Electrical / Technical / Engineering NCCER
ELECTRICAL LEVEL 2 MODULE 2 STUDY GUIDE
2026 – COMPLETE CONCEPT REVIEW &
PRACTICE MATERIALS (LATEST EDITION)
1. What is the primary difference between AC (Alternating Current) and DC (Direct Current)?
A: AC periodically reverses direction, while DC flows in one constant direction. AC is typically
used for power distribution; DC is common in batteries and electronics.
2. Define the term "Hertz" (Hz) in relation to AC power.
A: Hertz is the unit of frequency, indicating the number of complete cycles per second. In North
American power systems, the standard frequency is 60 Hz.
3. What are the three basic requirements for generating an alternating current (AC)?
A: A conductor, a magnetic field, and relative motion between them.
4. What is the relationship between frequency (f) and period (T) of a sine wave?
A: 𝑓 = 1/𝑇 and 𝑇 = 1/𝑓, where period is the time in seconds for one complete cycle.
5. In a purely resistive AC circuit, how are voltage and current related in terms of phase?
A: They are in phase—the voltage and current reach their peaks and zero crossings at the same
time.
6. In a purely inductive AC circuit, how does the current relate to the voltage in terms of
phase?
A: The current lags the voltage by 90 degrees.
7. What is inductive reactance (XL), and what is its formula?
A: Inductive reactance is the opposition to current change in an inductor. Formula: 𝑋𝐿 = 2𝜋𝑓𝐿,
where f is frequency and L is inductance in Henries.
8. In a purely capacitive AC circuit, how does the current relate to the voltage in terms of
phase?
A: The current leads the voltage by 90 degrees.
9. What is capacitive reactance (XC), and what is its formula?
1
A: Capacitive reactance is the opposition to current change in a capacitor. Formula: 𝑋𝐶 = 2𝜋𝑓𝐶,
where f is frequency and C is capacitance in Farads.
,10. Define "impedance" (Z) in an AC circuit.
A: Impedance is the total opposition to current flow in an AC circuit, combining resistance (R)
and reactance (X). It is measured in ohms (Ω).
11. What is the power factor of an AC circuit?
A: The ratio of true power (Watts) to apparent power (Volt-Amps). It represents the efficiency
with which current is being converted into useful work. PF = cos(θ), where θ is the phase angle.
12. What does a power factor of 1 (or unity) indicate?
A: The circuit is purely resistive (no reactive power). Voltage and current are in phase.
13. What is the formula for three-phase apparent power (in Volt-Amps)?
A: 𝐴𝑝𝑝𝑎𝑟𝑒𝑛𝑡𝑃𝑜𝑤𝑒𝑟(𝑉𝐴) = √3 × 𝑉𝑙𝑖𝑛𝑒 × 𝐼𝑙𝑖𝑛𝑒
14. In a balanced three-phase system, what is the phase relationship between the voltage
waveforms?
A: They are 120 electrical degrees apart.
15. What is the primary advantage of three-phase power over single-phase for motors and
distribution?
A: It provides a more constant power delivery, allows for smaller conductors for the same
power, and three-phase motors are simpler, more efficient, and self-starting.
Section 2: Motors & Motor Controls
16. What are the two main components of any electric motor?
A: The stator (stationary part) and the rotor (rotating part).
17. How does a three-phase induction motor develop torque?
A: The three-phase stator windings create a rotating magnetic field. This field induces a current
in the rotor conductors, creating its own magnetic field that interacts with the stator field,
producing torque.
18. What is the difference between a motor's synchronous speed and its rated full-load
speed?
A: Synchronous speed is the speed of the rotating magnetic field (determined by frequency and
poles). Full-load speed is the actual operating speed under load, which is slightly less due to
"slip."
,19. Define "slip" in an AC induction motor.
A: Slip is the difference between synchronous speed and rotor speed, expressed as a percentage
(𝑁𝑠 −𝑁𝑟 )
of synchronous speed. 𝑆𝑙𝑖𝑝(%) = × 100.
𝑁𝑠
20. What is the purpose of the centrifugal switch in a split-phase motor?
A: To disconnect the start winding once the motor reaches approximately 75% of rated speed,
preventing it from overheating.
21. Which single-phase motor type has the highest starting torque?
A. Capacitor-start motor.
22. What is the function of the start capacitor in a capacitor-start induction motor?
A: To create a greater phase shift between the start and run winding currents, resulting in higher
starting torque.
23. How is the rotation direction of a three-phase motor reversed?
A: By swapping any two of the three line connections to the motor terminals (reversing the
phase sequence).
24. What is the primary purpose of motor overload protection?
A: To protect the motor windings from damage due to excessive current from prolonged
overloads or failure to start.
25. What NEMA classification describes a general-purpose, across-the-line magnetic motor
starter?
A: NEMA 1 (for indoor use, provides dust and finger protection).
26. What is the difference between a motor "starter" and a motor "controller"?
A: A starter is a specific type of controller designed to start and stop a motor, providing overload
protection. A controller is a broader term for any device used to govern motor performance
(e.g., variable frequency drives).
27. In a magnetic motor starter, what holds the contactor closed after the start button is
released?
A: The holding or sealing circuit—an auxiliary contact in parallel with the start button that
maintains power to the coil.
28. What does the acronym "VFD" stand for, and what is its primary function?
A: Variable Frequency Drive. Its primary function is to control AC motor speed and torque by
varying the frequency and voltage of the power supplied to the motor.
, 29. List two major benefits of using a VFD.
A: 1. Energy savings by matching motor speed to load requirements. 2. Soft starting, reducing
inrush current and mechanical stress.
30. Where must a disconnecting means for a motor be located?
A: In sight from and within 15 meters (50 ft) of the motor controller (NEC 430.102), with
exceptions.
Section 3: Transformers
31. What is the fundamental principle of operation for all transformers?
A: Electromagnetic induction—a changing magnetic field in one coil induces a voltage in a
second coil.
32. What are the four basic types of transformer losses?
A: Copper losses (I²R), hysteresis losses, eddy current losses, and stray losses.
33. What is the "turns ratio" of a transformer, and how does it relate to voltage and current?
A: Turns ratio (a) = N_primary / N_secondary. It is equal to V_primary / V_secondary and
I_secondary / I_primary (for an ideal transformer).
34. A transformer has a primary voltage of 480V and a secondary voltage of 120V. What is the
turns ratio?
A: Turns ratio = 480/120 = 4:1 (a step-down transformer).
35. If the above 4:1 transformer supplies a 20A load on the secondary, what is the primary
current (neglecting losses)?
A: I_primary = I_secondary / a = 20A / 4 = 5A.
36. What is the difference between an isolation transformer and an autotransformer?
A: An isolation transformer has separate, electrically isolated primary and secondary windings.
An autotransformer uses a single winding with a tap, providing no electrical isolation.
37. What is the purpose of a "taps" on a transformer winding?
A: To allow for small adjustments to the turns ratio to compensate for variations in supply
voltage.
38. How are most dry-type transformers cooled?
A: By air (natural convection or forced air with fans).
39. What does the "X" and "Y" designation refer to in transformer terminal markings (e.g., H1,
H2, X1, X2)?
ELECTRICAL LEVEL 2 MODULE 2 STUDY GUIDE
2026 – COMPLETE CONCEPT REVIEW &
PRACTICE MATERIALS (LATEST EDITION)
1. What is the primary difference between AC (Alternating Current) and DC (Direct Current)?
A: AC periodically reverses direction, while DC flows in one constant direction. AC is typically
used for power distribution; DC is common in batteries and electronics.
2. Define the term "Hertz" (Hz) in relation to AC power.
A: Hertz is the unit of frequency, indicating the number of complete cycles per second. In North
American power systems, the standard frequency is 60 Hz.
3. What are the three basic requirements for generating an alternating current (AC)?
A: A conductor, a magnetic field, and relative motion between them.
4. What is the relationship between frequency (f) and period (T) of a sine wave?
A: 𝑓 = 1/𝑇 and 𝑇 = 1/𝑓, where period is the time in seconds for one complete cycle.
5. In a purely resistive AC circuit, how are voltage and current related in terms of phase?
A: They are in phase—the voltage and current reach their peaks and zero crossings at the same
time.
6. In a purely inductive AC circuit, how does the current relate to the voltage in terms of
phase?
A: The current lags the voltage by 90 degrees.
7. What is inductive reactance (XL), and what is its formula?
A: Inductive reactance is the opposition to current change in an inductor. Formula: 𝑋𝐿 = 2𝜋𝑓𝐿,
where f is frequency and L is inductance in Henries.
8. In a purely capacitive AC circuit, how does the current relate to the voltage in terms of
phase?
A: The current leads the voltage by 90 degrees.
9. What is capacitive reactance (XC), and what is its formula?
1
A: Capacitive reactance is the opposition to current change in a capacitor. Formula: 𝑋𝐶 = 2𝜋𝑓𝐶,
where f is frequency and C is capacitance in Farads.
,10. Define "impedance" (Z) in an AC circuit.
A: Impedance is the total opposition to current flow in an AC circuit, combining resistance (R)
and reactance (X). It is measured in ohms (Ω).
11. What is the power factor of an AC circuit?
A: The ratio of true power (Watts) to apparent power (Volt-Amps). It represents the efficiency
with which current is being converted into useful work. PF = cos(θ), where θ is the phase angle.
12. What does a power factor of 1 (or unity) indicate?
A: The circuit is purely resistive (no reactive power). Voltage and current are in phase.
13. What is the formula for three-phase apparent power (in Volt-Amps)?
A: 𝐴𝑝𝑝𝑎𝑟𝑒𝑛𝑡𝑃𝑜𝑤𝑒𝑟(𝑉𝐴) = √3 × 𝑉𝑙𝑖𝑛𝑒 × 𝐼𝑙𝑖𝑛𝑒
14. In a balanced three-phase system, what is the phase relationship between the voltage
waveforms?
A: They are 120 electrical degrees apart.
15. What is the primary advantage of three-phase power over single-phase for motors and
distribution?
A: It provides a more constant power delivery, allows for smaller conductors for the same
power, and three-phase motors are simpler, more efficient, and self-starting.
Section 2: Motors & Motor Controls
16. What are the two main components of any electric motor?
A: The stator (stationary part) and the rotor (rotating part).
17. How does a three-phase induction motor develop torque?
A: The three-phase stator windings create a rotating magnetic field. This field induces a current
in the rotor conductors, creating its own magnetic field that interacts with the stator field,
producing torque.
18. What is the difference between a motor's synchronous speed and its rated full-load
speed?
A: Synchronous speed is the speed of the rotating magnetic field (determined by frequency and
poles). Full-load speed is the actual operating speed under load, which is slightly less due to
"slip."
,19. Define "slip" in an AC induction motor.
A: Slip is the difference between synchronous speed and rotor speed, expressed as a percentage
(𝑁𝑠 −𝑁𝑟 )
of synchronous speed. 𝑆𝑙𝑖𝑝(%) = × 100.
𝑁𝑠
20. What is the purpose of the centrifugal switch in a split-phase motor?
A: To disconnect the start winding once the motor reaches approximately 75% of rated speed,
preventing it from overheating.
21. Which single-phase motor type has the highest starting torque?
A. Capacitor-start motor.
22. What is the function of the start capacitor in a capacitor-start induction motor?
A: To create a greater phase shift between the start and run winding currents, resulting in higher
starting torque.
23. How is the rotation direction of a three-phase motor reversed?
A: By swapping any two of the three line connections to the motor terminals (reversing the
phase sequence).
24. What is the primary purpose of motor overload protection?
A: To protect the motor windings from damage due to excessive current from prolonged
overloads or failure to start.
25. What NEMA classification describes a general-purpose, across-the-line magnetic motor
starter?
A: NEMA 1 (for indoor use, provides dust and finger protection).
26. What is the difference between a motor "starter" and a motor "controller"?
A: A starter is a specific type of controller designed to start and stop a motor, providing overload
protection. A controller is a broader term for any device used to govern motor performance
(e.g., variable frequency drives).
27. In a magnetic motor starter, what holds the contactor closed after the start button is
released?
A: The holding or sealing circuit—an auxiliary contact in parallel with the start button that
maintains power to the coil.
28. What does the acronym "VFD" stand for, and what is its primary function?
A: Variable Frequency Drive. Its primary function is to control AC motor speed and torque by
varying the frequency and voltage of the power supplied to the motor.
, 29. List two major benefits of using a VFD.
A: 1. Energy savings by matching motor speed to load requirements. 2. Soft starting, reducing
inrush current and mechanical stress.
30. Where must a disconnecting means for a motor be located?
A: In sight from and within 15 meters (50 ft) of the motor controller (NEC 430.102), with
exceptions.
Section 3: Transformers
31. What is the fundamental principle of operation for all transformers?
A: Electromagnetic induction—a changing magnetic field in one coil induces a voltage in a
second coil.
32. What are the four basic types of transformer losses?
A: Copper losses (I²R), hysteresis losses, eddy current losses, and stray losses.
33. What is the "turns ratio" of a transformer, and how does it relate to voltage and current?
A: Turns ratio (a) = N_primary / N_secondary. It is equal to V_primary / V_secondary and
I_secondary / I_primary (for an ideal transformer).
34. A transformer has a primary voltage of 480V and a secondary voltage of 120V. What is the
turns ratio?
A: Turns ratio = 480/120 = 4:1 (a step-down transformer).
35. If the above 4:1 transformer supplies a 20A load on the secondary, what is the primary
current (neglecting losses)?
A: I_primary = I_secondary / a = 20A / 4 = 5A.
36. What is the difference between an isolation transformer and an autotransformer?
A: An isolation transformer has separate, electrically isolated primary and secondary windings.
An autotransformer uses a single winding with a tap, providing no electrical isolation.
37. What is the purpose of a "taps" on a transformer winding?
A: To allow for small adjustments to the turns ratio to compensate for variations in supply
voltage.
38. How are most dry-type transformers cooled?
A: By air (natural convection or forced air with fans).
39. What does the "X" and "Y" designation refer to in transformer terminal markings (e.g., H1,
H2, X1, X2)?
