Soft start wiring

[sparkyhotmix]

I have one soft start and a bypass contactor driving 2 - 125 hp motors each motor has overloads fla are 140 amp what size wire is needed to feed the drive and bypass Contactor also what size breaker I think a 400 amp breaker with 350 mcm is right

 

[don_resqcapt19]

350 is too small...the minimum ampacity for a feeder conductor supplying two 3 phase, 480 volt, 125 hp motors would be 351 amps.
The code would permit the feeder breaker to be 600 amps.

 

[sparkyhotmix]

350 is too small...the minimum ampacity for a feeder conductor supplying two 3 phase, 480 volt, 125 hp motors would be 351 amps.
The code would permit the feeder breaker to be 600 amps.

Is that based on 139 amps on each motor looks like that is based on 156 amps

 

[ptonsparky]

Overload settings are dependent on fla on label of motor. Feeder/branch circuit size is based on NEC table values.

 

[JoeStillman]

125 HP @ 460V = 156A. (156 x 1.25) + 156 = 351A = 500kCM CU @75°C.

 

[don_resqcapt19]

Is that based on 139 amps on each motor looks like that is based on 156 amps

Yes as the code requires the conductors for motors to be sized per the full load current found in Table 430.250 for this motor. See 430.24

 

[sparkyhotmix]

The 125 hp motor nameplate is 139

 

[augie47]

The 125 hp motor nameplate is 139

as don points out, by Code, that number (139) is only used for sizing overload devices. All other calculations are sized per the Tables such as 430.250.

 

[Jraef]

350 is too small...the minimum ampacity for a feeder conductor supplying two 3 phase, 480 volt, 125 hp motors would be 351 amps.
The code would permit the feeder breaker to be 600 amps.

But check the technical data on the soft starter, it’s UL listing might require a specific OCPD and size.

 

[zbang]

I have one soft start...

In the future, please add some punctuation to the questions, it makes them easier to understand what's being asked. Thanks.

 

[don_resqcapt19]

But check the technical data on the soft starter, it’s UL listing might require a specific OCPD and size.

True, but that would not change the conductor size.