Garage Electric Help

[xraymtb]

Home electrics question - feel free to move this if I'm in the wrong place!

Looking to add a few more sockets to the garage - currently a double socket running on a spur from the kitchen ring main. There is an FCU in the kitchen so I understand I can continue the spur safely as the total load will be protected by that FCU.

Where I am confused is at the garage - there is a single switch and an FCU where the cable enters the garage. The cable goes into the switch and then on to the FCU - within the FCU there are two cables exiting - one for the lights that runs off the LOAD terminals, and one for the socket that runs off the IN terminals. So only the lights go through the fuse?

As the spur runs through the FCU in the kitchen it is all protected but I'm confused by the garage setup.

 

[n0legs]

My guess, and without seeing it in person that's all I'm going to give you, is the FCU in the garage was installed to drop down the fuse size for the light.
I would imagine in the Kitchen FCU it's a 13A fuse and quite possibly in the garage FCU it's a 3A or a 5A fuse.
Pull the fuse in the garage FCU to confirm my reasoning, if the light goes out and the socket stays on that's the set up.
The FCU in the kitchen is the limiting device in this installation. If the total load in the garage goes over 13 amps the fuse might fail.

Hope this helps.

 

[xraymtb]

Makes sense - I just presumed it was a 13A in the garage - will check tomorrow. The garage FCU is definitely lights only.

 

[Woody2Shoes]

It's a while since I carried all the details in my head, but from memory, a spur from a ring final circuit can only have a maximum of one socket on it.

Re. the garage, maybe if you post a photo?

Cheers, W2S

 

[LancsRick]

That's my recollection of the regs too Woody.

 

[flying haggis]

I thought a spur fed from a FCU can have as many sockets as you like as the overall load cannot be more than 13A

 

[xraymtb]

The understanding I had from reading is that, as it is a fused spur, there isn't a limit on the sockets as the entire installation is protected at 13A, well within the rating of the wiring. Obviously I need to be aware of that limit or could end up standing in a dark garage when the fuse goes!

I'm not sure it's the recommended way to do it but isn't against regs?

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[LancsRick]

Seems logical, and I'm dredging my memory for the regs anyways.

I'm confused by your description of the FCU though. What you should have is the supply coming to the IN terminals, so in your diagram the switch would then connect to the IN terminals. the totality of the garage (i.e. socket and light) should be fed by the N Load and L Load terminals from the FCU.

If that's the case then by all means hook into the FCU. Be aware though that 13A isn't much if you're adding sockets (plural) for use in a workshop environment.

The other thing to check if you're on an FCU at the moment is that a large enough cable is run for 13A. From memory (again) it should be 1.5mm2 minimum if it's clipped and exposed to air (i.e. not embedded or in a conduit), otherwise 2.5mm2.

 

[xraymtb]

There are two FCUs, one at the kitchen end and one at the garage. So the kitchen one protects the entire spur, the garage protects the lights only at present. As n0legs suggests I think this is to reduce the lighting circuit to a 3A fuse.

I'll check the cable to be sure but it looks heavy, maybe even more than 2.5mm.

The new sockets are to save trailing extensions around the garage, wouldn't ever run more than one machine and a shop vac or air filter.

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[n0legs]

Is this a detached, attached or an integral garage Mike?

 

[xraymtb]

Detached. It's a townhouse with the garages around 15m away. That's the reason I'm limited to the single spur that is already there!

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[Arron]

Detached. It's a townhouse with the garages around 15m away. That's the reason I'm limited to the single spur that is already there!

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If it's a detached garage, it should 'by the books' have its own independent supply direct from the main consumer unit. I suppose it depends on what you are using in your garage as to whether or not it's worth doing it properly, how is the cable protected between the house and the garage?

 

[Woody2Shoes]

I'm wondering if there's potential confusion over what "FCU" is referring to here, is it a:

- 'Fused Connection Unit', intended to allow a fused 13A spur off a ring final circuit for a fixed appliance e.g. wall heater, like this: http://www.screwfix.com/p/mk-13a-dp-swi ... hite/13479

- or is it some kind of switched consumer unit "CU" that may or may not contain fuses/MCBs etc. e.g. like this http://www.screwfix.com/p/mk-sentry-4-w ... itch/6885g

I would have expected to find the latter in the garage, fed from a separate circuit (probably in buried steel wire armoured cable) out of the main domestic CU.

Cheers, W2S

 

[xraymtb]

It's the first - a fused connection unit, definitely no consumer unit for the garage. I'm presuming it's a spur as the FCU is in the kitchen by the back door and the main consumer unit is by the front door - I suppose it could be an independent supply, will need to check the breaker labels properly.

I've no idea how the cable is protected, it's not visible at the house end and comes out of the concrete slab in a thick black plastic looking sheath.