#14 Cu on a 100A breaker

[wwhitney]

(a) 430.24 says the feeder conductors must have an ampacity of at least 200A.
(b) 430.62 has options A and B
(A) would say that the feeder OCPD must be at most 100A.
430.62(B) Can apply where feeder conductors have an
ampacity greater than required by 430.24.
We'll choose 4/0 Cu with 90C insulation, 75C ampacity 230A.

(c) 430.63 says that the feeder OCPD must be at least 250A.
QED

So your result is that the feeder conductor size determined by 430.24, 3/0 Cu with 75C ampacity 200A, is actually not allowed, and you have to bump up one size to 4/0 Cu?

That's way less plausible than the common understanding that the word "only" is implicit in 430.62(A), as in "a feeder supplying only a specific fixed motor load(s)." I just made a PI special for you, it changes 430.62(A) to "a feeder supplying only fixed motor load(s)" to improve clarity.

I would agree with your understanding of the wording in 430.62 if 430.63 were absent from the NEC. Except that then 430.62 would need to be fixed to add in the non-motor loads.

Cheers, Wayne

 

[tortuga]

I just made a PI special for you, it changes 430.62(A) to "a feeder supplying only fixed motor load(s)" to improve clarity.

Yes great idea thanks for doing that, I enjoy your thought experiments. I think that deserves another milkshake or beverage of your choice.
Next time I get to Berkley

 

[brycenesbitt]

In my area we still have some Edison base fuse boxes feeding dwelling loads

And we have test results showing how robust and reliable that fuse based system is, was, and will continue (unless someone hacks it up and messes with it).

 

[ramsy]

And we have test results showing how robust and reliable that fuse based system is, was, and will continue (unless someone hacks it up and messes with it).

Much more reliable than AFCI, or GFCI. Fuses work with harmonic loads, without constant nuisance trips, or reset-button failures.