Electrical wiring in shed & heat damage

[stuarbr]

Hi,

I'm installing a new shed in Brisbane made with colorbond. Obviously it will get quite warm inside so will be insulating with appropriate materials - probably foilboard. The question I have is with regards to running electrical cabling inside plastic conduit next to the colorbond and/or insulation. The heat insulation works best with a gap between it and the colorbond. Can the wiring safely be run inside conduit, inside the gap? It will get quite warm here, will this damage the electrical insulation?

If this is not a good idea, I'm open to any other practical solutions....

Thanks

 

[telectrix]

you would need to derate the cable's capacity due to the insulation. e.g. if your current demand is 25A, 2.5mm cable would normally suffice, with a ccc of 27A, but this might be down to 15A due to insulation, so maybe 4.0mm or 6.0mm cable in yur case.i nt UK we have tables showing derating factors dependent on the installation method.

 

[stuarbr]

Thanks, I'm happy to overspec the cables to 4/6mm for outlets, and can use 1.5mm to led lighting. I'm also concerned about the longevity of the insulation (& conduit) being located in closed conduit, in relatively high temps for X number of years. I'd assume no more that 1x6mm or 2x4mm cable in a single 25mm conduit?

I'd appreciate further info on these or any other factors that may influence the installation.

 

[Marvo]

If the ambient temperature between the colourbond sheet and the insulation is going to get over 60 Celsius in the sunshine then I wouldn't install the conduit and cabling there. In hot climates prolonged temperatures over 60C will degrade the cable prematurely. PVC cables are rated to 80 - 90C and in cooler climates they'd only normally reach anything close to these temperatures for short periods under extreme load conditions.

We have the same problem in Africa where I've seen PVC insulated cables installed in the air-void between chromadek roof sheet and 50mm high-impact polystyrene insulation sheets and they've become brittle after less than 2 years.