27 amps, so a 32 amp supply to the shed should cover all of this, so unless it is a excessively long cable 4 mm SWA cable will be sufficient. The next size up cable is 6 mm SWA which should be okay with a 40 amp breaker on it.
Ideally you probably want the sockets to be protected by a B32 MCB as a a lower rated one may trip if you have for example a chopsaw with a brush motor or you plug a 110 volt transformer in, using a lower rated device isn’t impossible, but your electrician will need to work out what is okay. Everything including the lights will have to be protected by one or more RCDs, just give some thought to what happens if you are using a angle grinder or the like and you have the lights protected by the same RCD as the sockets, if you Nick the power tool call or it falls onto a piece of hot metal you could be left holding a machine that is running to a stop in the dark, so I’d suggest having the lights and sockets on two separate RCDs just in case.
I suggest that you dig a trench 600 mm deep if it’s running under a flower bed, not many gardeners dig more than two spades depth say 450 mm turning over a flower bed, then put the marker tape around a depth of 450 mm, less if it’s under paving, when you bury the 4.0 mm SWA cable making sure there’s no sharp stones, if there are stones that are likely to damage the cable surround it with sand.
Most houses in the UK now have a 60 amp main fuse for the whole house, so assuming you need power in the house as well you can’t put a huge supply into the shed.
Leave the electrician cable to spare at both ends to be able to terminate it properly into boxes or fittings, cutting spare cable of is easy, extending a cable that is too short isn’t. Your electrician will also get all technical about how to earth it and start muttering about “exporting PME” that probably not the best of discussions to get involved with on a landscapers discussion forum.
I trust that makes sense.
Andy.
Thank you all of you for your replies to my question! I very much appreciate all of them, as I truly have (had) no idea how to best go about this now.
From what I am reading now, I will most probably run the cable over-ground, as I do have a party wall running from the house (it is attached to the house in the back) to the back of the garden, where the shed will be loaded. I thought of digging a trench for a conduit under the patio (laid to natural stone and some patio slabs), then underneath stairs (which I am building at the moment) and then underneath a artificial grass area (which I am also building at the moment), but if all it takes is an armoured cable, I might as well just run this from the consumer unit through the house wall, along the wall (maybe at hight of say 7-8ft, next to the satellite cables) to the back of the house and then along the party wall to the back, and finally a couple of meters across the very back wall of the garden into the shed. All in all, it will be a distance/length for the cable of about 25-30m, taking into account the path from the junction box, along the house, all twists and turns to the arriving at the shed - not sure if that is considered extreme or average.
Sounds much easier and cheaper than trench digging, especially since I am the only one doing all this work. I will probably get an electrician to finalise the spec on the cable and exact set up, but I do like the thought of having lights and tools on different circuits (would I have to have a 4-core SWA cable then?), and also want to be able to switch off the power to the shed from inside the house regularly (would it be sufficient to do that At the consumer unit, or would I best have a dedicated 'off'-switch for that?)
All in all, again thank you so much for your help, each and eery answer on here was very helpful!
Nik
The plastic sheath covering SWA is made from carbon loaded plastic, which means it doesn’t degrade in sunlight to the same extent due to the ultraviolet light as ordinary grey plastic twin and earth cable, so SWA is it is much more suitable for running along an outside wall.
Personally I would still try and bury it if I could to get it out of sight, it’s not the most attractive of things to put on a wall, but you maybe able to train some wisteria or the like across the wall to hide it.
Andy