any sparkies out there?

[steve bain]

I have happily used the double 13A socket on a radial circuit with 20A mcb in my garage for welding, lighting etc but wanted a big compressor and thought i might make the wiring better and be able to handle more. I want to add a consumer unit into my garage and i wanted to pass my thoughts past someone. I have rewired my whole house inc new cu and all so i am pretty clued up with domestic wiring and when it was all checked i was told it was spot on. However garages are a bit different and power is much higher.

My plan is to use a 42A mcb in my house feeding a 4mm XLPE SWA cable with all the associated banjos, boxes etc. the tlc online voltage drop calcuator suggests this will be good for 9KW at 39A and max cable load will be 43.3A (garage is less than 5m away so cable length should be under 10m).

i plan to run a 3hp compressor - say 300W to run and 800W on start up.
other than that its just welders (mine is 140A so runs off a 13A plug), grinders, drills etc, but only really one at a time and they should be less than 2000W each i'd say
My lighting is 300W
Maybe a flood light at 500W
heater at 1000W

so maybe 5000W if all the lights are on and the compressor kicked in whilst i am grinding and heater is on!
does 9KW sound about right or should i bump it up to a 6mm cable which will be good for 12KW on a 52A mcb
at 52.2A with max cable load of 54.6A

I know the answer is just stick the biggest one in, but a 6mm cable has a larger bend radius etc so is a pain to install and does seem a bit over the top

so i was thinking in the garage to have an isolator with 3 mcb's, 6a for lighting, 16a with 2 16a radial sockets for compressor and welder if i ever buy a bigger one and a 32a ring main for everything else.

Anyone done or had this done recently?

any thoughts? (other than pay an electrician!)

[james butler]

Always run the biggest cables you can or you will be doing it again and believe me ressetting tripped rcb gets boring after a while and especially in the dark!
It sounds like you know what you are doing but I would strongly recommend getting a sparky in to hook it up if only for insurance purposes.

[Nate]

You have to also take into account the length of the cable run, buried or in the open blah blah

I'm also reasonably sure that it is considered as notifiable works as it is in an outbuilding