Will my garage handle my planned usage?

[LHensh]

Hi,

Just looking to get some advice before I get too carried away with plans for using my garage as a home office/ManCave.

The garage has an old fusebox (photo attached) with 15amp and 5amp fuses which is fed by a 2.5mm cable coming from the house.
The feed to the garage comes from the main consumer unit in the house.

I'm trying to work out if my expected maximum power consumption could be safely handled by both fuses.

Sockets:

Oil filled radiator (photo attached) 1000w @ 240v = 4.17A
Router = <0.5A
TV = <0.5A
Beer Fridge = 0.75A
Coffee Machine = 5.5A
Laptop = <0.5A
Monitor = <0.5A
Projector = 1.9A
LED strip lights =<0.5A

Total Amps = 14.8

Lights:
10x LED downlights 5W X 10 X 240V = 0.21A
2x LED outside lights (4 bulbs) 5.5W X 240V = 0.09A

Total Amps = 0.3

For the sockets, assuming that all of the lower usage appliances all run at 0.5A and are all running at the same time (which wouldn't be the case) I should be within the 15A limit.

Lights are no concern as would be well under the limit.

Am I on the right lines here?

 

[littlespark]

The 2.5mm cable from house could carry 20A depending on installation method… One issue is what is feeding this 2.5mm cable and distance between house and garage.

It should be rcd protected, and if not… the board in the garage needs to incorporate rcd protection.

 

[timhoward]

Exactly as @littlespark said. Main questions being:
What is the circuit breaker rating for the garage circuit in the house? A photo of this consumer unit would help.
Is this an RCD protected circuit?
What is rough length of circuit?

My gut reaction is that this will probably be ok from a loading point of view as the heater, coffee machine, and fridge will cycle on thermostats. While you wouldn't do it like this if starting again, subject to answers above it should meet the needs.

My advice is to pay a sparks for 2 or 3 hours to IR test the current wiring garage supply, confirm the total earth loop impendence (making sure it will trip the house breaker in fault conditions), and stick a modern garage consumer unit in. It's not a big job.
(You'd also get an installation certificate and building control notification certificate which helps if you ever sell the house.)

 

[LHensh]

The 2.5mm cable from house could carry 20A depending on installation method… One issue is what is feeding this 2.5mm cable and distance between house and garage.

It should be rcd protected, and if not… the board in the garage needs to incorporate rcd protection.

Yeah the board in the house is RCD protected. May well have someone replace the fuse board with something a bit more up to date. Not sure if they'd put a second RCD on the garage end or of that would be counter intuitive?

Hard to say the length of cable run from house to garage as it not clear where/how it runs, but I expect it will be 10-15 metres

 

[littlespark]

There is no benefit of having 2 x RCDs,one at source and one at garage… If there’s one at source already, that’s fine.
The cable feeding the garage may demand it anyway.

The sub main fuse board in the garage needs replaced though.

 

[LHensh]

My advice is to pay a sparks for 2 or 3 hours to IR test the current wiring garage supply, confirm the total earth loop impendence (making sure it will trip the house breaker in fault conditions), and stick a modern garage consumer unit in. It's not a big job.
(You'd also get an installation certificate and building control notification certificate which helps if you ever sell the house.)

Thanks, this is exactly what I was thinking/hoping would be the case.

I have attached pictures of the board. The garage supply runs off the far right breaker which is also used for the kitchen sockets.

From there it runs to a module faceplate (not sure on correct term) which has a switch dedicated to the garage supply.

 

[DPG]

That puts a slightly different slant on it if all your kitchen stuff is fed from the same circuit as your garage feed.

 

[littlespark]

Yes… that’s more of an issue. It’s now a spur from an ring final circuit and not a radial from source.

Quite a lot of high power items from that one switch bank already.

 

[DPG]

Is there an easy route from your consumer unit to the garage? I'm thinking probably not and that's why the feed was taken from the ktichen grid switch.

 

[LHensh]

Unfortunately no easy route to the garage from the consumer unit.

How much of an issue would it be having my planned usage run through the setup as it stands?