Wiring an outbuilding from the domestic CU

[mickhorne342]

I have almost completed re-wiring my newly modernised home and just need to run power to an old out house. I want to be sure that I get the job right so that certification is not a problem.
I have a spare RCD protected bay in the CU and have purchased a "Garage CU" for the outbuilding. The outbuilding will have 2 double sockets and two light fittings.
My initial thoughts are to run a 6mm cable (I believe 4mm would be adequate, but I have lots of 6mm left over) from a 32A MCB in the domestic CU, to the Garage CU. Then run a "mini" ring in 2.5mm from the 32A MCB for the sockets and a 1.5mm spur from the 6A MCB for the lights. Is this a sensible way to do this, or what should be done differently?

Also, how do you track down an electrician qualified to inspect then issue an electrical safety certificate for DIY work? I have spoken to the local (Weymouth, Dorset) firm who I have used for various electrical jobs over the years, but when DIY was mentioned there was the famous sharp intake of breath and "I dont know about that" response.

Any advice would be very much appreciated.
Mick

 

[Spark123]

It is sounding like the work you are doing is notifiable to your local area building control (LABC) under part p of the building regs.
To carry out notifiable work there are 2 methods to comply with the law:
1) Notify your LABC, pay their fee before you start and let them oversee compliance with the building regs.
2) Employ a firm who is a member of a comptent person scheme and let them look after the notification.
The firm you spoke to is probably a member of a competent person scheme, they can certify their own work as compliant with the building regs but not anyone elses work.
As for your fuse board, if you are only using 2 sockets then you probably won't need a ring, what are you using it for? Is a 20A radial sufficient?

 

[mickhorne342]

Regarding the overall project, the house modernisation has been ongoing for around 3 years and has planning and building regs approval. I have had all necessary building inspections to date. The only one outstanding being completion, which requires an electrical safety certificate (?). This was not actually specified in the initial building regs (Sep 2004) but was notified in a subsequent letter the following year.
We had professional electricians remove the old fuse box, instal a modern CU and do the earth bonding (Nov 2004). Since then, as the building work has progressed, I have been replacing the wiring, sockets and light fittings, pretty much like-for-like. The only new circuit required being power to the outbuildings.
To answer your question, the building will run the freezer, the tumble dryer and the lawn mower /strimmer / power tools for the garden.

Mick

 

[CallEdsFirst]

Your first problem is having the freezer on an RCD protected circuit in a damp environment. Once that baby trips without you knowing, its goodbye £100 worth of fish fingers and lollies! (unless you claim for it when it becomes £500! Surprising what's in a freezer as far as insurance companies are concerned, very rarely is it anything other than smoked salmon, whole rainbow trout and caviar. Can you even freeze that stuff?)

 

[mickhorne342]

Point taken, but there's nowhere else for it to go! Until all the kids leave home and we can make do with a combined fridge/freezer, its staying put.
Clearly it must be RCD protected, mustn't it?
Anyway, the Asda icepops are well insured.

Mick

 

[CallEdsFirst]

The shed supply doesnt have to be RCD's only sockets that might reasonably supply outdoors equipment.

Supply the shed/garage/whatever with appropriate overcurrent protection but not RCD, then stick a split load board on the other end (bit overkill) or just make sure the sockets you put in there are RCD sockets.

Then if hardwire the freezer into a spur (Fused Connection Unit), it doesn't have to be at risk from defrosting "automatically"

 

[mickhorne342]

Understood (I think).
So I run from a 16A MCB (or 32A?) non RCD in the domestic CU, to the "Garage" CU. The freezer is non RCD on a spur with a FCU, while the sockets are RCD protected.

 

[CallEdsFirst]

Indeed, but as stated, it is notifiable! LABC must be informed or it could be a hefty fine.

 

[luminaire]

My initial thoughts are to run a 6mm cable (I believe 4mm would be adequate, but I have lots of 6mm left over) from a 32A MCB in the domestic CU, to the Garage CU.

How far away from the house is the garage/outbuilding?
How are you running the cable to it?
What sort of cable are you using? Is it SWA?