I85PREP
⌘ K
CT Electrician study materials
CT Electrician study resources

CT Electrician practice questions

One question at a time. Build your CT 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 and Electrical Theory

A 24-ohm resistor is connected across a 120-volt DC source. What current flows through the resistor?

  1. 0.2 A
  2. 5 A Correct answer.
  3. 2.88 A
  4. 2880 A

Explanation

Ohm's law states that current equals voltage divided by resistance, so I = 120 V / 24 ohms = 5 A. The resistance limits the current to this value for the applied voltage.

Question 2General Electrical Knowledge and Electrical Theory

A 120-volt circuit carries a current of 10 amperes. What is the power consumed by the load?

  1. 12 W
  2. 1200 W Correct answer.
  3. 12,000 W
  4. 120 W

Explanation

In a resistive DC circuit, power equals voltage multiplied by current: P = 120 V × 10 A = 1200 W. The same result is obtained from P = I squared times R once the resistance is known.

Question 3General Electrical Knowledge and Electrical Theory

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

  1. 60 ohms Correct answer.
  2. 6.0 ohms
  3. 20 ohms
  4. 600 ohms

Explanation

In a series circuit the total resistance is the sum of the individual resistances, so 10 + 20 + 30 = 60 ohms. The same current passes through each resistor, and each contributes its full resistance to the path.

Question 4General Electrical Knowledge and Electrical Theory

Two 12-ohm resistors are connected in parallel. What is the equivalent resistance of the pair?

  1. 1.2 ohms
  2. 12 ohms
  3. 6 ohms Correct answer.
  4. 24 ohms

Explanation

For two equal resistors in parallel, the equivalent resistance is half of one resistor's value, or 12/2 = 6 ohms. The product-over-sum method gives the same result: (12 × 12)/(12 + 12) = 6 ohms.

Question 5General Electrical Knowledge and Electrical Theory

What is the period of a 60-hertz alternating current waveform?

  1. 8.3 ms
  2. 16.7 ms Correct answer.
  3. 60 ms
  4. 166 ms

Explanation

Period is the reciprocal of frequency, so T = 1/60 s = 0.01667 s, or about 16.7 milliseconds. One complete cycle therefore takes roughly 16.7 ms at 60 Hz.

Question 6General Electrical Knowledge and Electrical Theory

At a junction, 8 amperes enter and two conductors carry 3 amperes and 2 amperes away from the junction. What must the remaining conductor carry?

  1. 5 A leaving the junction
  2. 3 A leaving the junction Correct answer.
  3. 2 A leaving the junction
  4. 13 A entering the junction

Explanation

Kirchhoff's current law requires that total current entering a node equal total current leaving it. The two known outgoing currents total 5 A, so the remaining path must carry 8 - 5 = 3 A away from the junction.

Question 7General Electrical Knowledge and Electrical Theory

A 4-ohm resistor and a 6-ohm resistor are in series across a 50-volt supply. What is the voltage drop across the 6-ohm resistor?

  1. 50 V
  2. 20 V
  3. 12 V
  4. 30 V Correct answer.

Explanation

Total series resistance is 10 ohms, so the current is 50/10 = 5 A. The drop across the 6-ohm resistor is 5 A × 6 ohms = 30 V, which is the same as applying the voltage-divider ratio 50 × (6/10).

Question 8General Electrical Knowledge and Electrical Theory

A 26.5-microfarad capacitor is connected to a 60-hertz source. What is its capacitive reactance?

  1. 0.01 ohm
  2. 10 ohms
  3. 100 ohms Correct answer.
  4. 1000 ohms

Explanation

Capacitive reactance is Xc = 1/(2 times pi times frequency times capacitance). Substituting gives 1/(2 × 3.1416 × 60 × 26.5 × 10^-6), which is approximately 100 ohms.

Question 9General Electrical Knowledge and Electrical Theory

A 0.1-henry inductor is connected to a 60-hertz source. What is its inductive reactance?

  1. 377 ohms
  2. 37.7 ohms Correct answer.
  3. 6.0 ohms
  4. 0.106 ohm

Explanation

Inductive reactance is XL = 2 times pi times frequency times inductance. Substituting gives 2 × 3.1416 × 60 × 0.1, which equals about 37.7 ohms. Reactance rises in direct proportion to frequency and inductance.

Question 10General Electrical Knowledge and Electrical Theory

A load draws 10 kilovolt-amperes at a power factor of 0.8. What is the real power consumed?

  1. 10 kW
  2. 12.5 kW
  3. 6 kW
  4. 8 kW Correct answer.

Explanation

Real power equals apparent power multiplied by the power factor: P = 10 kVA × 0.8 = 8 kW. The remaining 6 kVAR is reactive power that does no useful work but still loads the conductors.

Question 11General Electrical Knowledge and Electrical Theory

A balanced wye-connected source has a phase voltage of 277 volts. What is the line-to-line voltage?

  1. 831 V
  2. 160 V
  3. 277 V
  4. 480 V Correct answer.

Explanation

In a wye connection the line voltage is the square root of three times the phase voltage. Multiplying 277 V by 1.732 gives approximately 480 V between any two lines.

Question 12General Electrical Knowledge and Electrical Theory

A transformer with a 480-volt primary and a 120-volt secondary supplies 30 amperes to its load. What current flows in the primary?

  1. 7.5 A Correct answer.
  2. 120 A
  3. 4 A
  4. 30 A

Explanation

The voltage ratio is 480/120, or 4 to 1, so the current ratio is the inverse: primary current is one quarter of secondary current. Thus 30 A / 4 = 7.5 A in the primary.

Question 13General Electrical Knowledge and Electrical Theory

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

  1. It increases. Correct answer.
  2. It drops to zero.
  3. It stays the same.
  4. It decreases.

Explanation

Copper has a positive temperature coefficient, so its resistance rises as temperature rises. Higher temperature increases lattice vibration, which impedes the drift of electrons through the metal.

Question 14General Electrical Knowledge and Electrical Theory

A series circuit contains a 10-ohm resistor, an inductor with 40 ohms of reactance, and a capacitor with 40 ohms of reactance. What is the circuit impedance?

  1. 30 ohms with a lagging power factor
  2. 50 ohms with a lagging power factor
  3. 10 ohms with a unity power factor Correct answer.
  4. 90 ohms with a leading power factor

Explanation

The inductive and capacitive reactances are equal and opposite, so they cancel and the circuit is at resonance. The impedance reduces to the resistance alone, 10 ohms, and current is in phase with voltage.

Question 15General Electrical Knowledge and Electrical Theory

A balanced delta-connected load has a phase current of 20 amperes. What is the line current?

  1. 34.6 A Correct answer.
  2. 11.5 A
  3. 60 A
  4. 20 A

Explanation

In a delta connection the line current is the square root of three times the phase current. Multiplying 20 A by 1.732 gives approximately 34.6 A in each line conductor.

Question 16General Electrical Knowledge and Electrical Theory

A 10-horsepower single-phase motor operating at 240 volts draws 40 amperes at full load. What is its efficiency?

  1. 78 percent Correct answer.
  2. 72 percent
  3. 96 percent
  4. 64 percent

Explanation

Rated output is 10 × 746 = 7460 W, and input is 240 V × 40 A = 9600 W. Efficiency is output divided by input, or 7460/9600, which equals about 0.78, or 78 percent.

Question 17Wiring and Protection

In a dwelling unit, which receptacle outlets require ground-fault circuit-interrupter protection?

  1. Bathroom receptacle outlets Correct answer.
  2. Hallway receptacle outlets
  3. Living room receptacle outlets
  4. Bedroom receptacle outlets

Explanation

Section 210.8(A) of the NEC requires GFCI protection for all 125-volt, 15- and 20-ampere receptacle outlets installed in dwelling unit bathrooms, because of the shock hazard created by water and grounded surfaces. Bedrooms, living rooms, and hallways are addressed by arc-fault protection rules instead.

Question 18Wiring and Protection

Within what maximum distance from a box must Type NM cable be secured?

  1. 12 inches Correct answer.
  2. 24 inches
  3. 8 inches
  4. 18 inches

Explanation

Section 334.30 requires Type NM cable to be secured within 300 mm (12 in.) of every box and at intervals not exceeding 1.4 m (4.5 ft) along the run. The short distance near the box keeps strain off the conductors and terminations.

Question 19Wiring and Protection

In a dwelling unit bathroom, at least one receptacle outlet must be installed within what maximum distance from the outside edge of the basin?

  1. 36 inches Correct answer.
  2. 24 inches
  3. 18 inches
  4. 48 inches

Explanation

Section 210.52(D) requires at least one receptacle outlet in each dwelling unit bathroom, located within 900 mm (3 ft) of the outside edge of each basin. This allows small appliances to be used without an extension cord across a wet area.

Question 20Wiring and Protection

A 15-ampere branch circuit supplies receptacle outlets in a dwelling unit bedroom. Which protection does the NEC require for this circuit?

  1. Neither arc-fault nor ground-fault protection
  2. Combination arc-fault and ground-fault protection
  3. Arc-fault circuit-interrupter protection Correct answer.
  4. Ground-fault circuit-interrupter protection only

Explanation

Section 210.12(A) requires arc-fault circuit-interrupter protection for branch circuits supplying outlets in dwelling unit living areas, and bedrooms are included in that list. GFCI protection is not required for bedroom receptacles.

Question 21Wiring and Protection

In general, overcurrent devices must be installed in a location that is which of the following?

  1. Readily accessible Correct answer.
  2. Locked against unauthorized operation
  3. Within sight of the equipment served
  4. Accessible to qualified persons only

Explanation

Section 240.24(A) requires overcurrent devices to be readily accessible so they can be reached quickly for operation, renewal, or inspection without climbing over obstacles or using portable ladders. Certain lockable devices are permitted only in specific supervised installations.

Question 22Wiring and Protection

What is the minimum number of 20-ampere small-appliance branch circuits required for a dwelling unit kitchen?

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

Explanation

Section 210.11(C)(1) requires at least two 20-ampere small-appliance branch circuits to supply receptacle outlets in the kitchen, pantry, dining room, and similar areas. Additional circuits are required only where the load calculations demand them.

Question 23Wiring and Protection

Which statement about a junction box installed in a finished wall is correct?

  1. It must be located within 12 inches of a lighting outlet.
  2. It may be buried in concrete when marked with the circuit number.
  3. It must be accessible without removing any part of the building finish. Correct answer.
  4. It may be covered by building finish if a blank cover is installed.

Explanation

Section 314.29 requires boxes, conduit bodies, and fittings to be installed so that the wiring inside can be rendered accessible without removing any part of the building or structure. Buried or concealed boxes trap splices and prevent inspection and repair.

Question 24Wiring and Protection

A general-use snap switch controlling a lighting outlet must be connected so that it opens which conductor?

  1. The bonding jumper
  2. The neutral conductor
  3. The equipment grounding conductor
  4. The ungrounded conductor Correct answer.

Explanation

Section 404.2(A) requires switches to be connected so that the switching action occurs in the ungrounded circuit conductor. Switching the grounded conductor would leave the luminaire energized even with the switch in the open position.

Question 25Wiring and Protection

In a dwelling unit living room, receptacle outlets along the wall must be spaced so that no point along the floor line is more than what distance from a receptacle outlet?

  1. 12 feet
  2. 4 feet
  3. 8 feet
  4. 6 feet Correct answer.

Explanation

Section 210.52(A)(1) requires receptacle outlets so that no point along the floor line of any usable wall space is more than 1.8 m (6 ft) from an outlet in that space. Applied to two outlets, this rule keeps them no more than 12 feet apart.

Question 26Wiring and Protection

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

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

Explanation

Chapter 9, Table 1 limits conductor fill to 40 percent of the raceway's internal cross-sectional area when three or more conductors are installed. The 31 percent and 53 percent limits apply to two conductors and one conductor, respectively.

Question 27Wiring and Protection

What is the maximum standard ampere rating of an overcurrent device permitted to protect a 14 AWG copper branch-circuit conductor that is not part of a motor circuit?

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

Explanation

Section 240.4(D)(1) limits overcurrent protection for 14 AWG copper to 15 amperes, regardless of the conductor's higher ampacity in Table 310.16. The small-conductor rule protects the conductor from damage that its physical size could not tolerate.

Question 28Wiring and Protection

A 60-ampere circuit is protected by a 60-ampere circuit breaker. What is the minimum size copper equipment grounding conductor required?

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

Explanation

Table 250.122 sizes the equipment grounding conductor by the rating of the overcurrent device protecting the circuit, and a 60-ampere device requires 10 AWG copper. The equipment grounding conductor is sized for fault-current clearing rather than for the load.

Question 29Wiring and Protection

A single driven ground rod has a measured resistance to earth greater than 25 ohms. What does the NEC require?

  1. Nothing further is required if the rod is 8 feet long.
  2. The grounding electrode conductor must be increased to 2 AWG.
  3. A supplemental grounding electrode must be installed. Correct answer.
  4. The rod must be replaced with a larger-diameter rod.

Explanation

Section 250.53(A)(2) requires a single rod, pipe, or plate electrode to have a resistance to earth of 25 ohms or less, and if it does not, one additional electrode of any type permitted by 250.52 must be installed. The supplemental electrode must be bonded to the first electrode.

Question 30Wiring and Protection

A raceway contains eight 12 AWG THHN copper current-carrying conductors supplying a 75 degrees C rated breaker. What is the largest standard ampere rating of overcurrent device permitted to protect this circuit?

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

Explanation

Eight current-carrying conductors require a 70 percent ampacity adjustment under 310.15(C)(1), giving 30 amperes times 0.70, or 21 amperes. Because 12 AWG copper branch-circuit conductors are limited to 20 amperes by 240.4(D), the largest standard device permitted is 20 amperes.

Question 31Wiring and Protection

Which 125-volt receptacle outlets in a dwelling unit must be listed as tamper-resistant?

  1. Only receptacles in bedrooms and hallways
  2. All 15- and 20-ampere receptacles Correct answer.
  3. Only receptacles within 6 feet of a sink
  4. Only receptacles in bathrooms and garages

Explanation

Section 406.12 requires all 125-volt, 15- and 20-ampere receptacle outlets installed in dwelling units to be listed tamper-resistant, with only the limited exceptions stated in the section. The shutters resist insertion of foreign objects by children.

Question 32Wiring and Protection

The service disconnecting means for a dwelling unit must be installed at which location?

  1. Inside the attached garage
  2. Within 15 feet of the meter enclosure
  3. At any accessible point on the load side of the meter
  4. Nearest the point of entry of the service conductors Correct answer.

Explanation

Section 230.70(A)(1) requires the service disconnecting means to be installed at a readily accessible location either outside the building or inside nearest the point of entry of the service conductors. This limits unfused service conductors inside the building.

Question 33Wiring and Protection

Which location is acceptable for installing Type NM cable?

  1. In a wet location
  2. In a location subject to continuous moisture
  3. Inside a dry interior wall of a dwelling Correct answer.
  4. Buried directly in the earth

Explanation

Section 334.10 permits Type NM cable in normally dry locations such as inside the framed walls of a dwelling, where it is protected from physical damage as required. Section 334.12(B) prohibits its use in wet or damp locations.

Question 34Wiring and Protection

The laundry branch circuit required for a dwelling unit must have what minimum rating and what outlet restriction?

  1. 20 amperes, with no other outlets Correct answer.
  2. 20 amperes, with additional outlets permitted
  3. 30 amperes, with no other outlets
  4. 15 amperes, with no other outlets

Explanation

Section 210.11(C)(2) requires at least one 20-ampere branch circuit for the dwelling unit laundry area, and that circuit is not permitted to supply any other outlets. Keeping the laundry circuit dedicated prevents other loads from overloading it.

Question 35Wiring and Protection

What is the minimum length of free conductor that must be provided at each outlet box for splices or terminations?

  1. 6 inches Correct answer.
  2. 4 inches
  3. 3 inches
  4. 8 inches

Explanation

Section 300.14 requires at least 150 mm (6 in.) of free conductor measured from the point where it emerges from the raceway or cable sheath, with at least 75 mm (3 in.) extending outside the box opening. The slack allows splices and devices to be made up without tension.

Question 36Wiring and Protection

How must a panelboard be protected against overcurrent?

  1. By a fused switch installed inside the panelboard enclosure
  2. On the load side, rated at 125 percent of the panelboard rating
  3. On the supply side, rated not over the panelboard rating Correct answer.
  4. Only when the panelboard contains more than 42 circuits

Explanation

Section 408.36 requires each panelboard to be protected by an overcurrent device with a rating not greater than that of the panelboard, installed on the supply side. This prevents the busbars from being subjected to current beyond their rating.

Question 37Wiring and Protection

A metal box with internal cable clamps contains six 12 AWG current-carrying conductors, two 12 AWG equipment grounding conductors, and one receptacle. What minimum box volume is required?

  1. 22.5 cubic inches Correct answer.
  2. 18.0 cubic inches
  3. 24.75 cubic inches
  4. 20.25 cubic inches

Explanation

Under 314.16(B), each 12 AWG conductor counts 2.25 cubic inches, so six conductors give 13.5 and the grounding conductors count as one conductor for 2.25. The clamp counts as one conductor (2.25) and the device counts as two conductors (4.5), totaling 22.5 cubic inches.

Question 38Wiring and Protection

A 4-inch by 4-inch by 1-1/2-inch metal box contains no devices, no cable clamps, and no grounding conductors. What is the maximum number of 12 AWG conductors permitted in the box?

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

Explanation

Chapter 9, Table 314.16(A) gives a volume of 21 cubic inches for a 4 by 4 by 1-1/2 inch box, and Table 314.16(B) assigns 2.25 cubic inches to each 12 AWG conductor. Dividing 21 by 2.25 gives 9.3, so a maximum of 9 conductors is permitted.

Question 39Wiring and Protection

A dwelling unit is served by a 200-ampere service. Using the dwelling unit provisions of 310.12, what minimum size copper service-entrance conductor is permitted?

  1. 4/0 AWG
  2. 2/0 AWG Correct answer.
  3. 3/0 AWG
  4. 1/0 AWG

Explanation

Section 310.12 permits service conductors for a dwelling unit rated 100 through 400 amperes to have an ampacity of at least 83 percent of the service rating, so 200 amperes requires 166 amperes. From Table 310.16 at 75 degrees C, 2/0 AWG copper provides 175 amperes and is the minimum that satisfies the rule.

Question 40Wiring and Protection

A service is supplied by 2/0 AWG copper service-entrance conductors. What minimum size copper grounding electrode conductor is required?

  1. 2 AWG
  2. 4 AWG Correct answer.
  3. 6 AWG
  4. 1/0 AWG

Explanation

Table 250.66 sizes the grounding electrode conductor from the largest service-entrance conductor, and a 2/0 copper service conductor falls in the range that requires a 4 AWG copper grounding electrode conductor. The conductor must be continuous and installed as required by 250.64.

Question 41Wiring and Protection

A 480Y/277-volt switchboard is installed where there are grounded parts on one side of the working space and no live parts on the other. What minimum depth of working space is required in front of the switchboard?

  1. 3 feet
  2. 4 feet Correct answer.
  3. 3-1/2 feet
  4. 5 feet

Explanation

Table 110.26(A)(1) sets working space depth by voltage to ground and by the conditions on either side of the space. For equipment operating at 151 to 600 volts to ground under condition 2, the minimum depth is 1.2 m (4 ft).

Question 42Wiring and Protection

Which receptacle outlets in a dwelling unit garage must be provided with ground-fault circuit-interrupter protection?

  1. Only receptacles within 6 feet of a sink
  2. All 125-volt, 15- and 20-ampere receptacles Correct answer.
  3. Only receptacles installed outdoors
  4. Only receptacles that supply motor-driven appliances

Explanation

Section 210.8(A)(2) requires GFCI protection for all 125-volt, 15- and 20-ampere receptacle outlets installed in a dwelling unit garage. The requirement applies regardless of the equipment that may be plugged in.

Question 43Wiring and Protection

A 15-ampere branch circuit supplies receptacle outlets in a dwelling unit bedroom. What protection does the NEC require for this circuit?

  1. No special protection
  2. Arc-fault circuit-interrupter protection Correct answer.
  3. Ground-fault circuit-interrupter protection only
  4. Both arc-fault and ground-fault protection

Explanation

Section 210.12(A) requires arc-fault circuit-interrupter protection for branch circuits supplying outlets in dwelling unit bedrooms. GFCI protection is not triggered by the bedroom location itself.

Question 44Wiring and Protection

A single 20-ampere branch circuit supplies the bathroom receptacle outlets in two bathrooms of a dwelling unit. Which other outlets may this circuit supply?

  1. No other outlets Correct answer.
  2. A receptacle in an adjacent hallway
  3. Lighting outlets in both bathrooms
  4. Exhaust fans in both bathrooms

Explanation

Section 210.11(C)(3) requires a 20-ampere branch circuit for bathroom receptacle outlets with no other outlets. The allowance for supplying other outlets in the same bathroom applies only when the circuit serves a single bathroom.

Question 45Wiring and Protection

Along a dwelling unit kitchen countertop, receptacle outlets must be installed so that no point along the wall line is more than what distance from a receptacle outlet?

  1. 24 inches Correct answer.
  2. 12 inches
  3. 36 inches
  4. 18 inches

Explanation

Section 210.52(C)(1) requires countertop receptacle outlets so that no point along the wall line is more than 24 inches measured horizontally from a receptacle outlet.

Question 46Wiring and Protection

Type NM cable must be secured within what maximum distance of an outlet box and at what maximum intervals along the run?

  1. 12 inches from the box and every 4-1/2 feet Correct answer.
  2. 12 inches from the box and every 6 feet
  3. 8 inches from the box and every 3 feet
  4. 18 inches from the box and every 4-1/2 feet

Explanation

Section 334.30 requires Type NM cable to be secured within 12 inches of every box and at intervals not exceeding 4-1/2 feet along the run.

Question 47Wiring and Protection

Type NM cable is run through a bored hole in a wood stud, and the hole is 1 inch from the edge of the stud. What protection is required?

  1. Two wraps of electrical tape around the cable
  2. A plastic bushing at the hole
  3. No additional protection is required if the cable is listed
  4. A steel plate at least 1/16 inch thick Correct answer.

Explanation

Section 300.4(A)(1) requires a steel plate not less than 1/16 inch thick where cable passes through a bored hole closer than 1-1/4 inches from the nearest edge of the framing member. The plate protects the cable from nails and screws driven into the wall.

Question 48Wiring and Protection

What is the minimum width of the working space in front of a 24-inch-wide panelboard?

  1. 30 inches Correct answer.
  2. 42 inches
  3. 24 inches
  4. 36 inches

Explanation

Section 110.26(A)(2) requires a working space at least 30 inches wide, or the width of the equipment if greater. A 24-inch panel therefore needs a 30-inch-wide working space.

Question 49Wiring and Protection

The dedicated equipment space above a panelboard must extend from the floor to what height above the top of the panelboard, or to the structural ceiling, whichever is lower?

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

Explanation

Section 110.26(E)(1)(a) requires the dedicated equipment space to extend from the floor to 6 feet above the top of the equipment or to the structural ceiling, whichever is lower.

Question 50Wiring and Protection

A service drop crosses a residential driveway at a point 11 feet above the driveway surface. Is this installation permitted?

  1. No; the minimum clearance is 18 feet
  2. Yes; clearance rules apply only over roadways
  3. No; the minimum clearance is 12 feet Correct answer.
  4. Yes; 11 feet satisfies the 10-foot minimum

Explanation

Section 230.24(B)(1) requires a minimum vertical clearance of 12 feet over residential driveways and commercial areas not subject to truck traffic. An 11-foot clearance is therefore not permitted.