4 core SWA - 2 circuits OK?

[diy_dude]

Hi,
I have run about 10m of 4 core 4mm2 SWA from an existing shed to a new shed. I would like to use two cores for a socket, 2 cores for a light and the armour for the earth. I will connect the cable to the light and socket at one end, and to the CU in the shed at the other end, a 6A MCB and a 16A MCB. Does this sound OK? Is the shared earth over the armour OK?

I have Part P notified to LABC along with other electrical work.

 

[700mb]

im not to sure about running the 2 circuits down the same swa.
but im quite sure that the armor wouldnt be a decent earth for the 2 circuits.

in my opinion id say no

 

[fattony]

Spot on, years ago the armour was just used as the earth but these days when using SWA you buy 3 core instead of 2 core (1 core for the earth) Unless you intend running a seperate earth?

If I was you then I'd use the SWA to feed a socket and a fused spur outlet, on a 32A radial, once inside the shed the lights can be wired from the load side of the fused spur outlet, remembering to drop the size of the fuse down.

 

[Spark123]

On the grounds of a single point of isolation, I wouldn't do as described. It would be better to have a small consumer unit at the shed.

The armour of SWA is quite OK to use as an earth providing it meets the correct criteria i.e. if the ratio of the K factors for copper and the armour multiplied by the CSA of the armour is equal to or greater than the requirement for table 54G then it is fine. Some info here //www.diynot.com/wiki/electrics:swa-earthing. Using a spare core of the SWA as an earth will comply with table 54G and saves on maths!! Also, the adaibatic equation can be used.

 

[CallEdsFirst]

On the grounds of a single point of isolation, I wouldn't do as described. It would be better to have a small consumer unit at the shed.

Agreed, but a 4 pole isolator would do the trick!