Cables in dry lining insulation

[tireetim]

I've got an extension which has been dry lined with timber stud work and plasterboard and the gap between the wall has been stuffed with loft insulation. The electrical cable for the sockets is running down from ceiling level and clipped against the solid wall but the insulation is ontop of this. Is this ok?

 

[EFLImpudence]

With that method of installation 2.5mm² cable is derated to 21A so not a problem on a Ring circuit - or a Radial circuit protected by a 20A mcb.

 

[tireetim]

Thanks EFLI, just checked - it's on a 20A mcb so no problems then.
Tim.

 

[tireetim]

Just out of interest, what would 2.5mm cable be derated to if completely buried in insualtion rather than clipped to a solid wall (such as in the centre of a partition wall)?
Thanks.

 

[Chri5]

The key to this is the word "insulation", cable can get warm near full load and the makers tend to give it a operating temp in open air (which will have a cooling effect).

So a cable not in open air tends to need derating, insulation being one such derating category. Others include in trunking, conduit, in plaster.

There also derating for grouping, so a bundle of cable together will also require a derating factor.

 

[Scoby_Beasley]

@tireetim
I get that as Ref method 103 which would cut it down to 13.5A

 

[tireetim]

Thanks all.
Scoby, if that is the case can I just clear away the insulation for a few inches around the cables to keep the 21A rating?

 

[Scoby_Beasley]

Thanks all.
Scoby, if that is the case can I just clear away the insulation for a few inches around the cables to keep the 21A rating?

I'd have said no. Its the being attached to the boards / stud work that allows it to dissipate the heat. Who's to say that your nicely cleared hole doesn't collapse back in on itself and enclose the bottom 2/3's again?

Ref Method A (enclosed in conduit in an insulated wall) will push the rating back up to 20A (airspace around cable). Whether this can be plastic conduit I'm honestly not sure! But that would keep the insulation away from it.

 

[EFLImpudence]

You don't need to keep the insulation away if, as said, the cable is clipped to the wall.

 

[tireetim]

Yes but in the case of a partition wall where the cable wouldn't be clipped to a solid wall?

 

[Scoby_Beasley]

I'd try the conduit method, if you can get it in!

Otherwise 4mm cable would give you 17.5A and 6mm cable would give you 23.5A