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Power and heating

New garden workshop

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John Wills 120/02/2019 11:17:16
14 forum posts

Hi, while having an extension built I'm getting the builder to put up a 3.4m x 2.85m internal dimensions, thermalite, block wall workshop. The biggest I can fit in the garden. I want to take my low skill DIY woodworking to a higher level (to make guitars initially) and the workshop is the start. I'll probably want to take on other interesting projects for the house. One I've already thought of is a bespoke double door frame so will need to consider other power tools.

I've got guitar making books which cover the tools required but can someone give me an idea of a "sensible" figure for power requirement so that I can tell the builder what I need so he'll instruct his electrician. A bit of spare capacity would seem sensible.

Am I looking at a sub CB board?

Also suggestions for heating?

I hate the idea of electric heating because of the expense, but to get gas to the building 30m away from the house? Gas bottles an option? Solar panels?

Any advice for this novice.

I've also messaged regarding this subject to a couple of private messages in my inbox so thanks to Colin & Paul.



Julian20/02/2019 12:22:25
543 forum posts
28 photos

Hi John, I think a chat with your electrician will be the best way to deal with this as there may be local issues with your supply. I have a separate 40A RCD going to the workshop via 12mm 3-core SWA (only because I already had the cable) you may get away with 6mm as you will probably only be using one machine at a time. I would definitely use electric heating in the form of oil filled radiators (your supply will need to accommodate this) as gas will create a fire hazard with airborne sawdust as will most other types of heating. Good luck with the build -- Julian

Paul Bodiam20/02/2019 16:50:51
99 forum posts
45 photos

I've already replied to John's private message but, for the benefit of others, here is what I said:

When planning the electrickery for my workshop I listed the power consumption of each of my tools: e.g:

- bandsaw 1.5 kW

- planer thicknesser 1.2 kW

- sanding thicknesser 1.5 kW

- lathe 1 kW

- linnisher 700 W

- pillar drill 600 W

- heater 1.5 kW

- dust extractor 1.1 kW

- lighting 150 W

Then I worked out the worst case of machines in combination - using the bandsaw or sanding thicknesser with dust extraction on a cold winter's evening = 1.5 kW (bandsaw) + 1.1 kW (dust extractor) + 1.5 kW (heater) + 150 W (lights) = 4.25 kW

Divide the number of Watts by 240 to get the maximum current draw:

4250 / 240 = 17.7 Amps

So my workshop needs to have a supply capable of delivering *at least* 17.7 amps. Double this for safety.

Then you need to consider getting electricity from your house down to the workshop. My workshop is at the bottom of the back garden and the house fuse-box is by my front door, so we ended up routing an armoured cable all the way around the outside of my house, through the garage, and then burried it under the back garden. This was a run of around 20 metres.

My friendly local electrical contractor quoted me for supply and fit of appropriate gauge armoured cable to allow for 40 Amps over a run of 20 metres. They charged me £705 (inc VAT) to install a 40A breaker into my fusebox, install the armoured cable (I had to dig and backfill the trench) and safety-check and certify my wiring in the workshop.

As far as the workshop wiring is concerned, I bought a "garage consumer unit" from Screwfix which provides a 30 Amp breaker for sockets and a 5 Amp breaker for lighting. We (my brother in law and me) put a ring-main into the workshop, run through 20mm trunking with armoured wall-mounted sockets at just above bench height. We allowed two double-gang sockets per machine (power for the machine + power for a light + 2 spare) and 4 double sockets behind the main workbench (to allow for powered hand tools, plus radio). I also set up a "charger shelf" beside my bench with 4 power sockets with the chargers for my battery-powered devices permanently plugged in, rather than having to dig out the chargers and plug them in when I need them. In total, I installed 20 double-gang sockets around the walls of a 3m x 5m workshop. This may seem like far too many sockets, but they are pretty cheap from Screwfix (especially when purchased in bulk) and I don't want to have to add more sockets later, and I appreciate the flexibility of always having a spare socket right where I need one - for instance, the other day I needed to do some power sanding on the lathe so I needed to use 3 out of the 4 sockets by the lathe (lathe + worklight + orbital sander).

John Wills 121/02/2019 12:48:14
14 forum posts

Hi Paul,

Thanks for very interesting reply.

There’s a load factor that electrical designers employ and I’ll talk to my electrician about that as I won’t ever run everything together.



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