A question relating to wooden outside structures...........

[Chris4564]

I can't lie, it's yet another question about everybodies favourite subject, sheds!

I've spent the last couple of days reading through as many posts about this subject as I can but have still not managed to find the answer to my questions. Hopefully one of you may know the answer.

I have just built a shed in the rear garden and wish to supply it with some basic power (light and a couple of sockets). Unfortunately the shed is an afterthought to some major work just completed at the house so I am unable to run a cable directly to my CU and will therefore have to take a spur from my existing ring, this is where my problems arise.

I know all sockets which will be used for exterior work need to be RCD protected (the house has no RCD protection and I don't want to add it), the electrician I consulted said that I would need to put an 30mA RCD FCU inside the house then run a 2.5mm SWA out to the shed. This differs from my understanding of the regs as I don't believe I have to RCD protect the SWA just the sockets, as I plan to put a garage CU into the shed which will have RCD protection isn't this sufficient?

To comply with the fact that Every outbuilding with an electrical supply should be provided with a means of isolation to disconnect all live conductors including the neutral. I was planning on fitting one of these to the start of the spur http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=102079&ts=94364&id=28563 )

Would this be a satisfactory setup (shed is only a 10m cable run).

Thanks in advance for any help (and I am aware of Part P)

 

[ibruceuk]

Hi,

I can't see a problem with adding a 13A FCU with the outlet going through the outside wall to an adaptable box with T+E and then change to SWA in the box outside.

Run this to shed CU with RCD.

The main switch on your shed CU should provide the disconnection in accordance with the regs as it is an RCD it will disconnect both poles.

I await to be corrected by those more knowledgable.......

 

[Chris4564]

Thanks for the info, 13A FCU it is then!

 

[Steve]

I know all sockets which will be used for exterior work need to be RCD protected

All sockets which MAY possibly be used for outdoor work need to be RCD protected. So basically most of your downstairs sockets then eh . . . ?

 

[ban-all-sheds]

(the house has no RCD protection and I don't want to add it),

Why not?

I plan to put a garage CU into the shed which will have RCD protection isn't this sufficient?

Yes

To comply with the fact that Every outbuilding with an electrical supply should be provided with a means of isolation to disconnect all live conductors including the neutral. I was planning on fitting one of these to the start of the spur http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=102079&ts=94364&id=28563 )

Would this be a satisfactory setup (shed is only a 10m cable run).

No - that is a switch, not an FCU, so it will not limit the load on the SWA - you'd have 2.5mm² cable protected by the 32A socket circuit MCB, and that is not right.

 

[Chris4564]

(the house has no RCD protection and I don't want to add it),

Why not?

Plenty of bad experience with RCD's tripping for minor faults and causing more problems than they prevented (admittedly in non domestic environment)

I plan to put a garage CU into the shed which will have RCD protection isn't this sufficient?

Yes

Thanks just what I thought!

To comply with the fact that Every outbuilding with an electrical supply should be provided with a means of isolation to disconnect all live conductors including the neutral. I was planning on fitting one of these to the start of the spur http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=102079&ts=94364&id=28563 )

Would this be a satisfactory setup (shed is only a 10m cable run).

No - that is a switch, not an FCU, so it will not limit the load on the SWA - you'd have 2.5mm² cable protected by the 32A socket circuit MCB, and that is not right.

Hadn't thought of it like that when originally posted but have chosen http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=101470&ts=28639&id=13479 instead.

Thanks for the info, much appreciated!

Out of interest if i'd chosen to run 6/10mm SWA would it then have been acceptable to use the 32A MCB as protection???

 

[ban-all-sheds]

Plenty of bad experience with RCD's tripping for minor faults and causing more problems than they prevented (admittedly in non domestic environment)

The thing is, the problem they prevent is death..

Out of interest if i'd chosen to run 6/10mm SWA would it then have been acceptable to use the 32A MCB as protection???

Yup.

4mm² would also be OK.

 

[Steve]

Out of interest if i'd chosen to run 6/10mm SWA would it then have been acceptable to use the 32A MCB as protection???

afaik, no, too much current being drawn from one point on the ring

EDIT i stand corrected by ban, but does my arguement have some strength?

 

[ban-all-sheds]

That's a load issue at the other end, not a cable protection one.