Garage installation - cable size and run.

DoBBY · Feb 24, 2011

I am putting ring and a lighting circuit in a garage.

20m from house DB to garage CU. Can I use pvc/pvc twin and earth from house DB to a designated JB at the end of the house (10m), then terminate SWA at that JB to the garage CU, (10m)?

Is there a JB available which will incorparate twin and earth to SWA?

Also would this have to be wired in 4.0mm SWA or could 2.5m SWA be used? The load on the ring is never going to be upto 32a as the sockets are only going to be used for a radio and a hoover etc. In this case would a radial circuit be better?

Thanks

Deleted member 26818 · Feb 24, 2011

Use what is usually known as an adaptable box as a JB with some terminal strip, this will allow both the T&E and the SWA to be made off.
Some I believe ALTO from either CEF or WF come with a terminal strip that clips inside.

If you intend having a 32A Ring Final Circuit at the end of a distribution circuit, you would normally use 6mm².
2.5mm² T&E has a current carrying capacity between about 13.5A and 27A depending on installation methods, the SWA between 29A and 31A.
4mm² T&E has a current carrying capacity between 17.5A and 37A, again depending on installation methods, the SWA between 37A and 41A.
Might be able to use 4mm² T&E with 2.5mm² SWA.
Do you intend using a Consumer Unit at the Garage?

You could run it as a radial circuit, and use an FCU in the garage for the lights, obviously you would have to choose an appropriate Circuit Protective Device, depending on the current carrying capacity of the cable you choose.
You would of course in any event be required to provide RCD protection for the socket-outlets, and perhaps for the T&E feed to the garage, again depending on installation methods.

DoBBY · Feb 24, 2011

There is a spare on the RCD side of the DB at the origin of the installation, where I intend to put the breaker protecting the garage circuit. I am just trying to get an idea on the best way to do this as the sockets do not really need to be on a 32a breaker as they will have minimal use.

So I may put a radial in on a 16a breaker and lights on a 6 amp breaker, so maximum demand would drop rapidly to 22a.

Its for my full scope Napit assessment so want to get it bang on!

i=p/u · Feb 24, 2011

just take from mcb40amp in house to junction box in t&e then swa to garage 4 way board with rcd and 32amp and 6amp

somersetsparks · Feb 24, 2011

I would put in a 2.5 Circuit on 20A breaker. The you can put a 16a on the skts. and a 6a for the Lights. Or just take it into a fcu for the lights with no DB. Were you planning to stake down the garage seperate!

Hawk81 · Feb 24, 2011

We had to have the earth spike question! If it were me i would run in a bit of 4mm T&E to the joint box then 4mm SWA to garage. Put this on a 32amp mcb. this will leave you plenty of power out there without being over the top. Leaves a bit of room for future proofing it.