LADWP ELECTRICAL REPAIRER
INDUSTRIAL ELECTRICAL SYSTEMS EXAM
WITH QUESTIONS AND VERIFIED
ANSWERS, PLUS DETAILED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
1.
An industrial motor driving a large centrifugal pump repeatedly trips its
overload relay during normal operation. The motor has been properly
sized, the supply voltage is balanced, and the overload settings
correspond to the motor nameplate. During inspection, the pump shaft is
found to rotate with substantially more resistance than normal. Which
condition should the electrical repairer investigate FIRST?
A. Incorrect control-transformer secondary voltage
B. Mechanical overload or binding in the driven equipment
C. Excessive resistance in the motor starter coil
D. Incorrect phase sequence at the disconnect
Answer: B. Mechanical overload or binding in the driven equipment
Rationale: A motor operating under excessive mechanical load draws
increased current, which can cause the overload relay to trip even
when the electrical supply and overload settings are correct. A binding
pump, damaged bearing, misalignment, or other mechanical
restriction can produce this condition. The repairer should determine
whether the electrical overload is a consequence of excessive
mechanical loading before replacing electrical components.
2.
1
,A three-phase motor produces an audible hum but fails to accelerate
when the starter is energized. Voltage measurements at the motor
terminals show normal voltage on two phases but nearly zero voltage on
the third phase. Which fault is MOST likely?
A. Open phase or failed contact in the power circuit
B. Incorrect motor horsepower rating
C. Shorted control-transformer secondary
D. Excessive motor bearing lubrication
Answer: A. Open phase or failed contact in the power circuit
Rationale: A missing phase can prevent a three-phase motor from
developing normal starting torque while causing abnormal current in
the remaining phases. Possible causes include a failed contactor pole,
blown fuse, loose connection, broken conductor, or defective
disconnect contact. Operating the motor in this condition can rapidly
overheat the windings.
3.
When troubleshooting a 480-V industrial motor circuit, an electrician
discovers that the motor disconnect is open but the line-side terminals
remain energized. What is the MOST important conclusion?
A. The disconnect is functioning normally
B. The motor must be internally shorted
C. The circuit has not been electrically isolated from the source
D. The overload relay must be reset
Answer: C. The circuit has not been electrically isolated from the
source
Rationale: Opening a disconnect should isolate the downstream circuit
from the supply. If voltage remains present where it is expected to be
absent, the worker must determine the source and establish proper
2
,isolation before touching conductors. Safe troubleshooting requires
verification of absence of voltage at the point of work rather than
assuming a disconnect has created a safe condition.
4.
A motor starter repeatedly chatters when its contactor attempts to close.
The control voltage measured directly across the coil drops substantially
whenever the contactor pulls in. Which condition is MOST likely
responsible?
A. Excessive motor horsepower
B. Control-circuit voltage drop or inadequate control voltage
C. Incorrect motor rotation
D. Excessive grounding-electrode resistance
Answer: B. Control-circuit voltage drop or inadequate control
voltage
Rationale: A contactor coil requires sufficient voltage to pull in and
remain magnetically sealed. A weak control transformer, undersized
conductors, loose connection, damaged contacts, or excessive circuit
resistance can cause the coil voltage to collapse when energized.
Chattering can rapidly damage the contactor and should be corrected
rather than ignored.
5.
An electrical repairer measures 480 V phase-to-phase on a three-phase
system but discovers approximately 277 V phase-to-ground. What
configuration does this MOST likely indicate?
A. 480-V delta system with no grounding
B. 480Y/277-V grounded wye system
3
, C. 240-V split-phase system
D. 208-V corner-grounded delta system
Answer: B. 480Y/277-V grounded wye system
Rationale: In a balanced 480Y/277-V system, the line-to-line voltage is
approximately 480 V while the line-to-neutral voltage is approximately
277 V. This arrangement is common in industrial facilities because it
provides both 480-V three-phase power for equipment and 277-V
power for suitable lighting and other loads.
6.
A motor's overload relay trips after several minutes of operation rather
than immediately when the motor starts. The motor current is
consistently above its nameplate full-load current. Which explanation is
MOST appropriate?
A. The motor is likely experiencing sustained overloading
B. The motor has an open control circuit
C. The contactor coil is undersized
D. The phase sequence is reversed
Answer: A. The motor is likely experiencing sustained overloading
Rationale: Thermal overload devices are designed to respond to
sustained excessive current rather than instantaneous starting current.
If operating current remains above the motor's rated full-load current,
the motor can accumulate excessive heat until the overload operates.
The repairer should investigate mechanical loading, voltage
conditions, motor condition, and incorrect application rather than
simply increasing the overload setting.
7.
4
INDUSTRIAL ELECTRICAL SYSTEMS EXAM
WITH QUESTIONS AND VERIFIED
ANSWERS, PLUS DETAILED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
1.
An industrial motor driving a large centrifugal pump repeatedly trips its
overload relay during normal operation. The motor has been properly
sized, the supply voltage is balanced, and the overload settings
correspond to the motor nameplate. During inspection, the pump shaft is
found to rotate with substantially more resistance than normal. Which
condition should the electrical repairer investigate FIRST?
A. Incorrect control-transformer secondary voltage
B. Mechanical overload or binding in the driven equipment
C. Excessive resistance in the motor starter coil
D. Incorrect phase sequence at the disconnect
Answer: B. Mechanical overload or binding in the driven equipment
Rationale: A motor operating under excessive mechanical load draws
increased current, which can cause the overload relay to trip even
when the electrical supply and overload settings are correct. A binding
pump, damaged bearing, misalignment, or other mechanical
restriction can produce this condition. The repairer should determine
whether the electrical overload is a consequence of excessive
mechanical loading before replacing electrical components.
2.
1
,A three-phase motor produces an audible hum but fails to accelerate
when the starter is energized. Voltage measurements at the motor
terminals show normal voltage on two phases but nearly zero voltage on
the third phase. Which fault is MOST likely?
A. Open phase or failed contact in the power circuit
B. Incorrect motor horsepower rating
C. Shorted control-transformer secondary
D. Excessive motor bearing lubrication
Answer: A. Open phase or failed contact in the power circuit
Rationale: A missing phase can prevent a three-phase motor from
developing normal starting torque while causing abnormal current in
the remaining phases. Possible causes include a failed contactor pole,
blown fuse, loose connection, broken conductor, or defective
disconnect contact. Operating the motor in this condition can rapidly
overheat the windings.
3.
When troubleshooting a 480-V industrial motor circuit, an electrician
discovers that the motor disconnect is open but the line-side terminals
remain energized. What is the MOST important conclusion?
A. The disconnect is functioning normally
B. The motor must be internally shorted
C. The circuit has not been electrically isolated from the source
D. The overload relay must be reset
Answer: C. The circuit has not been electrically isolated from the
source
Rationale: Opening a disconnect should isolate the downstream circuit
from the supply. If voltage remains present where it is expected to be
absent, the worker must determine the source and establish proper
2
,isolation before touching conductors. Safe troubleshooting requires
verification of absence of voltage at the point of work rather than
assuming a disconnect has created a safe condition.
4.
A motor starter repeatedly chatters when its contactor attempts to close.
The control voltage measured directly across the coil drops substantially
whenever the contactor pulls in. Which condition is MOST likely
responsible?
A. Excessive motor horsepower
B. Control-circuit voltage drop or inadequate control voltage
C. Incorrect motor rotation
D. Excessive grounding-electrode resistance
Answer: B. Control-circuit voltage drop or inadequate control
voltage
Rationale: A contactor coil requires sufficient voltage to pull in and
remain magnetically sealed. A weak control transformer, undersized
conductors, loose connection, damaged contacts, or excessive circuit
resistance can cause the coil voltage to collapse when energized.
Chattering can rapidly damage the contactor and should be corrected
rather than ignored.
5.
An electrical repairer measures 480 V phase-to-phase on a three-phase
system but discovers approximately 277 V phase-to-ground. What
configuration does this MOST likely indicate?
A. 480-V delta system with no grounding
B. 480Y/277-V grounded wye system
3
, C. 240-V split-phase system
D. 208-V corner-grounded delta system
Answer: B. 480Y/277-V grounded wye system
Rationale: In a balanced 480Y/277-V system, the line-to-line voltage is
approximately 480 V while the line-to-neutral voltage is approximately
277 V. This arrangement is common in industrial facilities because it
provides both 480-V three-phase power for equipment and 277-V
power for suitable lighting and other loads.
6.
A motor's overload relay trips after several minutes of operation rather
than immediately when the motor starts. The motor current is
consistently above its nameplate full-load current. Which explanation is
MOST appropriate?
A. The motor is likely experiencing sustained overloading
B. The motor has an open control circuit
C. The contactor coil is undersized
D. The phase sequence is reversed
Answer: A. The motor is likely experiencing sustained overloading
Rationale: Thermal overload devices are designed to respond to
sustained excessive current rather than instantaneous starting current.
If operating current remains above the motor's rated full-load current,
the motor can accumulate excessive heat until the overload operates.
The repairer should investigate mechanical loading, voltage
conditions, motor condition, and incorrect application rather than
simply increasing the overload setting.
7.
4
