- Location
- Bremerton, Washington
Each month the Washington State has a question of the month in its Electrical Currents, I got a PM with this question and am reposting it here:
"The subject publication, in Question 3, asks how many volt-amperes are drawn by a 5HP 460v 3-phase air compressor. Their answer was 6311 - calculated by multiplying 480 x 7.6 x 1.73. I contacted Olympia L&I and asked why they used 480v instead of 460v for the calculation. I was referred to Example D3(a) in Inf. Annex D from the 2014 NEC.
I have a difficulty understanding, the NEC notwithstanding, how the above calculation makes sense. Why would the volt-amperes, i.e., HP, change for motor that is operated at a voltage level within its intended operational range (440 to 480 in this case)?"
"The subject publication, in Question 3, asks how many volt-amperes are drawn by a 5HP 460v 3-phase air compressor. Their answer was 6311 - calculated by multiplying 480 x 7.6 x 1.73. I contacted Olympia L&I and asked why they used 480v instead of 460v for the calculation. I was referred to Example D3(a) in Inf. Annex D from the 2014 NEC.
I have a difficulty understanding, the NEC notwithstanding, how the above calculation makes sense. Why would the volt-amperes, i.e., HP, change for motor that is operated at a voltage level within its intended operational range (440 to 480 in this case)?"