Garage Electrics

[Jim]

Hi guys,

I'm looking at upgrading the electrics in my garage.

Current set-up is SWA cable via 20 amp MCB in main CU to basic metal switch and single socket in garage.

I'm going to install a 3 way CU for lights, power and a seperate dedicated

16A circuit for my compressor and welder (neither of which run off a 13a plug). If I want to install 8 x double sockets on the power circuit should I do this as a ring or radial ?

I'll only ever be running 2 or 3 small bits of kit at any one time but I want the praticality of having a socket wherever I need it.

Thanks

Jim

[Owain]

Up to you, but if you want to run up to 32A you will need to use 2.5mm cable on a ring or 4mm cable on a 32A radial. 2.5mm radials must be fused at 20A.

Owain

[David Hansen]

On Thu, 08 Mar 2007 20:56:06 GMT someone who may be "Jim" wrote this:-

This normally depends on where the sockets are. However, since the supply is limited by a 20A MCB anything more than a 20A radial is pointless, unless you have plans to upgrade the supply in the future.

[Dave Fawthrop]

|!Hi guys, |! |!I'm looking at upgrading the electrics in my garage. |! |!Current set-up is SWA cable via 20 amp MCB in main CU to basic metal switch |!and single socket in garage. |! |!I'm going to install a 3 way CU for lights, power and a seperate dedicated |!16A circuit for my compressor and welder (neither of which run off a 13a |!plug). If I want to install 8 x double sockets on the power circuit should |!I do this as a ring or radial ? |! |!I'll only ever be running 2 or 3 small bits of kit at any one time but I |!want the praticality of having a socket wherever I need it.

I am about to do the same thing and will install a separate ring main with a spur for the lights. I always overdo things first because my plans always change over the years. Someone here will know if you can put a 16 amp spur on a ring main.

[Owain]

You shouldn't, because (a) FCUs are limited to 13A; (b) unfused 16A plugs/sockets could allow the maximum assumed spur current of ~20A to be exceeded; (c) the 16A socket would be protected by a 32A MCB which might not be adequate to protect the appliance flex - although most 16A industrial appliances should have fairly hefty flexes anyway.

And it's a ring final circuit, not a ring main.

Owain

[robgraham]

circuit' ! ( who's a pedant then?). If the ring trips you'll be floundering around without any lights - could be pretty dangerous while any machinery is running down - big, or even hand circular saws, come to mind. " Ouch, that's another finger away"

The same applies if you run the whole lot off one RCD. I've seen a comment here recently about a domestic system involvng an RCD on both the power and lights circuits; that seems excessive but may apply in an outdoors application. I've just split the power and lights in all my external buldings with an RCD on the power in each.

Rob

[Dave Fawthrop]

|!Dave Fawthrop wrote: |!> Someone here will know if you can put a 16 |!> amp spur on a ring main. |! |!You shouldn't, because (a) FCUs are limited to 13A; (b) unfused 16A |!plugs/sockets could allow the maximum assumed spur current of ~20A to be |!exceeded; (c) the 16A socket would be protected by a 32A MCB which might |!not be adequate to protect the appliance flex - although most 16A |!industrial appliances should have fairly hefty flexes anyway. |! |!And it's a ring final circuit, not a ring main.

So 16 amps *on* the ring would be OK?

[David Hansen]

On Fri, 09 Mar 2007 11:01:46 +0000 someone who may be Dave Fawthrop wrote this:-

Better to have a separate circuit, so the lights stay on if there is a fault with the power circuit (assuming the correct discrimination between protective devices in the shed and house).

One can do, provided the spur is protected by a 16A circuit breaker and it will not overload the circuit.

However, there is a lot to be said for providing BS4343 (they have a more difficult to remember number now) sockets for that sort of equipment. The smallest size of these can be wired radially in unlimited numbers from a 20A protective device. Obviously there is a limit to the number of high current devices that can be plugged into such a circuit.

[Ian_m]

Remember to get all your part P certificates for the wiring etc.

[Owain]

Inasmuch as a double socket on the ring is okay, and that's nominally

20A max.

But it's not a standard circuit arrangement so full compliance with the Regs must be demonstrated by calculation.

Owain

[James]

Wouldn't lights with battery backup be an even better solution. The frequency of short power cuts (which affect everything) is generally much higher than RCD's tripping.

James

[Andy Wade]

Err, I refer the honourable gentleman to page 153 of the On-Site Guide, where, under the heading "Permanently connected equipment" it sayeth:

"Permanently connected equipment is locally protected by a fuse complying with BS 1362 of rating not exceeding 13 A or by a circuit breaker of rating not exceeding 16 A and of a type listed above and is controlled by a switch meeting the requirements of Regulation 476-03-04. A separate switch is not required where compliance with 476-03-04 is provided by the circuit breaker."

[John Rumm]

It was the solution I used in my workshop to save the need for using a split load CU in there.

[Owain]

This is for 16A socket(s), not "permanently connected equipment" though.

Owain