Garage Power query again with a twist

[Nomolos]

Hello all

I am looking to renew my garages electrics; previous owner was an electrician I am told many years ago.
He was running a 3 core extension cable flex into an old style baker light consumer unit, with a small circuit for a few sockets and an overhead fluorescent light.

I have spent a few pleasant hours running through permutations of garage electrics, outside sockets etc, but not quite found the information I am looking for.

What I would like to do is run a suitable armoured cable from the main consumer, into a sub box in the garage, and to the use that to run a ring main round the outside of the garage walls, with 7 twin sockets spread about I am thinking 6mm twin and earth for this?, and a light supply and the kicker question a single feed to run a 25A, 4.2Kw pottery Kiln for the wife to play at pots.

The run from the main consumer unit to the garage unit would be 36ft or 10.97 meters, The garage is 38ft long by 9ft wide.

The information I have winkled out so far is I need the internal cables in conduit, with sealing glands ideally going into metal back boxes.

I am hoping to run a compressor and welder of the ring circuit as well.

I have attached a diagram outlining what I would like to do, I am aware that I need the cable to be correctly rated, I am also aware that building control need to inspect this before commencing.

I have a spare on the main consumer unit, it’s a new unit only 4 years old it’s fitted with its own RCD unit, the main house was rewired at the same time, me being a donkey did not think to get the garage done at the same time.

For my own piece of mind I was hoping to get a pointer into if the above is doable, what sort of armoured cable I would be looking for size wise?

I don’t want to scrimp on this as the idea of melting cables when the wife turns the kiln on does not fill me with happy thoughts.

My plan is to get a sparky in to advise and connect, with me doing the donkey work for him, if that makes sense, but would like to have some idea of what’s involved so I can detect any cow smells that may emanate my way.

Thanks for looking.

 

[plugwash]

What I would like to do is run a suitable armoured cable from the main consumer, into a sub box in the garage, and to the use that to run a ring main round the outside of the garage walls, with 7 twin sockets spread about I am thinking 6mm twin and earth for this?, and a light supply and the kicker question a single feed to run a 25A, 4.2Kw pottery Kiln for the wife to play at pots.

The run from the main consumer unit to the garage unit would be 36ft or 10.97 meters

Given your requirements i'd suggest rating the breaker in the house and the armoured cable run at 50A. By my calculations that means 10mm^2 SWA cable would be appropriate. I reccomend using three core SWA to make sure you have a solid low resistance earth.

If possible it would be best to put the submain on a non-RCD way of the main consumer unit and have a seperate RCD in the consumer unit in the garage.

There is no specific requirement for conduit or metal accessories in a garage but there is the general requirement that equipment must be suitable for it's environment. You mention pottery so depending on the ammount of water involved you may want to consider IP rated accessories in some areas.

This work is notifiable under part P

 

[Nomolos]

Thanks for the answer,

No water involved as such the kilns going to be used for glass slumping, so no water spray around the place. The main box could I believe be wired as you suggest, in fact thinking about it, it actually makes good sense.

Many thanks for the reply.

 

[ericmark]

Working on 32A then 4mm is minimum but I would say 10mm was a more sensible size. To work out the sizes really one should be looking at earth loop impedance and since you have not give us that information we can't be certain as to sizes. I would not want the garage on the house RCD and RBCO's seem to be slightly smaller than a MCB so 45A would seem the maximum in many makes. As to if RCD in garage or RCBO in house it would depend on the run and likely hood of the supply cable being damaged. The system designer will need to consider these points and I would point out that to do any DIY work without talking to the guy who will sign the installation certificate could result in it being all having to be done again.

As to Part P I am not sure as to if it would be considered like for like replacement or not and I realise many people do break the law. But you will still want your wife to be safe and so you will still need to test what you install. The meters even to hire are expensive around £60 to hire so you do need to consider if the work is DIY or not? So often it can work out more expensive to DIY than to get a member of the competent persons scheme to do the work for you.

 

[Nomolos]

Hi there Ericmark

I appreciate the candour, I class myself as an experienced DIYer to the point where I could tackle the job above, but as you point out it needs to be safe and i just don’t have the equipment or experience to test and be 100% confident in my work.

The point in the post is more for my understanding of what’s involved, the materials I should see being specified so I can better judge what’s being advised as good or shoddy practise.

Unfortunately in my experience just because somebody’s “qualified” it does not always follow that the work being done or the materials being used are correct and for my own piece of mind i like to try and understand what’s being done and what I should expect to see, if that makes sense?