#14 Cu on a 100A breaker

W

wwhitney

Senior Member
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Berkeley, CA
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Retired
Say I have a 240V 2-wire feeder supplying a 1 HP motor (Table 430.248 FLC = 8A) plus a 3A non-continuous non-motor load. It is wired with a 100A breaker (nothing smaller upstream) supplying #14 Cu 90C conductors. What NEC section is violated?

Of relevance are 240.4(G) and 430.63, but I'm not finding a violation.

Thanks,
Wayne
 
wwhitney said:
Say I have a 240V 2-wire feeder supplying a 1 HP motor (Table 430.248 FLC = 8A) plus a 3A non-continuous non-motor load. It is wired with a 100A breaker (nothing smaller upstream) supplying #14 Cu 90C conductors. What NEC section is violated?
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If 100A Instantaneous trip feeds Motor FLC = 8A
8A x 125% = 10A + 3A = 13A for #14cu
Per Table 430.52, 8 x 11 = 88 + 3 = 91
Next size up = 100A
Feeder breaker must be instantaneous trip, and motor type must be class B energy efficient
 
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@wwhitney Well I still owe you a milkshake form the last time I bet you a milkshake I am gonna tread more carefully this time, guess you see a loophole in 430.62(A)?
Have you now ran into the 690 volt 3-phase motor with 90°C terminations and free air bare conductors on a off shore platform in the arctic also?
690V systems got cheated when the code migrated '600V or less' to '1000V or less' in 2017, which moved low amp 690 volt stuff from 110.40 (90°C default) to to 110.14. and a similar move in article 430. A 690V motor was a "High Voltage" motor. You followed the Part XI rules.

@ramsy If I recall 430.52(C)(3) has to be part of listed combination motor controller
 
wwhitney said:
Because that's part of my hypothetical? Let's say the #14 Cu supplies a 15A OCPD for the motor and a separate 15A OCPD for the non-motor load.

Cheers, Wayne
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There is a loop hole in 430.63 but not sure how to fix it. The problem it says the OCPD shall not be less than, permitting any size OCPD that is larger.
 
You say this is a feeder, so does it terminate in a panel that has branch circuit over current protection for the motor and the other load? Otherwise, it doesn't seem like a feeder. Even with terminating breakers to begin the branch circuits, this feeder seems like a tap and should be protected and length limited as such, but don't see a requirement for that.

240.4 says you must protect the conductors at their ampacity (which is a maximum limit), but allows rounding up and some exceptions such as 240.4(G). 240.4(G) can send you to 430.63 which says the feeder overcurrent device shall not be less than .... So the overcurrent can be larger than normal that follows 430.52. I don't see how any type of breaker permitted in 430.52 could be 100A. What type of overcurrent is the 100A (e.g. Inverse time, instantaneous, non time delay fuse)? Is the motor Design B energy efficient?

So I would say the not less than size is the maximum size since that minimum is way over the ampacity of the conductor.
 
suemarkp said:
So I would say the not less than size is the maximum size since that minimum is way over the ampacity of the conductor.
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That is not how the code language works...not less than, permits any rating that is greater than the minimum. The code rule needs a maximum, but does not have it.
 
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
 
don_resqcapt19 said:
That is not how the code language works...not less than, permits any rating that is greater than the minimum. The code rule needs a maximum, but does not have it.
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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.
 
ramsy said:
Not seeing where instantaneous trip, or current limiting fuses, are prohibited.

Grasshopper wants to finish this lesson with a code reference please.
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A code reference about what?
The OP was about breakers not fuses.

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