TX SINGLE PHASE PUMP ACTUAL EXAM 2026/2027 COMPLETE
ACCURATE QUESTIONS AND CORRECT DETAILED ANSWERS WITH
RATIONALES (VERIFIED SOLUTIONS) CURRENTLY UPDATED VERSION
2026 EDITION |GUARANTEED PASS A+ |INSTANT DOWNLOAD PDF
1. A single-phase pump motor fails to start but hums. The most likely cause is:
A) Open running winding
B) Correct Answer: Open starting winding
C) Low voltage only
D) Shorted centrifugal switch
Rationale: A humming sound with no rotation typically indicates that the
starting winding is open, preventing the necessary phase shift for startup; the
running winding alone cannot produce starting torque.
2. Which component disconnects the starting winding in a single-phase induction
motor after reaching 70–80% of full speed?
A) Thermal overload relay
B) Correct Answer: Centrifugal switch
C) Start capacitor
D) Potential relay
Rationale: The centrifugal switch is mechanically activated by rotor speed and
opens the starting winding circuit once the motor approaches synchronous speed
to prevent overheating.
3. A pump draws excessive current and trips the breaker immediately on startup.
The probable fault is:
A) Open run capacitor
B) Correct Answer: Shorted start capacitor
C) Low line voltage
D) Worn bearings
Rationale: A shorted start capacitor creates a near-direct short across the line
during start, causing inrush current far above the breaker rating.
4. For a single-phase pump motor, the run capacitor is connected in series with
which winding during normal operation?
A) Start winding only
B) Correct Answer: Auxiliary winding
C) Main winding only
D) Both windings
,Rationale: In permanent split capacitor (PSC) motors, the run capacitor remains
in series with the auxiliary (start) winding even after the motor reaches running
speed to improve efficiency and power factor.
5. A pump runs but delivers no water. The pressure gauge reads zero. The first
check should be:
A) Replace the motor
B) Correct Answer: Check for loss of prime
C) Increase capacitor size
D) Adjust the centrifugal switch
Rationale: Loss of prime (air in the pump casing) prevents water from being
drawn up; it is the most common cause of no flow with a running motor.
6. The resistance reading between the common (C) and start (S) terminals on a
good single-phase pump motor should be:
A) Zero ohms
B) Correct Answer: Higher than C to run (R)
C) Lower than C to run (R)
D) Infinite
Rationale: The start winding has more turns of finer wire, thus higher resistance
than the run winding. C-R is low resistance, C-S is higher.
7. A potential relay is used to disconnect the start winding. Its coil is wired in
parallel with:
A) Start capacitor
B) Correct Answer: Run winding
C) Centrifugal switch
D) Thermal protector
Rationale: The potential relay coil senses back EMF across the run winding;
when voltage reaches a threshold (about 70–80% speed), the relay opens the start
circuit.
8. What is the typical capacitance range for a start capacitor in a residential single-
phase pump?
A) 1–5 µF
B) Correct Answer: 50–500 µF
C) 1000–2000 µF
D) 0.1–1 µF
*Rationale: Start capacitors are electrolytic, high-capacitance units (often 50–
500 µF) designed for brief duty cycles to provide high starting torque.*
, 9. A pump motor overheats and trips the internal overload after 10 minutes of run
time. The most likely cause is:
A) Correct Answer: Low voltage at motor terminals
B) Defective start capacitor
C) Open centrifugal switch
D) Wrong rotation direction
Rationale: Low voltage causes increased current draw in the run winding,
leading to overheating over several minutes; a start capacitor issue would affect
starting only.
10. Which of the following would cause the centrifugal switch to remain closed
after the motor reaches full speed?
A) Correct Answer: Welded contacts
B) Weak starting capacitor
C) High line voltage
D) Open run winding
Rationale: Welded or stuck contacts keep the start winding energized, leading to
rapid overheating and possible smoke from the start winding.
11. A single-phase 230V pump motor has a run capacitor rated at 10 µF. To test it
with a digital multimeter (capacitance mode), you must:
A) Test while connected
B) Correct Answer: Discharge it first
C) Apply 230V during test
D) Use resistance mode only
Rationale: Run capacitors retain charge; discharging prevents meter damage
and false readings. Always short terminals with a resistor before measuring.
12. The correct rotation for most single-phase centrifugal pumps when viewed
from the motor fan end is:
A) Counterclockwise
B) Correct Answer: Clockwise
C) Either direction is fine
D) Depends on capacitor polarity
Rationale: Standard NEMA conventions and pump volute designs typically
require clockwise rotation from the motor back (fan end) for proper impeller
operation.
13. A pump starts, runs for 2 seconds, then stops. Repeated cycle. The most likely
fault is:
A) Correct Answer: Defective run capacitor
ACCURATE QUESTIONS AND CORRECT DETAILED ANSWERS WITH
RATIONALES (VERIFIED SOLUTIONS) CURRENTLY UPDATED VERSION
2026 EDITION |GUARANTEED PASS A+ |INSTANT DOWNLOAD PDF
1. A single-phase pump motor fails to start but hums. The most likely cause is:
A) Open running winding
B) Correct Answer: Open starting winding
C) Low voltage only
D) Shorted centrifugal switch
Rationale: A humming sound with no rotation typically indicates that the
starting winding is open, preventing the necessary phase shift for startup; the
running winding alone cannot produce starting torque.
2. Which component disconnects the starting winding in a single-phase induction
motor after reaching 70–80% of full speed?
A) Thermal overload relay
B) Correct Answer: Centrifugal switch
C) Start capacitor
D) Potential relay
Rationale: The centrifugal switch is mechanically activated by rotor speed and
opens the starting winding circuit once the motor approaches synchronous speed
to prevent overheating.
3. A pump draws excessive current and trips the breaker immediately on startup.
The probable fault is:
A) Open run capacitor
B) Correct Answer: Shorted start capacitor
C) Low line voltage
D) Worn bearings
Rationale: A shorted start capacitor creates a near-direct short across the line
during start, causing inrush current far above the breaker rating.
4. For a single-phase pump motor, the run capacitor is connected in series with
which winding during normal operation?
A) Start winding only
B) Correct Answer: Auxiliary winding
C) Main winding only
D) Both windings
,Rationale: In permanent split capacitor (PSC) motors, the run capacitor remains
in series with the auxiliary (start) winding even after the motor reaches running
speed to improve efficiency and power factor.
5. A pump runs but delivers no water. The pressure gauge reads zero. The first
check should be:
A) Replace the motor
B) Correct Answer: Check for loss of prime
C) Increase capacitor size
D) Adjust the centrifugal switch
Rationale: Loss of prime (air in the pump casing) prevents water from being
drawn up; it is the most common cause of no flow with a running motor.
6. The resistance reading between the common (C) and start (S) terminals on a
good single-phase pump motor should be:
A) Zero ohms
B) Correct Answer: Higher than C to run (R)
C) Lower than C to run (R)
D) Infinite
Rationale: The start winding has more turns of finer wire, thus higher resistance
than the run winding. C-R is low resistance, C-S is higher.
7. A potential relay is used to disconnect the start winding. Its coil is wired in
parallel with:
A) Start capacitor
B) Correct Answer: Run winding
C) Centrifugal switch
D) Thermal protector
Rationale: The potential relay coil senses back EMF across the run winding;
when voltage reaches a threshold (about 70–80% speed), the relay opens the start
circuit.
8. What is the typical capacitance range for a start capacitor in a residential single-
phase pump?
A) 1–5 µF
B) Correct Answer: 50–500 µF
C) 1000–2000 µF
D) 0.1–1 µF
*Rationale: Start capacitors are electrolytic, high-capacitance units (often 50–
500 µF) designed for brief duty cycles to provide high starting torque.*
, 9. A pump motor overheats and trips the internal overload after 10 minutes of run
time. The most likely cause is:
A) Correct Answer: Low voltage at motor terminals
B) Defective start capacitor
C) Open centrifugal switch
D) Wrong rotation direction
Rationale: Low voltage causes increased current draw in the run winding,
leading to overheating over several minutes; a start capacitor issue would affect
starting only.
10. Which of the following would cause the centrifugal switch to remain closed
after the motor reaches full speed?
A) Correct Answer: Welded contacts
B) Weak starting capacitor
C) High line voltage
D) Open run winding
Rationale: Welded or stuck contacts keep the start winding energized, leading to
rapid overheating and possible smoke from the start winding.
11. A single-phase 230V pump motor has a run capacitor rated at 10 µF. To test it
with a digital multimeter (capacitance mode), you must:
A) Test while connected
B) Correct Answer: Discharge it first
C) Apply 230V during test
D) Use resistance mode only
Rationale: Run capacitors retain charge; discharging prevents meter damage
and false readings. Always short terminals with a resistor before measuring.
12. The correct rotation for most single-phase centrifugal pumps when viewed
from the motor fan end is:
A) Counterclockwise
B) Correct Answer: Clockwise
C) Either direction is fine
D) Depends on capacitor polarity
Rationale: Standard NEMA conventions and pump volute designs typically
require clockwise rotation from the motor back (fan end) for proper impeller
operation.
13. A pump starts, runs for 2 seconds, then stops. Repeated cycle. The most likely
fault is:
A) Correct Answer: Defective run capacitor
