# Nec question???



## HARRY304E (Sep 15, 2010)

Elephante said:


> Determine the Minimum standard size circuit breaker that may be used as the disconnecting means for an 11.3 kw, 208 volt, single phase heat pump.
> A. 50 amperes
> B.55 amperes
> C. 60 amperes
> ...


430.110 (A) applies here,then you go back to 240.6(A)


240.6 Standard Ampere Ratings.
(A) Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601. The use of fuses and inverse time circuit breakers with nonstandard ampere ratings shall be permitted.


430.110 Ampere Rating and Interrupting Capacity.
(A) General. The disconnecting means for motor circuits rated 600 volts, nominal, or less shall have an ampere rating not less than 115 percent of the full-load current rating of the motor.
Exception:  A listed unfused motor-circuit switch having a horsepower rating not less than the motor horsepower shall be permitted to have an ampere rating less than 115 percent of the full-load current rating of the motor.


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## Elephante (Nov 16, 2011)

HARRY304E said:


> 430.110 (A) applies here,then you go back to 240.6(A)
> 
> 240.6 Standard Ampere Ratings.
> (A) Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601. The use of fuses and inverse time circuit breakers with nonstandard ampere ratings shall be permitted.
> ...


So is the book wrong? I got 70 too.


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## bkmichael65 (Mar 25, 2013)

11300/746=15 hp
table 430.250 gives flc of 46.2 x 115%= 53 amps- next size up is 60


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## bkmichael65 (Mar 25, 2013)

Oops, that was off the chart for 3 phase motors


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## macmikeman (Jan 23, 2007)

Nameplate. Say's right on there.


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## J_Captain (Jul 14, 2013)

Elephante said:


> Determine the Minimum standard size circuit breaker that may be used as the disconnecting means for an 11.3 kw, 208 volt, single phase heat pump.
> A. 50 amperes
> B.55 amperes
> C. 60 amperes
> ...



(Single phase motor) 11.3kw/208V = 54A 

Minimum disconnecting means must be rated for 115% FLC 

54A * 1.15 = 62A

Next standard size up. 70A breaker


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## Deep Cover (Dec 8, 2012)

What about this being a continuous load?


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## BBQ (Nov 16, 2010)

Deep Cover said:


> What about this being a continuous load?


Is it one?

I don't think it is.


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## Deep Cover (Dec 8, 2012)

I guess it isn't...I was thinking of space heating. Carry on:whistling2:


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## Elephante (Nov 16, 2011)

Would this question fall under 430.110 a exception? It's a circuit breaker and not a fuse, so can you just multiply by 100%?


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## Elephante (Nov 16, 2011)

The exception says motor circuit switch.The book just probably forgot to add the 1.15%.


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## Glennsparky (Nov 30, 2011)

Elephante, did the question originally have the Hp or nameplate ratings of all the motors in the heat pump?


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## Elephante (Nov 16, 2011)

Glennsparky said:


> Elephante, did the question originally have the Hp or nameplate ratings of all the motors in the heat pump?


No it didn't... What you see is exactly what they wrote as the question.


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## Glennsparky (Nov 30, 2011)

The formula for a heat pump is 125% of the largest motor's amps plus 100% of all the other loads(usually that's just the fan motor with the controls being negligible.) Use this formula and it will match the Minimum Circuit Ampacity on the nameplate.

I'm guessing they used this formula and gave you minimum circuit watts. So the MCA is 54.33A. I'm also guessing that the book is 3 or 4 code cycles old, when 55A was a standard breaker size.

So...*B* :detective: That's my final answer.


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## don_resqcapt19 (Jul 18, 2010)

I would think that 440.12 and not 430.110 would apply here....not that it changes anything.


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## VasZenyn1732 (Jul 25, 2021)

So, using the 2017 DeWalt practice test and the question is still here, and the answer is still 60A. They still reference 430.110(A). Pretty annoying.


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## Dennis Alwon (May 9, 2009)

VasZenyn1732 said:


> So, using the 2017 DeWalt practice test and the question is still here, and the answer is still 60A. They still reference 430.110(A). Pretty annoying.


Probably because no one told them that the heat pump should be in art 440 not 430. Either way I believe the answer is incorrect. 60 amps is NOT "at least 115% of the FLC"


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## argile_tile (Aug 12, 2021)

I can't say the book is wrong but I'm saying _the book is way wrong_.

NEC says to use 440 WHEN A MANUFACTURER LABEL IS PROVIDED. But OP didn't give us any listed label so he must go by "motors" 430.

However: the motors section doesn't say how to choose breakers it says they must be chosen. So now you go to EATON's website, use their online calculator. Else you need SCA curves and eventually: time. Time for short failure. Time for motor start.

You don't even have a listed motor label. 430 says not to use a motor you have no listed label for - not on the power company's line's let's say.

I'd put a low cost quick-blow fuse on it because I was afraid of burning out a motor I knew nothing about ?


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