Garage wiring

[eds_taff]

Hi

I am in the process of wiring out my new garage and I am not sure on a few things.

The cable that is run from the house is a 2core SWA 10mm cable, this is joined in a junction box at the house where 10mm twin & earth is then run to a 40A mcb at the fusebox.
What sort of earthing arrangements do I need to have, considering there is no earth conductor apart from the armour of the cable? Is this sufficient? The house is of a TT design with an earth rod outside. Do I have to install another earth rod at the garage?

The other question I have is regarding the sockets in the garage, I am using 3core 2.5mm SWA on a ring circuit fed from a 32A mcb, and metal clad socket outlets. Do I *have* to use the earth rings (banjos) with the SWA cable glands at the sockets? Whenever I have seen metal clad sockets used with SWA cable before, I have noticed that the earth rings have not been used.

Thanks for any help

 

[Steve]

With metalclad sockets, my understanding is that as long as the sheath of the armour is earthed, you dont need a banjo. however, you should run an earth from the backbox to the socket face.

 

[Maxxy]

The banjo does have a use as a 'washer' though. Some Armoured glands are a bit cack and dont completely fill the hole because of the shape of them.

 

[eds_taff]

Great.

They are decent glands, I *acquired* them from work. I have earthed the socket and the backbox so that should be sufficient then.

Oh yeah, the two core SWA that is run to the garage was already in the ground when I moved into the house, I MEGGARed it out and it was fine. If it was me I would have run a 3core cable, would this have been better? Is there any need for it to be 10mm also, as the run is only around 7 or 8 meters at the most?

 

[RF Lighting]

If it was me I would have run a 3core cable, would this have been better?

Providing the SWA is PVC insulated then there is no need to use 3 core or run an additional earth wire, but many electricians like to do so 'to be sure'

SWA Earthing

Is there any need for it to be 10mm also, as the run is only around 7 or 8 meters at the most?

Depends entirely on the intended load in the garage.
I have a 16.0mm² SWA suppling my garage

 

[eds_taff]

Fed from a 40A mcb in the house, the garage cu has one 32A mcb for a ring circuit and one 6A mcb for the lights.

Probably use a heater in the winter, and also various power tools and maybe a welding set.

 

[RF Lighting]

10.0mm² sounds like an entirely reasonable sized supply for your intended load.

You may want to consider wiring a dedicated socket from the garage CU for your welder, and use a type 'D' MCB, as welders often trip standard MCBs when first switched on.

 

[eds_taff]

Thanks, I did not think of that.
The problem I have though is that there are no spare ways in the cu.

Another question, if I use the armour of the 10mm cable as the earth, when I terminate it at the garage cu what size tail should I use between the banjo and the earth terminal in the cu? Would it be 10mm also? How would you calculate this?
I am asking because I have seen (this is not diy stuff I know) bigger SWA cables used before (120mm, 4core) for 3-phase applications and they used the armour as an earth. But when the cable was glanded at the panel or whatever, there was only a 35mm earth lead run from the banjo to the earthing terminal in the panel. Is this sufficient, does the earth not have to be the same diameter as the live conductors?