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I'm in the process of building a medium sized workshop (2.5x5m). All seems to be going swimmingly so far - epdm roof on, double glazing in, etc. Thinking of trying to get the power sorted over xmas.
Now I'm not an electrician but i'm reasonably handy and have done a bit of electrics in the past (wiring up my van). Obviously I'll need someone to come and sign off my work and do the final connection to the main Consumer unit. Any online guides on what I need to do? At the moment i'm thinking:
- Armoured cable in a trench across a drive and then along a fence to the workshop. Then i'm not sure what to do - ideally i'd want it coming up under the floor (it's on a preexisting concrete pad) - is it acceptable to run the cable from the fence along the ground surface under the workshop and then up through the floor? If not what is the best way of getting it from the fence to the workshop - the gap is about 3ft.
- Garage consumer unit - 6A circuit, 16A circuit and a 32A circuit. I'd probably only use the 32A and a 6A for the lights.
- I then want to put a ring main in for 4 double sockets on the 32A circuit. Max load would be about 3kW (my table saw + my extractor)
- LED light panels on the ceiling to a single switch
Reasonable chance of us selling in the next year, so needs to be legit.
Why not get an electrician to do it? You might even need to produce a certificate for the work when you sell the house.
Rate your armoured accordingly is the first step. I came up under the floor in to my shed/summer house but I had a void as its mounted on an old deck area.
Some on here will no doubt state you need to bury it 500mm blah blah. Personally it just needs buying enough to be protected, plus the very fact you know where it's running. Avoid burying in areas likely to be dog over though, such as beds or veg patches etc.
I dug a 600mm trench then buried an armoured cable. under a path and into my utility room at the back of my garage to a large "cooker" type switch which cabled to my main board. At the other end bought it up at the side of the summer house, into a small RCD. Mate is a spark so he did the glands at each end. The switch at the house end is useful as I can isolate the summer house if I want to from the main building which gives me reassurance.
If you need it signing off, speak to an electrician now. There are issues around earthing which need to be sorted (is it permissible to export an earth from the house, or should you set the shed up as a TT system, for example.) Answer depends on what your existing system is, how far to shed & may affect cable sizing.
Once there’s a plan, you can do the grunt work of laying the cable and let the electrician waltz in at the end to test, terminate and sign off.
Why not get an electrician to do it? You might even need to produce a certificate for the work when you sell the house.
Because my time is free, and I enjoy doing this kind of thing.
Tillydog - good idea.
Anyone know an electrician in the woking area?
I DIYed and had Building Control test and sign it off.
[url= https://live.staticflickr.com/7300/15767580703_79619641f2_c.jp g" target="_blank">https://live.staticflickr.com/7300/15767580703_79619641f2_c.jp g"/> [/img][/url][url= https://flic.kr/p/q2jYpH ]Workshop Electrics 1[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr
[url= https://live.staticflickr.com/7456/16201362809_b4a90423ee_c.jp g" target="_blank">https://live.staticflickr.com/7456/16201362809_b4a90423ee_c.jp g"/> [/img][/url][url= https://flic.kr/p/qFEdHx ]Workshop Electrics 2[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr
New mini consumer unit in the house:
[url= https://live.staticflickr.com/7382/16338950476_84cd619b1f_c.jp g" target="_blank">https://live.staticflickr.com/7382/16338950476_84cd619b1f_c.jp g"/> [/img][/url][url= https://flic.kr/p/qTPoJG ]Consumer Units[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr
10mm cable egress into 25mm steel conduit...
[url= https://live.staticflickr.com/7441/16338951076_ba86709f46_c.jp g" target="_blank">https://live.staticflickr.com/7441/16338951076_ba86709f46_c.jp g"/> [/img][/url][url= https://flic.kr/p/qTPoV3 ]10mm cable exit point from house[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr
I ran 1" steel conduit down the fence..
[url= https://live.staticflickr.com/8229/8601173230_750c150702_c.jp g" target="_blank">https://live.staticflickr.com/8229/8601173230_750c150702_c.jp g"/> [/img][/url][url= https://flic.kr/p/e74g9b ]Kitchen end[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr
Consumer unit in workshop:
[url= https://live.staticflickr.com/8654/16012857649_a21eb61e30_c.jp g" target="_blank">https://live.staticflickr.com/8654/16012857649_a21eb61e30_c.jp g"/> [/img][/url][url= https://flic.kr/p/qp15Gz ]Workshop Consumer Unit[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr
Surface wired sockets etc in the workshop
[url= https://live.staticflickr.com/8613/15743466164_4780fea57d_c.jp g" target="_blank">https://live.staticflickr.com/8613/15743466164_4780fea57d_c.jp g"/> [/img][/url][url= https://flic.kr/p/pZcnZN ]Surface wiring in 20mm PVC pipe[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr
Thanks Footflaps - very helpful. Couple of questions:
Why have you got two consumer units / got the mini consumer unit? I have a spare RCD on my main consumer unit. I'd have thought 32A would be plenty for the workshop - i'm never going to have a lathe or mill in that - 7500w should be plenty.
Did you run steel conduit to avoid armoured cable? (i assume if it's in steel conduit you don't need armoured cable)
How much was it for an sparky to sign it all off?
I did what tillydog said.
Sparky was happy not to have to dig 40 metres of trench!
The workshop is on it's own CU rather than fed from house CU. That way if there is a fault in the workshop the house is unaffected. That might be what footflaps was aiming at.
But he's got three CUs - two at one end and one in the workshop? If there was an issue at the workshop, wouldn't you just flip the breaker on the workshop RCU in the main CU?
Why have you got two consumer units / got the mini consumer unit? I have a spare RCD on my main consumer unit. I’d have thought 32A would be plenty for the workshop – i’m never going to have a lathe or mill in that – 7500w should be plenty.
I wanted it totally separate, so I could isolate it to work on the workshop without affecting the house.
That might be what footflaps was aiming at.
Yep, I wanted complete separation so I can faff with one whilst the other is unaffected. I wanted some protection for the cable / conduit, just in case it got damaged, which it did when my neighbours demolished their kitchen by collapsing it through the fence outside my back door. The steel conduit didn't survive several 100kg of bricks falling on it, it snapped the thread clean off at one of the joints....
Did you run steel conduit to avoid armoured cable? (i assume if it’s in steel conduit you don’t need armoured cable)
Yes, although either would have worked. If I was doing it again I'd go for armoured cable, threading 10mm twin & earth through 50m of conduit was a complete nightmare, esp all the corner junctions - took days!
How much was it for an sparky to sign it all off?
I think about £200, was years ago and all wrapped up in the Building Control fee for the whole build, I just ticked a box saying 'approve electrics' and it added a set fee.
NB alanl, of the STW Parish, acted as consultant (he's a sparkie) and was most helpful when I was working on it...
Ah I see - thanks!
Nothing to add from the sparky side, but if you're not already, I'd seriously consider running water and a good few runs of cat6 in the trench as well 🙂
I have a spare RCD on my main consumer unit. I’d have thought 32A would be plenty for the workshop
Do you mean RCD? (MCB maybe?)
One also needs to consider the total loading on the existing consumer unit - It may be that adding another 30A+ supply (50A in the case above) could overload the main isolator (e.g. if the house has an electric shower and an electric cooker, etc. running off a 70A isolator). The easiest thing in that case (assuming the incoming supply has sufficient capacity) is probably to add a second CU.
I did indeed mean MCB - there is a 32A one already allocated to the 'garage' (it was actually old shed, which i had disconnected when i moved in as it looked a bit dodgy).
I doubt we'd overload it - no electric shower and the isolator is 100A.
Will get some advice from a sparky before i do anything.
It may be that adding another 30A+ supply (50A in the case above) could overload the main isolator (e.g. if the house has an electric shower and an electric cooker, etc. running off a 70A isolator). The easiest thing in that case (assuming the incoming supply has sufficient capacity) is probably to add a second CU.
Not really a problem as its extremely unlikely everything would be drawing max power simultaneously and even if it did, the supply fuse would protect the system. As long as the weakest link in every path is a fuse and not an under dimensioned cable, then you're generally ok.
Not really a problem as its extremely unlikely everything would be drawing max power simultaneously
True - At the risk of pedantry, I didn't mean adding up the fuse ratings, I meant that someone may have assessed the *actual* loads that could foreseeably be on at the same time, applied diversity factors, etc. and decided that the existing CU was not capable of safely supplying the additional load of whatever is on the other end of that 50A MCB in the photo - hence second CU. Just one reason it might have been fitted.