CO Master Electrician Exam Questions
and Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
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1. What is the minimum size copper grounding electrode conductor
required for a service supplied by 2/0 AWG copper ungrounded
conductors, assuming the grounding electrode conductor is
connected to a concrete-encased electrode?
A. 6 AWG
B. 4 AWG
C. 2 AWG
D. 1/0 AWG
Answer: A. 6 AWG
Rationale: For a concrete-encased electrode, the grounding electrode
conductor is not required to be larger than 4 AWG copper, but Table
,250.66 is used to determine the conductor size. For 2/0 AWG copper
service conductors, the table would normally indicate 4 AWG;
however, when the electrode is a concrete-encased electrode, the
conductor is limited by the special rule applicable to that electrode
type. Always verify the specific electrode and connection requirements
before installation.
2. What is the primary purpose of the grounded conductor in a
typical single-phase 120/240-volt system?
A. To provide overcurrent protection
B. To carry current only during a fault
C. To provide a current-return path for line-to-neutral loads
D. To serve as the equipment grounding conductor
Answer: C. To provide a current-return path for line-to-neutral loads
Rationale: The grounded conductor, commonly called the neutral,
normally carries current from line-to-neutral loads back to the source.
It is different from the equipment grounding conductor, which is
intended primarily to carry fault current and facilitate operation of the
overcurrent protective device.
3. A 120-volt branch circuit supplies a continuous load of 16
amperes. What is the minimum ampere rating of the branch-
, circuit conductors and overcurrent device when no adjustment or
correction factors apply?
A. 15 A
B. 16 A
C. 20 A
D. 25 A
Answer: C. 20 A
Rationale: Continuous loads are generally calculated at 125 percent of
the continuous load. Sixteen amperes × 125 percent = 20 amperes.
Therefore, a 20-ampere circuit is required when the calculated load is
exactly 20 amperes and the conductors and overcurrent protection are
properly sized.
4. Which device is specifically designed to interrupt a circuit when it
detects a difference between current flowing in ungrounded and
grounded conductors?
A. AFCI
B. GFCI
C. Surge protective device
D. Thermal overload relay
Answer: B. GFCI
, Rationale: A ground-fault circuit interrupter monitors current balance
between the circuit conductors. A difference indicates that some
current may be flowing through an unintended path, such as a person
or equipment grounding path. The GFCI trips rapidly to reduce the risk
of electric shock.
5. What is the maximum number of current-carrying conductors
generally permitted in a raceway before adjustment factors for
conductor ampacity must be considered?
A. 2
B. 3
C. 4
D. 6
Answer: B. 3
Rationale: Under the general ampacity adjustment rules, when more
than three current-carrying conductors are installed together in a
raceway, cable, or similar enclosure, conductor ampacity generally
must be adjusted according to the applicable table. Other rules and
exceptions can affect whether a particular conductor is counted as
current carrying.
6. What is the purpose of an equipment grounding conductor?
and Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
Download Pdf
1. What is the minimum size copper grounding electrode conductor
required for a service supplied by 2/0 AWG copper ungrounded
conductors, assuming the grounding electrode conductor is
connected to a concrete-encased electrode?
A. 6 AWG
B. 4 AWG
C. 2 AWG
D. 1/0 AWG
Answer: A. 6 AWG
Rationale: For a concrete-encased electrode, the grounding electrode
conductor is not required to be larger than 4 AWG copper, but Table
,250.66 is used to determine the conductor size. For 2/0 AWG copper
service conductors, the table would normally indicate 4 AWG;
however, when the electrode is a concrete-encased electrode, the
conductor is limited by the special rule applicable to that electrode
type. Always verify the specific electrode and connection requirements
before installation.
2. What is the primary purpose of the grounded conductor in a
typical single-phase 120/240-volt system?
A. To provide overcurrent protection
B. To carry current only during a fault
C. To provide a current-return path for line-to-neutral loads
D. To serve as the equipment grounding conductor
Answer: C. To provide a current-return path for line-to-neutral loads
Rationale: The grounded conductor, commonly called the neutral,
normally carries current from line-to-neutral loads back to the source.
It is different from the equipment grounding conductor, which is
intended primarily to carry fault current and facilitate operation of the
overcurrent protective device.
3. A 120-volt branch circuit supplies a continuous load of 16
amperes. What is the minimum ampere rating of the branch-
, circuit conductors and overcurrent device when no adjustment or
correction factors apply?
A. 15 A
B. 16 A
C. 20 A
D. 25 A
Answer: C. 20 A
Rationale: Continuous loads are generally calculated at 125 percent of
the continuous load. Sixteen amperes × 125 percent = 20 amperes.
Therefore, a 20-ampere circuit is required when the calculated load is
exactly 20 amperes and the conductors and overcurrent protection are
properly sized.
4. Which device is specifically designed to interrupt a circuit when it
detects a difference between current flowing in ungrounded and
grounded conductors?
A. AFCI
B. GFCI
C. Surge protective device
D. Thermal overload relay
Answer: B. GFCI
, Rationale: A ground-fault circuit interrupter monitors current balance
between the circuit conductors. A difference indicates that some
current may be flowing through an unintended path, such as a person
or equipment grounding path. The GFCI trips rapidly to reduce the risk
of electric shock.
5. What is the maximum number of current-carrying conductors
generally permitted in a raceway before adjustment factors for
conductor ampacity must be considered?
A. 2
B. 3
C. 4
D. 6
Answer: B. 3
Rationale: Under the general ampacity adjustment rules, when more
than three current-carrying conductors are installed together in a
raceway, cable, or similar enclosure, conductor ampacity generally
must be adjusted according to the applicable table. Other rules and
exceptions can affect whether a particular conductor is counted as
current carrying.
6. What is the purpose of an equipment grounding conductor?
