Sizing Conductors per NEC tables.

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milmat1

milmat1

"It Can't Do That !"
Location
Siler City, NC USA
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Controls Engineer
For example, I am sizing the feeders and breaker for a VFD, The max input current from the manual is 86 Amps, so 86 x 1.25= 107,5A (110A)

If I select the conductor size from the table, What dictates which column is use. 60*, 75* or 90* Column. Is this decided simply by the wire type I plan to use (THHN).
 
Decided by wire type in part, adjusted and corrected for conditions of use, using the column which the wire type is in and THHN is in 90?C column. The ampacity after adjustment and correction must equal or exceed 107.5A. I don't know your conditions of use, but baseline size will be not less than the size determined by the following...

The other part is termination temperature limitation per 110.14(C). In your case, you most likely have 75?C terminals and equipment ratings at both ends, so for this part you use the 75?C column and match or exceed 107.5A... which would be #2 copper, #1/0 aluminum.
 
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