Hi all!

I thought I would ask the LCB collective as this is the source of all knowledge!

I have a garage behind and to the left of my house. Theres about a 2m gap between the garage and the house. The garage wiring was put in by a previous owner, and it's a bit... ropey, to say the least. There appears to be a spur from an upstairs socket which goes through a hole in the wall, is left unsupported on its 2m journey to the garage, where it is spurred again into 3 sockets & a lighting circuit. This would probably be "okay" if I were just a regular garage user, but with the lathe etc. out there and now a desire to get into TiG welding, I think it's time for an upgrade.

I have space for two spare circuits on my current Wylex BS3036, and having spoken to a sparks they have confirmed that as the cable I'm running is externally clipped and then run in solid conduit, it would be within regulations to add circuits to this existing consumer unit (obviously with a sparks doing the final connection as it falls under Part P).

So, my plan is as follows:

1) The consumer unit is located in the centre of the house, and in order to enable this installation to take place I will have to run the new cable for the garage to the outside somehow. My plan is to run the cable in hard conduit down from the consumer unit to a rotary isolator, and then from that through the wall, and then around the kitchen under the kitchen cabinets attached to the wall with cable clips, exiting through a hole in the outside wall, where I can run it in solid conduit up the side of the house and across to the garage. I've found a minimum specified requirement of 3.5m in height for a catenary, but I'm unclear if this applies for conduit installations as well. Does anybody know if there is a minimum height for this run? 3.5m from the ground would be higher than the garage I think.

2) Once inside the garage, I would like to install a small, 2 MCB consumer unit from which the garage power can be taken using the following rated MCB's:
a) 6A - Lighting. Powers two fluorescent lights and two LED panels.
b) 20A - Sockets & hard wired machine tools. Used for powering small power tools, 12v battery chargers etc. as well as hard wired machine tools. Wired to emergency stop button & momentary pedals, eventually reaching a lathe & bench drill.

I'm intending to wire all of the devices as Radials with junction boxes. My intention is to install 3 rotary isolators underneath the small consumer unit. One for hard wired machine tools. One for sockets. And one for future proofing for the installation of an electric garage door.

I'm planning to run the wiring both inside and outside the garage in 20mm heavy duty PCV round conduit as I have a bunch of it already left over from a CCTV install.

So, my questions for the collective are:

1) Do you see any issues with my design?
2) Can you think of anything I could do better/any suggestions for the install?
3) Do you have any recommended consumer units etc. that would be good for the job?

Any and all thoughts greatly appreciated!

I suspect the 3.5m for catenary cables is when they are over roads
also
it might be worth installing a 'cat5' network cable at the same time

3.5 is the minimum for cables going over roads
I have a cable in conduit that’s 2.0 m from the top of the garage to my shed if that helps
The cable is 2.5
Graham

For future proofing and making house more attractive to future buyers, if 2 spaces are available in house consumer unit, and Sparks would sign off on both, then run a parallel 32A cable out to garage for future installation of an Electric Vehicle charger point.

Or run a 40A cable to the garage and split it to 20A sockets, 6A lighting and capacity for other use. Diversity will allow for more than 40A total - you are unlikely to be welding or using machine tools while a car is charging overnight for instance, so 6A lighting and 32A charging would be sufficient ... and you can actually pull more than 40A for a period without problems.

In my garage (not easily accessible for daily use by a car) I have only sockets and lighting - a double socket (permanently live for battery charging and freezer), lighting (with a switch by the door) and the rest of the sockets (on a 20A switch by the door, so that I can ensure that everything is turned off when I am locking up).

If your earthing arrangement is TN-C-S(PME) then consider running a 10mm2 three core SWA cable so that you can potentially export your earth to the garage. 10mm2 is the minimum size for a bonding conductor.
That will also allow considerably more capacity on your sub-main.

quote:

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Originally posted by Prof_Cook
For future proofing and making house more attractive to future buyers, if 2 spaces are available in house consumer unit, and Sparks would sign off on both, then run a parallel 32A cable out to garage for future installation of an Electric Vehicle charger point.

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My EV charger is on a 40A breaker, but pulls only 32A (those are the manufacturer's requirements). That will provide 7.2kW. Higher powered chargers (next step is 11kW) and cars capable of taking higher powers, require a 3-phase supply, so on single phase, anything larger, for future requirements is likely of no use.

I used this in my garage.

https://www.screwfix.com/p/british-general-fortress-5-module-2-way-populated-garage-consumer-unit/453vf

have a read of the regs, theres something in the about making sure the cables dont sag under fire so you have to use metal clips on the conduit. Or at least that was my understanding.

TLC do a handy calculator for the size of the cable going to the garage too

https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

Supporting of cables is only a requirement where they may fall and impede access or egress by the fire brigade, in a hall for instance AFAIK. From house to garage, you'd usually use steel conduit anyway.

So recently was happily welding my frame tubes. Decided to switch to grinding out a bad weld. Everything worked fine. Then switched off the welder and other stuff. Went to close the garage door and lock up. For some reason I decided to switch the garage light on. Didn't work. Turned out the RCB in the house had tripped.... No power to garage - including the chest freezer full of food.... Reset the breaker and everything fine.

Moral of the story is that a separate spur into the garage notionally for a EV charge point but powering "domestic" loads like a food freezer (or a drinks fridge) could be a good thing. My garage is separated from the house by only a 3ft concrete path and the house distribution box is just the other side of the external wall facing the garage. Might consider how I could chase in a piece of conduit, concrete it in and then ask my local sparks to run a "domestic" spur through...

BS3036 suggests that your consumer unit is pretty old, does it have RCD protection? I assume you will need / want an RCD somewhere either locally in the garage or at the consumer unit, based on the presumption that there is a good chance you will use power outside the garage also.

Regards
David