Chicago DOB – Supervising Electrician License
Examination Questions and Correct Answers
(Verified Answers) Plus Rationale 2027 Q&A|
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1. What is the primary purpose of an overcurrent protective device?
A. To increase circuit voltage
B. To improve power factor
C. To protect conductors and equipment from excessive current
D. To provide a grounding electrode
Answer: C. To protect conductors and equipment from excessive
current
Rationale: Overcurrent protective devices such as circuit breakers and
fuses are intended to interrupt excessive current before conductors or
equipment are damaged by overheating, short circuits, or other
abnormal conditions.
2. A 120-volt branch circuit supplies a continuous load of 16
amperes. What is the minimum circuit ampacity generally
required when the continuous load is calculated at 125%?
,A. 16 A
B. 18 A
C. 20 A
D. 25 A
Answer: C. 20 A
Rationale: A continuous load is generally multiplied by 125% for
conductor and overcurrent-protection calculations. Sixteen amperes ×
1.25 = 20 amperes.
3. Which conductor is normally identified by a continuous white or
gray finish?
A. Ungrounded conductor
B. Grounded conductor
C. Equipment grounding conductor
D. Bonding jumper
Answer: B. Grounded conductor
Rationale: The grounded circuit conductor is commonly identified by a
white or gray insulation color or appropriate marking. Black, red, and
similar colors are generally used for ungrounded conductors.
4. What is the primary function of an equipment grounding
conductor?
,A. Carry normal circuit current
B. Increase circuit voltage
C. Provide a low-impedance path for fault current
D. Reduce the size of the grounding electrode
Answer: C. Provide a low-impedance path for fault current
Rationale: The equipment grounding conductor provides a conductive
path intended to facilitate operation of the overcurrent protective
device during a ground fault.
5. Which condition is most likely to cause excessive voltage drop?
A. A short conductor run with large conductors
B. A long conductor run with undersized conductors
C. A circuit with no load
D. A circuit with a properly sized conductor
Answer: B. A long conductor run with undersized conductors
Rationale: Voltage drop increases as conductor length and circuit
current increase and decreases as conductor impedance is reduced.
Long runs with undersized conductors therefore produce greater
voltage drop.
6. What is the approximate full-load current of a 12,000-watt, 240-
volt single-phase resistive load?
, A. 25 A
B. 40 A
C. 50 A
D. 60 A
Answer: C. 50 A
Rationale: For a single-phase resistive load, current is calculated as I =
P ÷ V. Thus, 12,000 ÷ 240 = 50 amperes.
7. A 120-volt circuit has a resistance of 20 ohms. What current will
flow?
A. 3 A
B. 6 A
C. 10 A
D. 20 A
Answer: B. 6 A
Rationale: Ohm's law states I = V ÷ R. Therefore, 120 volts ÷ 20 ohms =
6 amperes.
8. What is the purpose of bonding normally non-current-carrying
metal parts?
A. To increase resistance
B. To provide a path for fault current
Examination Questions and Correct Answers
(Verified Answers) Plus Rationale 2027 Q&A|
Instant Download Pdf
1. What is the primary purpose of an overcurrent protective device?
A. To increase circuit voltage
B. To improve power factor
C. To protect conductors and equipment from excessive current
D. To provide a grounding electrode
Answer: C. To protect conductors and equipment from excessive
current
Rationale: Overcurrent protective devices such as circuit breakers and
fuses are intended to interrupt excessive current before conductors or
equipment are damaged by overheating, short circuits, or other
abnormal conditions.
2. A 120-volt branch circuit supplies a continuous load of 16
amperes. What is the minimum circuit ampacity generally
required when the continuous load is calculated at 125%?
,A. 16 A
B. 18 A
C. 20 A
D. 25 A
Answer: C. 20 A
Rationale: A continuous load is generally multiplied by 125% for
conductor and overcurrent-protection calculations. Sixteen amperes ×
1.25 = 20 amperes.
3. Which conductor is normally identified by a continuous white or
gray finish?
A. Ungrounded conductor
B. Grounded conductor
C. Equipment grounding conductor
D. Bonding jumper
Answer: B. Grounded conductor
Rationale: The grounded circuit conductor is commonly identified by a
white or gray insulation color or appropriate marking. Black, red, and
similar colors are generally used for ungrounded conductors.
4. What is the primary function of an equipment grounding
conductor?
,A. Carry normal circuit current
B. Increase circuit voltage
C. Provide a low-impedance path for fault current
D. Reduce the size of the grounding electrode
Answer: C. Provide a low-impedance path for fault current
Rationale: The equipment grounding conductor provides a conductive
path intended to facilitate operation of the overcurrent protective
device during a ground fault.
5. Which condition is most likely to cause excessive voltage drop?
A. A short conductor run with large conductors
B. A long conductor run with undersized conductors
C. A circuit with no load
D. A circuit with a properly sized conductor
Answer: B. A long conductor run with undersized conductors
Rationale: Voltage drop increases as conductor length and circuit
current increase and decreases as conductor impedance is reduced.
Long runs with undersized conductors therefore produce greater
voltage drop.
6. What is the approximate full-load current of a 12,000-watt, 240-
volt single-phase resistive load?
, A. 25 A
B. 40 A
C. 50 A
D. 60 A
Answer: C. 50 A
Rationale: For a single-phase resistive load, current is calculated as I =
P ÷ V. Thus, 12,000 ÷ 240 = 50 amperes.
7. A 120-volt circuit has a resistance of 20 ohms. What current will
flow?
A. 3 A
B. 6 A
C. 10 A
D. 20 A
Answer: B. 6 A
Rationale: Ohm's law states I = V ÷ R. Therefore, 120 volts ÷ 20 ohms =
6 amperes.
8. What is the purpose of bonding normally non-current-carrying
metal parts?
A. To increase resistance
B. To provide a path for fault current
