CO Master Electrician Exam
Questions And Correct Answers
(Verified Answers) Plus Rationale2026
Q&A| Instant Download Pdf
1. Which of the following is the primary purpose of a grounding electrode
system?
A. To increase voltage
B. To protect equipment from overheating
C. To provide a path for fault current to earth
D. To reduce electromagnetic interference
Rationale: Grounding electrodes protect people and equipment by
providing a low-resistance path for fault currents to flow safely to earth.
2. The maximum allowable ampacity of a conductor is based on:
A. Conductor length
B. Conductor insulation type and temperature rating
C. Number of outlets on the circuit
D. Voltage drop
Rationale: Ampacity is determined primarily by insulation type,
temperature rating, and conductor size, ensuring safe operation without
overheating.
3. According to the NEC, which conductor color is typically used for a
grounded (neutral) conductor?
A. Red
B. Black
, C. White
D. Green
Rationale: The NEC standardizes white or gray for grounded (neutral)
conductors to ensure consistent identification.
4. What is the primary function of a circuit breaker?
A. Step up voltage
B. Interrupt current during an overload or short circuit
C. Increase conductor ampacity
D. Provide continuous current
Rationale: Circuit breakers protect circuits by automatically interrupting
current flow under overload or short-circuit conditions.
5. Which device is required to protect personnel from ground faults in wet
or damp locations?
A. Fuse
B. Circuit breaker
C. Ground Fault Circuit Interrupter (GFCI)
D. Switch
Rationale: GFCIs detect ground faults and disconnect power to prevent
electric shock.
6. A 3-phase, 4-wire system has a line voltage of 480V. What is the phase
voltage?
A. 480V
B. 120V
C. 277V
D. 208V
Rationale: In a wye system, phase voltage = line voltage ÷ √3. 480 ÷ 1.732 ≈
277V.
7. Which type of conduit is most resistant to corrosion in outdoor
environments?
A. EMT
B. PVC
, C. Rigid Metal Conduit (RMC)
D. Flexible Metal Conduit
Rationale: RMC is heavy-duty and offers superior corrosion resistance
compared to EMT or FMC, especially outdoors.
8. What is the minimum depth for underground branch circuit wiring in
residential areas?
A. 6 inches
B. 12 inches
C. 18 inches
D. 24 inches
Rationale: The NEC requires 18 inches minimum burial depth for non-
metallic sheathed cables underground in residential settings.
9. When sizing a feeder, which load calculation method is used for
continuous loads?
A. Multiply by 0.75
B. Multiply by 1.25
C. Multiply by 1.0
D. Multiply by 1.5
Rationale: NEC requires feeder ampacity to be 125% of the continuous
load to prevent overheating.
10. Which of the following is considered a continuous load?
A. Refrigerator
B. Lighting that operates for 3 hours or more continuously
C. Dishwasher
D. Microwave
Rationale: Continuous loads are defined as loads expected to run for 3
hours or more, requiring derating of the conductors.
11. The purpose of a bonding jumper is to:
A. Increase voltage
B. Maintain electrical continuity and ensure a low-impedance path
to ground
Questions And Correct Answers
(Verified Answers) Plus Rationale2026
Q&A| Instant Download Pdf
1. Which of the following is the primary purpose of a grounding electrode
system?
A. To increase voltage
B. To protect equipment from overheating
C. To provide a path for fault current to earth
D. To reduce electromagnetic interference
Rationale: Grounding electrodes protect people and equipment by
providing a low-resistance path for fault currents to flow safely to earth.
2. The maximum allowable ampacity of a conductor is based on:
A. Conductor length
B. Conductor insulation type and temperature rating
C. Number of outlets on the circuit
D. Voltage drop
Rationale: Ampacity is determined primarily by insulation type,
temperature rating, and conductor size, ensuring safe operation without
overheating.
3. According to the NEC, which conductor color is typically used for a
grounded (neutral) conductor?
A. Red
B. Black
, C. White
D. Green
Rationale: The NEC standardizes white or gray for grounded (neutral)
conductors to ensure consistent identification.
4. What is the primary function of a circuit breaker?
A. Step up voltage
B. Interrupt current during an overload or short circuit
C. Increase conductor ampacity
D. Provide continuous current
Rationale: Circuit breakers protect circuits by automatically interrupting
current flow under overload or short-circuit conditions.
5. Which device is required to protect personnel from ground faults in wet
or damp locations?
A. Fuse
B. Circuit breaker
C. Ground Fault Circuit Interrupter (GFCI)
D. Switch
Rationale: GFCIs detect ground faults and disconnect power to prevent
electric shock.
6. A 3-phase, 4-wire system has a line voltage of 480V. What is the phase
voltage?
A. 480V
B. 120V
C. 277V
D. 208V
Rationale: In a wye system, phase voltage = line voltage ÷ √3. 480 ÷ 1.732 ≈
277V.
7. Which type of conduit is most resistant to corrosion in outdoor
environments?
A. EMT
B. PVC
, C. Rigid Metal Conduit (RMC)
D. Flexible Metal Conduit
Rationale: RMC is heavy-duty and offers superior corrosion resistance
compared to EMT or FMC, especially outdoors.
8. What is the minimum depth for underground branch circuit wiring in
residential areas?
A. 6 inches
B. 12 inches
C. 18 inches
D. 24 inches
Rationale: The NEC requires 18 inches minimum burial depth for non-
metallic sheathed cables underground in residential settings.
9. When sizing a feeder, which load calculation method is used for
continuous loads?
A. Multiply by 0.75
B. Multiply by 1.25
C. Multiply by 1.0
D. Multiply by 1.5
Rationale: NEC requires feeder ampacity to be 125% of the continuous
load to prevent overheating.
10. Which of the following is considered a continuous load?
A. Refrigerator
B. Lighting that operates for 3 hours or more continuously
C. Dishwasher
D. Microwave
Rationale: Continuous loads are defined as loads expected to run for 3
hours or more, requiring derating of the conductors.
11. The purpose of a bonding jumper is to:
A. Increase voltage
B. Maintain electrical continuity and ensure a low-impedance path
to ground
