R

ringer

Customer has installed a single-room summerhouse (wooden construction) in his garden, triangular shape with two 2.5m long back walls. Wants me to connect electrics from house. Summerhouse is 15m away from house, on opposite side of house to where main intake and consumer unit are. House consumer unit has 30mA RCD main switch which protects all circuits in house except shower which has its own RCD board. Nearest room to summerhouse is kitchen.

Propose to take feed from ring main in kitchen, through wall at back of a socket to adaptable box on outside wall. From there run 6943X 4.0mm under flagstone path (1m wide) then buried 300mm deep under edge of flower border (14m long) with warning tape buried at 150mm, to adaptable box on summerhouse, then in through wall of summerhouse to 2-way consumer unit (16A+6A mcbs). One power circuit supplying 2 x 2G flush mounted socket outlets inside and one 2G weatherproof socket on outside, and one light circuit supplying pendant in ceiling, surface mounted (mini trunking) inside summerhouse to socket outlets, though partly fed inside inner skin to flush mounted sockets. Light will be partly mini-trunking, partly clipped to surface (wooden roof structure) and partly hidden under board in ceiling.

Power usage is likely to be TV, games console, 2kw heater. Possible occasional use of electric mower, though they have a petrol mower at present.

Comments about proposed install please, particularly whether summerhouse cu should have RCD (if so how to mitigate discrimination with main CU RCD) and buried route/depth of swa. There is a fence but it is very rickety and customer wants cable buried, not in sight.

Have tried searching internet for 20mA RCDs but can not find where they can be bought from.

Position of CU - can it be put 18 inches above floor level, keeping it out of sight from windows, or does it have to be above a certain height?
 
Personally I would have extended the ring out to the summer house I don't think there is a lot of difference between 2 core 4mm and 4 core 2.5mm SWA. So instead of having a spur feeding that little 2 way CU it would be fed by the ring. That is just personal opinion and there is nothing wrong with you way.

As for RCD protection well again as the main CU already as it, and the less of the 2 evils is having the RCD protection at the house rather than trying to get a cable back to the intake, then if you have a fault in the summer house it will trip the main CU in the house which we no is not perfect. So I would rely on the additional protection at the main CU.

The only thing I would say for me the 300mm is not deep enough in the garden I would have like to put it about 500-600mm. under the flags it's ok really, much preferable the same depth all through.
 
Personally I would have extended the ring out to the summer house I don't think there is a lot of difference between 2 core 4mm and 4 core 2.5mm SWA. So instead of having a spur feeding that little 2 way CU it would be fed by the ring. That is just personal opinion and there is nothing wrong with you way.

As for RCD protection well again as the main CU already as it, and the less of the 2 evils is having the RCD protection at the house rather than trying to get a cable back to the intake, then if you have a fault in the summer house it will trip the main CU in the house which we no is not perfect. So I would rely on the additional protection at the main CU.

The only thing I would say for me the 300mm is not deep enough in the garden I would have like to put it about 500-600mm. under the flags it's ok really, much preferable the same depth all through.

Sounds good to me ...lol!!! You could also go a little further and do away with the CU and just use a FCU to feed the lights off the ring at the summerhouse.

As you quite rightly suggest, 300mm is definitely ''NOT deep enough, especially in flower beds where it will be prone to digging, 600mm is far more sensible. A warning tape at just 150mm won't last 5 minutes in a flower bed, and the fork/spade will go straight through it....

And don't forget that the backfill and base, needs to be free of stone and other debris ....
 
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Summerhouse electrics
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Electrical Wiring, Theories and Regulations
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ringer,
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Engineer54,
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