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NASCLA Journeyman Electrician study materials
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NASCLA Journeyman Electrician practice questions

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Question 1Electrical Principles, Theory and Code Fundamentals

A 12-ohm resistive heating element is connected across a 24-volt source. What current flows through the element?

  1. 288 A
  2. 0.5 A
  3. 12 A
  4. 2 A Correct answer.

Explanation

Ohm's law relates current, voltage, and resistance as I = E/R. Substituting the values gives 24 volts divided by 12 ohms, which equals 2 amperes.

Question 2Electrical Principles, Theory and Code Fundamentals

A 120-volt branch circuit supplies a 15-ampere resistive load. What is the power consumed by the load?

  1. 2400 W
  2. 1800 W Correct answer.
  3. 8 W
  4. 135 W

Explanation

For a resistive load the power equals voltage multiplied by current, P = E x I. Multiplying 120 volts by 15 amperes gives 1800 watts.

Question 3Electrical Principles, Theory and Code Fundamentals

Which of the following copper conductors has the largest cross-sectional area?

  1. 16 AWG
  2. 14 AWG
  3. 12 AWG
  4. 10 AWG Correct answer.

Explanation

The American Wire Gauge system works in reverse: the smaller the AWG number, the larger the conductor. Of the choices listed, 10 AWG has the lowest number and therefore the greatest cross-sectional area.

Question 4Electrical Principles, Theory and Code Fundamentals

Three resistors rated 6 ohms, 9 ohms, and 15 ohms are connected in series. What is the total resistance of the circuit?

  1. 3.3 ohms
  2. 30 ohms Correct answer.
  3. 810 ohms
  4. 0.5 ohm

Explanation

In a series circuit the total resistance is the sum of the individual resistances because the same current passes through each element in turn. Adding 6 + 9 + 15 gives 30 ohms.

Question 5Electrical Principles, Theory and Code Fundamentals

Two resistors of different values are connected in parallel across an ideal voltage source. Which statement about the circuit is true?

  1. The voltage across each branch is the same. Correct answer.
  2. The total voltage equals the sum of the branch voltages.
  3. The total resistance equals the sum of the branch resistances.
  4. The current through each branch is the same.

Explanation

Parallel branches are connected to the same two circuit nodes, so each branch sees the identical source voltage. The branch currents differ whenever the resistances differ, and the equivalent resistance is always less than the smallest branch resistance.

Question 6Electrical Principles, Theory and Code Fundamentals

The frequency of an alternating-current waveform is expressed in hertz. One hertz is equal to which of the following?

  1. One watt per hertz
  2. One cycle per minute
  3. One cycle per second Correct answer.
  4. One volt per second

Explanation

The hertz is the SI unit of frequency and represents one complete cycle of the waveform each second. A 60-hertz supply therefore completes 60 full alternations per second.

Question 7Electrical Principles, Theory and Code Fundamentals

A 120/240-volt single-phase system uses a grounded conductor. What color or colors are permitted to identify that grounded conductor?

  1. White or gray Correct answer.
  2. Green
  3. Red or blue
  4. Black

Explanation

The NEC requires the grounded circuit conductor to be identified by a continuous white or gray finish, or by three continuous white stripes on other than green insulation. Green is reserved for equipment grounding conductors and the other colors are used for ungrounded conductors.

Question 8Electrical Principles, Theory and Code Fundamentals

According to the informational notes in the NEC, the total voltage drop for a feeder plus branch circuit should not exceed what percentage of the supply voltage?

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

Explanation

The NEC recommends that feeders and branch circuits be sized so the total voltage drop does not exceed 5 percent, with no more than 3 percent on the branch circuit alone. These are performance recommendations rather than mandatory rules.

Question 9Electrical Principles, Theory and Code Fundamentals

A branch circuit supplies a single 40-ampere continuous load and no other load. What is the minimum standard rating of the overcurrent device protecting the circuit?

  1. 40 A
  2. 45 A
  3. 60 A
  4. 50 A Correct answer.

Explanation

Overcurrent devices serving continuous loads must be sized at not less than 125 percent of the continuous load. Multiplying 40 amperes by 1.25 gives 50 amperes, which is also a standard rating.

Question 10Electrical Principles, Theory and Code Fundamentals

A 50-ampere branch circuit is to be wired with copper THWN conductors terminating on equipment marked for 75 degrees C. What is the minimum conductor size permitted?

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

Explanation

The circuit ampacity is limited by the lowest temperature rating in the circuit, which here is the 75 degrees C termination. In the ampacity tables, 8 AWG copper at 75 degrees C carries 50 amperes.

Question 11Electrical Principles, Theory and Code Fundamentals

A metal outlet box has a marked capacity of 21.0 cubic inches. If each 14 AWG conductor requires 2.0 cubic inches, what is the maximum number of 14 AWG conductors the box may contain, assuming no devices, fittings, or equipment grounding conductors?

  1. 10 Correct answer.
  2. 9
  3. 8
  4. 12

Explanation

Dividing the box volume by the volume allowance per conductor gives 21.0 divided by 2.0, or 10.5 conductor allowances. Since a partial conductor cannot be counted, the box may hold a maximum of 10 conductors.

Question 12Electrical Principles, Theory and Code Fundamentals

A balanced three-phase 480-volt load draws 50 amperes at unity power factor. What is the power consumed by the load?

  1. 41.6 kW Correct answer.
  2. 36.0 kW
  3. 24.0 kW
  4. 20.8 kW

Explanation

Three-phase power equals the square root of three times line voltage times line current times power factor. Multiplying 1.732 by 480 volts by 50 amperes at unity power factor gives about 41,570 watts, or 41.6 kilowatts.

Question 13Electrical Principles, Theory and Code Fundamentals

A Class A ground-fault circuit interrupter is designed to open the circuit at what level of current imbalance?

  1. 15 to 20 milliamperes
  2. 4 to 6 milliamperes Correct answer.
  3. 1 to 2 milliamperes
  4. 30 to 50 milliamperes

Explanation

Class A ground-fault circuit interrupters are listed to trip when the differential current between the ungrounded and grounded conductors reaches 4 to 6 milliamperes. This threshold is low enough to protect people from ventricular fibrillation.

Question 14Electrical Principles, Theory and Code Fundamentals

In a dwelling unit, general-purpose receptacle outlets along a wall must be installed so that no point on the wall is more than what distance from a receptacle outlet?

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

Explanation

The NEC requires receptacle spacing such that no point along the floor line of a wall space is more than 6 feet from a receptacle. This effectively limits the spacing between receptacles to 12 feet and requires one within 6 feet of any break in the wall.

Question 15Electrical Principles, Theory and Code Fundamentals

For a conductor of fixed material and temperature, the resistance is directly proportional to which quantity?

  1. Cross-sectional area
  2. Insulation thickness
  3. Length Correct answer.
  4. Ambient temperature

Explanation

Resistance varies directly with conductor length and inversely with cross-sectional area. Doubling the length of a conductor doubles its resistance, which is why long runs produce greater voltage drop.

Question 16Electrical Principles, Theory and Code Fundamentals

Which of the following is a standard ampere rating for a circuit breaker as listed in the NEC?

  1. 75 A
  2. 55 A
  3. 70 A Correct answer.
  4. 65 A

Explanation

The standard ampere ratings for fuses and inverse-time circuit breakers include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, and 100 amperes, continuing in the standard steps. The value 70 amperes appears in that list, while 55, 65, and 75 do not.

Question 17Electrical Principles, Theory and Code Fundamentals

A single-phase transformer rated 5 kVA has a 480-volt primary and a 120-volt secondary. What is the primary full-load current?

  1. 24 A
  2. 41.7 A
  3. 4.2 A
  4. 10.4 A Correct answer.

Explanation

For a single-phase transformer, current equals volt-amperes divided by voltage. Dividing 5,000 volt-amperes by 480 volts gives about 10.4 amperes on the primary side.

Question 18Electrical Principles, Theory and Code Fundamentals

A load draws 10 kVA at a power factor of 0.8. What is the true power drawn by the load?

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

Explanation

True power equals apparent power multiplied by the power factor. Multiplying 10 kVA by 0.8 gives 8 kW of real power, with the remainder being reactive power.

Question 19Electrical Principles, Theory and Code Fundamentals

For a fixed capacitor, what happens to its capacitive reactance as the frequency of the applied alternating voltage increases?

  1. It decreases. Correct answer.
  2. It drops to zero.
  3. It increases.
  4. It remains constant.

Explanation

Capacitive reactance is inversely proportional to frequency and capacitance, following the relationship Xc = 1/(2 pi f C). Raising the frequency lowers the reactance, so the capacitor passes more alternating current.

Question 20Electrical Principles, Theory and Code Fundamentals

A raceway contains six current-carrying 12 AWG THHN conductors, and no ambient temperature correction is required. What percentage of the table ampacity applies to these conductors?

  1. 80 percent Correct answer.
  2. 75 percent
  3. 70 percent
  4. 90 percent

Explanation

Because more than three current-carrying conductors share a raceway without maintaining spacing, the ampacity adjustment table applies. For four through six current-carrying conductors the adjustment factor is 80 percent of the table ampacity.

Question 21Electrical Principles, Theory and Code Fundamentals

A 240-volt single-phase load draws 30 amperes through 8 AWG copper conductors. The one-way circuit length is 150 feet and the conductor resistance is 0.778 ohm per 1,000 feet. What is the approximate voltage drop of the circuit?

  1. 1.75 V
  2. 3.5 V
  3. 14 V
  4. 7.0 V Correct answer.

Explanation

The voltage drop in a two-wire circuit equals two times the current times the conductor resistance times the one-way length in thousands of feet. Computing 2 x 30 x 0.778 x 0.150 gives approximately 7.0 volts.

Question 22Electrical Principles, Theory and Code Fundamentals

In a balanced three-phase delta-connected load, each phase winding draws 20 amperes. What is the line current supplied to the load?

  1. 11.5 A
  2. 20.0 A
  3. 34.6 A Correct answer.
  4. 40.0 A

Explanation

In a delta connection the line current equals the square root of three times the phase current. Multiplying 1.732 by 20 amperes gives approximately 34.6 amperes.

Question 23Electrical Principles, Theory and Code Fundamentals

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

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

Explanation

The equipment grounding conductor is sized from the overcurrent device rating using the equipment grounding conductor table. For a 60-ampere overcurrent device, the minimum copper equipment grounding conductor is 10 AWG.

Question 24Electrical Principles, Theory and Code Fundamentals

A 12-ohm resistor is connected in series with a parallel pair made up of a 12-ohm resistor and a 6-ohm resistor. What is the total resistance of the combination?

  1. 10 ohms
  2. 18 ohms
  3. 16 ohms Correct answer.
  4. 4 ohms

Explanation

First find the parallel section: the reciprocal of 1/12 plus 1/6 is 1/4, so those two resistors equal 4 ohms. Adding that 4 ohms to the 12-ohm series resistor gives a total of 16 ohms.

Question 25Services, Feeders and Branch Circuits

What is the minimum vertical clearance required for overhead service-drop conductors passing above a residential driveway?

  1. 10 ft
  2. 18 ft
  3. 15 ft
  4. 12 ft Correct answer.

Explanation

NEC 230.24(B) sets vertical clearances from final grade: 10 ft in general, 12 ft over residential driveways and commercial areas not subject to truck traffic, and 18 ft over public streets and roads. A residential driveway therefore requires 12 ft.

Question 26Services, Feeders and Branch Circuits

A branch circuit supplies a 30-ampere continuous load and no other load. What is the minimum standard rating of the overcurrent device protecting the circuit?

  1. 45 A
  2. 30 A
  3. 50 A
  4. 40 A Correct answer.

Explanation

Continuous loads must be calculated at 125 percent, so the circuit load is 30 A x 1.25 = 37.5 A. The overcurrent device must be sized at least this large, and the next standard rating above 37.5 A is 40 A.

Question 27Services, Feeders and Branch Circuits

In a dwelling unit, receptacle outlets along wall space must be installed so that no point measured horizontally along the floor line is more than what distance from a receptacle outlet?

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

Explanation

NEC 210.52(A)(1) requires that no point along the floor line of any wall space be more than 6 ft from a receptacle outlet in that space. This spacing rule applies to dwelling unit rooms covered by 210.52(A).

Question 28Services, Feeders and Branch Circuits

What is the minimum number and rating of small-appliance branch circuits required for a one-family dwelling kitchen?

  1. Two 20-ampere circuits Correct answer.
  2. Two 15-ampere circuits
  3. Three 15-ampere circuits
  4. One 20-ampere circuit

Explanation

NEC 210.11(C)(1) requires at least two 20-ampere small-appliance branch circuits to supply the kitchen, pantry, dining, and similar receptacle outlets. These circuits may serve countertop receptacles and may not be smaller than 20 amperes.

Question 29Services, Feeders and Branch Circuits

Receptacles installed in a dwelling unit bathroom must be provided with which of the following?

  1. Ground-fault circuit-interrupter protection Correct answer.
  2. Combination arc-fault circuit-interrupter protection only
  3. Standard circuit-breaker protection only
  4. Isolation transformer protection

Explanation

NEC 210.8(A) requires ground-fault circuit-interrupter protection for all 125-volt through 250-volt receptacles installed in dwelling unit bathrooms. Bathroom receptacles are one of the classic GFCI-protected locations.

Question 30Services, Feeders and Branch Circuits

Where a feeder and a branch circuit together supply a load, the total voltage drop recommended by Code informational notes is limited to what maximum percentage?

  1. 2 percent
  2. 3 percent
  3. 5 percent Correct answer.
  4. 10 percent

Explanation

Informational notes in Article 210 and Article 215 recommend a maximum voltage drop of 3 percent on a branch circuit and 5 percent for the feeder plus branch circuit combined. These values are recommendations for reasonable efficiency of operation, not mandatory rules.

Question 31Services, Feeders and Branch Circuits

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

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

Explanation

NEC 210.11(C)(2) requires at least one 20-ampere branch circuit for the laundry receptacle outlet(s). This circuit is in addition to the small-appliance and bathroom circuits.

Question 32Services, Feeders and Branch Circuits

In a switchboard room, what is the minimum depth of working space in front of a 480-volt panelboard where the opposite wall is concrete with no live or grounded parts?

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

Explanation

Table 110.26(A)(1) gives a minimum working space depth of 3 ft (36 in) for equipment operating at 600 volts or less where live parts are exposed on one side and no live or grounded parts are on the other side.

Question 33Services, Feeders and Branch Circuits

A one-family dwelling is served by a 200-ampere service. Using the allowances of NEC 310.12, what is the minimum size copper service-entrance conductors?

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

Explanation

NEC 310.12 permits service-entrance conductors for a dwelling to have an ampacity of at least 83 percent of the service rating, so 200 A x 0.83 = 166 A. Copper 2/0 AWG is rated 175 A and is the smallest size that satisfies this.

Question 34Services, Feeders and Branch Circuits

A 200-ampere service is supplied by 2/0 AWG copper service-entrance conductors with a metal water pipe grounding electrode. What is the minimum size copper grounding electrode conductor?

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

Explanation

Table 250.66 sizes the grounding electrode conductor from the largest service-entrance conductor; for 2/0 AWG copper the required copper grounding electrode conductor is 4 AWG.

Question 35Services, Feeders and Branch Circuits

In a commercial building, how many 125-volt receptacle outlets rated at 180 volt-amperes each may be connected to a 20-ampere, 120-volt branch circuit?

  1. 10
  2. 16
  3. 12
  4. 13 Correct answer.

Explanation

A 20-ampere, 120-volt circuit provides 20 A x 120 V = 2,400 VA. Dividing 2,400 VA by 180 VA per receptacle outlet gives 13.3, so no more than 13 outlets may be connected.

Question 36Services, Feeders and Branch Circuits

A multiwire branch circuit supplies only line-to-neutral loads. What is required at the point where the circuit originates?

  1. A separate single-pole breaker for each ungrounded conductor
  2. A neutral conductor reduced below the ungrounded conductor size
  3. A means to disconnect all ungrounded conductors simultaneously Correct answer.
  4. A separate equipment grounding conductor run for each ungrounded conductor

Explanation

NEC 210.4(B) requires a means that simultaneously opens all ungrounded conductors of a multiwire branch circuit at the point of origin, typically a two- or three-pole breaker or listed handle ties.

Question 37Services, Feeders and Branch Circuits

The dedicated equipment space above a panelboard enclosure must extend what distance above the top of the enclosure?

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

Explanation

NEC 110.26(E) requires a dedicated equipment space extending 6 ft above the top of a panelboard or switchboard, reserved for electrical equipment and free of foreign piping or ducts.

Question 38Services, Feeders and Branch Circuits

Branch circuits supplying 125-volt, 15- and 20-ampere outlets in dwelling unit bedrooms require which of the following?

  1. Arc-fault circuit-interrupter protection Correct answer.
  2. Surge protective device protection
  3. Overload-only protection
  4. Ground-fault circuit-interrupter protection

Explanation

NEC 210.12 requires arc-fault circuit-interrupter protection for branch circuits supplying outlets in dwelling unit bedrooms as well as other specified dwelling areas. The protection is in addition to the branch overcurrent device.

Question 39Services, Feeders and Branch Circuits

A 1/0 AWG THWN copper conductor is terminated on a lug marked 75°C. Which ampacity column of Table 310.16 is used for this termination?

  1. 75°C column Correct answer.
  2. Ambient temperature column
  3. 90°C column
  4. 60°C column

Explanation

NEC 110.14(C) limits conductor ampacity at terminations to the temperature rating of the terminal; with a lug marked 75°C, the 75°C column value is used. The higher 90°C insulation rating of THWN may be used only for derating calculations, not for the termination.

Question 40Services, Feeders and Branch Circuits

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

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

Explanation

NEC 210.52(C) requires countertop receptacle outlets so that no point along the wall line is more than 24 in measured horizontally from a receptacle outlet. Each space of countertop at least 12 in wide must have at least one receptacle.

Question 41Services, Feeders and Branch Circuits

A dwelling unit has 8,000 VA of general lighting and general-use receptacle load. Using Table 220.42, what is the calculated demand load?

  1. 5,600 VA
  2. 3,000 VA
  3. 8,000 VA
  4. 4,750 VA Correct answer.

Explanation

Table 220.42 applies 100 percent to the first 3,000 VA and 35 percent to the remainder of the general lighting load: 3,000 + (5,000 x 0.35) = 4,750 VA.

Question 42Services, Feeders and Branch Circuits

Receptacles installed in an attached garage of a dwelling unit must be provided with which of the following?

  1. Surge protective device protection
  2. Combination arc-fault circuit-interrupter protection
  3. Isolated grounding
  4. Ground-fault circuit-interrupter protection Correct answer.

Explanation

NEC 210.8(A) requires ground-fault circuit-interrupter protection for all 125-volt through 250-volt receptacles in dwelling unit garages and accessory buildings, including attached garages.

Question 43Services, Feeders and Branch Circuits

Service-drop conductors pass over a roof with a slope of 4 inches per foot. What is the minimum clearance required above the roof surface?

  1. 18 in
  2. 8 ft
  3. 10 ft
  4. 3 ft Correct answer.

Explanation

NEC 230.24(A) allows a reduced clearance of 3 ft above a roof where the roof slope is not less than 4 inches per foot. Steeper roofs and those subject to foot traffic require greater clearances.

Question 44Services, Feeders and Branch Circuits

What outdoor receptacle outlet provision is required for a one-family dwelling?

  1. One outlet only where a deck or balcony exists
  2. One outlet at the front entrance only
  3. At least one outlet accessible from grade at the front and one at the back Correct answer.
  4. One outlet at each attached garage

Explanation

NEC 210.52(E)(1) requires at least one outdoor receptacle outlet accessible from grade level for a one-family dwelling, and for one-family dwellings at least one at the front and one at the back of the dwelling.

Question 45Services, Feeders and Branch Circuits

A 10-ft feeder tap is taken from a 400-ampere feeder and terminates in a single circuit breaker. Under the 10-ft tap rule, what is the minimum ampacity of the tap conductors?

  1. 40 A Correct answer.
  2. 80 A
  3. 200 A
  4. 100 A

Explanation

NEC 240.21(B)(1) requires 10-ft tap conductors to have an ampacity not less than one-tenth of the rating of the overcurrent device protecting the feeder, so 400 A / 10 = 40 A. The tap must also terminate in an overcurrent device that does not exceed the tap conductor ampacity.

Question 46Services, Feeders and Branch Circuits

Using Table 220.55, Column C, what is the calculated demand load for a single 12-kilowatt electric range in a dwelling unit?

  1. 12 kW
  2. 6 kW
  3. 8 kW Correct answer.
  4. 9 kW

Explanation

Table 220.55, Column C permits a demand load of 8 kW for one range rated not over 12 kW. The nameplate rating is not used directly as the calculated load.

Question 47Services, Feeders and Branch Circuits

A 120/240-volt single-phase service has a calculated unbalanced neutral load of 300 amperes. Applying the demand factor of NEC 220.61(B), what neutral load is used?

  1. 224 A
  2. 300 A
  3. 210 A
  4. 270 A Correct answer.

Explanation

NEC 220.61(B) permits a 70 percent factor on that portion of the unbalanced neutral load in excess of 200 amperes. The calculation is 200 A + (100 A x 0.70) = 270 A.

Question 48Services, Feeders and Branch Circuits

A raceway contains eight current-carrying conductors. What ampacity adjustment factor applies for conductor bundling?

  1. 35 percent
  2. 80 percent
  3. 50 percent
  4. 70 percent Correct answer.

Explanation

The ampacity adjustment table for more than three current-carrying conductors in a raceway requires a 70 percent factor for seven to nine conductors. Four to six conductors use 80 percent.

Question 49Services, Feeders and Branch Circuits

Using the optional method for a one-family dwelling, the total connected load is 30 kVA. What is the calculated demand load?

  1. 22,000 VA
  2. 12,000 VA
  3. 30,000 VA
  4. 18,000 VA Correct answer.

Explanation

The optional method applies 100 percent to the first 10 kVA and 40 percent to the remainder: 10,000 + (20,000 x 0.40) = 18,000 VA. This yields a smaller service calculation than using the standard method for this load.

Question 50Services, Feeders and Branch Circuits

In a one-family dwelling, what is the minimum number of 20-ampere small-appliance branch circuits required to serve the receptacle outlets in the kitchen, pantry, breakfast room, and dining room?

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

Explanation

NEC 210.11(C)(1) requires at least two 20-ampere small-appliance branch circuits to supply the receptacle outlets in the kitchen, pantry, breakfast room, and dining room of a dwelling unit. These circuits are in addition to the laundry branch circuit and may not serve outlets outside those rooms. Two is a minimum, so a designer may install more, but never fewer.