Temperature Limitation of Conductors

[mjc1060]

I have a question regarding conduit on rooftops. 310.10 Temperature limitations of Conductors Table 310.12[a] and 310.13[C]2008 NEC. My question is does any body know if there is a recommended distance off the roof to maintain air flow. Further if you raise the conduit[say mounting it on a 4"X4" piece of wood]will this affect the ambient temperature of the conductors in the conduit[in this case sealtight]. I live in Chicago Il. and this is only an issue in the summer months.:?

 

[infinity]

A 4X4 gives you 3.5" above the roof deck. What does the table say about 3.5"?

 

[Dennis Alwon]

I certainly think that the ambient temp. on a rooftop should be considered even if it is 3.5" of the ground. Table 310.15(B)(3)(c) in the 2011 gives that info. Here is a nice product from arlington. Just set it on the rooftop

 

[cycotcskir]

Here is a good article on the issue.

http://www.iaei.org/magazine/2009/0...sure-on-ambient-temperatures-inside-conduits/

 

[fmtjfw]

What about winter only?

What about winter only?

If you have a unit on a roof that is only used in the winter (electric heater for instance), can you use the max winter temperature as the base to derate the rooftop conductors? Or do you still need to use the yearly peak temperature?:huh:

 

[Smart $]

If you have a unit on a roof that is only used in the winter (electric heater for instance), can you use the max winter temperature as the base to derate the rooftop conductors? Or do you still need to use the yearly peak temperature?:huh:

IMO, environmental heat-only rooftop circuits do not need to be ambient corrected at all for the roof-top. Assuming the circuit originates inside, the heating units run to maintain an ambient temperature inside higher than outside, thus making the inside portion of the circuit have a lower ampacity.