NYC DCAS Electrician Civil Service Exam Study Guide | Complete
Practice Exam Questions with 100 % Verified Correct Answers
& Detailed Rationales | Latest Edition 2026/2027
Question 1
Which formula is used to calculate current in a simple DC circuit?
A. I = V × R
B. I = V ÷ R
C. I = R ÷ V
D. I = V + R
Correct Answer: B. I = V ÷ R
Rationale: Ohm’s Law states that current (I) equals voltage (V) divided by
resistance (R). Increasing voltage while keeping resistance constant increases
current, while increasing resistance decreases current. This relationship is
fundamental to electrical calculations and troubleshooting.
Question 2
A 120-volt circuit has a resistance of 20 ohms. What current flows through the
circuit?
A. 2 A
B. 4 A
C. 6 A
D. 8 A
Correct Answer: C. 6 A
Rationale: Using Ohm’s Law, I = V ÷ R. Therefore, 120 ÷ 20 = 6 amperes.
Understanding this calculation is important when determining circuit loading
and evaluating whether conductors and overcurrent devices are appropriately
sized.
pg. 1
,Question 3
What is the primary purpose of a circuit breaker?
A. Increase circuit voltage
B. Reduce conductor resistance
C. Provide overcurrent protection
D. Improve power factor
Correct Answer: C. Provide overcurrent protection
Rationale: A circuit breaker is designed to open a circuit when current
exceeds its permitted level for a sufficient period. This protects conductors
and equipment from damage caused by overloads or short circuits. A breaker
should not be treated simply as an ordinary on/off switch.
Question 4
What happens to current in a series circuit if resistance increases while
voltage remains constant?
A. Current increases
B. Current decreases
C. Current becomes zero immediately
D. Voltage automatically increases
Correct Answer: B. Current decreases
Rationale: Ohm’s Law shows that current is inversely proportional to
resistance when voltage remains constant. If resistance increases, less current
flows through the circuit. This principle is useful when diagnosing changes in
circuit performance.
Question 5
In a parallel circuit, what is generally true about the voltage across each
branch?
pg. 2
,A. Each branch has the same voltage
B. Voltage is always zero in the last branch
C. Each branch must have a different voltage
D. Voltage exists only in the first branch
Correct Answer: A. Each branch has the same voltage
Rationale: In an ideal parallel circuit connected across the same two points,
each branch receives the same applied voltage. The current in each branch can
differ depending on that branch's resistance or impedance.
Question 6
Which instrument is commonly used to measure voltage?
A. Ammeter
B. Voltmeter
C. Megger only
D. Frequency counter only
Correct Answer: B. Voltmeter
Rationale: A voltmeter measures electrical potential difference between two
points. When measuring voltage, the meter is normally connected in parallel
with the portion of the circuit being tested. Connecting a conventional
voltmeter incorrectly in series can create an unsafe condition or produce an
incorrect measurement.
Question 7
How should an ammeter normally be connected to measure current in a
circuit?
A. In parallel
B. In series
C. Across the power supply
D. Between neutral and ground only
pg. 3
, Correct Answer: B. In series
Rationale: Current must flow through the ammeter so that the instrument
can measure the current passing through the circuit. Therefore, a
conventional ammeter is connected in series. A clamp meter is different
because it measures current by sensing the magnetic field around a conductor
without opening the circuit.
Question 8
What is the electrical unit of resistance?
A. Volt
B. Ampere
C. Ohm
D. Watt
Correct Answer: C. Ohm
Rationale: Resistance is measured in ohms (Ω). Resistance opposes the flow
of electric current. Conductors generally have relatively low resistance, while
materials such as rubber, glass, and many plastics have much higher
resistance and are commonly used as insulating materials.
Question 9
What is the electrical unit of power?
A. Watt
B. Ohm
C. Ampere
D. Coulomb
Correct Answer: A. Watt
pg. 4
Practice Exam Questions with 100 % Verified Correct Answers
& Detailed Rationales | Latest Edition 2026/2027
Question 1
Which formula is used to calculate current in a simple DC circuit?
A. I = V × R
B. I = V ÷ R
C. I = R ÷ V
D. I = V + R
Correct Answer: B. I = V ÷ R
Rationale: Ohm’s Law states that current (I) equals voltage (V) divided by
resistance (R). Increasing voltage while keeping resistance constant increases
current, while increasing resistance decreases current. This relationship is
fundamental to electrical calculations and troubleshooting.
Question 2
A 120-volt circuit has a resistance of 20 ohms. What current flows through the
circuit?
A. 2 A
B. 4 A
C. 6 A
D. 8 A
Correct Answer: C. 6 A
Rationale: Using Ohm’s Law, I = V ÷ R. Therefore, 120 ÷ 20 = 6 amperes.
Understanding this calculation is important when determining circuit loading
and evaluating whether conductors and overcurrent devices are appropriately
sized.
pg. 1
,Question 3
What is the primary purpose of a circuit breaker?
A. Increase circuit voltage
B. Reduce conductor resistance
C. Provide overcurrent protection
D. Improve power factor
Correct Answer: C. Provide overcurrent protection
Rationale: A circuit breaker is designed to open a circuit when current
exceeds its permitted level for a sufficient period. This protects conductors
and equipment from damage caused by overloads or short circuits. A breaker
should not be treated simply as an ordinary on/off switch.
Question 4
What happens to current in a series circuit if resistance increases while
voltage remains constant?
A. Current increases
B. Current decreases
C. Current becomes zero immediately
D. Voltage automatically increases
Correct Answer: B. Current decreases
Rationale: Ohm’s Law shows that current is inversely proportional to
resistance when voltage remains constant. If resistance increases, less current
flows through the circuit. This principle is useful when diagnosing changes in
circuit performance.
Question 5
In a parallel circuit, what is generally true about the voltage across each
branch?
pg. 2
,A. Each branch has the same voltage
B. Voltage is always zero in the last branch
C. Each branch must have a different voltage
D. Voltage exists only in the first branch
Correct Answer: A. Each branch has the same voltage
Rationale: In an ideal parallel circuit connected across the same two points,
each branch receives the same applied voltage. The current in each branch can
differ depending on that branch's resistance or impedance.
Question 6
Which instrument is commonly used to measure voltage?
A. Ammeter
B. Voltmeter
C. Megger only
D. Frequency counter only
Correct Answer: B. Voltmeter
Rationale: A voltmeter measures electrical potential difference between two
points. When measuring voltage, the meter is normally connected in parallel
with the portion of the circuit being tested. Connecting a conventional
voltmeter incorrectly in series can create an unsafe condition or produce an
incorrect measurement.
Question 7
How should an ammeter normally be connected to measure current in a
circuit?
A. In parallel
B. In series
C. Across the power supply
D. Between neutral and ground only
pg. 3
, Correct Answer: B. In series
Rationale: Current must flow through the ammeter so that the instrument
can measure the current passing through the circuit. Therefore, a
conventional ammeter is connected in series. A clamp meter is different
because it measures current by sensing the magnetic field around a conductor
without opening the circuit.
Question 8
What is the electrical unit of resistance?
A. Volt
B. Ampere
C. Ohm
D. Watt
Correct Answer: C. Ohm
Rationale: Resistance is measured in ohms (Ω). Resistance opposes the flow
of electric current. Conductors generally have relatively low resistance, while
materials such as rubber, glass, and many plastics have much higher
resistance and are commonly used as insulating materials.
Question 9
What is the electrical unit of power?
A. Watt
B. Ohm
C. Ampere
D. Coulomb
Correct Answer: A. Watt
pg. 4
