Motor wire and breaker sizing

[ammklq143]

I need to have a panel built for a 480V part of a job. Before I do I just wanted to check to make sure I have them put in the correct breakers. There are two motor controllers that will need to be fed by this panel. The customer bought this equipment used.
The first has a 25 hp with a FLA on the nameplate of 30 amps. The code book says the FLC is 34 amps at 460V. Currently the motor has #10's feeding it but would I be required to put in #8's to accommodate 125% of the FLC? Also, 250% of the FLC is 85 amps. Would I be allowed to us a 90A breaker?

The other motor controller feeds a 5 hp 460V motor. The FLA on the nameplate is 6.5 and the code book says the FLC is 7.6A. 7.6A x 125% is 9.5A. I should be fine to use #12's easily enough and fuse it with a 20A breaker --- 250% of 7.6 = 19A.....right?

I want to be very sure that I build the panel with the correct breakers since it's pretty costly.

Thank you.

 

[petersonra]

I need to have a panel built for a 480V part of a job. Before I do I just wanted to check to make sure I have them put in the correct breakers. There are two motor controllers that will need to be fed by this panel. The customer bought this equipment used.
The first has a 25 hp with a FLA on the nameplate of 30 amps. The code book says the FLC is 34 amps at 460V. Currently the motor has #10's feeding it but would I be required to put in #8's to accommodate 125% of the FLC? Also, 250% of the FLC is 85 amps. Would I be allowed to us a 90A breaker?

The other motor controller feeds a 5 hp 460V motor. The FLA on the nameplate is 6.5 and the code book says the FLC is 7.6A. 7.6A x 125% is 9.5A. I should be fine to use #12's easily enough and fuse it with a 20A breaker --- 250% of 7.6 = 19A.....right?

I want to be very sure that I build the panel with the correct breakers since it's pretty costly.

Thank you.

I think you are OK code wise.

 

[ammklq143]

I think you are OK code wise.

While I want to make sure I don't have issues with a breaker tripping.....a 90 amp seems like overkill. The controller that operates the 25hp motor has a VFD in it. Would it be pretty safe to put a 60A breaker in the panel to feed that?

 

[petersonra]

While I want to make sure I don't have issues with a breaker tripping.....a 90 amp seems like overkill. The controller that operates the 25hp motor has a VFD in it. Would it be pretty safe to put a 60A breaker in the panel to feed that?

that is an important factor you left out. the vfd manual will tell you what ocpd is allowed and what the maximum rating should be.

From 2014 NEC

430.130 Branch-Circuit Short-Circuit and Ground Fault
Protection for Single Motor Circuits Containing
Power Conversion Equipment.
(A) Circuits Containing Power Conversion Equipment.
Circuits containing power conversion equipment shall be
protected by a branch-circuit short-circuit and ground-fault
protective device in accordance with the following:
(1) The rating and type of protection shall be determined
by 430.52(C)(l), (C)(3), (C)(5), or (C)(6), using the
full-load current rating of the motor load as determined
by 430.6.
(2) Where maximum branch-circuit short-circuit and
ground-fault protective ratings are stipulated for specific
device types in the manufacturer's instructions for
the power conversion equipment or are otherwise
marked on the equipment, they shall not be exceeded
even if higher values are permitted by 430.130(A)(l).
(3) A self-protected combination controller shall only be
permitted where specifically identified in the manufacturer's
instructions for the power conversion equipment
or if otherwise marked on the equipment.
Informational Note: The type of protective device, its rating,
and its setting are often marked on or provided with the
power conversion equipment.

 

[OldSparks]

I see no mention of the length of the wire run, but don't forget to factor that into your wire size calcs.