VFD Conductor/Breaker sizing

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wcfalk

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430.122 States conductors will be sized at 125% of VFD rated input.
If a VFD has multiple ratings which do you use? The rating for the service it will be in or max rating listed?
 
430.122 States conductors will be sized at 125% of VFD rated input.
If a VFD has multiple ratings which do you use? The rating for the service it will be in or max rating listed?
Multiple voltage ratings? If so max current rating for the voltage you will be using.

10 amps @ 480 volts is same power rating as 20 amps @ 240 volts. Chances are you need to configure something differently to change voltage so the unit is essentially "fixed" at whatever you set it up for.

208 vs 240 isn't a dramatic change but I could see a unit rated for either with some difference in power rating.
 
My bad, Amperage. 1 drive with three different Hp/ Amperage ratings.
I will check and see if it requires a config change.

The "rated input" as it applies to 430.122 is either what the mfr shows for the rating you are using it as, or if not clear, then you must default to the worst case scenario. Some drive mfrs understand this and provide you with a chart with those values on it. Others don't bother with it, or don't understand (because they are not really that interested in North American sales issues).

So case in point: A-B drives come with a chart telling you the Input Amps based on whether you are using the drive as HD or ND (Normal Duty, aka Variable Torque). So a 100HP 125A ND drive shows the Input as 117A, but that exact same drive used as HD is only rated for 75HP, in which case the Input is 90.1A. So if you are using it for 100HP ND, you would size the conductors at 125% of 117A, or if using it at 75HP HD you would size them at 125% of 90.1A. If you sized the conductors based on the ND raring, you have them OVER sized for the HD rating, so that's not a problem (from the Code standpoint).

Some of the Japanese and Chinese suppliers have trouble with this concept, so you have to go by what the drive actually says right on it's nameplate, because that's what the AHJ will go by. That has burned me on several occasions... Older Mitsubishi drives were notorious for this, so when this rule was adopted in 2002, it caught a lot of people off guard. they may have fixed that now, but I stopped using them for that reason a long time ago, they burned me twice.
 
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