I have exterior 3/4 metal conduit for my PV wires that'll be getting direct sunlight exposure for several hours a day in Phoenix, Arizona. The max current through the conduit will be 450v @ 19 amps. Are things gonna get too hot for my 10 awg THWN-2 wire? It's rated for 90 celsius (194 f).
How hot can exterior metal conduit get?
- Thread starter Ubby
- Start date
hwy17
Anti-Solar Enthusiast
The NEC has derating calcs for environmental temperature, and somebody maintains an industry database for what temp to use for different areas. It's like a copper association or something.
hwy17
Anti-Solar Enthusiast
hwy17
Anti-Solar Enthusiast
Here's both outdoor and rooftop:
www.copper.org
Building Wire - Outdoor and Rooftop Temperatures for Selected U.S and Canadian Locations
The National Electrical Code Section 310.15(A)(3), and good design practice, requires adjustment of ampacity of wires and cables installed in ambient temperature conditions that are higher than those upon which the listed ampacities of Table 310.15(B)(16) are based.
www.copper.org
hwy17
Anti-Solar Enthusiast
I think maybe when you derate you get to replace a 1.25 so instead of x 1.25 x 1.25 = 1.56x it's x derate x 1.25 = ampacity required. But not positive about that.
Fantastic. This is perfect info. Looks like I'm good! Thanks!Here's both outdoor and rooftop:
Building Wire - Outdoor and Rooftop Temperatures for Selected U.S and Canadian Locations
The National Electrical Code Section 310.15(A)(3), and good design practice, requires adjustment of ampacity of wires and cables installed in ambient temperature conditions that are higher than those upon which the listed ampacities of Table 310.15(B)(16) are based.
chrisski
Solar Boondocker
- Joined
- Aug 14, 2020
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- 5,366
I hope so. There’s tens of thousands of installations like that in the phoenix valley.
Mine is one. I have 145 volts going though 10 AWG in metal conduit painted to the color of the house.
hwy17
Anti-Solar Enthusiast
Did you do a derating calculation?
zanydroid
Solar Wizard
How did it get to 19A? That sounds like a weird number to me.
Probably said already but I don’t believe the EMT per se has any meaningful temp limit. (Unlike plastic conduits)
Two 9.5 amp arrays in parallel. I’m more concerned about the wire’s temp rating.
zanydroid
Solar Wizard
OK. You have a pretty large margin to chew through with the derating factors (40A/19A = 2.11). You wouldn’t want to add more current carrying conductors in there.
Also shouldn’t the AHJ be expecting derating calculations. And hiring out a plans package would do this for you.
Also shouldn’t the AHJ be expecting derating calculations. And hiring out a plans package would do this for you.
