NYC DCAS Electrician Exam – Complete
2026/2027-Question Study Guide with Answers &
Detailed Explanations (Based on NEC & NYC
Electrical Code) PDF
SECTION 1: ELECTRICAL THEORY & OHM'S LAW
1. According to Ohm's Law, if a circuit has a voltage of 120 volts and a resistance of
30 ohms, what is the current flow in amperes?
Answer: 4 amperes (120 V ÷ 30 Ω = 4 A).
*Explanation: Ohm's Law states I = E ÷ R (Current = Voltage ÷ Resistance). This
fundamental calculation is essential for sizing conductors, selecting overcurrent protection,
and troubleshooting electrical circuits. A 120-volt circuit with 30 ohms of resistance draws 4
amperes, which would require a minimum of #14 AWG copper wire (rated for 15 amperes).*
2. State Ohm's Law formula for voltage.
Answer: V = I × R (Voltage = Current × Resistance).
Explanation: This relationship is the foundation of all electrical calculations. Voltage
(measured in volts) is the electrical pressure that pushes current through a circuit.
Increasing either current or resistance will proportionally increase voltage. This formula is
used daily by NYC electricians to calculate voltage drops, determine if a circuit is
overloaded, and size transformers.
3. What is the unit of electrical resistance?
Answer: The ohm (symbol Ω).
Explanation: The ohm is the SI unit of electrical resistance, named after German
physicist Georg Simon Ohm who established Ohm's Law in 1827. Resistance is the
opposition to current flow. One ohm is defined as the resistance that allows one ampere of
current to flow when one volt of electrical pressure is applied. Electricians measure
resistance with ohmmeters (megohmmeters for insulation resistance testing).
,4. What is the unit of electric power?
Answer: The watt (symbol W).
*Explanation: The watt is the SI unit of electrical power, named after Scottish inventor
James Watt. One watt equals one joule per second, representing the rate at which electrical
work is performed. Power in DC circuits is calculated as P = V × I. NYC electricians use
power calculations to size transformers, generators, and branch circuits. One horsepower
(HP) equals 746 watts.*
5. State the formula for electrical power (DC).
Answer: P = V × I (Power = Voltage × Current).
*Explanation: This formula calculates the rate at which electrical energy is converted to
another form (heat, light, motion). For AC circuits, power factor must be considered: P = V ×
I × PF. In NYC buildings, electricians use this formula to determine if circuits are
overloaded, to size feeders, and to calculate energy consumption. A 120-volt circuit drawing
10 amperes consumes 1,200 watts (1.2 kW).*
6. In a DC circuit, what direction does current flow?
Answer: Current flows in only one direction (unidirectional), from the positive terminal
through the external circuit to the negative terminal of the source.
Explanation: Direct current (DC) maintains constant polarity and flows in a single
direction. Batteries, solar panels, and rectifiers produce DC. In contrast, alternating current
(AC) reverses direction periodically (typically 60 Hz in the United States). NYC buildings
primarily use AC distribution, but DC is found in battery backup systems, fire alarm panels,
and electronic equipment.
7. What is the frequency of alternating current (AC) in the United States?
Answer: 60 hertz (Hz), meaning the current changes direction 60 times per second (120
reversals per second).
Explanation: Frequency is the number of complete cycles per second. In the United
States, Canada, and parts of South America, the standard is 60 Hz. Europe and most other
countries use 50 Hz. NYC electricians must ensure that motors, transformers, and other
equipment are rated for the system frequency; using 50 Hz equipment on a 60 Hz system
can cause overheating or reduced performance.
,8. In a series circuit, how does the total resistance compare to individual
resistances?
Answer: Total resistance equals the sum of all individual resistances (R_total = R₁ + R₂
+ R₃ + ...).
Explanation: In a series circuit, current flows through each resistor one after another.
The total resistance increases with each added resistor, reducing total current. This
principle affects voltage drop calculations. For example, three 10Ω resistors in series have a
total resistance of 30Ω. NYC electricians use series connections in control circuits,
emergency lighting, and some fire alarm systems.
9. In a parallel circuit, how does the total resistance compare to the smallest
individual resistance?
Answer: Total resistance is always less than the smallest resistance in the parallel
network.
Explanation: Parallel circuits provide multiple paths for current flow. Adding more
parallel paths reduces total resistance, increasing total current. This property is why branch
circuits in buildings are wired in parallel—each outlet receives full voltage regardless of
other loads on the circuit. The formula for two parallel resistors is R_total = (R₁ × R₂) ÷ (R₁
+ R₂).
10. In a series circuit, how does the current throughout the circuit behave?
Answer: Current is the same at every point in a series circuit.
Explanation: Series circuits have only one path for electron flow. Therefore, the current
measured at the beginning, middle, or end of the circuit is identical. This is expressed as
I_total = I₁ = I₂ = I₃ = ... This principle is used in Christmas tree light strings (if one bulb
fails, all go out), and in series testing of continuity with a multimeter.
11. In a parallel circuit, how does the voltage behave across all branches?
Answer: Voltage is the same across each branch of a parallel circuit (E_total = E₁ = E₂ =
E₃ = ...).
*Explanation: Parallel circuits connect loads across the same two conductors, so each
load receives the same voltage. This is why building electrical systems use parallel wiring—
, each outlet receives 120 volts (or 208/240/277/480 volts depending on the system),
regardless of how many other outlets are on the same circuit, as long as the circuit is not
overloaded.*
12. What is the difference between alternating current (AC) and direct current (DC) in
terms of electron flow?
Answer: AC electrons periodically reverse direction (typically 60 times per second in the
US), while DC electrons flow continuously in one direction.
*Explanation: AC (used for building power distribution, lighting, motors) reverses
polarity and current direction 120 times per second. DC (used for batteries, electronics, fire
alarm systems, elevator controls) maintains constant polarity. AC is more efficient for long-
distance transmission because transformers can step voltage up or down. NYC building
distribution is primarily AC (208Y/120V, 480Y/277V), with DC only for specific low-voltage
systems.*
13. A circuit has a resistance of 15 ohms and a current of 8 amperes. What is the
voltage?
Answer: 120 volts (V = I × R = 8 A × 15 Ω = 120 V).
*Explanation: This calculation demonstrates that a standard 120-volt residential circuit
operating at 8 amperes would have a total load resistance of 15 ohms. Eight amperes is
within the capacity of a 15-ampere or 20-ampere branch circuit. NYC electricians use this
formula daily to verify circuit conditions, calculate voltage drops, and ensure that connected
loads do not exceed circuit ratings.*
14. A 480-volt, three-phase motor draws 10 amperes. What is the power in watts
(approximate, assuming unity power factor)?
Answer: Approximately 8,310 watts (P = √3 × V × I × PF = 1.732 × 480 V × 10 A × 1.0 ≈
8,313 W).
*Explanation: Three-phase power calculation requires the √3 (1.732) factor because
phase voltages and currents are 120 degrees apart. Unity power factor (PF=1.0) is
assumed for heating loads; motors typically have lower power factors (0.7-0.9). NYC
electricians use three-phase power for elevators, HVAC equipment, pumps, and large
machinery in commercial buildings. Real power (watts) determines heating and real work;
apparent power (VA) determines conductor and transformer sizing.*
2026/2027-Question Study Guide with Answers &
Detailed Explanations (Based on NEC & NYC
Electrical Code) PDF
SECTION 1: ELECTRICAL THEORY & OHM'S LAW
1. According to Ohm's Law, if a circuit has a voltage of 120 volts and a resistance of
30 ohms, what is the current flow in amperes?
Answer: 4 amperes (120 V ÷ 30 Ω = 4 A).
*Explanation: Ohm's Law states I = E ÷ R (Current = Voltage ÷ Resistance). This
fundamental calculation is essential for sizing conductors, selecting overcurrent protection,
and troubleshooting electrical circuits. A 120-volt circuit with 30 ohms of resistance draws 4
amperes, which would require a minimum of #14 AWG copper wire (rated for 15 amperes).*
2. State Ohm's Law formula for voltage.
Answer: V = I × R (Voltage = Current × Resistance).
Explanation: This relationship is the foundation of all electrical calculations. Voltage
(measured in volts) is the electrical pressure that pushes current through a circuit.
Increasing either current or resistance will proportionally increase voltage. This formula is
used daily by NYC electricians to calculate voltage drops, determine if a circuit is
overloaded, and size transformers.
3. What is the unit of electrical resistance?
Answer: The ohm (symbol Ω).
Explanation: The ohm is the SI unit of electrical resistance, named after German
physicist Georg Simon Ohm who established Ohm's Law in 1827. Resistance is the
opposition to current flow. One ohm is defined as the resistance that allows one ampere of
current to flow when one volt of electrical pressure is applied. Electricians measure
resistance with ohmmeters (megohmmeters for insulation resistance testing).
,4. What is the unit of electric power?
Answer: The watt (symbol W).
*Explanation: The watt is the SI unit of electrical power, named after Scottish inventor
James Watt. One watt equals one joule per second, representing the rate at which electrical
work is performed. Power in DC circuits is calculated as P = V × I. NYC electricians use
power calculations to size transformers, generators, and branch circuits. One horsepower
(HP) equals 746 watts.*
5. State the formula for electrical power (DC).
Answer: P = V × I (Power = Voltage × Current).
*Explanation: This formula calculates the rate at which electrical energy is converted to
another form (heat, light, motion). For AC circuits, power factor must be considered: P = V ×
I × PF. In NYC buildings, electricians use this formula to determine if circuits are
overloaded, to size feeders, and to calculate energy consumption. A 120-volt circuit drawing
10 amperes consumes 1,200 watts (1.2 kW).*
6. In a DC circuit, what direction does current flow?
Answer: Current flows in only one direction (unidirectional), from the positive terminal
through the external circuit to the negative terminal of the source.
Explanation: Direct current (DC) maintains constant polarity and flows in a single
direction. Batteries, solar panels, and rectifiers produce DC. In contrast, alternating current
(AC) reverses direction periodically (typically 60 Hz in the United States). NYC buildings
primarily use AC distribution, but DC is found in battery backup systems, fire alarm panels,
and electronic equipment.
7. What is the frequency of alternating current (AC) in the United States?
Answer: 60 hertz (Hz), meaning the current changes direction 60 times per second (120
reversals per second).
Explanation: Frequency is the number of complete cycles per second. In the United
States, Canada, and parts of South America, the standard is 60 Hz. Europe and most other
countries use 50 Hz. NYC electricians must ensure that motors, transformers, and other
equipment are rated for the system frequency; using 50 Hz equipment on a 60 Hz system
can cause overheating or reduced performance.
,8. In a series circuit, how does the total resistance compare to individual
resistances?
Answer: Total resistance equals the sum of all individual resistances (R_total = R₁ + R₂
+ R₃ + ...).
Explanation: In a series circuit, current flows through each resistor one after another.
The total resistance increases with each added resistor, reducing total current. This
principle affects voltage drop calculations. For example, three 10Ω resistors in series have a
total resistance of 30Ω. NYC electricians use series connections in control circuits,
emergency lighting, and some fire alarm systems.
9. In a parallel circuit, how does the total resistance compare to the smallest
individual resistance?
Answer: Total resistance is always less than the smallest resistance in the parallel
network.
Explanation: Parallel circuits provide multiple paths for current flow. Adding more
parallel paths reduces total resistance, increasing total current. This property is why branch
circuits in buildings are wired in parallel—each outlet receives full voltage regardless of
other loads on the circuit. The formula for two parallel resistors is R_total = (R₁ × R₂) ÷ (R₁
+ R₂).
10. In a series circuit, how does the current throughout the circuit behave?
Answer: Current is the same at every point in a series circuit.
Explanation: Series circuits have only one path for electron flow. Therefore, the current
measured at the beginning, middle, or end of the circuit is identical. This is expressed as
I_total = I₁ = I₂ = I₃ = ... This principle is used in Christmas tree light strings (if one bulb
fails, all go out), and in series testing of continuity with a multimeter.
11. In a parallel circuit, how does the voltage behave across all branches?
Answer: Voltage is the same across each branch of a parallel circuit (E_total = E₁ = E₂ =
E₃ = ...).
*Explanation: Parallel circuits connect loads across the same two conductors, so each
load receives the same voltage. This is why building electrical systems use parallel wiring—
, each outlet receives 120 volts (or 208/240/277/480 volts depending on the system),
regardless of how many other outlets are on the same circuit, as long as the circuit is not
overloaded.*
12. What is the difference between alternating current (AC) and direct current (DC) in
terms of electron flow?
Answer: AC electrons periodically reverse direction (typically 60 times per second in the
US), while DC electrons flow continuously in one direction.
*Explanation: AC (used for building power distribution, lighting, motors) reverses
polarity and current direction 120 times per second. DC (used for batteries, electronics, fire
alarm systems, elevator controls) maintains constant polarity. AC is more efficient for long-
distance transmission because transformers can step voltage up or down. NYC building
distribution is primarily AC (208Y/120V, 480Y/277V), with DC only for specific low-voltage
systems.*
13. A circuit has a resistance of 15 ohms and a current of 8 amperes. What is the
voltage?
Answer: 120 volts (V = I × R = 8 A × 15 Ω = 120 V).
*Explanation: This calculation demonstrates that a standard 120-volt residential circuit
operating at 8 amperes would have a total load resistance of 15 ohms. Eight amperes is
within the capacity of a 15-ampere or 20-ampere branch circuit. NYC electricians use this
formula daily to verify circuit conditions, calculate voltage drops, and ensure that connected
loads do not exceed circuit ratings.*
14. A 480-volt, three-phase motor draws 10 amperes. What is the power in watts
(approximate, assuming unity power factor)?
Answer: Approximately 8,310 watts (P = √3 × V × I × PF = 1.732 × 480 V × 10 A × 1.0 ≈
8,313 W).
*Explanation: Three-phase power calculation requires the √3 (1.732) factor because
phase voltages and currents are 120 degrees apart. Unity power factor (PF=1.0) is
assumed for heating loads; motors typically have lower power factors (0.7-0.9). NYC
electricians use three-phase power for elevators, HVAC equipment, pumps, and large
machinery in commercial buildings. Real power (watts) determines heating and real work;
apparent power (VA) determines conductor and transformer sizing.*
