Electrical2021
Member
- Location
- USA
- Occupation
- 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:
Component sizing:
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
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
Last edited: