Cable Derating due to Exposure to Direct Sun Light

[MagnusElec]

What are the rules NEC etc. for derating of cables exposed to direct sun light?

I intend to install three conductor cables -- low and medium voltage, in uncovered cable trays outdoors -- where the typical maximum ambient temperature is specified to reach 110 °F or ~44°C. I derate the cables in the usual manner due to this temperature but what additional derating is required due to the exposure to direct sunlight?

I came across one document for a specific installation for a pulp and paper mill in Canada (my installation is in Utah, US) that specified derating due to the exposure of direct sun light. Supposedly, the latitude of the installation site should matter too.

Thanks for your input, Magnus.

 

[dpc]

See Article 310.10, and FPN No. 2. You would be expected to exercise good engineering practices to limit the maximum temperature of the cable.

 

[controlsdude]

If you have exposed cable laying in a tray, do you spec out sun resistant cables? I remember a job where I had to use cable tray rated cabling that was oil, water, and sun resistant.

 

[RRaghunath]

It is a practice to cover the cable trays, in case of direct exposure to sun rays.
More than the temperature, it is the ultraviolet rays in the sun rays which can adversely affect the cable insulation by breaking up the bonds in the chemical chain, on prolonged exposure. Generally, cables with black outer sheath are expected to be ultraviolet resistant.