430.122 (A) says to size the conductors feeding a variable speed drive based on the input rating of the drive.
That's simple enough to understand.
What I have trouble with is finding and making sense of the ratings. Some drives actually list the input amperage as LESS than the output amperage. Sounds like an energy machine to me. Others list the input amps much higher than the output rating. I assume those are usually higher rated chassis nameplated down to some lower hp for marketing reasons. Here's an example:
Allen Bradley PF400 150 HP 480v drive: Output amps 208, input amps 200.
With Allen Bradley PF70s, there is a whole string of them that are listed this way from 7.5 up to 50 hp.
Any insights here? How would you size your conductors?
That's simple enough to understand.
What I have trouble with is finding and making sense of the ratings. Some drives actually list the input amperage as LESS than the output amperage. Sounds like an energy machine to me. Others list the input amps much higher than the output rating. I assume those are usually higher rated chassis nameplated down to some lower hp for marketing reasons. Here's an example:
Allen Bradley PF400 150 HP 480v drive: Output amps 208, input amps 200.
With Allen Bradley PF70s, there is a whole string of them that are listed this way from 7.5 up to 50 hp.
Any insights here? How would you size your conductors?
