LADWP ELECTRICAL REPAIRER
TROUBLESHOOTING EXAM WITH
QUESTIONS AND VERIFIED ANSWERS,
PLUS DETAILED RATIONALES/EXPERT
VERIFIED FOR GUARANTEED PASS
2026/LATEST UPDATE/INSTANT
DOWNLOAD PDF
1.
An electrical repairer is troubleshooting a 480-V three-phase motor that
suddenly stopped operating. The disconnect is ON, but the motor starter
will not pull in when the START pushbutton is pressed. The control
circuit is supplied by a 120-V control transformer. The first
measurement at the control transformer secondary shows 0 V. Which
troubleshooting step should be performed first?
A. Replace the motor starter contactor
B. Check the motor overload relay
C. Verify the control transformer primary supply and protective device
D. Replace the START pushbutton
Answer: C. Verify the control transformer primary supply and
protective device
Rationale: When the control transformer secondary has no voltage,
the technician should work backward toward the source rather than
replacing downstream components. Checking the transformer primary
voltage, fuses, circuit breaker, and associated connections establishes
whether the transformer is receiving power. Replacing the contactor or
pushbutton before confirming control-circuit power would be
premature.
1
,2.
A 208-V three-phase motor exhibits a severe humming sound when
energized but does not accelerate. Measurements show 208 V between
L1-L2, 208 V between L2-L3, but only 35 V between L1-L3. What is
the most likely problem?
A. A missing or severely impaired phase
B. An oversized overload relay
C. Excessive motor lubrication
D. A defective START pushbutton
Answer: A. A missing or severely impaired phase
Rationale: A healthy three-phase supply should have approximately
equal line-to-line voltages. The 35-V L1-L3 reading indicates a major
phase imbalance or open/high-resistance condition. A motor
attempting to operate under this condition can hum, fail to accelerate,
draw excessive current, and overheat rapidly.
3.
While troubleshooting a control panel, an electrician measures 120 V
from the control hot conductor to ground but 0 V across the control relay
coil terminals when the relay is supposed to energize. What does this
most strongly indicate?
A. The relay coil is necessarily shorted
B. The control circuit has an open or missing return path
C. The transformer secondary is necessarily overloaded
D. The ground conductor is carrying excessive current
Answer: B. The control circuit has an open or missing return path
Rationale: Measuring voltage to ground on one side of the circuit does
not prove that voltage is actually available across the load. The coil
2
,requires a complete circuit with the appropriate potential difference
across its two terminals. A broken neutral, open control contact,
disconnected conductor, or other interruption in the return path can
produce this symptom.
4.
A motor overload relay repeatedly trips after approximately 10 minutes
of operation. The motor current is measured and found to be
significantly above its nameplate full-load current on all three phases.
Which condition should be investigated most closely?
A. A loose START pushbutton
B. Mechanical overload or excessive driven-load resistance
C. A defective pilot light
D. An open auxiliary contact
Answer: B. Mechanical overload or excessive driven-load resistance
Rationale: Excessive current on all phases commonly indicates that
the motor is being subjected to excessive mechanical load, incorrect
operating conditions, or another condition causing increased torque
demand. The technician should investigate bearings, pumps, fans,
belts, couplings, driven machinery, and other mechanical causes while
also verifying voltage and motor condition.
5.
A circuit breaker trips immediately whenever a motor branch circuit is
energized. The motor terminals are disconnected, and the breaker still
trips immediately when the circuit is energized. What is the most
appropriate next step?
3
, A. Replace the motor
B. Increase the breaker rating
C. Test the branch-circuit wiring for a short circuit or ground fault
D. Replace the motor overload relay
Answer: C. Test the branch-circuit wiring for a short circuit or
ground fault
Rationale: Because the motor has been disconnected and the breaker
still trips, the fault is likely upstream of the motor. The wiring,
terminal box, disconnect, conduit conductors, and associated
components should be examined and tested for phase-to-phase or
phase-to-ground faults. Increasing the breaker rating without
identifying the fault would create a serious safety hazard.
6.
An electrical repairer encounters a motor that has been operating
normally but now has an unusually high winding temperature. The
measured supply voltage is correct and balanced. Current is also
balanced but is approximately 15% above the nameplate rating. Which
condition is most likely?
A. Mechanical overload
B. Open control-circuit conductor
C. Oversized control transformer
D. Failed indicator lamp
Answer: A. Mechanical overload
Rationale: Correct and balanced voltage combined with balanced but
excessive current points away from a supply imbalance and toward
excessive motor loading or an abnormal motor operating condition.
Mechanical binding, overloaded equipment, excessive process demand,
4
TROUBLESHOOTING EXAM WITH
QUESTIONS AND VERIFIED ANSWERS,
PLUS DETAILED RATIONALES/EXPERT
VERIFIED FOR GUARANTEED PASS
2026/LATEST UPDATE/INSTANT
DOWNLOAD PDF
1.
An electrical repairer is troubleshooting a 480-V three-phase motor that
suddenly stopped operating. The disconnect is ON, but the motor starter
will not pull in when the START pushbutton is pressed. The control
circuit is supplied by a 120-V control transformer. The first
measurement at the control transformer secondary shows 0 V. Which
troubleshooting step should be performed first?
A. Replace the motor starter contactor
B. Check the motor overload relay
C. Verify the control transformer primary supply and protective device
D. Replace the START pushbutton
Answer: C. Verify the control transformer primary supply and
protective device
Rationale: When the control transformer secondary has no voltage,
the technician should work backward toward the source rather than
replacing downstream components. Checking the transformer primary
voltage, fuses, circuit breaker, and associated connections establishes
whether the transformer is receiving power. Replacing the contactor or
pushbutton before confirming control-circuit power would be
premature.
1
,2.
A 208-V three-phase motor exhibits a severe humming sound when
energized but does not accelerate. Measurements show 208 V between
L1-L2, 208 V between L2-L3, but only 35 V between L1-L3. What is
the most likely problem?
A. A missing or severely impaired phase
B. An oversized overload relay
C. Excessive motor lubrication
D. A defective START pushbutton
Answer: A. A missing or severely impaired phase
Rationale: A healthy three-phase supply should have approximately
equal line-to-line voltages. The 35-V L1-L3 reading indicates a major
phase imbalance or open/high-resistance condition. A motor
attempting to operate under this condition can hum, fail to accelerate,
draw excessive current, and overheat rapidly.
3.
While troubleshooting a control panel, an electrician measures 120 V
from the control hot conductor to ground but 0 V across the control relay
coil terminals when the relay is supposed to energize. What does this
most strongly indicate?
A. The relay coil is necessarily shorted
B. The control circuit has an open or missing return path
C. The transformer secondary is necessarily overloaded
D. The ground conductor is carrying excessive current
Answer: B. The control circuit has an open or missing return path
Rationale: Measuring voltage to ground on one side of the circuit does
not prove that voltage is actually available across the load. The coil
2
,requires a complete circuit with the appropriate potential difference
across its two terminals. A broken neutral, open control contact,
disconnected conductor, or other interruption in the return path can
produce this symptom.
4.
A motor overload relay repeatedly trips after approximately 10 minutes
of operation. The motor current is measured and found to be
significantly above its nameplate full-load current on all three phases.
Which condition should be investigated most closely?
A. A loose START pushbutton
B. Mechanical overload or excessive driven-load resistance
C. A defective pilot light
D. An open auxiliary contact
Answer: B. Mechanical overload or excessive driven-load resistance
Rationale: Excessive current on all phases commonly indicates that
the motor is being subjected to excessive mechanical load, incorrect
operating conditions, or another condition causing increased torque
demand. The technician should investigate bearings, pumps, fans,
belts, couplings, driven machinery, and other mechanical causes while
also verifying voltage and motor condition.
5.
A circuit breaker trips immediately whenever a motor branch circuit is
energized. The motor terminals are disconnected, and the breaker still
trips immediately when the circuit is energized. What is the most
appropriate next step?
3
, A. Replace the motor
B. Increase the breaker rating
C. Test the branch-circuit wiring for a short circuit or ground fault
D. Replace the motor overload relay
Answer: C. Test the branch-circuit wiring for a short circuit or
ground fault
Rationale: Because the motor has been disconnected and the breaker
still trips, the fault is likely upstream of the motor. The wiring,
terminal box, disconnect, conduit conductors, and associated
components should be examined and tested for phase-to-phase or
phase-to-ground faults. Increasing the breaker rating without
identifying the fault would create a serious safety hazard.
6.
An electrical repairer encounters a motor that has been operating
normally but now has an unusually high winding temperature. The
measured supply voltage is correct and balanced. Current is also
balanced but is approximately 15% above the nameplate rating. Which
condition is most likely?
A. Mechanical overload
B. Open control-circuit conductor
C. Oversized control transformer
D. Failed indicator lamp
Answer: A. Mechanical overload
Rationale: Correct and balanced voltage combined with balanced but
excessive current points away from a supply imbalance and toward
excessive motor loading or an abnormal motor operating condition.
Mechanical binding, overloaded equipment, excessive process demand,
4
