What derating table do I use for multicore armoured thermosetting cable in insulation.

Taking submain through loft of a house, I think it only needs to be rated at 60 amps, 80 amps would be nice. But ideally don't want to be fighting with 25mm swa cable, I have found out the hard way that it makes life very difficult, getting it through the house and also routing inside a fused switch.

At the moment thinking that buried in insulation a 16mm 3 core cable would probably have a capacity of about 60 amps. Looks like I will have to clip to batons screwed on to roof beams to keep the cable clear of insulation, still easier than fighting with 25mm cable.


A 16mm 70 deg C thermoplastic cable is rated at 57 amps with reference method 100. I have seen plenty of domestic consumer units supplied with 16mm twin and earth and never seen any heat issues.

 Therefore thinking 16mm swa would be good enough, your thoughts.

Parents
  • Hi Alan, why are you using SWA ?

  • I have to cut a hole next week to double check, but I think the cable is running less than 50mm from the surface of a cupboard built in to the roof space. As far as I can see the cable is sitting in or very close to the eaves of the roof,  the cupboard is built so that it also goes as close as possible to the eaves. There is a good chance that there's just 9mm of plasterboard between the surface of the cupboard and the cable.

    Life would be much easier and cheaper for the customer if I could just leave the existing 16mm twin and earth in place.

Reply
  • I have to cut a hole next week to double check, but I think the cable is running less than 50mm from the surface of a cupboard built in to the roof space. As far as I can see the cable is sitting in or very close to the eaves of the roof,  the cupboard is built so that it also goes as close as possible to the eaves. There is a good chance that there's just 9mm of plasterboard between the surface of the cupboard and the cable.

    Life would be much easier and cheaper for the customer if I could just leave the existing 16mm twin and earth in place.

Children
No Data