3 phase supply to garage cable spec

[earthling]

Hi - first post, so I hope I get the tone right. I do pay professionals to do the work, but have a technical background and like to understand what's being proposed and why.

My house has a 3 phase supply. Everything in the house runs off a single phase. We've just had a 7kW car charging point installed in the garage. I asked the supplier to provide a cable that would allow us to install 2nd charger in the future, since running the cable is usually the most expensive and disruptive part of the job. There is also no other power in the garage (previous owner had run overhead twin and earth as a spur off a socket in an upstairs bedroom which obviously had to be disconnected), so I'd like to have that option too - I was thinking to have an electrician fit a small consumer unit in the garage to separate the lighting and power from the car charger(s).

The cable provided was 3 core 6mm SWA which is clipped to the external wall and the cable run is 30m. (There is a short section in an underground duct - 110mm twinwall at 500mm depth with warning tape.) The car charger is on a different phase to the house. Will this cable be suitable if I get an electrician in to add the consumer unit, or do I need to upgrade it. The car charger installer told me the cable supplied wouldn't be up to the job. Would it make a difference if the extra load was on the 3rd (unused) phase, or would that require a 4 core cable?

Many thanks

 

[James]

unfortunately the cable is not suitable to supply either 2 chargers or a 3phase and neutral distribution board.

ideally a 4 or 5 core cable would be used.

L1 Brown
L2 Black
L3 Grey
N Blue
PE wire armour (sometimes an earth core is required to give a good enough earth)

it MAY be possible to use the cable to supply a 2 phase distribution board,

2 cores for L1 and L2, 3rd core for Neutral , armour for earth.

because this setup would be unconventional, it may be difficult to find a spark that will do this work for you.

The regs do not prevent you from using a 2 phase distribution like this, it is Simpley the case that it is rarely done, so many sparks will not understand what you are trying to do.

2 chargers on the same phase down that cable would probably take you over the max current rating of the cable, so that is a not possible (it would also involve a shared neutral and that is not allowed)

 

[earthling]

Thank you.

My original plan was a 5 core 10mm or 16mm cable, but I asked for a cable to do what I described above and was sent the 3 core 6mm.

I guess my choice is whether to run an additional cable or replace the one that's just been installed.