The circuit breaker or fuses have tripped. What might be the cause?

Circuit breakers and fuses trip for numerous reasons: Undervoltage, incorrectly designed circuit breaker or fuses, too low a setting for the motor-protective circuit breaker, asymmetric three-phase current, a short circuit on the motor, incorrect wiring or faulty electrical connections, a worn or blocked pump, a defective capacitor for single-phase motors, a motor-protective circuit breaker exposed to a higher ambient temperature than the motor.

However, the pump may also be undersized for the application in question, and may be operating in excess of its nominal flow rate.