I85PREP
⌘ K
Master Electrician study materials
Master Electrician study resources

Master Electrician practice questions

One question at a time. Build your Master Electrician understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1General Electrical Knowledge, Theory, and Definitions

A 15-ohm resistor is connected across a 120-volt DC source. What current flows through the resistor?

  1. 0.125 A
  2. 1,800 A
  3. 135 A
  4. 8 A Correct answer.

Explanation

Ohm's law states that current equals voltage divided by resistance, so I = 120 V / 15 Ω = 8 A. The relationship is linear for a constant resistance, so doubling the voltage would double the current.

Question 2General Electrical Knowledge, Theory, and Definitions

Three resistors rated 10 ohms, 20 ohms, and 30 ohms are connected in series. What is the total resistance of the combination?

  1. 600 Ω
  2. 30 Ω
  3. 60 Ω Correct answer.
  4. 20 Ω

Explanation

In a series circuit the same current passes through every element, so the individual resistances simply add: 10 + 20 + 30 = 60 Ω. The total is always larger than the largest individual resistor.

Question 3General Electrical Knowledge, Theory, and Definitions

A 240-volt circuit supplies 10 amperes to a purely resistive load. What is the power consumed by the load?

  1. 240 W
  2. 2,400 W Correct answer.
  3. 24 W
  4. 24,000 W

Explanation

For a resistive load the power equals voltage multiplied by current: P = 240 V × 10 A = 2,400 W. Because the load is purely resistive, the power factor is unity and no reactive term is needed.

Question 4General Electrical Knowledge, Theory, and Definitions

How many electrical degrees are contained in one complete cycle of an AC waveform?

  1. 360° Correct answer.
  2. 90°
  3. 270°
  4. 180°

Explanation

One full cycle of a sine wave spans 360 electrical degrees, corresponding to one complete rotation of the generating vector. Half a cycle is 180 degrees and a quarter cycle is 90 degrees.

Question 5General Electrical Knowledge, Theory, and Definitions

In a purely resistive AC circuit, the current waveform is best described as being in what relationship to the voltage waveform?

  1. In phase Correct answer.
  2. 90° out of phase
  3. 45° out of phase
  4. 180° out of phase

Explanation

A purely resistive circuit contains no reactance, so current rises and falls at exactly the same instants as voltage and both reach zero together. Phase displacement appears only when inductance or capacitance is present.

Question 6General Electrical Knowledge, Theory, and Definitions

A 6-ohm resistor and a 3-ohm resistor are connected in parallel. What is the equivalent resistance of the pair?

  1. 2 Ω Correct answer.
  2. 9 Ω
  3. 4.5 Ω
  4. 18 Ω

Explanation

For two resistors in parallel, the reciprocal of the total equals the sum of the reciprocals: 1/6 + 1/3 = 1/2, so the equivalent resistance is 2 Ω. The result must be smaller than the smallest branch resistance.

Question 7General Electrical Knowledge, Theory, and Definitions

A single-phase load draws 10 amperes at 120 volts and consumes 960 watts of real power. What is the power factor of the load?

  1. 1.25
  2. 0.96
  3. 0.80 Correct answer.
  4. 0.13

Explanation

Apparent power is 120 V × 10 A = 1,200 VA, and power factor is real power divided by apparent power: 960 / 1,200 = 0.80. Power factor can never exceed unity.

Question 8General Electrical Knowledge, Theory, and Definitions

A sinusoidal voltage has an RMS value of 120 volts. What is its approximate peak value?

  1. 85 V
  2. 120 V
  3. 170 V Correct answer.
  4. 240 V

Explanation

For a sine wave the peak equals the RMS value multiplied by the square root of two, about 1.414, so 120 × 1.414 ≈ 170 V. The RMS value is the effective heating value and is always lower than the peak.

Question 9General Electrical Knowledge, Theory, and Definitions

At a junction in a circuit, 5 amperes and 3 amperes enter along two conductors. Assuming no charge accumulates at the junction, what total current leaves along the remaining conductors?

  1. 8 A Correct answer.
  2. 2 A
  3. 1.6 A
  4. 15 A

Explanation

Kirchhoff's current law requires that the total current entering a node equal the total current leaving it, since charge is conserved. The leaving current is therefore 5 + 3 = 8 A.

Question 10General Electrical Knowledge, Theory, and Definitions

A balanced three-phase load operates at 480 volts line-to-line, 100 amperes line current, and 0.9 power factor. What is the approximate real power drawn by the load?

  1. 43.2 kW
  2. 129.6 kW
  3. 74.8 kW Correct answer.
  4. 24.9 kW

Explanation

For a balanced three-phase load, P = √3 × V(line) × I(line) × power factor = 1.732 × 480 × 100 × 0.9 ≈ 74.8 kW. The square root of three accounts for the relationship between line and phase quantities.

Question 11General Electrical Knowledge, Theory, and Definitions

A 100-foot length of a particular conductor has a resistance of 0.50 ohm. What is the resistance of 200 feet of the same conductor at the same temperature?

  1. 0.25 Ω
  2. 1.0 Ω Correct answer.
  3. 2.0 Ω
  4. 0.50 Ω

Explanation

Resistance is directly proportional to conductor length when material and cross-sectional area are unchanged. Doubling the length from 100 to 200 feet doubles the resistance to 1.0 ohm.

Question 12General Electrical Knowledge, Theory, and Definitions

How does the resistance of a copper conductor change as its operating temperature rises?

  1. It remains constant
  2. It decreases
  3. It increases Correct answer.
  4. It doubles exactly

Explanation

Copper has a positive temperature coefficient, so its resistance rises as temperature increases because increased molecular vibration impedes electron flow. The change is gradual rather than a fixed doubling.

Question 13General Electrical Knowledge, Theory, and Definitions

A 240-volt single-phase branch circuit is permitted a voltage drop of 5 percent. What is the maximum permitted voltage drop in volts?

  1. 12 V Correct answer.
  2. 5 V
  3. 24 V
  4. 48 V

Explanation

Five percent of 240 volts is 0.05 × 240 = 12 volts. Voltage drop limits are expressed as a percentage of the source voltage so the same rule can be applied at any system voltage.

Question 14General Electrical Knowledge, Theory, and Definitions

A load draws 500 kW at a power factor of 0.80 lagging. What is the reactive power associated with this load?

  1. 400 kvar
  2. 375 kvar Correct answer.
  3. 500 kvar
  4. 300 kvar

Explanation

Apparent power is 500 kW / 0.80 = 625 kVA, and reactive power is the square root of (625² − 500²), which equals 375 kvar. Reactive power forms the vertical leg of the power triangle while real power forms the horizontal leg.

Question 15General Electrical Knowledge, Theory, and Definitions

A 6-ohm resistor and an 8-ohm inductive reactance are connected in series across a 120-volt AC source. What is the true power dissipated by the circuit?

  1. 1,440 W
  2. 864 W Correct answer.
  3. 1,152 W
  4. 1,200 W

Explanation

Impedance is the square root of (6² + 8²) = 10 Ω, so the current is 120 / 10 = 12 A. True power is dissipated only in the resistance: I²R = 144 × 6 = 864 W.

Question 16General Electrical Knowledge, Theory, and Definitions

A motor delivers 10 horsepower of mechanical output while operating at 85 percent efficiency. What is the approximate electrical input power?

  1. 6.34 kW
  2. 8.78 kW Correct answer.
  3. 7.46 kW
  4. 10.3 kW

Explanation

Ten horsepower equals 10 × 746 = 7,460 W of output. Input power is output divided by efficiency: 7,460 / 0.85 ≈ 8,776 W, or about 8.78 kW.

Question 17Wiring Methods, Materials, and Installation Practices

What is the maximum distance between supports for Type NM cable run through the open stud bays of a dwelling?

  1. 4 1/2 ft Correct answer.
  2. 8 ft
  3. 6 ft
  4. 10 ft

Explanation

Section 334.30 requires Type NM cable to be secured at intervals not exceeding 4 1/2 ft and within 12 in of each box. The 4 1/2 ft spacing is the maximum permitted support interval.

Question 18Wiring Methods, Materials, and Installation Practices

Type UF cable is direct-buried with no concrete cover. What minimum burial depth is required?

  1. 36 in
  2. 24 in Correct answer.
  3. 18 in
  4. 30 in

Explanation

Table 300.5 requires 24 in of cover for Type UF cable directly buried without concrete or other approved protection. A lesser depth is permitted only where the table grants a specific reduction.

Question 19Wiring Methods, Materials, and Installation Practices

What is the maximum spacing between supports for a straight horizontal run of 1-inch electrical metallic tubing?

  1. 12 ft
  2. 6 ft
  3. 10 ft Correct answer.
  4. 8 ft

Explanation

Section 358.30 limits support spacing for EMT to intervals not exceeding 10 ft, with additional support required within 3 ft of boxes and fittings. The 10 ft interval applies to 1-inch EMT.

Question 20Wiring Methods, Materials, and Installation Practices

When calculating box fill, how many conductors does each yoke or strap containing one or more devices count as?

  1. Four conductors
  2. One conductor
  3. Two conductors Correct answer.
  4. Three conductors

Explanation

Section 314.16(B)(4) counts each yoke or strap containing one or more devices as two conductors based on the largest conductor connected to the device. This accounts for the space the device occupies in the box.

Question 21Wiring Methods, Materials, and Installation Practices

What is the minimum earth cover for rigid metal conduit buried beneath a lawn at a dwelling?

  1. 18 in
  2. 12 in
  3. 24 in
  4. 6 in Correct answer.

Explanation

Table 300.5 permits rigid metal conduit to be buried with only 6 in of cover where the conduit is not under a street, driveway, or other special surface. The 6 in dimension applies to RMC and IMC in ordinary earth.

Question 22Wiring Methods, Materials, and Installation Practices

Which color is reserved for the grounded conductor of a branch circuit?

  1. Orange
  2. Green
  3. White or gray Correct answer.
  4. Bare copper

Explanation

Section 200.6 requires the grounded conductor to be identified by a continuous white or gray outer finish. Green and bare are reserved for equipment grounding conductors.

Question 23Wiring Methods, Materials, and Installation Practices

What is the smallest copper conductor permitted for a 15-ampere branch circuit?

  1. 14 AWG Correct answer.
  2. 18 AWG
  3. 12 AWG
  4. 16 AWG

Explanation

Section 240.4(D) and common branch-circuit sizing rules permit 14 AWG copper for a 15-ampere circuit. Smaller sizes are not permitted for branch-circuit conductors.

Question 24Wiring Methods, Materials, and Installation Practices

A raceway contains four THHN conductors. What maximum percentage of the conduit's interior cross-sectional area may the conductors occupy?

  1. 31 percent
  2. 60 percent
  3. 53 percent
  4. 40 percent Correct answer.

Explanation

Chapter 9, Table 1 permits 40 percent fill where three or more conductors are installed in a raceway. The 40 percent limit provides room for pulling and heat dissipation.

Question 25Wiring Methods, Materials, and Installation Practices

Seven current-carrying 12 AWG THHN conductors are installed in one EMT. What adjustment factor applies?

  1. 70 percent Correct answer.
  2. 45 percent
  3. 80 percent
  4. 50 percent

Explanation

Table 310.15(C)(1) applies a 70 percent adjustment factor where seven to nine current-carrying conductors are installed in a single raceway. The factor accounts for reduced heat dissipation.

Question 26Wiring Methods, Materials, and Installation Practices

An outdoor PVC conduit run is subject to a temperature change that will cause a length change of at least what amount before an expansion fitting is required?

  1. 1/4 in Correct answer.
  2. 1/8 in
  3. 1 in
  4. 1/2 in

Explanation

Section 352.44 requires expansion fittings where the expected temperature change will cause a length change of 1/4 in or more. The fitting accommodates the calculated movement of the PVC run.

Question 27Wiring Methods, Materials, and Installation Practices

Which of the following raceways is permitted to serve as an equipment grounding conductor without a supplementary wire?

  1. Rigid nonmetallic conduit
  2. Schedule 40 PVC
  3. EMT Correct answer.
  4. LFNC

Explanation

Section 250.118 lists electrical metallic tubing as a permitted equipment grounding conductor where it is installed and bonded as required. Nonmetallic raceways do not provide a grounding path.

Question 28Wiring Methods, Materials, and Installation Practices

A splice in a branch-circuit conductor is permitted in which location?

  1. A conduit body without a removable cover
  2. A concealed ceiling space
  3. An accessible junction box Correct answer.
  4. Plaster embedded in a wall

Explanation

Splices must be made in an enclosure that remains accessible, such as a junction box with a removable cover. Concealed or inaccessible locations are not permitted for splices.

Question 29Wiring Methods, Materials, and Installation Practices

What is the maximum support interval for Type MC cable?

  1. Every 10 ft
  2. Every 6 ft Correct answer.
  3. Every 3 ft
  4. Every 4 1/2 ft

Explanation

Section 330.30 requires Type MC cable to be supported at intervals not exceeding 6 ft and within 12 in of boxes and fittings. The 6 ft limit applies unless the cable is specifically listed for support at greater intervals.

Question 30Wiring Methods, Materials, and Installation Practices

A 4 in x 4 in x 1 1/2 in square metal box has a volume of 21 cu in. How many 12 AWG THHN conductors, each counted at 2.25 cu in, can it contain?

  1. 9 conductors Correct answer.
  2. 11 conductors
  3. 10 conductors
  4. 8 conductors

Explanation

Divide the box volume by the volume per conductor: 21 cu in divided by 2.25 cu in equals 9.33. Because a partial conductor cannot be counted, the maximum is 9 conductors, before any allowances for devices, fittings, or grounding conductors.

Question 31Wiring Methods, Materials, and Installation Practices

Where Type NM cable passes through a floor and is exposed to physical damage, it must be ____.

  1. Protected by a sleeve Correct answer.
  2. Installed in Schedule 80 PVC
  3. Encased in 2 in of concrete
  4. Supported at 12 in intervals

Explanation

Section 334.15(b) requires Type NM cable to be protected from physical damage where necessary, such as by a raceway or sleeve where it passes through a floor. The protection must be suitable for the exposure.

Question 32Wiring Methods, Materials, and Installation Practices

What is the minimum earth cover for Schedule 80 PVC conduit installed beneath a residential driveway?

  1. 30 in
  2. 12 in
  3. 18 in Correct answer.
  4. 24 in

Explanation

Table 300.5 requires 18 in of cover for PVC conduit under a one- or two-family dwelling driveway or outdoor parking area. The 24 in depth applies where the conduit is under a public street or roadway.

Question 33Wiring Methods, Materials, and Installation Practices

What minimum size copper equipment grounding conductor is required for a 60-ampere branch circuit?

  1. 12 AWG
  2. 8 AWG
  3. 10 AWG Correct answer.
  4. 6 AWG

Explanation

Table 250.122 requires a 10 AWG copper equipment grounding conductor for a circuit protected at 60 amperes. The equipment grounding conductor size is based on the rating of the overcurrent device.

Question 34Wiring Methods, Materials, and Installation Practices

A raceway contains two current-carrying conductors. What maximum percentage of the conduit's interior cross-sectional area may the conductors occupy?

  1. 31 percent Correct answer.
  2. 60 percent
  3. 40 percent
  4. 53 percent

Explanation

Chapter 9, Table 1 permits 31 percent fill where two conductors are installed in a raceway. The reduced fill allows for pulling and heat dissipation.

Question 35Wiring Methods, Materials, and Installation Practices

What is the maximum distance from a box to the first support for rigid metal conduit?

  1. 2 ft
  2. 5 ft
  3. 3 ft Correct answer.
  4. 1 ft

Explanation

Section 344.30 requires rigid metal conduit to be securely fastened within 3 ft of each box or fitting and at intervals not exceeding 10 ft. The 3 ft dimension applies to the first support.

Question 36Wiring Methods, Materials, and Installation Practices

A straight pull of 3-inch rigid metal conduit enters a pull box. What minimum length must the box provide in the direction of the pull?

  1. 16 in
  2. 24 in Correct answer.
  3. 12 in
  4. 20 in

Explanation

Section 314.28(A)(1) requires the pull box length in a straight pull to be at least eight times the trade diameter of the largest raceway. For 3-inch conduit, eight times three equals 24 in.

Question 37Wiring Methods, Materials, and Installation Practices

A 1-inch EMT contains 12 current-carrying 12 AWG THHN copper conductors. Before ambient correction, what is the adjusted ampacity of each conductor?

  1. 15 A Correct answer.
  2. 24 A
  3. 30 A
  4. 20 A

Explanation

Twelve AWG THHN has a 90°C ampacity of 30 A, and Table 310.15(C)(1) applies a 50 percent factor for 10 to 20 current-carrying conductors. Thirty amperes times 0.50 equals 15 A.

Question 38Wiring Methods, Materials, and Installation Practices

A box contains four 12 AWG current-carrying conductors, two 12 AWG equipment grounding conductors, and one duplex receptacle. What minimum box volume is required?

  1. 15.75 cu in Correct answer.
  2. 18.00 cu in
  3. 20.25 cu in
  4. 13.50 cu in

Explanation

Four 12 AWG conductors count as 9.00 cu in, the two equipment grounding conductors count as one conductor at 2.25 cu in, and the duplex receptacle counts as two conductors at 4.50 cu in. The total is 15.75 cu in.

Question 39Wiring Methods, Materials, and Installation Practices

A raceway nipple is 24 inches long. What maximum percentage of its interior cross-sectional area may the conductors occupy?

  1. 50 percent
  2. 60 percent Correct answer.
  3. 70 percent
  4. 40 percent

Explanation

Chapter 9, Table 1, Note 4 permits a nipple 24 in long or less to be filled to 60 percent of its cross-sectional area. The larger fill is allowed because the short length makes pulling easier.

Question 40Wiring Methods, Materials, and Installation Practices

What is the maximum number of 12 AWG THHN conductors permitted in a 1/2-inch EMT?

  1. 10 conductors Correct answer.
  2. 7 conductors
  3. 8 conductors
  4. 9 conductors

Explanation

Using the 40 percent fill limit from Chapter 9, Table 1 and the conductor areas in Chapter 9, Table 5, a 1/2-inch EMT accepts nine 12 AWG THHN conductors. Table C.1 confirms this count.

Question 41Branch Circuits, Feeders, and Load Calculations

For load calculation purposes, what general lighting load per square foot is used for a dwelling unit?

  1. 2 VA per square foot
  2. 1 VA per square foot
  3. 5 VA per square foot
  4. 3 VA per square foot Correct answer.

Explanation

Table 220.12 assigns a general lighting load of 3 VA per square foot for dwelling units. This unit load is multiplied by the floor area computed from the outside dimensions of the dwelling. The result becomes the basis for the general lighting demand calculation.

Question 42Branch Circuits, Feeders, and Load Calculations

What is the minimum number of 20-ampere small-appliance branch circuits required to serve the kitchen and similar areas of a dwelling unit?

  1. Four
  2. Two Correct answer.
  3. One
  4. Three

Explanation

At least two 20-ampere small-appliance branch circuits must be provided for the kitchen, pantry, breakfast room, dining room, or similar area of a dwelling unit. These circuits supply all wall and floor receptacle outlets covered by that provision. They may also supply other specified outlets but must serve the required kitchen receptacles.

Question 43Branch Circuits, Feeders, and Load Calculations

Branch-circuit conductors and overcurrent devices supplying a continuous load must be sized at not less than what percentage of the continuous load?

  1. 100 percent
  2. 125 percent Correct answer.
  3. 150 percent
  4. 110 percent

Explanation

A continuous load is one expected to operate at maximum current for three hours or more. Conductors and overcurrent devices for such loads are sized at 125 percent of the load to account for heat buildup. The 125 percent factor is applied before any adjustment or correction factors.

Question 44Branch Circuits, Feeders, and Load Calculations

In a dwelling unit, what is the maximum permitted distance from any point along a wall line to the nearest receptacle outlet?

  1. 8 feet
  2. 6 feet Correct answer.
  3. 4 feet
  4. 5 feet

Explanation

Receptacle outlets must be installed so that no point along the floor line of any wall space is more than 6 feet from an outlet in that space. Because outlets may be placed within 6 feet of any point, spacing between outlets is generally 12 feet or less. The rule is intended to prevent the use of long extension cords.

Question 45Branch Circuits, Feeders, and Load Calculations

What is the minimum rating of the branch circuit that supplies the laundry receptacle outlet or outlets in a dwelling unit?

  1. 25 amperes
  2. 20 amperes Correct answer.
  3. 15 amperes
  4. 30 amperes

Explanation

In addition to the small-appliance circuits, a dwelling unit must have at least one 20-ampere branch circuit for the laundry receptacle outlet or outlets. This circuit has no other outlets. The 20-ampere minimum provides capacity for the washer and other laundry equipment.

Question 46Branch Circuits, Feeders, and Load Calculations

On a 15-ampere, 120-volt branch circuit supplying receptacle outlets, what is the maximum cord-and-plug-connected load permitted?

  1. 15 amperes
  2. 11 amperes
  3. 10 amperes
  4. 12 amperes Correct answer.

Explanation

For a 15- or 20-ampere branch circuit supplying two or more outlets, the cord-and-plug load must not exceed 80 percent of the circuit rating. Eighty percent of 15 amperes is 12 amperes. This limitation does not apply to a circuit supplying a single appliance with a fixed load.

Question 47Branch Circuits, Feeders, and Load Calculations

Receptacle outlets installed in which of the following dwelling unit rooms require ground-fault circuit-interrupter protection?

  1. A dining room
  2. A living room
  3. A bathroom Correct answer.
  4. A bedroom

Explanation

All 125-volt through 250-volt receptacle outlets in dwelling unit bathrooms require GFCI protection. Bathrooms are included because of the presence of water and grounded surfaces near the outlets. Living rooms, dining rooms, and bedrooms are covered by other rules, such as arc-fault protection rather than GFCI.

Question 48Branch Circuits, Feeders, and Load Calculations

Which of the following is a standard ampere rating for fuses and inverse-time circuit breakers?

  1. 90 amperes Correct answer.
  2. 55 amperes
  3. 65 amperes
  4. 75 amperes

Explanation

The standard ampere ratings include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, and 100 amperes, continuing in the listed increments above 100. Ninety amperes appears in that list. Ratings such as 55, 65, and 75 amperes are not standard values.

Question 49Branch Circuits, Feeders, and Load Calculations

A single household electric range rated 8 kW is supplied by a branch circuit. Using Column C of Table 220.55, what maximum demand is permitted for this range?

  1. 4,800 VA
  2. 7,200 VA
  3. 8,000 VA
  4. 6,400 VA Correct answer.

Explanation

Column C of Table 220.55 permits a single range rated 8 kW to be calculated at 80 percent of its rating. Eighty percent of 8,000 VA is 6,400 VA. Column B would apply to a single range rated 12 kW or less, but for an 8 kW range Column C gives the lower permitted demand.

Question 50Branch Circuits, Feeders, and Load Calculations

A household electric clothes dryer rated 4.5 kW is included in a dwelling unit feeder calculation. What minimum demand load must be used for the dryer?

  1. 5,000 VA Correct answer.
  2. 3,000 VA
  3. 4,500 VA
  4. 4,000 VA

Explanation

Household electric clothes dryers are calculated at a minimum of 5,000 VA, or the nameplate rating if that is higher. Because 4.5 kW is less than 5,000 VA, the 5,000 VA minimum controls. This 5,000 VA figure is used in both the standard and optional feeder calculations.