CO Electrical Contractor Exam
Questions 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
system?
a. Increase circuit voltage
b. Store electrical energy
c. Interrupt current when an overcurrent condition occurs
d. Reduce conductor resistance
Rationale: A circuit breaker is an overcurrent protective device designed
to open a circuit when current exceeds the permitted level. This helps
protect conductors and equipment from overheating, damage, and fire.
2. Which unit is used to measure electrical current?
a. Volt
b. Ohm
, c. Watt
d. Ampere
Rationale: The ampere (amp) is the SI unit of electric current. Voltage
measures electrical potential difference, resistance is measured in
ohms, and power is measured in watts.
3. According to Ohm's law, which formula correctly expresses the
relationship among voltage, current, and resistance?
a. V = I/R
b. V = I × R
c. R = V × I
d. I = V × R
Rationale: Ohm's law states that voltage equals current multiplied by
resistance. Therefore, V = I × R, while current can be calculated as I =
V/R.
4. What is the main function of the grounding electrode system?
a. Increase circuit voltage
b. Provide additional circuit capacity
c. Connect the electrical system to earth for grounding purposes
d. Replace overcurrent protection
Rationale: The grounding electrode system establishes a connection
between the electrical system and earth. It helps stabilize system
,voltage with respect to ground and provides a path for certain fault and
surge conditions.
5. Which conductor normally carries current back to the source in a
single-phase branch circuit?
a. Equipment grounding conductor
b. Grounding electrode conductor
c. Neutral conductor
d. Bonding jumper
Rationale: In a typical single-phase circuit, the neutral conductor carries
return current from the load to the source. The equipment grounding
conductor normally carries current only during fault conditions.
6. What is the purpose of bonding metal electrical enclosures?
a. Increase normal operating current
b. Provide an effective fault-current path
c. Eliminate the need for circuit breakers
d. Reduce conductor size
Rationale: Bonding connects conductive metal parts together so that a
fault can travel along a low-impedance path back to the source. This
facilitates operation of the overcurrent protective device.
7. Which device is specifically designed to protect people from
certain ground-fault conditions?
, a. Transformer
b. Disconnect switch
c. Ground-fault circuit interrupter (GFCI)
d. Surge protector
Rationale: A GFCI monitors the current leaving and returning through
the circuit. If it detects an imbalance indicating possible leakage to
ground, it rapidly interrupts the circuit.
8. What is the primary purpose of an equipment grounding
conductor?
a. Carry normal load current
b. Provide a low-impedance path for fault current
c. Increase available voltage
d. Balance the utility load
Rationale: The equipment grounding conductor provides a conductive
path for fault current from exposed metal parts back to the source. This
helps cause the protective device to open promptly.
9. Which material is commonly used for electrical conductors
because of its high conductivity?
a. PVC
b. Concrete
Questions 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
system?
a. Increase circuit voltage
b. Store electrical energy
c. Interrupt current when an overcurrent condition occurs
d. Reduce conductor resistance
Rationale: A circuit breaker is an overcurrent protective device designed
to open a circuit when current exceeds the permitted level. This helps
protect conductors and equipment from overheating, damage, and fire.
2. Which unit is used to measure electrical current?
a. Volt
b. Ohm
, c. Watt
d. Ampere
Rationale: The ampere (amp) is the SI unit of electric current. Voltage
measures electrical potential difference, resistance is measured in
ohms, and power is measured in watts.
3. According to Ohm's law, which formula correctly expresses the
relationship among voltage, current, and resistance?
a. V = I/R
b. V = I × R
c. R = V × I
d. I = V × R
Rationale: Ohm's law states that voltage equals current multiplied by
resistance. Therefore, V = I × R, while current can be calculated as I =
V/R.
4. What is the main function of the grounding electrode system?
a. Increase circuit voltage
b. Provide additional circuit capacity
c. Connect the electrical system to earth for grounding purposes
d. Replace overcurrent protection
Rationale: The grounding electrode system establishes a connection
between the electrical system and earth. It helps stabilize system
,voltage with respect to ground and provides a path for certain fault and
surge conditions.
5. Which conductor normally carries current back to the source in a
single-phase branch circuit?
a. Equipment grounding conductor
b. Grounding electrode conductor
c. Neutral conductor
d. Bonding jumper
Rationale: In a typical single-phase circuit, the neutral conductor carries
return current from the load to the source. The equipment grounding
conductor normally carries current only during fault conditions.
6. What is the purpose of bonding metal electrical enclosures?
a. Increase normal operating current
b. Provide an effective fault-current path
c. Eliminate the need for circuit breakers
d. Reduce conductor size
Rationale: Bonding connects conductive metal parts together so that a
fault can travel along a low-impedance path back to the source. This
facilitates operation of the overcurrent protective device.
7. Which device is specifically designed to protect people from
certain ground-fault conditions?
, a. Transformer
b. Disconnect switch
c. Ground-fault circuit interrupter (GFCI)
d. Surge protector
Rationale: A GFCI monitors the current leaving and returning through
the circuit. If it detects an imbalance indicating possible leakage to
ground, it rapidly interrupts the circuit.
8. What is the primary purpose of an equipment grounding
conductor?
a. Carry normal load current
b. Provide a low-impedance path for fault current
c. Increase available voltage
d. Balance the utility load
Rationale: The equipment grounding conductor provides a conductive
path for fault current from exposed metal parts back to the source. This
helps cause the protective device to open promptly.
9. Which material is commonly used for electrical conductors
because of its high conductivity?
a. PVC
b. Concrete
