Using twin & earth for sub board

[JakeC]

I've been wiring up my shed and just want to check this is acceptable..

A SWA cable is ran from the CU to the shed (about 10 meters) but where it enters the shed is too short so my plan is to run a normal twin & earth from a junction box to the subboard (2 meters). Simply to save me buying more cable.

Assuming that measured earth loop impedance below maximum would this be ok? I'm only running a socket and light off a 6amp mcb.

 

[telectrix]

what size SWA? what size T/E? whatever the cpc size is in the SWA, you want to keep it the same csa ti the sub.

 

[malcolmsanford]

Yes you should be OK. Provided as you say you prove your CPC size is ok with the T + E which it should be really.

Personally I would rather get a small piece of PVC conduit terminate the SWA into an adaptable box and Klippons, then conduit from box into CU .....................IMO just looks the job

 

[DurhamSparky]

socket off a 6A mcb??? you will find soon as you power a drill/lawnmower up it will pop!! install in 2.5mm and use a 16A mcb

 

[JakeC]

The SWA is 2 core so the screened will be the cpc, the t&e is 2.5mm..

The socket is purely for a radio but if the earth fault loop is low enough I can always stick a higher rating one in

Thanks for the replies

 

[Octopus]

Hum, its always best to use 3 core SWA and next time do better calcs on the load and length to avoid such mishaps. If you've got a CU in the shed why don't you spend another £4.00 and buy a 16A MCB?

I take it you're a sparky and will be doing this for paying customers!!

 

[telectrix]

what i would do, then, where you join the SWA to T/E, is to run a 6mm cpc single to the sub, rather than relying on the 1.5mm in the T/E. that should also reduce your EFLI. and i would go with a 16A at source.

 

[JakeC]

It's my old folks house, using it as one of the jobs to get registered providing i've passed the 2391!

The SWA was ran years ago while they were having work done so going to have to make do, i'll know to run 3 core though if i ever do one

Good idea too for the 6mm, it won't be much extra work and gives peace of mind. Cheers

 

[Octopus]

Why don't you register without the 2391?

 

[telectrix]

and make sure you gland the SWA correctly and use banjos. 1 thing you ain't yet made clear, is where is the RCD protection. ? is it in the CU or are you fitting it in the sub?

 

[JakeC]

I was going to register with NAPIT who say you must obtain 2391?

I've fitted the glands so all nice and secure now. There was a 15 mark question on a SWA in on the 2391 I would have got full marks now :stuart:

RCD protected at main board and the sub board

 

[Octopus]

RCD protected at main board and the sub board

Hum, values of the RCD's??

 

[telectrix]

you don't want 2 30mA RCDs in series. if there's one in the CU, ditch the garage one.

 

[JakeC]

63A 30mA at main and 40A 30mA

Edit : Just done some research and see the most sensitive will trip first

 

[rich.250]

They are the same sensitivity....