rabtrfld
Member
- Location
- Milwaukee, Wisconsin
A) Conduit fill derating does not apply to a JB,
B) Terminal temperatures do not apply to conduit.
For example, eight #12 THHN enter a JB, where some wire nuts are rated 75C. In the conduit, the 70% derating factor applies to the 90C column of table 310-16: 30A * 70% = 21A.
In the JB, use the 75C column of 310-16, 25 amps with no derating. So the ampacity of the circuit is 21A.
The point is, not to apply the 70% factor to the 75C column, which would only give 17.5 amps.
B) Terminal temperatures do not apply to conduit.
For example, eight #12 THHN enter a JB, where some wire nuts are rated 75C. In the conduit, the 70% derating factor applies to the 90C column of table 310-16: 30A * 70% = 21A.
In the JB, use the 75C column of 310-16, 25 amps with no derating. So the ampacity of the circuit is 21A.
The point is, not to apply the 70% factor to the 75C column, which would only give 17.5 amps.