# Man cave / garden workshop



## Superwhite (12 May 2018)

Hi everyone just joined.

Have planning permission for a shed/ building at bottom of garden 10m x5.25m

Have a question about wiring/ cabling power feed, length of distance is 85ft from house fuse box, will be running lathes mig/tig welders, amongst other wood/metal machines wondering what size cable I would need or how to work out what I would need, from what I research most of the cost is the cable and laying it so I should be able to do this myself then get an electrician to connect. 

Also wondering if anyone else has a workshop on this scale on this site I could see a build journal of. Plan on using shiplap for sides, flat roof, probably metal/tin but still toying with felt just thinking long term tin will be harder wearing. Base 6 inch of concrete reinforced with mesh 

Any help or pointers be greatly appreciated 

Thanks Martin


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## nabs (12 May 2018)

your electrician will specify the cable size but if you want an estimate to get an idea of how much the cable will cost there is a voltage drop calculator here:

https://www.tlc-direct.co.uk/Technical/ ... eDrop.html

You will need to estimate the likely max power consumption of your equipment, lighting etc assuming more than one of the machines might be running at once. 

10x5 is a pretty big shed! You might want to look at Steve's:
1-steve-s-workshop-the-build-t79315.html

and Mike's guide:
build-a-shed-mike-s-way-t39389.html


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## HappyHacker (12 May 2018)

I agree with Nabs. Get an electrician involved from the start so they can do the design of the installation and ensure the correct cable size is used. 85m is a long run and the volt drop will be high so you will need a cable much bigger than you may think. They should be able to provide the calculations they have used, be prepared to pay for this, so that if you decide to use someone else you have the paperwork to back up the design.


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## deema (12 May 2018)

I’d look at putting up an insulated industrial building, it will be far cheaper at that size with galvanised steel framework, white internal walls, insulated roof lights with no windows, an insulated pedestrian and roller shutter door. 

The floor at 150mm with wire mesh is incredibly thick unless your planning on storing tractors / heavy plant inside it. I would add insulation into the floor say 100mm and reduce the concrete to 100mm with wire mesh. 

Rather than running a feed from your house I’d get a quote for hooking it up to the mains. You can reduce the cost by digging the trench and back filling yourself. It will probably be not much more than getting a cable laid from your house. It will also allow you to let the shop to a third party if you wish in the future.


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## Sideways (12 May 2018)

Don't build it without getting your sparky to do the calculations first. 
The tlc calculator is OK as far as it goes but it misses out a step so in some situations it will undersize the cable. 
The correct design process is to work out the max running load, then work out the amps using 230V for your supply voltage, then select the next standard size circuit breaker up and of the correct type (which can be several amps more), then size the cable based on the circuit breaker rating, not the load.
It's notifiable work which has to be designed, installed and tested according to the wiring regs.
Including making sure your main supply has the spare capacity needed.
The principle is that a cable must be big enough to take a specified amount of overload current, or a fault current for as long as it takes that circuit's breaker to trip - without overheating.


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## Yojevol (12 May 2018)

Hi Martin,
I put up my 10 x 6m 'shed' at the bottom of my garden about 12 years ago. I had to get planning permission for it due to proximity to the road and my neighbours property (a field!). This meant the building inspectors got involved and had me put an enormous quantity of concrete in the ground. They had difficulty in conceiving that it was a wooden hut to be used for my hobby, not a block of flats!. They imposed an activity restriction due to noise generation - I'm not supposed to make a noise on Sundays or weekdays between the hours of 8pm - 8am! Needless to say nobody has ever attempted to police it and my neighbour has never complained. In fact he put the electrics in for me.
Oh yes and they needed extra fire protection for my other neighbour because the building was to be within 2m of the boundary, ie, the field fence. It didn't matter that his house was 200m away across the field. The acceptable fire protection is a single layer of plasterboard on the interior of the offending wall.
Regarding the supply, I looked into a separate 3ph supply but it was going to cost about £3K. A 1ph supply was also expensive. So I opted for a 50m armoured cable from my house. The trench was dug by the guy doing the ground works for minimal extra cost. My neighbour sized the cable and did the connections once the building was complete. From memory the cable cost was £400.
Don't forget to put a water pipe in the trench while you've got it open.
I hope this is of interest
Brian


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## MikeG. (12 May 2018)

deema":3b0t9jfr said:


> .........The floor at 150mm with wire mesh is incredibly thick unless your planning on storing tractors / heavy plant inside it. I would add insulation into the floor say 100mm and reduce the concrete to 100mm with wire mesh. ........



This is awful advice. In fact, it is just wrong and misleading. 

Mesh, or any reinforcing in concrete, needs 50mm "cover". This means the only place for mesh in a 100 thick slab is on the centreline..........but the only place where mesh is any structural use is when it is in tension. The centreline of a slab is neutral, neither in tension nor compression whatever forces are applied to the slab. Putting mesh there is just wasting your money. Further, the thickness of a slab is determined either by calculation with reference to ground type and so on, or using a rule of thumb ratio to the perimeter. That rule of thumb calc for this size building gives a slab thickness of 175mm.

Further, we haven't established whether this slab is in fact acting as a raft (ie bearing the weight of the walls). If it is, with the size of building we are talking about, it will require calculation by a structural engineer because this building requires Building Regulations approval.

To the OP: ignore this sort of advice. Your building needs designing properly, and with calculations provided by an engineer (unless you are going for strip footings and a ground bearing slab). Further, you have planning permission, so you are constrained to build whatever you have permission for. You can't just change to "an industrial building with roller shutter doors and sheet cladding" if you've got permission for something quite different...unless you fancy going back to the planners to change your permission. As for your question about cabling: get your electrician to calculate its size, and order the cable for you. He will buy it cheaper than you ever can. Then you do the donkey work of digging the trench and backfilling (don't forget sand and a warning tape). This installation will require testing by an electrician, so come what may you'll be employing one.


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