Garage consumer unit - clarification

[DJB71]

Hi guys, go easy on me please first post.
I was asked to go and put in an outdoor supply to a shed at the end of a garden last night. Not feasible for me to run a dedicated circuit from CU in house but load is minimal so I was just going to spur off main ring (only a TV, sewing machine and lights)
Howver, they have an RCD protected board, and I gave a price that included a 2 way CU for the shed which obviously put price up.
Just wandering whether it was a necesite to have this afteraqll, the main board is RCD protected? I guess all you are doing is if there is a problem within the shed then this should trip and not interrupt house power.
Would really appreciate any views as I seem to be asked alot for outdoor supplies at the moment - guess with the recession people are living in sheds more.
Cheers

 

[pushrod]

How are you getting the power to the shed (cable-wise) and what is the distance (voltage drop) and are there any services in the shed (earthing arrangements)?

 

[DJB71]

Shed is only about 5m from house so VD no an issue. Was going to use 2.5mm 3 core SWA to shed with earthing provided by from the supply.
No other services in shed.
Cheers

 

[pushrod]

Think that if it is just the spur option you will be limited to 13 amps in the shed. If that is enough i don't see any problems.

 

[DJB71]

amps isnt a problem - it is just having to add approx £50 for a garage CCU when essentially doubling up on RCD protection (minus possibility of nuisance tripping in house in te event of a fault. I know these people have very little at the moment and are using extension leads across the garden ( covered in a suitably IP rated Tescos carrier bag )

 

[pushrod]

I'm obviously not the most experienced person on here but if 13amps is enough then i don't see that you need the garage CU - also prevents problems with discrimination between the 2 rcds.
edit : just noticed you said you will use 3 core swa - if you are using one of the cores as an earth you still need to earth the armouring.

 

[sparkdog]

As pushrod says you wouldn't want to have two RCDs on the same circuit anyway as no discrimination.

 

[TPES]

just noticed you said you will use 3 core swa - if you are using one of the cores as an earth you still need to earth the armouring.

Alright pushrod, I think the tutors recomended that you do that at LouColl, but you dont HAVE to do it. its just an additional earth, The CSA of the cored earth is sufficiant enough.

 

[pushrod]

Alright pushrod, I think the tutors recomended that you do that at LouColl, but you dont HAVE to do it. its just an additional earth, The CSA of the cored earth is sufficiant enough.

Hi Sid , its not to do with the csa but protection. I did a little project to my own shed and wired it in 3 core swa as DJB71 was suggesting and was told that i definitely should be earthing the armouring at the CU end, even if i'm not using that as the cpc.

Have you finished now? how did the exams go?

 

[TPES]

Isn't the CSA of the CPC the earth fault protection, If you have an earth the same size as the live conductor surely that is large enough to carry any fault current that could flow back in the circuit. Adding additional earthing conductor (armouring) which could be greater than the live conductor is not needed is it? It may be good practice but not essential? Am getting confussed?

Alright pushrod, 3rd year is a killer! well was for me..

How you getting on?

 

[Guest123]

The armouring of an SWA if not used as the CPC still needs to be connected to earth at the supply end in order to bond it to earth

 

[pushrod]

The armouring of an SWA if not used as the CPC still need to connected to earth at the supply end in order to bond them earth.

Well at least i'm learning something at college

Sid I think full time is much easier than evening classes plus a lot of the theory is easier for me because of previous experience

 

[TPES]

The armouring of an SWA if not used as the CPC still need to connected to earth at the supply end in order to bond them earth.

Yeah of course it does, I wasnt thinking of bonding issues, but yeah makes obvious sense.

 

[willosparky]

with the swa make sure the armour is connected to earth at the house end. this will give the cable the protection it needs against mechanical damage. no need to connect the armour to earth at the shed end.

if you have a socket in the house on an external wall near the shed, another option would be to drill though to outside and fit a water proof socket (wired with 2.5 t and e) and then from there take a 2.5 3 core swa over to the shed. using the brown as live, grey (marked blue) as neutral, and black (marked green/yellow) as earth. Cw glad kits should be used to glad the swa as they will be out side. If you are having lights in the shed then a switched fcu should be fitted next inline after the socket and fused down to 5A. fitting an rcd socket in the shed wouldn't be a good idear as if it trips u will not know it has done so until you go to the shed, therefore things in the freezer may ruin. if the ring in the house is rcd protected then fair enough, if not then there is no need to worry.

 

[r10ley]

If you use the method regarding an outside socket im pritty sure you will need to put a fused spur in the garage otherwise youl be limited to one socket. Also again im pritty sure if you do this youl beable to wire your sockets after the spur in 1.5mm if you so wish not sure why you would but never mind.

Hope this helps

r10ley