Feeder size for Variable Frequency Drives

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nichols21vt

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At a wastewater plant I do some work for they want to install 16 - 10hp 460V 3 phase motors for their aeration lagoons. All 16 are to be controlled by VFD's in a separate VFD building close to the lagoons.

My question has to do with sizing the feeder to this building. According to 430.122 (A) these circuit conductors shall have an ampacity not less than 125 percent of the rated input to the power conversion equipment. The rated input of the drives we are using is 15.4 amps. Am I to size the feeder by applying the 125% rating to all 16 drives? 15.4A X 16 X 1.25

Or am I to apply the 125% to ONE drive plus the sum of the other 15; in keeping with 430.22 and 430.24?
 
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petersonra

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engineer
nichols21vt said:
At a wastewater plant I do some work for they want to install 16 - 10hp 460V 3 phase motors for their aeration lagoons. All 16 are to be controlled by VFD's in a separate VFD building close to the lagoons.

My question has to do with sizing the feeder to this building. According to 430.122 (A) these circuit conductors shall have an ampacity not less than 125 percent of the rated input to the power conversion equipment. The rated input of the drives we are using is 15.4 amps. Am I to size the feeder by applying the 125% rating to all 16 drives? 15.4A X 16 X 1.25

Or am I to apply the 125% to ONE drive plus the sum of the other 15; in keeping with 430.22 and 430.24?
Click to expand...

If you are running one feeder for all the VFDs, IMO, the feeder would be sized in the normal way (per 220), and the individual BCs to the VFDs sized at 125%. I do not think the feeder itself has any motor loads at all, thus it should be sized according to 220, and not anything in 430.
 
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bob

bob

Senior Member
Location
Alabama
nichols21vt said:
At a wastewater plant I do some work for they want to install 16 - 10hp 460V 3 phase motors for their aeration lagoons. All 16 are to be controlled by VFD's in a separate VFD building close to the lagoons.

My question has to do with sizing the feeder to this building. According to 430.122 (A) these circuit conductors shall have an ampacity not less than 125 percent of the rated input to the power conversion equipment. The rated input of the drives we are using is 15.4 amps. Am I to size the feeder by applying the 125% rating to all 16 drives? 15.4A X 16 X 1.25

Or am I to apply the 125% to ONE drive plus the sum of the other 15; in keeping with 430.22 and 430.24?
Click to expand...
How are you making the connection from the VFD to the feeder? Do you have a breaker panel with breakers feeding each VFD?
 
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nichols21vt

Member
bob said:
How are you making the connection from the VFD to the feeder? Do you have a breaker panel with breakers feeding each VFD?
Click to expand...

Yes,
This is a new bldg. In addition to the VFD's there will be an AC unit, some lighting and receptacles.
The plan is for a MDP (with breakers for the drives), a dry type transformer, and a small 120/208 panel.
 
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