GARAGE - SPLIT LOAD CONSUMER UNIT

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leerichards3500

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Hello all.

Im in the early stages of re-wiring my garage to encompass a split load consumer unit as im adding an outside light and outside double socket (IP55) to my decking utilising the existing feed from my house to the garage(which has been wired in proffesionally). I have prepared the outside light wiring and i am about to start on the socket. My questions to the forum are these:

1, Are there any legal requirements for the height of the outside socket from the floor of the decking? Or any other requirements that i need to be aware off?

Also

2, Are there any legal requirements for mounting/location of the Consumer unit? Ie: Height from the floor etc.....

I have a good friend who is a competent electrician, (Although not qualified), and before the project can move forward, he needs to know the ins and outs of the legailities first.

Any help or guidance would be appreciated.

Thank You

Lee
 
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Unless you start looking into disability access regs then I don't think there are any laws as such regarding heights.
They have to be high enough up so it isn't detremental to them, such as them getting flooded or bashed.
Also this work is notifiable to your LABC under part P of the building regs.
 
why split load? If theres only two circuits, fit a 4-way unit with a mainswitch and an RCBO for the circuit you need protecting.

I'll find you a picture of mine.
 
Cover on:
DSC00844.jpg


Cover off:
DSC00839.jpg


This is cheaper than a split load, because your only paying for an RCBO instead of both an MCB and RCD.

The lighting needn't be RCD protected (theres a safety issue with it being protected). The cable to the garage needn't be protected either (you may well find it is - check this)
 
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Hello

I decided to use the split load as i was advised to RCD protect the two outside circuits separately and use the main MCB's to protect the further 3 circuits within the garage, (internal lighting, security lights, 2 x wall sockets). Is that ok?

Can you please explain the safety risk regarding RCD protecting a lighting circuit?

Thank you

Lee
 
You may well find that you DO need RCD protection on the lighting circuit. If it is surface wiring, which you often have in a garage, then you probably won't.

There's nothing wrong with using a main RCD in the garage CU. The safety implication is that if there is an electrical fault or a fire, the lights may go off due to the RCD tripping. Not normally a big issue in a domestic garage. In your house, you shouldn't install whole-installation-RCDs because of the complications of the lights going off in the event of a fire.

If you're bothered about this, then fit an emergency light fitting somewhere, or fit two RCBOs. (Or, as you are suggesting, a split load board. This will be OTT, but nothing wrong with doing it.) But you MUST employ RCD protection on all of the socket circuts, indoors or outdoors. I would suggest putting all sockets on one circuit and alll lights on another. You can use an RCD garage board for this purpose, or a dual split load board, or RCBOS!
 
leerichards3500 said:
I decided to use the split load as i was advised to RCD protect the two outside circuits separately and use the main MCB's to protect the further 3 circuits within the garage, (internal lighting, security lights, 2 x wall sockets). Is that ok?
Click to expand...
The two internal sockets will also need RCD protection.

leerichards3500 said:
Can you please explain the safety risk regarding RCD protecting a lighting circuit?
Click to expand...
You are using a circular saw. It develops an electrical fault. The RCD protecting both your lights and this saw trips. You are now in darkness with a spinning blade in your hands. You're startled as the lights go off, so you jump up. . . . What happens to the saw?

Even worse if the lights are RCD'd on their own, and the saw continues.
 
Thank you all for your replies.

I have a two further points which need clarification:

The armoured cable supply from the house to the garage is terminated 1 metre too short from my consumer unit. (Power to the garage was an existing fit), what is the best method of extending the armoured cable in order to supply the consumer unit.

Also

Will i have to upgrade the MCB in the main consumer unit in my house supplying power to the garage to 32A. At present it is 16A?

Thank you for your advice.

Lee Richards
 
1.5mm SWA for lights and sockets!! I think, but have left my books in the van that you need a bigger cable, I'm sure Rob or someone will clarify this
 
2.5mm^2 SWA underground is rated 29A assuming no other derating factors, so a 32A MCB is out of the question.

Due to voltage drop limits the maximum current down that length of 2.5 SWA feeding a lighting circuit is about 19A - and that's without allowing for voltage drop in the garage wiring.

So technically 16A MCB is the maximum due to VD but IMO you'd be OK with a 20A MCB as it's very close and the Zs should be well within the 2.4R limit for 20A type B even assuming Ze of 0.8R.

But your electrician friend should be able to work all this out!
 
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