reduced wire size after current limiting VFD

[M.Lee.Evans]

Hey Guys, Was wondering if its allowable to reduce the wire size below the name plate listing if thecurrent limits are VFD is adjusted to meet a smaller wire size?
Thanks eh, Mike

 

[cpal]

check out 430.22 and part X of Article 430.

 

[M.Lee.Evans]

reduced wire size

reduced wire size

Thanks Charlie, Part X, 430.122 A allows this reduction limited by VFD size. Mike

 

[mcclary's electrical]

I wouldn't. What happens if they change the VFD to a contactor later? I would size the wire per the nameplate to cover my butt.

 

[M.Lee.Evans]

Good Idea, The situation follows, A Company is renting some of our land to do algae growth trials with some equipment from the UK. The techs came in to set up the equip. They were to provide everything. As these things go the information transfer suffered and we were left in the dark about most of the specs. When I saw the smaller sized cable I started dragging my feet. At lease I did know our availiable power would accomodate them. They assured me our frequency differences wouldn't matter. The experiments are of a temporary nature, so I am good with that reduced wire size. Thanks to you guys I feel confident allowing the instulation to proceed. Regards, Mike

 

[don_resqcapt19]

I don't see how 430.122 changes the size of the motor conductors. It only applies to the supply conductors to the VFD. I don't find anything that changes the rule in 430.22 for the conductors that connect to the motor.

 

[M.Lee.Evans]

Reduced wire sizes

Reduced wire sizes

Hey, It can read that way. The article states conductors supplying power conversion equip. as part of a system. Doesn't this imply the load side can be reduced too? Why would you have larger load conducters than your line side if the VFD is current limited? Thanks for all the input guys. Mike

 

[don_resqcapt19]

Hey, It can read that way. The article states conductors supplying power conversion equip. as part of a system. Doesn't this imply the load side can be reduced too? Why would you have larger load conducters than your line side if the VFD is current limited? Thanks for all the input guys. Mike

Mike,
I just don't see a code rule that changes 430.22 and permits the conductors from the VFD to the motor to be reduced in size. The code is set up for worst case. With a VFD, it is often sized larger than the motor, but you still need to use supply conductors sized at 125% of the VFD rated input current. With the motor, the minimum permitted size of 125% of the full load current for the motor. This would provide the correct size of the motor if the VFD would be replaced with a starter.
As far as your actual case, being it is temporary, you may get the AHJ to permit you to use the smaller sized conductors between the VFD and the motor.

 

[M.Lee.Evans]

reduced wire size

reduced wire size

Don, I really appreciate your opinion. I've come to agree with it too. I believe in verbatium complience to the code or better is the correct practice when trying to impliment it. Thanks again,
Mike