CO Class E Electrical Contractor Exam
Questions and Correct Answers (Verified
Answers) Plus Rationale 2027 Q&A|
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1. What is the primary purpose of an electrical service disconnect?
A. To increase available fault current
B. To provide a means to disconnect the service conductors from the
premises wiring
C. To regulate the utility voltage
D. To protect only the grounding electrode conductor
Answer: B. To provide a means to disconnect the service conductors
from the premises wiring
Rationale: The service disconnecting means provides a readily accessible
method of disconnecting the premises wiring from the source of supply.
This allows the electrical installation to be safely isolated for
maintenance, emergency work, or other purposes.
, 2. Which conductor normally carries current back to the source in a
single-phase 120-volt circuit?
A. Equipment grounding conductor
B. Grounding electrode conductor
C. Neutral conductor
D. Bonding jumper
Answer: C. Neutral conductor
Rationale: In a typical 120-volt circuit, the neutral is the grounded
circuit conductor that provides the return path for current from the load
back to the source. The equipment grounding conductor is intended
primarily to carry fault current rather than normal operating current.
3. What is the basic relationship described by Ohm's law?
A. P = I/R
B. E = I × R
C. R = E × I
D. I = E × R
Answer: B. E = I × R
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.
, 4. A 120-volt load draws 10 amperes. What is its approximate power
consumption?
A. 12 watts
B. 120 watts
C. 1,200 watts
D. 12,000 watts
Answer: C. 1,200 watts
Rationale: Electrical power in a simple resistive circuit can be calculated
using P = E × I. Therefore, 120 volts × 10 amperes = 1,200 watts.
5. Which device is specifically designed to open a circuit
automatically when excessive current flows?
A. Transformer
B. Circuit breaker
C. Disconnect switch
D. Receptacle
Answer: B. Circuit breaker
Rationale: A circuit breaker provides overcurrent protection by opening
the circuit when current exceeds its rated or trip characteristics. It can
generally be reset after the fault or overload has been corrected.
, 6. What is the primary purpose of equipment grounding and
bonding?
A. To increase normal load current
B. To provide a low-impedance path for fault current
C. To reduce conductor resistance
D. To increase service voltage
Answer: B. To provide a low-impedance path for fault current
Rationale: Grounding and bonding establish conductive paths that help
fault current return to its source. A sufficiently low-impedance path
allows the overcurrent protective device to operate promptly.
7. Under the NEC, which article primarily covers grounding and
bonding?
A. Article 110
B. Article 210
C. Article 250
D. Article 430
Answer: C. Article 250
Rationale: NEC Article 250 contains the principal requirements for
grounding and bonding electrical systems and equipment. It addresses
Questions and Correct Answers (Verified
Answers) Plus Rationale 2027 Q&A|
Instant Download Pdf
1. What is the primary purpose of an electrical service disconnect?
A. To increase available fault current
B. To provide a means to disconnect the service conductors from the
premises wiring
C. To regulate the utility voltage
D. To protect only the grounding electrode conductor
Answer: B. To provide a means to disconnect the service conductors
from the premises wiring
Rationale: The service disconnecting means provides a readily accessible
method of disconnecting the premises wiring from the source of supply.
This allows the electrical installation to be safely isolated for
maintenance, emergency work, or other purposes.
, 2. Which conductor normally carries current back to the source in a
single-phase 120-volt circuit?
A. Equipment grounding conductor
B. Grounding electrode conductor
C. Neutral conductor
D. Bonding jumper
Answer: C. Neutral conductor
Rationale: In a typical 120-volt circuit, the neutral is the grounded
circuit conductor that provides the return path for current from the load
back to the source. The equipment grounding conductor is intended
primarily to carry fault current rather than normal operating current.
3. What is the basic relationship described by Ohm's law?
A. P = I/R
B. E = I × R
C. R = E × I
D. I = E × R
Answer: B. E = I × R
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.
, 4. A 120-volt load draws 10 amperes. What is its approximate power
consumption?
A. 12 watts
B. 120 watts
C. 1,200 watts
D. 12,000 watts
Answer: C. 1,200 watts
Rationale: Electrical power in a simple resistive circuit can be calculated
using P = E × I. Therefore, 120 volts × 10 amperes = 1,200 watts.
5. Which device is specifically designed to open a circuit
automatically when excessive current flows?
A. Transformer
B. Circuit breaker
C. Disconnect switch
D. Receptacle
Answer: B. Circuit breaker
Rationale: A circuit breaker provides overcurrent protection by opening
the circuit when current exceeds its rated or trip characteristics. It can
generally be reset after the fault or overload has been corrected.
, 6. What is the primary purpose of equipment grounding and
bonding?
A. To increase normal load current
B. To provide a low-impedance path for fault current
C. To reduce conductor resistance
D. To increase service voltage
Answer: B. To provide a low-impedance path for fault current
Rationale: Grounding and bonding establish conductive paths that help
fault current return to its source. A sufficiently low-impedance path
allows the overcurrent protective device to operate promptly.
7. Under the NEC, which article primarily covers grounding and
bonding?
A. Article 110
B. Article 210
C. Article 250
D. Article 430
Answer: C. Article 250
Rationale: NEC Article 250 contains the principal requirements for
grounding and bonding electrical systems and equipment. It addresses
