Garage CU

29 Mar 2010
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United Kingdom
I am having a new garage door fitted with an electric opener. As part of the electrical install is to fit at my request a garage CU to replace an old junction box with a more professional solution. The cables in the picture come through the wall from the main CU - modern with RCD etc. The large cable is for a shower and not to be disturbed. The line into the junction box is for power in the garage split 3 ways to 3 separate sockets.

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The lighting circuit is separate and fed through the Kitchen.

After the garage CU is installed and part P signed off I intend to run the cabling through conduit rather than just clipped to the joist. Is running through conduit minor work i.e. does not require signing off as well?

Basic question is, am I over engineering this? Would a better junction box be just as adequate with conduit?
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As you seem to be hinting, there's little point in installing any kind of DB here. The important thing is to ensure that the correct protection is installed back at the main consumer unit. Assuming it's 2.5mm T+E, you will likely be looking at a 16A protective device. You'll need to check on derating factors on account of moving the cables from clipped direct into conduit.
Sounds like you're making it a lot neater, and from what you've said the garage CU is a bit over engineered. Sounds like the garage is integral to the house, not a separate building, so your current cabling souinds OK (assuming the three garage sockets are on a radial and not a radial spur off the ring ...). Garage door openers are usually 12V so the power requirement from them is pretty minimal, and plugging it into one of your existing sockets would probably work perfectly well.

But hey, better to be neat and over-engineered than having the sort of dog's breakfast we so often see here.

Does that feed to the garage come from its own mcb in the main fuseboard?
If so, what is the value of that ?

You say that there is an RCD protecting the circuit. There's no point having another one in a garage CU, as stated above, all you need is a switched FCU for the lights.
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After the garage CU is installed and part P signed off I intend to run the cabling through conduit rather than just clipped to the joist.
Do you mean that you intend to run new final circuits?

If so they'll need testing and will be notifiable and there's little value in an EIC and Building Regulations certificate which don't cover all of the circuits.

If you mean you're going to take the wiring, disconnect it and put it through conduit then although that's not notifiable you ought to have the electricians do it as after what is essentially a rewire of the circuits using the old cable it ought to be tested.
Thanks for all the suggestions.

Yes it is an over engineered option but it will be tidy and neat. Protection is more than satisfactory at the main CU. All it will cost me is the new Garage unit & conduit & a few conduit boxes (£50 odd) and they are not charging extra on the fitting fee for the door so might as well use the fitters when there here. The door is costing an arm and a leg but is the best I could find so lets do a proper job. (£50 odd does not include bacon butties & mugs of tea of course)

I take on board the suggestion to test all the cables and conduit beforehand this does make a lot of sense. I do not intend adding any more sockets / spurs etc. after this so it will be a test of what is there.

Thanks for the prompt responses
Am I seeing that JB right?

Is that the JB for the shower?

If so, is the feed for the garage spliced off it?
I dont think so fella, the 6mm seems to pass the junction box and is propping the wayrock up off of the joist above.
The shower cable is separate to the power cable they just come through the same hole in the wall. Yes it does need sorting and the area above the cable clearing.

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