garden shed wiring

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soloheadbeg

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hello

I want to wire a recently acquired summerhouse. I have a detached study which has a sub cu with plenty of free slots on both the non-rcd and the rcd sides. I propose to run 4mm2 cable a distance of 18 metres from the sub cu in the study to the summerhouse. i will protect the circuit with a 20 A mcb. The circuit will consist of 3 double sockets and a spur from one of the sockets (fused down to 3A) for a couple of lights.

If I place the 20A mcb on the rcd side of the sub cu will this give me the required protection? I realise that if the rcd activates i will also lose the light in the summerhouse. Should I run two cables from the sub cu - one 4mm2 for the sockets on a 20A mcb on the rcd side of the sub cu and the other a 2.5mm2 cable for the summerhouse lights protected by a 10A mcb on the non-rcd side of the sub cu in the study.

I also realise that where these cables are outside they must be SWA and buried etc. can these SWA cables be connected directly at the sub cu or would I be better off bringing ordinary 4mm2 T&E from the sub cu and connecting to the SWA using the appropriate type of metal box on the outside of the study wall.

At the summerhouse end how do I terminate the 4mm2 SWA and join to 2.5mm2 T&E for sockets.

Please note i am in the Rep. of Ireland where P regulations do not apply.

Any thoughts would be appreciated.

Thanks
 
You are taking a far too simplistic view.

I wish it was all that easy. Out side the first consideration is earth type. This needs one to look at what you already have. You have not given even the supply type is it TT or TN and if TN is it TN-S or TN-C-S. You have not given the earth loop impedance or any other info about the installation.

Try looking in Wiki
 
If you're not sure about your supply, post some pictures of the meter and where the cable comes into the house.

If there's any visible cable on the outside, take some of that, too.
 
hello again

Thanks for your replies. i have verified that the earthing system is TN-C-S.

Cheers
 
Hello

Thanks for asking. I've laid 6mm 3 core armoured xple cable (using 3rd core for earth) to the summerhouse from the sub cu in the outside study. i'll put a 32A mcb on the rcd side of the sub cu. In the summerhouse i'll place a small cu with 20A mcb for three double sockets and 6A mcb for a few lights. the trench is about 20 inches deep. cable in 2 by two galvanised trunking as it comes down outside of study. Cable laid on bed of sand then covered with 2 inches sand. on top of that is a row of bricks and on top of that the warning tape. I've also brought over in the same trench hot and cold water qualpex pipes insulated and passing through 4 inch drainage pipe for easy withdrawal in the future if required. no electrical or water connections made at either end yet. i've insulated the summerhouse with 1 inch foil backed xtratherm leaving a 0.5 inch air gap. I intend to plasterboard and tape. Wiring in the summerhouse will be surface mounted to allow future modification. Will install a Belfast sink and L-shaped kitchen worktop - the summerhouse is for wife who is into flower arranging etc. Any comments would be greatly appreciated. Cheers
 
If it where me, I would of put cable on non rcd side of house cu and rcd protect the cu in the summer house.

That way, you haven't got to run to the house (in the dark) to restore power when rcd trips.
 
Yes, before the RCD would be good. Though I'm guessing you want all your work RCD protected? So a compromise would be to put a dedicated RCD for the summerhouse in the CU of the study. This will spread the load and you will not have to upgrade the original RCD for the study.
Downside as already said, if it does trip, it will be in the wrong building, and bear in mind everything will go lights and sockets.


Is herself any good at the flower arranging? Hobby or business?
 
Yeah she's pretty good at the flowers. thinking of starting business. R u an electrician?
 
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