LADWP ELECTRICAL REPAIRER MOTORS &
CONTROLS EXAM WITH QUESTIONS AND
VERIFIED ANSWERS, PLUS DETAILED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
1.
A three-phase induction motor is running under normal load, but an
electrician measures substantially higher current on one phase than on
the other two phases. The supply voltage is reasonably balanced, and the
motor has recently been rewound. Which condition should be
investigated FIRST?
A. Excessive bearing lubrication
B. Unequal winding impedance or an incorrect winding connection
C. Excessive rotor ventilation
D. Oversized motor overload relay
Answer: B. Unequal winding impedance or an incorrect winding
connection
Rationale: An appreciable current imbalance with reasonably
balanced supply voltage strongly suggests a motor-side problem. A
partially shorted winding, incorrect reconnection after rewinding,
unequal winding resistance, or another winding defect can cause
unequal phase currents. Excessive bearing lubrication would
generally produce mechanical heating rather than a phase-specific
electrical imbalance, while an oversized overload relay would affect
protection rather than directly create the imbalance.
1
,2.
A technician is troubleshooting a three-phase motor that hums when
energized but does not rotate. The shaft turns freely by hand when de-
energized. Voltage is present at the motor terminals on all three phases.
Which condition is MOST likely?
A. Open rotor bars
B. Single-phasing within the motor circuit or an open winding
C. Excessive bearing clearance
D. Incorrect grease viscosity
Answer: B. Single-phasing within the motor circuit or an open
winding
Rationale: A three-phase induction motor requires a properly
balanced three-phase magnetic field to develop starting torque. If one
phase is open because of a damaged conductor, contactor pole,
terminal connection, fuse, or winding, the motor may hum and fail to
start while drawing abnormal current. The fact that voltage is
measured at terminals does not automatically prove that the circuit
can deliver current under load; phase-to-phase and phase-to-ground
measurements must be interpreted correctly.
3.
A motor starter uses a three-wire control circuit. The START pushbutton
is normally open, the STOP pushbutton is normally closed, and an
auxiliary contact from the starter is wired in parallel with the START
button. What is the primary purpose of the auxiliary contact?
A. To reduce motor starting current
B. To provide electrical braking
C. To seal in the starter coil after the START button is released
D. To protect the motor from phase reversal
2
,Answer: C. To seal in the starter coil after the START button is
released
Rationale: The auxiliary or holding contact creates a maintained path
around the momentary START pushbutton. When START is pressed,
the contactor coil energizes and its auxiliary contact closes. Releasing
START then leaves the coil energized through the auxiliary contact.
Pressing STOP opens the control circuit and de-energizes the coil.
This is one of the fundamental control-circuit arrangements an
electrical repairer must understand when troubleshooting motor
starters.
4.
A motor starter repeatedly drops out even though the motor itself
appears mechanically sound. During troubleshooting, the technician
discovers that the control voltage measured directly across the contactor
coil falls substantially whenever the coil attempts to energize. Which
problem is MOST consistent with this symptom?
A. Excessively high motor horsepower
B. High resistance or poor connection in the control circuit
C. Excessive rotor speed
D. Incorrect motor bearing alignment
Answer: B. High resistance or poor connection in the control circuit
Rationale: A contactor coil requires adequate voltage to establish
sufficient magnetic force to remain closed. A loose terminal, damaged
conductor, failing control transformer, corroded contact, undersized
wiring, or excessive resistance elsewhere in the control circuit can
cause voltage at the coil to collapse. The correct diagnostic technique
is to measure voltage across the coil while the circuit is actually
3
, attempting to operate rather than relying only on an unloaded voltage
measurement.
5.
A motor has a nameplate full-load current of 18 A. During operation, a
clamp ammeter measures approximately 17.5 A, 17.8 A, and 17.6 A on
the three phases. What does this measurement MOST strongly indicate?
A. Severe phase imbalance
B. An approximately balanced operating current condition
C. A definite shorted winding
D. A failed overload relay
Answer: B. An approximately balanced operating current condition
Rationale: The three measured currents are close to one another and
reasonably close to the motor's rated full-load current. Although
current readings alone cannot establish that every component is
perfect, this pattern does not indicate a severe phase-current
imbalance. Additional measurements such as voltage balance,
temperature, insulation condition, mechanical loading, and power
factor may be required for a complete assessment.
6.
When testing a motor winding with an ohmmeter, a technician obtains
nearly identical resistance readings between all three phase pairs. What
is the BEST conclusion?
A. The winding is guaranteed to be free of insulation breakdown
B. The motor is guaranteed to have no shorted turns
C. The phase-to-phase DC resistance appears reasonably balanced
D. The rotor is definitely correctly aligned
4
CONTROLS EXAM WITH QUESTIONS AND
VERIFIED ANSWERS, PLUS DETAILED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
1.
A three-phase induction motor is running under normal load, but an
electrician measures substantially higher current on one phase than on
the other two phases. The supply voltage is reasonably balanced, and the
motor has recently been rewound. Which condition should be
investigated FIRST?
A. Excessive bearing lubrication
B. Unequal winding impedance or an incorrect winding connection
C. Excessive rotor ventilation
D. Oversized motor overload relay
Answer: B. Unequal winding impedance or an incorrect winding
connection
Rationale: An appreciable current imbalance with reasonably
balanced supply voltage strongly suggests a motor-side problem. A
partially shorted winding, incorrect reconnection after rewinding,
unequal winding resistance, or another winding defect can cause
unequal phase currents. Excessive bearing lubrication would
generally produce mechanical heating rather than a phase-specific
electrical imbalance, while an oversized overload relay would affect
protection rather than directly create the imbalance.
1
,2.
A technician is troubleshooting a three-phase motor that hums when
energized but does not rotate. The shaft turns freely by hand when de-
energized. Voltage is present at the motor terminals on all three phases.
Which condition is MOST likely?
A. Open rotor bars
B. Single-phasing within the motor circuit or an open winding
C. Excessive bearing clearance
D. Incorrect grease viscosity
Answer: B. Single-phasing within the motor circuit or an open
winding
Rationale: A three-phase induction motor requires a properly
balanced three-phase magnetic field to develop starting torque. If one
phase is open because of a damaged conductor, contactor pole,
terminal connection, fuse, or winding, the motor may hum and fail to
start while drawing abnormal current. The fact that voltage is
measured at terminals does not automatically prove that the circuit
can deliver current under load; phase-to-phase and phase-to-ground
measurements must be interpreted correctly.
3.
A motor starter uses a three-wire control circuit. The START pushbutton
is normally open, the STOP pushbutton is normally closed, and an
auxiliary contact from the starter is wired in parallel with the START
button. What is the primary purpose of the auxiliary contact?
A. To reduce motor starting current
B. To provide electrical braking
C. To seal in the starter coil after the START button is released
D. To protect the motor from phase reversal
2
,Answer: C. To seal in the starter coil after the START button is
released
Rationale: The auxiliary or holding contact creates a maintained path
around the momentary START pushbutton. When START is pressed,
the contactor coil energizes and its auxiliary contact closes. Releasing
START then leaves the coil energized through the auxiliary contact.
Pressing STOP opens the control circuit and de-energizes the coil.
This is one of the fundamental control-circuit arrangements an
electrical repairer must understand when troubleshooting motor
starters.
4.
A motor starter repeatedly drops out even though the motor itself
appears mechanically sound. During troubleshooting, the technician
discovers that the control voltage measured directly across the contactor
coil falls substantially whenever the coil attempts to energize. Which
problem is MOST consistent with this symptom?
A. Excessively high motor horsepower
B. High resistance or poor connection in the control circuit
C. Excessive rotor speed
D. Incorrect motor bearing alignment
Answer: B. High resistance or poor connection in the control circuit
Rationale: A contactor coil requires adequate voltage to establish
sufficient magnetic force to remain closed. A loose terminal, damaged
conductor, failing control transformer, corroded contact, undersized
wiring, or excessive resistance elsewhere in the control circuit can
cause voltage at the coil to collapse. The correct diagnostic technique
is to measure voltage across the coil while the circuit is actually
3
, attempting to operate rather than relying only on an unloaded voltage
measurement.
5.
A motor has a nameplate full-load current of 18 A. During operation, a
clamp ammeter measures approximately 17.5 A, 17.8 A, and 17.6 A on
the three phases. What does this measurement MOST strongly indicate?
A. Severe phase imbalance
B. An approximately balanced operating current condition
C. A definite shorted winding
D. A failed overload relay
Answer: B. An approximately balanced operating current condition
Rationale: The three measured currents are close to one another and
reasonably close to the motor's rated full-load current. Although
current readings alone cannot establish that every component is
perfect, this pattern does not indicate a severe phase-current
imbalance. Additional measurements such as voltage balance,
temperature, insulation condition, mechanical loading, and power
factor may be required for a complete assessment.
6.
When testing a motor winding with an ohmmeter, a technician obtains
nearly identical resistance readings between all three phase pairs. What
is the BEST conclusion?
A. The winding is guaranteed to be free of insulation breakdown
B. The motor is guaranteed to have no shorted turns
C. The phase-to-phase DC resistance appears reasonably balanced
D. The rotor is definitely correctly aligned
4
