VFD System

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jmanderson

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Scenario : 20 VFD's in a single panel fed by a single disconnect. All VFD's are rated for 3HP max but there is a mix of .75 / 1.0 HP and a few 3 HP motors. Each motor is fed by an individual VFD w/ electronic O/L set accordingly for each motor fed. Total HP =18 HP. What should the feeder to the panel be sized at?
 
sii

sii

Senior Member
Location
Nebraska
The minimum feeder should be 1.25 the FLA of the largest drive plus 1.00 the FLA of the remaining drives and any control power required. Remember you have to use the nameplate rating of the drives, not the motors themselves. Is there some means of control for these drives such as a PLC included in the panel?
 
david luchini

david luchini

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Location
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I think you would need the feeder to be sized at not less than 125% of the rated input current of all of the VFD's. See 430.122(A).
 
T

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
david luchini said:
I think you would need the feeder to be sized at not less than 125% of the rated input current of all of the VFD's. See 430.122(A).
Click to expand...

I would agree. In the OP's case this will mean a feeder sized for 20 each 3HP drives X1.25. This is going to make a mighty big feeder for his actual HP. This is an code requirement I just don't get. Is this where we get to use good professinal judgement and ignore the letter of the code? If this is a factory built panel to UL standards could it be done differently?
Maybe Jaref could comment on this.
 
J

jmanderson

Member
sii said:
The minimum feeder should be 1.25 the FLA of the largest drive plus 1.00 the FLA of the remaining drives and any control power required. Remember you have to use the nameplate rating of the drives, not the motors themselves. Is there some means of control for these drives such as a PLC included in the panel?
Click to expand...

PLC will control.
 
D

DARUSA

Senior Member
Location
New York City
jmanderson said:
Scenario : 20 VFD's in a single panel fed by a single disconnect. All VFD's are rated for 3HP max but there is a mix of .75 / 1.0 HP and a few 3 HP motors. Each motor is fed by an individual VFD w/ electronic O/L set accordingly for each motor fed. Total HP =18 HP. What should the feeder to the panel be sized at?
Click to expand...

You will have to size your wire 125% of the FLC of the larger motor + 100% of all the other motor + any load for control equipment.
NEC 430.24 Remember that is FLC not FLA you will have to find the values on the table 250.248,249,250 based on the motor type.
 
D

DARUSA

Senior Member
Location
New York City
DARUSA said:
You will have to size your wire 125% of the FLC of the larger motor + 100% of all the other motor + any load for control equipment.
NEC 430.24 Remember that is FLC not FLA you will have to find the values on the table 250.248,249,250 based on the motor type.
Click to expand...

Sorry but I didn't pay attention on the words VFD. now for a VFD wire size you will have to calculate 125% of all the rated input of each VFD. Based on 430.122
 
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