[czars]

Does anyone know where we can obtain official ambient and attic temperature information which can be used to compute the derating of NM and SE cables in attics with insulation?

 

[Dennis Alwon]

I doubt you will find that info. Here is the closest I have found

http://www.copper.org/applications/electrical/building/pdf/rooftop.pdf

 

[Dennis Alwon]

The problem I have with this is the term ambient. Ambient temp. is not average temp, it is not the highest temp, and it is nothing more than the temp at any given moment.

The ambient temperature is a non-specific phrase used to describe the outside temperature. When taking the temperature with a thermometer, you are getting a general idea of the temperature of the surrounding air without taking into account the daily maximum and minimum temperature. Ambient temperature also does not take into account the humidity or wind in the air. The amount of moisture (mugginess) or humidity in the air can create higher temperatures which will cause the heat index to increase. Winds can also play a role in how cold a temperature will feel to a human. The wind chill factor can cause the air to have a perceived lower temperature.

 

[czars]

Attic Temps

Thanks Dennis. I also found some info from the Florida Solar Energy Institute (http://www.fsec.ucf.edu/en/publications/html/FSEC-PF-336-98/) where they measured attic temps in Florida from houses with different types of roofs. It's interesting how much variation there is.