TX SINGLE-PHASE PUMP EXAM COMPLETE
QUESTIONS & DETAILED SOLUTIONS LATEST
UPDATE 2026-2027 TOPICS: ELECTRICAL
THEORY, MOTOR COMPONENTS, STARTING
CIRCUITS, TROUBLESHOOTING, SAFETY, NEC /
TDLR RULES
Section 1 – Single-Phase Motor Theory (Questions 1–15)
1. A single-phase induction motor does not self-start because:
A) It has low starting torque
B) The stator field does not rotate
C) The rotor is squirrel cage type
D) The capacitor is wired backwards
✔ Answer: B
� Rationale: A single-phase stator produces a pulsating, not rotating, magnetic field. Without a starting
mechanism (auxiliary winding), no starting torque is produced.
2. The two main windings in a single-phase pump motor are:
A) Series and parallel
B) Armature and field
C) Start and run
D) Primary and secondary
✔ Answer: C
� Rationale: Start winding (high resistance/inductive) provides phase shift; run winding (lower
resistance) maintains running torque.
3. Which component disconnects the start winding after the motor reaches ~75% of rated speed?
A) Run capacitor
B) Centrifugal switch
,C) Overload relay
D) Potential relay
✔ Answer: B
� Rationale: Centrifugal switch opens at ~75% speed. Some modern pumps use electronic relays, but
centrifugal is standard in many TX single-phase motors.
4. A capacitor-start induction-run motor has:
A) Low starting torque
B) High starting torque
C) No capacitor
D) Only a run capacitor
✔ Answer: B
� Rationale: Capacitor in series with start winding creates large phase shift → high starting torque (ideal
for pumps).
5. A pump motor hums but won’t start. The most likely electrical cause is:
A) Open run capacitor
B) Failed start capacitor or centrifugal switch stuck open
C) Low voltage on both windings
D) Reversed polarity
✔ Answer: B
� Rationale: If start cap or centrifugal switch fails in open position, start winding never energizes →
motor hums, rotor locked.
6. What is the typical phase shift provided by a start capacitor?
A) 30°
B) 45°
C) 90°
D) 180°
✔ Answer: C
� Rationale: Capacitor causes current in start winding to lead voltage by ~90°, creating rotating field for
startup.
7. The run capacitor in a permanent split capacitor (PSC) motor:
A) Is removed by a relay
B) Stays in circuit always
C) Only works during starting
D) Reduces starting torque
, ✔ Answer: B
� Rationale: PSC motors have run capacitor always in series with auxiliary winding, providing moderate
starting torque and good efficiency.
8. A dual-voltage pump motor rated 115/230V will draw ___ current at 230V compared to 115V.
A) Twice the current
B) Half the current
C) Same current
D) Four times the current
✔ Answer: B
� Rationale: Power = V × I. Doubling voltage halves current for same HP. Wiring diagram must be
followed for correct voltage.
9. Motor nameplate says 5 A at 230V, 10 A at 115V. HP is:
A) 0.5 HP
B) 1 HP
C) 1.5 HP
D) 2 HP
✔ Answer: B
� Rationale: HP = (V × I × PF × eff)/746. Approx: 230×5=1150W; 115×10=1150W. 1150/746 ≈ 1.54 input
→ 1 HP output typical.
10. A pump motor draws locked rotor current (LRA) of 40A. The correct overload trip class is:
A) Class 10
B) Class 20
C) Class 30
D) Class 5
✔ Answer: B
� Rationale: Pumps are moderate inertia start. Class 20 allows 20 seconds at LRA before trip, typical for
single-phase pumps.
11. What is the purpose of a start capacitor’s bleed resistor?
A) Increase starting torque
B) Discharge capacitor after motor stops
C) Reduce voltage spikes
D) Improve power factor
✔ Answer: B
� Rationale: Bleed resistor (15k–20k Ω) discharges capacitor when motor off, preventing shock hazard.
QUESTIONS & DETAILED SOLUTIONS LATEST
UPDATE 2026-2027 TOPICS: ELECTRICAL
THEORY, MOTOR COMPONENTS, STARTING
CIRCUITS, TROUBLESHOOTING, SAFETY, NEC /
TDLR RULES
Section 1 – Single-Phase Motor Theory (Questions 1–15)
1. A single-phase induction motor does not self-start because:
A) It has low starting torque
B) The stator field does not rotate
C) The rotor is squirrel cage type
D) The capacitor is wired backwards
✔ Answer: B
� Rationale: A single-phase stator produces a pulsating, not rotating, magnetic field. Without a starting
mechanism (auxiliary winding), no starting torque is produced.
2. The two main windings in a single-phase pump motor are:
A) Series and parallel
B) Armature and field
C) Start and run
D) Primary and secondary
✔ Answer: C
� Rationale: Start winding (high resistance/inductive) provides phase shift; run winding (lower
resistance) maintains running torque.
3. Which component disconnects the start winding after the motor reaches ~75% of rated speed?
A) Run capacitor
B) Centrifugal switch
,C) Overload relay
D) Potential relay
✔ Answer: B
� Rationale: Centrifugal switch opens at ~75% speed. Some modern pumps use electronic relays, but
centrifugal is standard in many TX single-phase motors.
4. A capacitor-start induction-run motor has:
A) Low starting torque
B) High starting torque
C) No capacitor
D) Only a run capacitor
✔ Answer: B
� Rationale: Capacitor in series with start winding creates large phase shift → high starting torque (ideal
for pumps).
5. A pump motor hums but won’t start. The most likely electrical cause is:
A) Open run capacitor
B) Failed start capacitor or centrifugal switch stuck open
C) Low voltage on both windings
D) Reversed polarity
✔ Answer: B
� Rationale: If start cap or centrifugal switch fails in open position, start winding never energizes →
motor hums, rotor locked.
6. What is the typical phase shift provided by a start capacitor?
A) 30°
B) 45°
C) 90°
D) 180°
✔ Answer: C
� Rationale: Capacitor causes current in start winding to lead voltage by ~90°, creating rotating field for
startup.
7. The run capacitor in a permanent split capacitor (PSC) motor:
A) Is removed by a relay
B) Stays in circuit always
C) Only works during starting
D) Reduces starting torque
, ✔ Answer: B
� Rationale: PSC motors have run capacitor always in series with auxiliary winding, providing moderate
starting torque and good efficiency.
8. A dual-voltage pump motor rated 115/230V will draw ___ current at 230V compared to 115V.
A) Twice the current
B) Half the current
C) Same current
D) Four times the current
✔ Answer: B
� Rationale: Power = V × I. Doubling voltage halves current for same HP. Wiring diagram must be
followed for correct voltage.
9. Motor nameplate says 5 A at 230V, 10 A at 115V. HP is:
A) 0.5 HP
B) 1 HP
C) 1.5 HP
D) 2 HP
✔ Answer: B
� Rationale: HP = (V × I × PF × eff)/746. Approx: 230×5=1150W; 115×10=1150W. 1150/746 ≈ 1.54 input
→ 1 HP output typical.
10. A pump motor draws locked rotor current (LRA) of 40A. The correct overload trip class is:
A) Class 10
B) Class 20
C) Class 30
D) Class 5
✔ Answer: B
� Rationale: Pumps are moderate inertia start. Class 20 allows 20 seconds at LRA before trip, typical for
single-phase pumps.
11. What is the purpose of a start capacitor’s bleed resistor?
A) Increase starting torque
B) Discharge capacitor after motor stops
C) Reduce voltage spikes
D) Improve power factor
✔ Answer: B
� Rationale: Bleed resistor (15k–20k Ω) discharges capacitor when motor off, preventing shock hazard.
