430.32 (A)(1)

[xavier2167]

Electrical question that i cannot seem to find the answer.
- Determine the MAXIMUM size overload protection permitted for a 480V, 3phase, 15HP continuous duty ac motor, where given the following related info. Assume the value you will select will permit the overload device to carry the motor load and modification of this value is not required.
-Design C
-temperature rise: 40 degrees Celsius
-service factor: 1.12
-name plate ampere rating: 18 amps

Im getting the answer online is 18 • 115%= 20.7 amps.

How is the answer 20.7 amps when the temperature rise is 40 degrees Celsius, and the nec 2017 code book states clearly max you can size overload protection for a motor is 125% of a marked temperature rise 40 degrees celsius or less at 430.32(A)(1)

 

[don_resqcapt19]

To use the 125%, the service factor must be 1.15 or greater AND the motor must be marked with a temperature rise of 40°C or less.
Your motor has a service factor of 1.12, so your motor falls into the "all other motors" category and the overload protection cannot exceed 115%.

 

[xavier2167]

Okay thank you so much Don!

 

[wwhitney]

To use the 125%, the service factor must be 1.15 or greater AND the motor must be marked with a temperature rise of 40°C or less.

That would explain the discrepancy in the OP, but that's certainly not how 430.32(A)(1) reads. It has a table with 3 line items, like so:

Motors with a marked service factor 1.15 or greater	125%
Motors with a marked temperature rise 40°C or less	125%
All other motors	115%

That means each row is an "or", not an "and". If the NEC wanted to communicate what you propose, then the table should have just 2 rows, where the top row reads "Motors with a marked service factor 1.15 or greater and with a marked temperature rise 40°C or less."

So as far as I can see the correct answer to the question in the OP is 125% * 18A = 22.5A

Cheers, Wayne

 

[xavier2167]

That would explain the discrepancy in the OP, but that's certainly not how 430.32(A)(1) reads. It has a table with 3 line items, like so:

Motors with a marked service factor 1.15 or greater	125%
Motors with a marked temperature rise 40°C or less	125%
All other motors	115%

That means each row is an "or", not an "and". If the NEC wanted to communicate what you propose, then the table should have just 2 rows, where the top row reads "Motors with a marked service factor 1.15 or greater and with a marked temperature rise 40°C or less."

So as far as I can see the correct answer to the question in the OP is 125% * 18A = 22.5A

Cheers, Wayne

Okay, my testing software must have made a typo or something, thats the way i would do it because I didn’t see an and nor did i see anything that would suggest they both have to be together in any way.