Adding power sockets to detached garage...

29 Nov 2012
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United Kingdom
Hi, I want to add more power sockets to the garage which I use as a workshop.

It's detached and about 20m from the house.

Here's the relevent part of the CU in the house:

And here's the CU in the garage:

Unfortunately I didn't measure the cable thickness from the house to the garage.

The garage is about 28 square meters and there is one double socket atm wired with 2.5mm cable.

I want to add another 7, mostly for convenience of location. I have a lot of power tools but generally only use one at a time (table saw, chop saw, milling machine, drill press etc).

So, in essence I want to wire up 8 double sockets in a Radial with 2.5mm T&E using the existing 16A breaker in the garage CU. Is this ok with regards to safety and the regs?

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Sure. You can have as many sockets as you like; but note that the max current you'll be able to draw from the sockets at any one time is 16 amps.

That should be plenty unless you're planning a MIG welder or something.
As Taylortwocities has stated, you can have as many sockets on the circuit as you wish, but you are restricted to 16A of current. So any tools with an inrush start up current or a combination of tools on load at the same time that will demand over 16A could be a trip nuisances.

I would consider a little more investigation in to the distribution cable sizing and you maybe able to upgrade you garage MCB size for socket outlets.
It would be possible to increase MCB to 20A on 2.5mm T&E cable and Steeple the badge model of garage CU, do do a 25A type B MCB (on the D2S series), which would also be okay on 2.5mm T&E, assuming no de-rating factors of circuits cable, such as routed in containment (conduit/trunking) or within thermal insulation.
Denmans deal with Steeple Units, might be worth contacting them regarding the profile fitting of these and type testing of these MCBs or if series E is available..
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I would consider a little more investigation in to the distribution cable sizing and you maybe able to upgrade you garage MCB size for socket outlets.
The cable supplying the garage is 4mm.

I will be putting up plasterboard ceiling and insulating - the cabling will be covered by the insulation. It has been clipped to the brickwork around the perimeter of the garage.

Is changing the MCB in the garage notifiable work, or only when dealing with main supply in the house CU? It makes sense to change it to 20A/25A if I can.

I should think about lighting too. I will be adding low energy lighting when the plasterboard goes up, something like 9-12 3w led spots. I plan to use 1.5mm T&E for this and the cable will go along the joists filled with insulation. Any concerns I need to worry about here?

Yes, totting up the lumens requirement I might have to settle for fluros. I already have 4 x 4ft singles and 1 x 4ft quad but I don't like the light it outputs, and it will get in the way when I lift the cars to full height (1m).
fluorescent tubes in a garage you say? Any chance there will be rotating parts or power tools in there?

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