Home Electrical advice query not car not motorbike

[Welly]

I've just erected a rather spiffing Shed onto a raised decking base in the Garden behind the garage. This decking has the potential to provide shelter for Rodents I guess.

What I plan to do is frig-up an outdoor electrical socket under the Decking and electrocute them all and plug in an Ultrasonic rodent scare'er-offer. The advise seems to be that these things are sh*t but I think people use them incorrectly. My plan is to fill this void with Ultrasonic shiz which will be my best defense I think, well better than doing nothing. My biggest fear is a family of Top Hats under there

Anyhoo, this power supply can tap into the Garage easily and I was planning on using the lighting circuit and protected by a 3A fused spur. The sounder-thing only consumes 9W but I guess the biggest risk is water ingress to the socket outlet but then it'll just pop the fuse if it's not happy? am I missing something? I was going to run 1.5mm T&E but routed so it can't be stood on or damaged etc. also going to fabricate a rain hood under the deck to protect from splashing etc. I don't really want to tap into the Power circuit, that seems OTT, and I'd still need fit a fused spur etc.

[gumby6371]

http://www.screwfix.com/c/electrical-li ... /cat830672

I fitted something similar to this for my MIL's fishpond

[Doggy]

Waterproof socket's a good idea. Ideally wants to be RCD protected, with the trip being inside the garage, so as to make all your extrenal wiring as safe as possible. I would not use the lighting circuit. If possible fit a 6A RCBO at the point where you tap off the supply.

[Welly]

Mmm, I see what you mean really, I suppose what I propose is akin to throwing a length of twin and earth out onto the lawn and 'going live' with it. That makes sense having a separate RCD, one thing: what should be the rating of the cable that supplies the RCD connection point? should I use 2.5mm as per the ring-main I connect to?

[Doggy]

Strictly speaking, 2.5 mm2 is too small, unless it's part of the ring, which effectively consists of 2 x 2.5 mm2 cables in parallel, protected by (typically) a 32A MCB. The fundamental issue is whether the protective device can remove the power before the cable gets too hot, under fault conditions.

[Welly]

I was going to tap into the ring with a junction box and take a 2.5mm radial out to this 'ere RCBO I think that'd be ok? although it wouldn't take much to divert the ring to be part of this new unit. Having said that I'd have to fit two junction boxes and in my mind they're far more at risk of causing trouble, especially in a garage roof space.

[Doggy]

The radial should be 4 mm2, (some would even say 6 mm2), or include it in the ring.
If you put your spur adjacent to an existing socket, you can usually include it without any junction boxes.

[Welly]

Thanks, actually I could bosh it in next to a socket thinking about it, cheers.

[Bailes1992]

You are allowed to spur off a ring with 2.5mm cable providing there is only one socket. If you want more than one socket then you would have to install a fused spur on the ring to spur off with. In theory a 13A socket can only draw 13A so the cable will be protected anyway.
I can scan the page out of the BS7671 if you like?

The RCD on the consumer unit is more than adequate.I remember you saying you live in a fairly new house so I would assume you would have an RCD covering all the circuits. You don't need any additional RCD's.
If you were looking to bury the cable outside I would look at maybe installing either an armored cable or at least some FP2000 GOLD which has an earthed outer sheath. With twin an earth there is always the risk of shoving something in the ground and just catching the line conductor.

[Welly]

The house has RCD's but the separate garage has a small fuse box (but fed from its own MCB in the house) so anything shorts out in the garage it should trip the house unit?

So your saying I can tap off the garage ring with no additional RCD, would it be wise to install a 3A fused spur though (just for this outside socket)?

Just getting a good mix of ideas here, which is good anyway.

[Rolebama]

Most consumer units ha ve a spare socket. Surely it would be better to run from this with a suitable amperage. Then if it blows, it will not affect the house circuits.

[Bailes1992]

Unless Welly has a board with individual RCBOs which I high doubt then it will be a single RCD or split load board. Unless Welly goes and buys a new bus bar to rearrange everything then the extra slots in the consumer unit is extremely likely to be Protected by the same RCD the rest of the house is on.

[Bailes1992]

I personally would spur off a ring in 2.5mm FP2000 Gold and bury it down the garden straight to a single socket. Anything else is unnecessary. The above would conform to BS7671.

[Welly]

I've got no spare ways at the CU, I've got 2 x MCB's for 'sockets' protected by a common RCD, there's at least 4 others (garage, cooker, etc and 4 separate MCB's for lighting. I think there's 10 in total. My experience has been that any tiny fault on the power side shuts the whole lot down but faults on the lighting just trip the individual lighting MCB.

That's a good call using the FP2000, I was going to use T&E neatly* secured* under the deck but that is a bit sh*t and wrong I guess. I may even frig up a light in me new shed while I'm at it, via a 1A fuse of course

[D4B]

I personally would spur off a ring in 2.5mm FP2000 Gold and bury it down the garden straight to a single socket. Anything else is unnecessary. The above would conform to BS7671.

I would Agree with Bailes1992.

Don't come off a lighting circuit though!

Of course it needs safe isolation BEFORE connecting into the existing ring of course, but then you knew that didn't you.