Garage re-wire

1 Jun 2011
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United Kingdom
Hi I wonder if anyone can advise me.

My garage currently has this set up:

Power in 1.5mm armoured cable travelling 29ft underground from Consumer unit in house. MCB on Consumer unit in house to garage is 6 amp (and keeps tripping)

In garage I have a consumer unit with a 25 amp RCD, a 20 amp fuse for sockets and a 5 amp fuse for lighting.

The garage has a total of 6 flourescent lights, 3 double 13 amp sockets, and two light switches.

The lighting circuit is running with 1.5mm cable and the power circuit with 2.5mm cable. All are earthed to a busbar in the garage consumer unit.

What I would like to do is replace the consumer unit in the garage with a new one including MCBs instead of fuses, and run new wiring for the lighting and power. Also I believe the 6 amp MCB in the house is too small and would like to know what rating I should change that too.

Can any one give me a spec to work to?


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That 29 foot of cable needs to be replaced, either by an electrician or by yourself with prior notifying of LABC.
As stated, your supply cable is wrong and needs replacing before you do anything else.
What is the Ze at the garage?

How much power do you draw at the garage?

You may get away with using the existing cable with a 20A fuseswitch at the house, and FCUs for the lights (3A) and sockets (13A) in the garage.

1.5mm² SWA is OK at 21A under ideal conditions, but you'll need an electrician to assess the installation method (if accessible), as there may be derating factors involved.
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Thank you all for your comments on this. Unfortunately the SWA 2 core 1.5mm2 cable can not be replaced as it is underground, and I don't want the aggro of trying to replace it. So I must work with what I've got.

So I need to work out the max power output in the garage, and go from there. Thanks again.
Assuming your cable is actually 1.5mm then it should be good for 22A (playing safe that it is pvc/pvc not xlpe).

Voltage drop should not be an issue over 29ft (10m rounded up)

Unfortunately you cannot just go uprating protective devices without checking certain criteria eg earth fault loop impedance and I would also be particularly weary about the earthing as this is 2 core so it will need to be checked that the armoured glands are made off correctly to ensure continuity - this is essential.
This will involve expensive test equipment which any decent electrician will own, so for peace of mind I would involve a competant one.
The armour off the cable has been twisted and inserted in the earthing bar in the consumer unit in the garage.

And the garage is currently running plastic plug boxes.
The armour off the cable has been twisted and inserted in the earthing bar in the consumer unit in the garage.

Not the correct way to terminate SWA - how about the supply end ?

And the garage is currently running plastic plug boxes.

That doesn't make the slightest bit of difference - each outlet still requires a satisfactory earth connection whatever it is made of. Remember most appliances that get plugged in still require an earth
You want to have an IR test done on that cable at the same time too.

If your lucky it could be that some numpty who clearly doesnt have a clue has changed the wiring from just a light (which I beleive it would have been) and bodged in a consumer unit and sockets. In which case this can prob all be rectified.
Thanks for all your comments guys.

I have just looked at the SWA cable into the CU in the house and the Armour (which is connected to the earch bar on the CU in the garage) has just been taped up and not connected to anything. So in essence the whole of the garage is unearthed. (If my thinking is correct)

So I think i am going to start from scratch.


3 twin sockets
wired using twin and earth 2.5mm2
Max power draw needed = 2.1kW

6 flourescent tubes
wired using twin and earth 1.5mm2

New 2 way insulated consumer unit with 63 amp RCD
6 amp MCB for lighting
20 amp MCB for power

New SWA cable:
4mm 3 core XLPE clipped over ground running through three walls

Breaker in House CU to be uprated to 32 A

All lighting and power cables in gargae run together in 25mm PVC conduit

All Plug and light sockets metal and earthed.

Please can you let me know your thought on this.



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