UK Wiring a 17mtr x 15 mtr Car Enthusiasts Garage UK

[Drumtochty]

The garage is 17 mtrs x 15 mtrs in the UKh

The house has a 100 amp supply to the house consumer unit.

The garage consumer unit is fed from a 63amp RCD to a 40 amp B rated mcb in the house consumer unit.

The feed cable to the garage is 10mmsq SWA 3 core with the swa bonded to the earth conductor at both ends via the earth bar on the consumer units.

The garage consumer unit has a 100 amp main switch with two 63 amp RCD's which in turn feed 4 mcb ways each.

All the lighting is by LED with a load around 2 amps.

The garage is heated via an oil burner using less than 1 amp of electricity to run the burner controls.

There is a 3kw air compressor fed via a 20 amp B rated mcb in the garage consumer unit via 2 mtrs of 2.5 twin and earth with no issues.

There is a car lift fed via a 32amp b type b mcb via 15 mtrs 2.5 twin and earth.

The question I have is about sockets.

The garage has an internal area of approx 255 sq mtrs.

The guidance in the UK tends to be to use a ring circuit for sockets with a max floor area of 100 sqmtrs per ring.

Therefore going by that guidance, it suggest that we have three ring circuits 5.7 mtrs wide by 15 mtrs deep via 32 amp mcbs but I am thinking of reducing the mcb rating to say 20 amps. Run with 2.5 twin and earth.

The main reason I am doing this is to prevent the owner who thinks he knows better and has no interest in keeping to any electrical regulations.

Does anyone have any issues with what is proposed.

 

[Welchyboy1]

There is a car lift fed via a 32amp b type b mcb via 15 mtrs 2.5 twin and earth.

what’s the demand of the car lift?


how many sockets are to be installed in the garage on these ring circuits

 

[Drumtochty]

There is a car lift fed via a 32amp b type b mcb via 15 mtrs 2.5 twin and earth.

what’s the demand of the car lift?


how many sockets are to be installed in the garage on these ring circuits

The lift runs at around 12 amps while lifting, with a start up current of around 25 amps. The clamp meter used to measure the current has a lag at startup.

In the UK we are allowed unlimited sockets on a ring circuit but say around 12 sockets per ring.

 

[davesparks]

The guidance in the UK tends to be to use a ring circuit for sockets with a max floor area of 100 sqmtrs per ring.

You can also use a radial circuit, it is up to you as the designer to decide what is best suited to the installation.

Therefore going by that guidance, it suggest that we have three ring circuits 5.7 mtrs wide by 15 mtrs deep via 32 amp mcbs but I am thinking of reducing the mcb rating to say 20 amps. Run with 2.5 twin and earth.

You're being far too mathematical about this and not thinking about the real world application.
Yes the guidance is that a ring should serve no more than 100sqm, that doesn't mean you need to mathematically divide the space into 100sqm sections!

The main reason I am doing this is to prevent the owner who thinks he knows better and has no interest in keeping to any electrical regulations.

Prevebt the owner from what?

 

[Lucien Nunes]

I am thinking of reducing the mcb rating to say 20 amps.

I would favour 32A circuits in this location as 20A MCBs are more likely to nuisance-trip with the startup current of large power tools and tool transformers. If you do use 20A devices, subject to suitable Zs it might be worth using C-type to avoid this. The guidance for general-purpose socket outlet circuits is not really applicable to a special-use location, one should consider the expected usage and equipment present.