Thermal/acoustic insulation and cable derating

Personally I'd say yes, because both types of insulation hold still air in a trap. Therefore, derate the cable by around 1.5 - 2 % per 10 mtr length within the insulation. If the length through the stud is only a couple of metres or so, then ignore the derating.

In article , BigWallop writes

Thanks for that.

As regards the length of cable going through the insulation, presumably I just need to look at the longest run through any insulation not the total in all parts of the cable.

Cheers

Martin

Yes. If the cable is passing through anything less than 3 mtrs of insulation, forget the rule. But only if it's one run of up to 3 mtrs of insulation. Any more insulation on the same run of cable, the whole run of cable needs to be derated.

An example. If the total cable run is 12 mtrs, of which 2 mtrs are buried in the insulation. Forget the derating. If the total run of cable is 15 mtrs, of which 10 mtrs are buried in the insulation. You have to derate the whole cable run.

If you have 50mm in insulation the cable is derated by about 10%. 500mm derates it by 50% Further length doesn't increas tis figure.

For accurate figures see the On Site Guide.