CO Master Electrician Exam Questions
and Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
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1. What is the primary purpose of a circuit breaker in an electrical
distribution system?
A. To increase circuit voltage
B. To improve power factor
C. To interrupt current when an overcurrent condition occurs
D. To reduce conductor resistance
Rationale: A circuit breaker is an overcurrent protective device
designed to open a circuit when current exceeds the permitted level.
This protects conductors and equipment from damage caused by
overloads and short circuits.
2. Which unit is used to measure electrical resistance?
,A. Volt
B. Ampere
C. Watt
D. Ohm
Rationale: Resistance is measured in ohms (Ω). Voltage is measured in
volts, current in amperes, and power in watts.
3. In a balanced three-phase system, the phase conductors are
separated electrically by what angle?
A. 60 degrees
B. 90 degrees
C. 120 degrees
D. 180 degrees
Rationale: The three phases of a balanced three-phase system are
displaced by 120 electrical degrees from one another. This
arrangement allows efficient transmission and distribution of
electrical power.
4. What is the main function of a grounding electrode system?
A. To increase circuit voltage
B. To provide a normal current-carrying path
,C. To establish a connection to earth for the electrical system
D. To eliminate all voltage in a circuit
Rationale: The grounding electrode system connects the electrical
system to earth. It helps stabilize system voltage relative to earth and
provides a path for certain fault and surge conditions.
5. Which conductor normally carries current back to the source in a
grounded single-phase circuit?
A. Equipment grounding conductor
B. Grounding electrode conductor
C. Neutral conductor
D. Bonding jumper
Rationale: In a typical grounded circuit, the neutral conductor is the
grounded circuit conductor and carries unbalanced current back to the
source. The equipment grounding conductor is normally intended for
fault-current conditions rather than normal load current.
6. What is the basic electrical relationship expressed by Ohm's law?
A. P = I × R
B. E = I × R
C. P = E × I
D. R = E × P
, Rationale: Ohm's law states that voltage (E) equals current (I)
multiplied by resistance (R). The relationship can also be rearranged
to calculate current or resistance.
7. A 120-volt circuit supplies a 10-ampere load. What is the
approximate power consumed by the load?
A. 12 watts
B. 120 watts
C. 1,200 watts
D. 12,000 watts
Rationale: Electrical power is calculated as P = E × I. Therefore, 120 V ×
10 A = 1,200 W.
8. Which type of circuit has all loads connected across the same two
points?
A. Series circuit
B. Parallel circuit
C. Open circuit
D. Ground-fault circuit
Rationale: In a parallel circuit, each branch is connected across the
same source voltage. This allows individual loads to operate
independently while receiving the branch voltage.
and Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
Download Pdf
1. What is the primary purpose of a circuit breaker in an electrical
distribution system?
A. To increase circuit voltage
B. To improve power factor
C. To interrupt current when an overcurrent condition occurs
D. To reduce conductor resistance
Rationale: A circuit breaker is an overcurrent protective device
designed to open a circuit when current exceeds the permitted level.
This protects conductors and equipment from damage caused by
overloads and short circuits.
2. Which unit is used to measure electrical resistance?
,A. Volt
B. Ampere
C. Watt
D. Ohm
Rationale: Resistance is measured in ohms (Ω). Voltage is measured in
volts, current in amperes, and power in watts.
3. In a balanced three-phase system, the phase conductors are
separated electrically by what angle?
A. 60 degrees
B. 90 degrees
C. 120 degrees
D. 180 degrees
Rationale: The three phases of a balanced three-phase system are
displaced by 120 electrical degrees from one another. This
arrangement allows efficient transmission and distribution of
electrical power.
4. What is the main function of a grounding electrode system?
A. To increase circuit voltage
B. To provide a normal current-carrying path
,C. To establish a connection to earth for the electrical system
D. To eliminate all voltage in a circuit
Rationale: The grounding electrode system connects the electrical
system to earth. It helps stabilize system voltage relative to earth and
provides a path for certain fault and surge conditions.
5. Which conductor normally carries current back to the source in a
grounded single-phase circuit?
A. Equipment grounding conductor
B. Grounding electrode conductor
C. Neutral conductor
D. Bonding jumper
Rationale: In a typical grounded circuit, the neutral conductor is the
grounded circuit conductor and carries unbalanced current back to the
source. The equipment grounding conductor is normally intended for
fault-current conditions rather than normal load current.
6. What is the basic electrical relationship expressed by Ohm's law?
A. P = I × R
B. E = I × R
C. P = E × I
D. R = E × P
, Rationale: Ohm's law states that voltage (E) equals current (I)
multiplied by resistance (R). The relationship can also be rearranged
to calculate current or resistance.
7. A 120-volt circuit supplies a 10-ampere load. What is the
approximate power consumed by the load?
A. 12 watts
B. 120 watts
C. 1,200 watts
D. 12,000 watts
Rationale: Electrical power is calculated as P = E × I. Therefore, 120 V ×
10 A = 1,200 W.
8. Which type of circuit has all loads connected across the same two
points?
A. Series circuit
B. Parallel circuit
C. Open circuit
D. Ground-fault circuit
Rationale: In a parallel circuit, each branch is connected across the
same source voltage. This allows individual loads to operate
independently while receiving the branch voltage.
