LADWP Electrical Craft Helper Exam 2026–2027 | Class No. 3799 | Los Angeles
Department of Water and Power Civil Service Exam Study Guide | Electrical Craft
Helper Test Prep | Electrical Fundamentals, Ohm’s Law, AC/DC Circuits, Voltage,
Current, Resistance, Power Calculations, Electrical Tools & Equipment, Wiring,
Transformers, Motors, Grounding, Conduit, Rigging & Knots, PPE, Lockout/Tagout,
OSHA & Electrical Safety, Construction Practices & Distribution Systems | Practice
Questions, Answers & Detailed Rationales
Question 1: According to the National Electrical Code (NEC), what is the minimum burial
depth for rigid metal conduit (RMC) under a residential driveway?
A. 6 inches
B. 12 inches
C. 18 inches
D. 24 inches
CORRECT ANSWER: D. 24 inches
Rationale: The NEC requires a minimum cover of 24 inches for rigid metal conduit (RMC) under
a driveway or other areas subject to vehicle traffic. This depth protects the conduit and
conductors from physical damage due to the weight and impact of vehicles.
Question 2: In a DC series circuit, if the resistance is doubled while the voltage remains
constant, what happens to the current?
A. It doubles.
B. It halves.
C. It remains the same.
D. It quadruples.
CORRECT ANSWER: B. It halves.
Rationale: According to Ohm's Law (I = V/R), current is inversely proportional to resistance. If
resistance (R) is doubled and voltage (V) is constant, the current (I) will be reduced by half.
Question 3: What is the primary purpose of a lockout/tagout (LOTO) procedure in an
electrical maintenance setting?
A. To increase the speed of repairs.
B. To ensure equipment is properly lubricated.
C. To prevent the accidental energization of equipment during servicing.
D. To test the efficiency of circuit breakers.
CORRECT ANSWER: C. To prevent the accidental energization of equipment during servicing.
Rationale: Lockout/Tagout is a safety procedure used to ensure that dangerous machines are
properly shut off and not started up again prior to the completion of maintenance or repair
,work. It is a critical safety standard to protect workers from unexpected energization or release
of hazardous energy.
Question 4: What type of electrical drawing shows the physical layout of the equipment and
the interconnecting wires between them?
A. A schematic diagram
B. A one-line diagram
C. A wiring diagram
D. A block diagram
CORRECT ANSWER: C. A wiring diagram
Rationale: Wiring diagrams (or connection diagrams) show the physical location of components
and the actual wire paths and connections between them. This is contrasted with schematic
diagrams, which focus on the functional relationship of components.
Question 5: Which of the following materials is classified as a good conductor of electricity?
A. Glass
B. Rubber
C. Copper
D. Mica
CORRECT ANSWER: C. Copper
Rationale: Copper is a metallic element with a single free electron in its outer shell, making it an
excellent conductor of electricity. Glass, rubber, and mica are all considered insulators.
Question 6: If a transformer is rated for 480V on the primary and 120V on the secondary,
what is its turns ratio?
A. 1:4
B. 4:1
C. 2:1
D. 1:2
CORRECT ANSWER: B. 4:1
Rationale: The turns ratio is directly proportional to the voltage ratio. The primary voltage
(480V) is 4 times the secondary voltage (120V), so the turns ratio is 4:1.
Question 7: What is the primary function of a ground rod in an electrical system?
A. To provide a return path for current.
B. To serve as a neutral conductor.
,C. To dissipate electrical faults safely into the earth.
D. To increase the voltage of the system.
CORRECT ANSWER: C. To dissipate electrical faults safely into the earth.
Rationale: A ground rod provides a low-impedance path for fault currents to flow into the
earth. This helps to stabilize voltages during transient conditions (like lightning strikes) and
ensure overcurrent protection devices operate correctly.
Question 8: What is the power rating in watts of a circuit that draws 5 amps at 120 volts?
A. 24 watts
B. 60 watts
C. 600 watts
D. 115 watts
CORRECT ANSWER: C. 600 watts
Rationale: Power (P) is calculated by multiplying Voltage (V) by Current (I), using the formula P =
V x I. In this case, P = 120V x 5A = 600 watts.
Question 9: What type of motor is commonly used for residential HVAC blower applications?
A. A split-phase motor
B. A shaded-pole motor
C. A permanent split capacitor (PSC) motor
D. A series-wound motor
CORRECT ANSWER: C. A permanent split capacitor (PSC) motor
Rationale: PSC motors are widely used in HVAC applications for blowers and fans due to their
high efficiency and quiet operation compared to other single-phase motor types. They provide
good starting torque and are reliable for continuous duty.
Question 10: What is the effect of inductors and capacitors in an AC circuit?
A. They only affect the DC component.
B. They store and release energy, affecting the phase relationship between voltage and current.
C. They always cancel each other out.
D. They only affect the circuit's resistance.
CORRECT ANSWER: B. They store and release energy, affecting the phase relationship
between voltage and current.
Rationale: Inductors store energy in a magnetic field and cause the current to lag voltage.
Capacitors store energy in an electric field and cause the current to lead voltage. Their presence
in an AC circuit impacts the phase angle and overall impedance.
, Question 11: A step-down transformer is used to:
A. Increase voltage.
B. Decrease voltage.
C. Increase frequency.
D. Decrease current.
CORRECT ANSWER: B. Decrease voltage.
Rationale: A step-down transformer has a lower number of turns on the secondary winding
than on the primary winding, resulting in a lower output voltage.
Question 12: What is the primary hazard of a "backfeed" condition in an electrical system?
A. It causes the motor to run backwards.
B. It can energize a circuit that is supposed to be de-energized, creating a shock hazard.
C. It increases the resistance of the circuit.
D. It reduces the capacity of the breaker.
CORRECT ANSWER: B. It can energize a circuit that is supposed to be de-energized, creating a
shock hazard.
Rationale: Backfeed occurs when a power source (like a portable generator) is connected
improperly, sending electricity back into the utility grid or into a circuit that is being worked on.
This poses a severe electrocution hazard to utility workers and maintenance personnel.
Question 13: In a three-phase system, what is the phase-to-phase voltage if the phase-to-
neutral voltage is 277V?
A. 120V
B. 208V
C. 240V
D. 480V
CORRECT ANSWER: D. 480V
Rationale: In a three-phase WYE system, the line-to-line voltage is equal to the line-to-neutral
voltage multiplied by the square root of 3 (approx. 1.73). 277V x 1.73 = 480V.
Question 14: What does the "T" rating on a fuse refer to?
A. The type of material it is made of.
B. The temperature rating of the fuse holder.
C. The time-delay characteristic of the fuse.
D. The maximum torque it can withstand.
CORRECT ANSWER: C. The time-delay characteristic of the fuse.
Department of Water and Power Civil Service Exam Study Guide | Electrical Craft
Helper Test Prep | Electrical Fundamentals, Ohm’s Law, AC/DC Circuits, Voltage,
Current, Resistance, Power Calculations, Electrical Tools & Equipment, Wiring,
Transformers, Motors, Grounding, Conduit, Rigging & Knots, PPE, Lockout/Tagout,
OSHA & Electrical Safety, Construction Practices & Distribution Systems | Practice
Questions, Answers & Detailed Rationales
Question 1: According to the National Electrical Code (NEC), what is the minimum burial
depth for rigid metal conduit (RMC) under a residential driveway?
A. 6 inches
B. 12 inches
C. 18 inches
D. 24 inches
CORRECT ANSWER: D. 24 inches
Rationale: The NEC requires a minimum cover of 24 inches for rigid metal conduit (RMC) under
a driveway or other areas subject to vehicle traffic. This depth protects the conduit and
conductors from physical damage due to the weight and impact of vehicles.
Question 2: In a DC series circuit, if the resistance is doubled while the voltage remains
constant, what happens to the current?
A. It doubles.
B. It halves.
C. It remains the same.
D. It quadruples.
CORRECT ANSWER: B. It halves.
Rationale: According to Ohm's Law (I = V/R), current is inversely proportional to resistance. If
resistance (R) is doubled and voltage (V) is constant, the current (I) will be reduced by half.
Question 3: What is the primary purpose of a lockout/tagout (LOTO) procedure in an
electrical maintenance setting?
A. To increase the speed of repairs.
B. To ensure equipment is properly lubricated.
C. To prevent the accidental energization of equipment during servicing.
D. To test the efficiency of circuit breakers.
CORRECT ANSWER: C. To prevent the accidental energization of equipment during servicing.
Rationale: Lockout/Tagout is a safety procedure used to ensure that dangerous machines are
properly shut off and not started up again prior to the completion of maintenance or repair
,work. It is a critical safety standard to protect workers from unexpected energization or release
of hazardous energy.
Question 4: What type of electrical drawing shows the physical layout of the equipment and
the interconnecting wires between them?
A. A schematic diagram
B. A one-line diagram
C. A wiring diagram
D. A block diagram
CORRECT ANSWER: C. A wiring diagram
Rationale: Wiring diagrams (or connection diagrams) show the physical location of components
and the actual wire paths and connections between them. This is contrasted with schematic
diagrams, which focus on the functional relationship of components.
Question 5: Which of the following materials is classified as a good conductor of electricity?
A. Glass
B. Rubber
C. Copper
D. Mica
CORRECT ANSWER: C. Copper
Rationale: Copper is a metallic element with a single free electron in its outer shell, making it an
excellent conductor of electricity. Glass, rubber, and mica are all considered insulators.
Question 6: If a transformer is rated for 480V on the primary and 120V on the secondary,
what is its turns ratio?
A. 1:4
B. 4:1
C. 2:1
D. 1:2
CORRECT ANSWER: B. 4:1
Rationale: The turns ratio is directly proportional to the voltage ratio. The primary voltage
(480V) is 4 times the secondary voltage (120V), so the turns ratio is 4:1.
Question 7: What is the primary function of a ground rod in an electrical system?
A. To provide a return path for current.
B. To serve as a neutral conductor.
,C. To dissipate electrical faults safely into the earth.
D. To increase the voltage of the system.
CORRECT ANSWER: C. To dissipate electrical faults safely into the earth.
Rationale: A ground rod provides a low-impedance path for fault currents to flow into the
earth. This helps to stabilize voltages during transient conditions (like lightning strikes) and
ensure overcurrent protection devices operate correctly.
Question 8: What is the power rating in watts of a circuit that draws 5 amps at 120 volts?
A. 24 watts
B. 60 watts
C. 600 watts
D. 115 watts
CORRECT ANSWER: C. 600 watts
Rationale: Power (P) is calculated by multiplying Voltage (V) by Current (I), using the formula P =
V x I. In this case, P = 120V x 5A = 600 watts.
Question 9: What type of motor is commonly used for residential HVAC blower applications?
A. A split-phase motor
B. A shaded-pole motor
C. A permanent split capacitor (PSC) motor
D. A series-wound motor
CORRECT ANSWER: C. A permanent split capacitor (PSC) motor
Rationale: PSC motors are widely used in HVAC applications for blowers and fans due to their
high efficiency and quiet operation compared to other single-phase motor types. They provide
good starting torque and are reliable for continuous duty.
Question 10: What is the effect of inductors and capacitors in an AC circuit?
A. They only affect the DC component.
B. They store and release energy, affecting the phase relationship between voltage and current.
C. They always cancel each other out.
D. They only affect the circuit's resistance.
CORRECT ANSWER: B. They store and release energy, affecting the phase relationship
between voltage and current.
Rationale: Inductors store energy in a magnetic field and cause the current to lag voltage.
Capacitors store energy in an electric field and cause the current to lead voltage. Their presence
in an AC circuit impacts the phase angle and overall impedance.
, Question 11: A step-down transformer is used to:
A. Increase voltage.
B. Decrease voltage.
C. Increase frequency.
D. Decrease current.
CORRECT ANSWER: B. Decrease voltage.
Rationale: A step-down transformer has a lower number of turns on the secondary winding
than on the primary winding, resulting in a lower output voltage.
Question 12: What is the primary hazard of a "backfeed" condition in an electrical system?
A. It causes the motor to run backwards.
B. It can energize a circuit that is supposed to be de-energized, creating a shock hazard.
C. It increases the resistance of the circuit.
D. It reduces the capacity of the breaker.
CORRECT ANSWER: B. It can energize a circuit that is supposed to be de-energized, creating a
shock hazard.
Rationale: Backfeed occurs when a power source (like a portable generator) is connected
improperly, sending electricity back into the utility grid or into a circuit that is being worked on.
This poses a severe electrocution hazard to utility workers and maintenance personnel.
Question 13: In a three-phase system, what is the phase-to-phase voltage if the phase-to-
neutral voltage is 277V?
A. 120V
B. 208V
C. 240V
D. 480V
CORRECT ANSWER: D. 480V
Rationale: In a three-phase WYE system, the line-to-line voltage is equal to the line-to-neutral
voltage multiplied by the square root of 3 (approx. 1.73). 277V x 1.73 = 480V.
Question 14: What does the "T" rating on a fuse refer to?
A. The type of material it is made of.
B. The temperature rating of the fuse holder.
C. The time-delay characteristic of the fuse.
D. The maximum torque it can withstand.
CORRECT ANSWER: C. The time-delay characteristic of the fuse.
