Yet another outdoor power Q

[keith dulwich]

Please can you let me know if I'm on the right lines here?

8 year old house, want to get power to shed. Consumer unit has 10 CB ways, 3 of which are RCB protected

marked as "protected by RCB" : bell transformer 6 , ring main 32 , shower

32 "not protected": cooker 32 , fixed appl 32 , down light 6, kitchen light 6, up light 6, smoke alarm 6,,family shower 40 (we have one in bathroom and one in ensuite) The RCB is marked 80A and 0.03A, and the main switch is 100A.

I'd use the "bell" position to get a separate feed to the shed (and power the bell off batteries instead). So that 'd be wired as : 2.5mm2 within the garage to a 4way joint box, (square metal back box, probably, ) joining to armoured cable in the garden, and terminated in a suitable socket in the shed - presumably also a metal back box to allow armoured cable termination. Plus a higher rated MCB in the fuse board bell, now marked as "shed"!

So questions are: Is this ok - using the consumer unit RCB or do I have to use a separate one instead or in addition? & if so where does it get mounted. Would it be better to use the "kitchen light" way instead with a separate RCB? What size CB for a single 13A Socket. Is this better than the alternative of taking a spur off one of the socket outlets nearer the shed?

Anything else I've got wrong? I did look at the FAQ!

Thanks

[Owain]

"keith dulwich" wrote | marked as "protected by RCB" : bell transformer 6 , ring main 32 , | shower 32 | "not protected": cooker 32 , fixed appl 32 , down light 6, kitchen | light 6, up light 6, smoke alarm 6,,family shower 40 (we have one | in bathroom and one in ensuite) | The RCB is marked 80A and 0.03A, and the main switch is 100A. | I'd use the "bell" position to get a separate feed to the shed (and power | the bell off batteries instead).

You could just move the bell supply to one of the 6A lighting circuits. If you do that remember to move the neutral to the non-RCD neutral bar when you're moving the live to one of the non-RCD MCBs.

It's probably preferable for the shed socket to have its own RCD and not be on the house RCD side. *If* your smoke alarms have integral battery back-up then you may run them off one of the non-RCD lighting circuits. I think this is preferable, as you're likely to notice loss of power to a lighting circuit more quickly. However, if your smoke alarms *do not* have integral battery back-up then you should keep them on their own dedicated circuit.

If you can run your smoke alarms off one of the lighting circuits, that would give you a free non-RCD circuit, which, as you are only supplying one

13A socket, should be MCB'd at 16 or 20A and you could use an RCD socket in the shed.

There is no point in using an RCD socket in the shed if you run the circuit off one of the RCD'd circuits in the house, as there will be no discrimination.

Owain

[keith dulwich]

Thanks, the smoke alarms do have battery back up, so moving them to a lighting circuit seems the best way. I'm surprised that the RCB can be at the end of the external cable - I naively assumed it neeed to be at the start in case of faults within the cable - butI suppose that's pretty rare! So it'll be:

2.5mm2 from spare non-RCB fuse way, metal joint box (inside garage) to armoured cable, through wall , garden, shed, then a RCB protected socket, on metal back box to allow termination using proper gland.

[Lurch]

On Sun, 23 May 2004 06:30:08 +0000 (UTC), "keith dulwich" strung together this:

That sounds spot on. Although the correct terminology for the socket, for when you're going to buy one, would be a metal clad RCD protected socket.

[Owain]

"keith dulwich" wrote | Thanks, the smoke alarms do have battery back up, so moving them | to a lighting circuit seems the best way. I'm surprised that the | RCB can be at the end of the external cable - I naively assumed | it neeed to be at the start in case of faults within the cable - | butI suppose that's pretty rare!

Yes, it's the socket that needs RCD protection (because it may be used to supply equipment used outdoors, and to ensure you achieve a 0.2s disconnection time), the cable only requires 4s disconnection time which should be achievable by the MCB

| So it'll be: | 2.5mm2 from spare non-RCB fuse way, metal joint box (inside garage) | to armoured cable,

For an extra few quid, I'd make the interior joint box a DP switch to allow complete isolation of the garage feed (the MCB will only disconnect the live).

| through wall , garden, shed, then a RCB protected socket, on | metal back box to allow termination using proper gland.

You should be able to get a proper gland that allows you to provide the earth whilst using a plastic box. (There are two sorts of gland for use on plastic boxes, one which provides the earth, and another which insulates the earth for when the shed is on a different earth to the cable armour.) A plastic box won't rust. You can get quite nice robust plastic RCD sockets with a little cover against splashing water quite cheaply now, even in the sheds.

Owain