USCG Exam PracticeElectrical fundamentals — DC/AC, motors, distribution
A DC shunt motor driving a centrifugal pump loses its field circuit due to an open connection. The most likely immediate consequence is:
- A. The motor stalls because torque is proportional to field flux.
- B. The motor runs at reduced speed because counter-EMF increases.
- ✓ The motor accelerates to a potentially destructive overspeed.Correct
- D. The motor reverses direction because back-EMF polarity changes.
Why C is correct
NEETS Mod. 5 §2-1 explains that a DC shunt motor speeds up when its field weakens in order to restore counter-EMF; an accidental open in the field circuit removes that limit and can allow the motor to race to a destructive overspeed. Field-loss relays are provided to guard against this hazard.
Cited:NEETS Mod. 5 §2-1