5 KV Cable derating

[steve blackmon]

Do you need to derate 5KV MV-90 XLP or EPE in conduit on a sunlit roof?
since the code says direct solar exposure can raise the ambient 17 degrees C, it appears that no derating is required?

 

[beanland]

Sunlight

Sunlight

You need to determine the ambient temperature then add the extra heating effect for exposure. Since tables are based on 30C ambient, you may have an issue. See derating in table 310.16. A conduit on a roof can easily be subject to temperatures above 30C and the conductors require derating.

 

[bob]

Do you need to derate 5KV MV-90 XLP or EPE in conduit on a sunlit roof?
since the code says direct solar exposure can raise the ambient 17 degrees C, it appears that no derating is required?

5 KV MV-90 XLP is not listed in table 310.16. Table 310.67 shows this cables
rating at 40C or 104F. Terminations at 5KV could be listed at 90C so you may be able to use the 90C rating of the cable. You still may need to reduce the ampacity for the temp increase.

 

[kingpb]

Just as in using the 90deg C column for LV cable to derate to the 75 deg C value, you can use the MV-105 Col for MV cable (as long as you purchase MV-105) and derate to the 90 deg C values. Worth mentioning, is that most manufacturers were going to stop making MV-90 and just make the MV-105 to reduce overall production costs. Might want to verify ahead of time.