#14 Cu on a 100A breaker

[wwhitney]

I agree it isnt clear, but 240.4 sets a maximum. Then 430 sets a minimum higher than the max, so what to do in that case? I would say the min is now also the max, but they should say that or cover it explicitly somehow.

240.4 does not set a maximum, as the base requirement in the first sentence of 240.4 is "unless otherwise permitted or required in 240.4(A) through (G)." And 240.4(G) tells us that for "motor circuit conductors" Article 430 Parts II through VII control instead.

So that means it's up to Article 430 Parts II through VII to set a maximum. Which 430.62 does, but 430.63 does not.

Cheers, Wayne

 

[don_resqcapt19]

So is the "not less than" language in 430.63 simply a longstanding mistake? Should it be "not greater than" when conductors are sized per 430.24?

Cheers, Wayne

not sure what it should be, but "not less than" is incorrect.

 

[don_resqcapt19]

Other than current limiters for cales, I do not remember ever seeing a true Instantaneous fuse.

I don't think I have ever seen one either, but I think that is what a "motor short-circuit protector" in 430.52(B)(7) is.

 

[jim dungar]

I don't think I have ever seen one either, but I think that is what a "motor short-circuit protector" in 430.52(B)(7) is.

Yes, the codes specifically calls it a fused device, however they do not say it is instantaneous.
It is relatively easy to build an electromagnetic device that has a vertical pickup characteristic. I know of no fuse element with that capability, the ones I have seen have some long time melt point. Maybe the 430.52(B)(7) device has a minimum melt point that is extremely high, kind of like cable limiters?

 

[Little Bill]

Yes, the codes specifically calls it a fused device, however they do not say it is instantaneous.
It is relatively easy to build an electromagnetic device that has a vertical pickup characteristic. I know of no fuse element with that capability, the ones I have seen have some long time melt point. Maybe the 430.52(B)(7) device has a minimum melt point that is extremely high, kind of like cable limiters?

Would a "fast blow" fuse be what they're talking about?

 

[jim dungar]

Would a "fast blow" fuse be what they're talking about?

No, they call that a non-time delay fuse.

 

[ramsy]

No, they call that a non-time delay fuse.

Little Fuse, and other OEM's prefer the term "fast-acting" vs "time delay"
See Time Current Curve on Page 4

 

[ramsy]

not sure what it should be, but "not less than" is incorrect.

430.63 is for OCP only, not conductor size.
"not less than" refers to non-motor loads, before motors are factored into OCP size.

In post #16, wwhitney mixed 430.24 for conductor sizing, with 430.63 for OCP

 

[wwhitney]

In post #16, wwhitney mixed 430.24 for conductor sizing, with 430.63 for OCP

Incorrect, if you mean "mixed up". The two are related issues though, as generally allowable OCPD size depends on conductor size.

The omission in the NEC is that for feeders subject to 430.63, there is nothing that provides an upper bound on the OCPD size. The computation in 430.63 is comparable to the computation in 430.62, and in 430.62 the result is an upper bound. In 430.63, the result is said to be a lower bound. I believe that's a mistake.

Just trying to get my ducks in a row for a PI and checking if I've overlooked something.

Cheers, Wayne

 

[jim dungar]

Little Fuse, and other OEM's prefer the term "fast-acting" vs "time delay"
See Time Current Curve on Page 4

What does the NEC call them?

 

[Tulsa Electrician]

The omission in the NEC is that for feeders subject to 430.63, there is nothing that provides an upper bound on the OCPD size. The computation in 430.63 is comparable to the computation in 430.62, and in 430.62 the result is an upper bound. In 430.63, the result is said to be a lower bound. I believe that's a mistake.

Just trying to get my ducks in a row for a PI and checking if I've overlooked something.

Cheers, Wayne

The way I read it, I agree.