VFD Caculation

[Gustav Eriksson]

I if you on a same 3 phase cable connect 5-10 3 phase VFD were they are working intermittent. How should we calaculate the cable and fuse ?

 

[mcclary's electrical]

You've given very limited info, but I would calculate as a multiple motor feeder. 125% of the LARGEST motor, and 100% of all remaining motors.per 430.24
also meet requirements of 430.2
but if you talk to your inspector 430. 26 leaves room for debate.

 

[Gustav Eriksson]

You've given very limited info, but I would calculate as a multiple motor feeder. 125% of the LARGEST motor, and 100% of all remaining motors.per 430.24
also meet requirements of 430.2
but if you talk to your inspector 430. 26 leaves room for debate.

Yes thats what i thought
but some in this forum wants to calculate for each VFD input current.

 

[Gustav Eriksson]

If you got a lots of conveyor on one group and each conveyor has an VFD how will we calculate the current for the cable and fuse.

 

[bob]

Yes thats what i thought
but some in this forum wants to calculate for each VFD input current.

Almost all of the participants on this forum are experts :roll: on the NEC and would back your effort in correctly sizing this circuit. I believe the only opposition you would get is from your inspector.

 

[don_resqcapt19]

The code does require that the feeder to the VFDs be calculated based on the VFD rated input current.

430.122 Conductors — Minimum Size and Ampacity.
(A) Branch/Feeder Circuit Conductors. Circuit conductors supplying power conversion equipment included as part of an adjustable-speed drive system shall have an ampacity not less than 125 percent of the rated input to the power conversion equipment.