Shed/workshop wiring questions

On Wed, 01 Dec 2004 20:27:14 +0000, Sloper strung together this:

No such thing, cables come in physical sizes, not ratings.

A Clipsal garage unit, from Screwfix, would do. As you only seem to have a modest size supply cable then you're not going to need much, but I have no idea what size your supply is.

I'd run it inside and terminate in the CU.

Standard T&E would be fine if it's all internal.

Here.

Is that 2.5 mm csa SWA then? Good enough for a 13 Amps Radial Circuit at that length. :-)

Yes its 3x2.5mm2. Thanks.

What types of things are you thinking of supplying in the shed?

With a cable of that size, all you'll be able to fit is a double gang socket, with RCD protection already on it, to the shed end, then connect the house end to a spare breaker way in the main consumer unit. It's not a great sized cable you know.

I was hoping to power a 2kw convector heater, though I doubt it will ever be required to run at max power. Its mainly for frost protection. Also, about 4 x 4ft fluorescents, and from the sockets, a motorcycle battery charger, and occasional power tool. I'm worried now! :(

On Thu, 02 Dec 2004 22:54:45 +0000, Sloper strung together this:

You'll get 16A through that, just about enough to do what you want, as I said a Clipsal garage unit is the best option as anything else would be excessive and expensive for the size of cable you've got.

Ah! *breathes a sigh of relief* Thanks for that, Lurch.

Would it be ok to have a PIR security light that could be switched on when I leave the shed at night (when the heater would not be in use)? Or is there a danger of forgetting the light is on and overloading? In which case, I presume something would trip in the house CU? Or worse than that? I *did* say I haven't much of a clue!

I'll leave it to an electrician from here on, but I'll mention the Clipsal garage CU to him.

It's pretty marginal, though, isn't it?

I was just totting up my worst case simultaneous power tool usage.. 1600W router + Henry (1000W). Bloody cold day, so 2kW heater could be on. Lighting - ok, negligible, radio/tv likewise. That's still >4.6Kw though, what's that - about 20A (approx, assuming resistive, which it isn't quite).

OP might not use this stuff, but given that power tools are becoming ever more prevalent it's a fair likelihood that future might bring gifts under trees and things...

On Fri, 03 Dec 2004 00:05:14 +0000, Sloper strung together this:

No, a 2kw heater and a 500w floodlight should be ok if on together. You should get around 3.6kw out of the supply you have. If you did happen to overload the shed then it would just be a case of the MCB in the house tripping.

Probably best!

It's perfectly OK to run a radial supply to any number of sockets you like with 2.5sq mm cable protected by a 20 amp MCB. This is one of the 'conventional circuits' listed in the appendix of the IEE On-site Guide.

The recommended maximum floor area to be served by such a radial feed is 50sq metres but for a garage or workshop feed I think sensible application of the diversity rules woud be a quite reasonable approach.

One more question! BW and Lurch say I will be able to draw 13 or 16 amps through my swa cable. As you say the circuit should be protected by a 20amp MCB, I presume the MCB would not trip until the current drawn is 20amps. So, if I inadvertently exceeded 16amps, but drew less than 20, would the cable get dangerously hot before the MCB trips? Would I have a lower rated MCB or RCD(?) in the shed CU?