90 deg. C to size coductor

[Toros]

Hi
in what circumstances I can use 90 deg colum of 310-16??
Can I use that to size large underground copper conductor feeding a big service (And temparture derate per correction factor)?????

Thank you

 

[infinity]

You can use the 90 degree rating for derating purposes but for the most part the terminals will limit you to the conductors 75 degree rating.

 

[JFletcher]

Hi
in what circumstances I can use 90 deg colum of 310-16??
Can I use that to size large underground copper conductor feeding a big service (And temparture derate per correction factor)?????

Thank you

You can use 90*C column if the terminations are 90*C or higher on both ends. An example of this would be Polaris connectors; the wire between them, you can use the 90*C column. For example, breaker panel/breaker (75*C) to j-box underneath with Polaris connectors (90*C), then the main run to another j-box with Polaris connectors (again, 90*C), up to say a disconnect (75*C).

It can make a big difference in wire use if you're right on the edge of wire size/ampacity. For example, using the 90*C table, you can use copper 500MCM for 425A. If you used the 75*C table, you'd need 750MCM or two sets of 4/0 vs 3/0 (or 1000MCM AL vs 750MCM, or two sets of 300MCM vs two sets of 250MCM AL), and probably larger conduit for those wires. From the connector to the breaker/disco, you'd need the copper 750MCM, but if we're talking a 1500+' run of cable, you could potentially save thousands of dollars by using the 90*C column 98% of the way. On top of that, by using two large j-boxes, instead of 90's, you're making your wire pull that much easier.

 

[Julius Right]

I agree with JFletcher. In my opinion, if the ends are free for-at least- 24"[600 mm] and rated for 75oC you may take 90oC for underground. A open cable tray-see NEC Art.392.80