VFD/Line Reactor Conductors and OCPD

[nhee2]

430.122A requires conductors supplying power conversion equipment be sized at 125% of the rated input to the equipment.

For a VFD with separate line reactor - is the line reactor included as part of the 'power conversion equipment'? And therefore the conductors are 125% of line reactor rating as well? I assume yes, and actually this isn't a big deal.

430.130 (A) says that Branch-circuit short circuit device can be sized per 430.52(C)(1). I interpret this to mean that the OCPD setting can be higher than the ampacity of the conductors between OCPD and drive. Although there are some historical posts i have seen which suggest conductors between OCPD and drive need to be protected at their ampacity.

What if the line reactor is installed - is this considered part of the 'power conversion equipment'?

Example - 100 HP motor, 100 HP drive rated 117A input, vendor specifies max inverse time CB of 375A.

Conductors require ampacity 117 x 1.25 = 146.25A or 1/0. I believe 430.130 says the 1/0 can be protected by the 375A breaker.

If we add a line side reactor - does this change the OCPD requirements for the circuit?

 

[Jraef]

No. The line reactor is a pass-through device.

 

[nhee2]

No. The line reactor is a pass-through device.

Thanks, i hoped you would respond on this VFD post.

Just to confirm - for my example - Do you agree then that the conductors from breaker to reactor and reactor to VFD are adequately protected by the 375 OCPD and compliant with 430.130 and 240.4 (2017 ed)

 

[Jraef]

Thanks, i hoped you would respond on this VFD post.

Just to confirm - for my example - Do you agree then that the conductors from breaker to reactor and reactor to VFD are adequately protected by the 375 OCPD and compliant with 430.130 and 240.4 (2017 ed)

Yes, you're fine. In reality the maximum allowable (in your case 375A) is just based on their UL listing, you can usually go smaller than that. A VFD will not have "motor starting current" to deal with, it controls all of that. Under no circumstances can the VFD draw more than 150% of its rated current for more than 1 minute, even less if it's a "Variable Torque" rated VFD. So for that drive, the breaker will never see more than 175A for 1 minute and on a drive that size, I've used 200A breakers and been fine. It saves you the cost and space of a frame size change in this case.

If you have a bypass starter though, or want the ability to toss in a FVNR starter if the drive is removed for servicing, that changes it and you may need to use the 375A rating to keep the breaker from tripping if restarted across-the-line.

240.4 is by the way already satisfied by using 430 sizing.

 

[nhee2]

Thanks.

Understood that 375A is more than needed - the intent of question was to confirm the OCPD be larger than the ampacity of the conductors based on the rules in 430. And your response answers that.