Extending Garage Supply

[shelby3]

Hi,

I have a Crabtree Starbreaker Garage Kit installed in my garage. The supply comes via 2.5mm SWA from a 32a breaker on my main house consumer unit (RCD protected).

The garage consumer unit only has 2 MCB slots (both protected via an RCD) and currently powers 6a breaker on lights and 16a breaker on sockets.

I am planning to upgrade the SWA to 4mm, and also upgrade the connections either end of the SWA to 4mm twin and earth (currently 2.5).

I want the ability to add power to my shed, and also outdoor garden lighting, therefore can I simply add a junction box to split the 4mm twin and earth to supply load to 2 Garage consumer units instead. I don't really want to buy a bigger consumer unit, as then I will waste my current one.

What would be the best action here ?

Your help is appreciated.

 

[Chri5]

Seperate circuits should have individual fuse and isolation.

So update to a 5 way board and use 4 positions.

A 32a supply should be enough, why do you need to update the feeder from the house CU to 4mm ??
Did you intend to jump the fuse on the SWA to 40 / 45a ? (and if so have you done the calcs?)

 

[ban-all-sheds]

I have a Crabtree Starbreaker Garage Kit installed in my garage. The supply comes via 2.5mm SWA from a 32a breaker on my main house consumer unit (RCD protected).

The garage consumer unit only has 2 MCB slots (both protected via an RCD)

You shouldn't have 2 RCDs in series like that.

I am planning to upgrade the SWA to 4mm.....

Are you planning to notify?

 

[shelby3]

Thanks Guy's.

I'm not planning to do the work myself, but via a proper electrical contractor. However I've had contradictory advice of a couple of electricians, and feel much more comfortable designing the solution myself and then telling them EXACTLY what I want.

It's funny you say that about the 4mm cable. I had a couple of guy's tell me that before they install the Garage Breaker they have to replace my 2.5mm armoured cable with 4mm - it's reg's ! but I said I would rather not, and after "not much" persuasion they installed the garage breaker anyway, so I just assumed I needed a 4mm cable.

Anyway here are the calcs:

- My largest power tool is 500W, and I never use two at once
- Shed Lighting max 60W
- Garage Lighting max 300W
- Outdoor Security Lighting max 200W
- Garden Lighting 1000W (generous)
- Pond Pump 300W

Obviously this is more than I need, but just scaling for the future. This all comes to 2.3kW .

Running it through the calculator to accomodate for 7 circuits and 3kw of power over a 10m length it say's my required cable size is 2.5mm -

Therefore I shouldn't need to replace it ?

The calc also says that the max cable load is 13.5 amps, so should i be running the output from the house CU on a 16amp breaker instead of a 32amp ?

So i'm assuming I can purchase a CU box (crabtree) that can take 7 MCB's, and to start with have the RCD and 2 MCB's in my garage unit put into that instead ?

Is there an issue with running 2 RCD's in parallel ? Just had my CU replaced and I already questioned the advice given by my local electricians, so that's how he set it up.