Garage electrics

I have a dethatched garage which currently has a small 2-way CU - 100amp Main Switch, B6 for lights and B16 for sockets.

(Pic attached).

We are doing a basic conversion on the garage into office space. Meaning I'll add probably 1 additional 2-gang socket.

We will be running some office equipment plus 1 or 2 electric heaters from the space, nothing to meaty.

Lighting-wise we wont be adding to the load so sure the B6 will be fine.

Sockets-wise I'm concerned we may overload it a bit.

Since we have a 100A Mains Switch, should the B16 be able to be switched out for a B32?

Any advice appreciated.

Thanks,

Where does the supply for this come from (any upstream protection?)?

Actually there is a 13A fused switch on the inside of the kitchen (where the garage feed leaves the house) - this isolates the garage.

Unsure how to find out where the feed comes from. I initially thought main house CU, but there is nothing marked for 'Garage'

jamesponge007 said:

Actually there is a 13A fused switch on the inside of the kitchen (where the garage feed leaves the house) - this isolates the garage.

Unsure how to find out where the feed comes from. I initially thought main house CU, but there is nothing marked for 'Garage'

Click to expand...

In that case it was installed by an idiot. There is no point in having a 16 amp MCB fed off a 13 amp fuse. Even less point in having a 32 amp MCB.

Yeah. Posting this thread promoted me to check the internal fuse, to find its 13A. Was installed by the developers ... hmmm

What size heaters do you what - a couple of 1KW?

2 x 1KW heaters is approx 8 amps
Computer and screen maybe another 2 amps

So that 10 amps on a cold day. Assuming you don't have a dryer / freezer in the garage then you should be okay on what you currently have but it's getting a bit close.

I would like to understand where this spur is off. If it's a kitchen ring then you're adding another 10 amps onto that circuit which might cause issues - and they are heaters so it's a continuous load not a burst.

Also - what cable have they used to get the power to the garage? You say it's a detached garage so I'm assuming it's buried. I'm hoping they used SWA but the driving a sub-CU off a spur from an existing circuit makes me wonder.

Personally I would run a separate circuit from the main CU on a 20 or 32 amp. Find a sparky that's happy for you to do the drilling / digging the trench and it shouldn't cost a lot. If you add the sockets onto the existing power circuit in the garage before they come (you're allowed - it's not notifiable) then the sparky would test as part of their testing of the new feed to give you some piece of mind (they won't give you a cert or anything like that - but they have to make sure it's safe because they've changed the design of the feed to the CU)

Thanks for that - all makes sense.

I think even if I can get away with the current setup it would be by the skin on my teeth ... so most probably not wise.

I've attached a pic of the cable from house to consumer - although is this just the conduit, so hard to tell ... ?

That's an Armoured cable how is it connected at the house?

Through wall and straight into a 13A fused socket ... but I'm a bit unsure what feeds that ...

One other thing - remember that building regs and maybe planning will come into play if your conversion is going to be permanent. If this is just to escape the kids / significant other during lockdown then I suspect no-one will care - but if you want to make this a permanent office then give a quick call to your local building and planning departments. It's a lot easier (and cheaper) to get these people on side first. You will still be able to do the building work yourself - but they'll inspect and signoff if required so avoid issues when you come to sell your house.

jamesponge007 said:

I've attached a pic of the cable from house to consumer - although is this just the conduit, so hard to tell ... ?

Click to expand...

The armoured cable (in your picture) will probably have the cable size embossed on it. It may say something like 3x2.5.
What does yours say?

jamesponge007 said:

I'm a bit unsure what feeds that ...

Click to expand...

Turn off each circuit in turn at the house consumer unit until the garage power goes off.
It will probably be one of the socket circuits.