Residential Load Calculation Question

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Keith Chitwood

Member
Location
Placerville, California
I hope that someone can help answer this question;

When calculating the required size of a dwelling unit using the "general" method of calculation to comply with 430.24 the largest motor in FLC is increased by 25%.

Can anyone point me to a hard and fast rule about whether or not an air-conditioner should be used at this step (if the air conditioner was not omitted) per 220.60?

I have taken several exams and have always used the air conditioner if it was indeed the largest motor in FLC and didn't get omitted per 220.60. Now I never did get to see which questions were answered right and which were wrong, but I always passed the exams using this method.:)

I am now having differences of opinion with other instructors as they say that an air conditioner can't be used for this step as it is technically a hermetic refrigerant motor-compressor and not a "motor". I say it's a motor just a motor of a different type which should be used for the 25% increase rule if not omitted.

What say you?
 
mcclary's electrical

mcclary's electrical

Senior Member
Location
VA
Keith Chitwood said:
I hope that someone can help answer this question;

When calculating the required size of a dwelling unit using the "general" method of calculation to comply with 430.24 the largest motor in FLC is increased by 25%.

Can anyone point me to a hard and fast rule about whether or not an air-conditioner should be used at this step (if the air conditioner was not omitted) per 220.60?

I have taken several exams and have always used the air conditioner if it was indeed the largest motor in FLC and didn't get omitted per 220.60. Now I never did get to see which questions were answered right and which were wrong, but I always passed the exams using this method.:)

I am now having differences of opinion with other instructors as they say that an air conditioner can't be used for this step as it is technically a hermetic refrigerant motor-compressor and not a "motor". I say it's a motor just a motor of a different type which should be used for the 25% increase rule if not omitted.

What say you?
Click to expand...



I agree with your instructor
 
mcclary's electrical

mcclary's electrical

Senior Member
Location
VA
Keith Chitwood said:
Based on what codes? That's really what I am looking for, not just opinion but codes to validate one way or the other. This is not matter of who's right or wrong but how to accurately teach calculations.
Click to expand...

When a circuit operates motor loads 430 applies.If the circuit supplies, a/c and refridgeration equipment 440 applies
 
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Keith Chitwood

Member
Location
Placerville, California
mcclary's electrical said:
When a circuit operates motor loads 430 applies.If the circuit supplies, a/c and refridgeration equipment 440 applies
Click to expand...

Agreed
:-? But that still doesn't answer the question! I don't dispute that a/c motors are covered in a different section. What I am trying to find is something that specifically states that an a/c motor is not to be used when applying the rules of 430.24 to a dwelling calculation.

If we look at 220.50 it tells us that motors shall be computed in accordance with sections 430.24, 430.25, 430.26 and 440.6 for hermetic refrigerant compressor-motors. This would lead me to believe that the a/c is indeed a motor when dealing with the calculation.

If we look at 440.6 it explains ampacity ratings and how to size conductors. 440.7 directly addresses complying with 430.24 which is where this question started. :D
 
Dennis Alwon

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Keith did my second response not answer the question. It appears that 220.14(C) say that an a/c would be calculated as motor load so if it is the largest you would use that. Am I missing your point
 
K

Keith Chitwood

Member
Location
Placerville, California
Dennis Alwon said:
Keith did my second response not answer the question. It appears that 220.14(C) say that an a/c would be calculated as motor load so if it is the largest you would use that. Am I missing your point
Click to expand...

:cool: Dennis, I think you're right!:grin:

That's pretty much what I hang my hat on, I was just hoping that others, like yourself, would either back me up or point me in a new direction.

Thanks
 
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