Wye-Delta motor tripping

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USA
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Engineer
Hello all,

Need some insight on why motor is tripping “Main circuit breaker” and “Main cabinet breaker” immediately when “Start” is pressed. Brand new system under commissioning. There is no load on motor and spins freely. When motor leads are disconnected, star-delta transition works properly without trip.

Motor nameplate:

Voltage – 460VAC
Phase – 3 phase
Frequency – 60Hz
Size – 40HP / 30kW
Efficiency – 94.1%
RPM – 1780
Power Factor – 0.80
Full load amps (FLA) – 50A
Number of leads - 6
Motor code - K

Component sizing:

Main cabinet disconnect setting - 63A
Branch circuit breaker setting (supplies feeder contactor) - 50A
Feeder contactor size (supplies main, delta and star) - 65A
Main contactor size - 32A
Delta contactor size - 32A
Star contactor size - 25A
Inrush current measured - 169A

Edit: I feel the “Branch circuit breaker” and “Main cabinet disconnect” are undersized. But I need to make sure before I speak to design team. I calculated these values:

• Branch circuit breaker - 2.50*50 = 125A
• Main cabinet disconnect - 125A + FLA of other motors in system
 
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