Motor Conductor Sizing / Motor leads

[milmat1]

I have a single 150HP VFD driving two 75hp motors. I have individual thermal overloads for each motor. The motor leads from the OL's to each motor are what I'm questioning.
According to 430.22 I need to size the conductors for 125% of 96 amps (From table 430.250) or 120 Amps. Which would indicate I need an 1 AWG motor conductor, correct ?
The motor itself has size 4 AWG leads coming out of the motor. Is this normal to see this large difference in conductor sizes ?
BTW the name tag FLA is 88.5A

Thanks for any input..

 

[Jraef]

430.22, are you using the 2011 Code? It’s 430.122 now. You don’t use the tables for this. 430.122 says 125% of the VFD rated INPUT current. In some brands that is LESS than the output current, some it is more. But again you do not use the tables for that.

 

[don_resqcapt19]

I have a single 150HP VFD driving two 75hp motors. I have individual thermal overloads for each motor. The motor leads from the OL's to each motor are what I'm questioning.
According to 430.22 I need to size the conductors for 125% of 96 amps (From table 430.250) or 120 Amps. Which would indicate I need an 1 AWG motor conductor, correct ?
The motor itself has size 4 AWG leads coming out of the motor. Is this normal to see this large difference in conductor sizes ?
BTW the name tag FLA is 88.5A

Thanks for any input..

It is very common...I did a 1500 hp DC motor and there were four 4/0s in the motor that we connected to six 535.3 kcmil conductors.

 

[milmat1]

430.22, are you using the 2011 Code? It’s 430.122 now. You don’t use the tables for this. 430.122 says 125% of the VFD rated INPUT current. In some brands that is LESS than the output current, some it is more. But again you do not use the tables for that.

Your referring to the VFD input conductors.
I'm talking about the motor conductors. Which even under 430.122 says 125% of FLC as determined by 430.6 A or B.
Which leads you to the table 430.250..

 

[infinity]

According to 430.22 I need to size the conductors for 125% of 96 amps (From table 430.250) or 120 Amps. Which would indicate I need an 1 AWG motor conductor, correct ?

Yes that's correct. #1 AWG is rated at 130 amps. How does a single drive run both motors?

 

[milmat1]

Yes that's correct. #1 AWG is rated at 130 amps. How does a single drive run both motors?

It is sized for the total HP. And they are simply run in parallel. But you must provide individual overload protection because the drive only sees the total load. It doesn't know what is happening at the motors.