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Licensed Electrical Inspector (LEI) G Class Theory study materials
Licensed Electrical Inspector (LEI) G Class Theory study resources

Licensed Electrical Inspector (LEI) G Class Theory practice questions

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Question 1Electrical Theory, Circuits, and Calculations

A resistor of 12 ohms carries a current of 2.5 amperes. What is the voltage across the resistor?

  1. 9.6 V
  2. 14.5 V
  3. 30 V Correct answer.
  4. 4.8 V

Explanation

Ohm's law states that voltage equals current multiplied by resistance, so 2.5 A times 12 ohms gives 30 volts. This relationship holds for any linear resistive element at constant temperature.

Question 2Electrical Theory, Circuits, and Calculations

Three resistors of 4, 6, and 12 ohms are connected in parallel. What is the equivalent resistance of the combination?

  1. 7.33 ohms
  2. 0.5 ohms
  3. 2 ohms Correct answer.
  4. 22 ohms

Explanation

For parallel resistors the reciprocals add: 1/4 + 1/6 + 1/12 = 3/12 + 2/12 + 1/12 = 6/12, so the reciprocal of the total is 0.5 and the equivalent resistance is 2 ohms. The result is always smaller than the smallest branch resistance.

Question 3Electrical Theory, Circuits, and Calculations

A 60-watt lamp operates from a 120-volt supply. What current does it draw?

  1. 2 A
  2. 7200 A
  3. 0.25 A
  4. 0.5 A Correct answer.

Explanation

Power equals voltage multiplied by current, so current equals power divided by voltage. Dividing 60 watts by 120 volts gives 0.5 ampere.

Question 4Electrical Theory, Circuits, and Calculations

Which quantity is defined as the rate of flow of electric charge past a point in a circuit?

  1. Power
  2. Voltage
  3. Current Correct answer.
  4. Resistance

Explanation

Electric current is the rate at which charge passes a given point, measured in amperes, where one ampere equals one coulomb per second. Voltage is a potential difference, resistance opposes current, and power is the rate of energy transfer.

Question 5Electrical Theory, Circuits, and Calculations

A circuit has a total resistance of 8 ohms and draws 3 amperes from the source. What power is dissipated in the circuit?

  1. 192 W
  2. 72 W Correct answer.
  3. 24 W
  4. 11 W

Explanation

Power can be found using P = I squared times R. Squaring 3 amperes gives 9, and multiplying by 8 ohms gives 72 watts.

Question 6Electrical Theory, Circuits, and Calculations

In a purely capacitive AC circuit, how does the current relate to the voltage?

  1. Current leads voltage by 45 degrees.
  2. Current leads voltage by 90 degrees. Correct answer.
  3. Current is in phase with voltage.
  4. Current lags voltage by 90 degrees.

Explanation

In a capacitor the current reaches its maximum before the voltage does, so current leads voltage by 90 electrical degrees. This occurs because the capacitor must charge, and its current depends on the rate of change of voltage.

Question 7Electrical Theory, Circuits, and Calculations

A coil has an inductive reactance of 30 ohms and a resistance of 40 ohms in series. What is the impedance of the coil?

  1. 35 ohms
  2. 50 ohms Correct answer.
  3. 70 ohms
  4. 10 ohms

Explanation

Impedance for a series resistance-inductance circuit is the square root of R squared plus X sub L squared. The square root of 1600 plus 900 is the square root of 2500, which is 50 ohms.

Question 8Electrical Theory, Circuits, and Calculations

What is the RMS value of a sinusoidal voltage whose peak value is 170 volts?

  1. 120 V Correct answer.
  2. 340 V
  3. 240 V
  4. 85 V

Explanation

For a sine wave the RMS value equals the peak value divided by the square root of 2, approximately 0.707 times the peak. Multiplying 170 volts by 0.707 gives about 120 volts.

Question 9Electrical Theory, Circuits, and Calculations

Two resistors of 10 ohms and 15 ohms are connected in series across a 50-volt supply. What is the voltage drop across the 10-ohm resistor?

  1. 10 V
  2. 50 V
  3. 30 V
  4. 20 V Correct answer.

Explanation

The total resistance is 25 ohms, so the current is 50 divided by 25, or 2 amperes. The drop across the 10-ohm resistor is 2 amperes times 10 ohms, or 20 volts.

Question 10Electrical Theory, Circuits, and Calculations

Which material is classified as a semiconductor?

  1. Copper
  2. Silicon Correct answer.
  3. Rubber
  4. Glass

Explanation

Silicon has a conductivity between that of conductors and insulators and is the classic semiconductor material. Its conductivity increases with temperature and can be controlled by doping.

Question 11Electrical Theory, Circuits, and Calculations

A capacitor of 100 microfarads is charged to 50 volts. How much charge is stored?

  1. 0.005 C Correct answer.
  2. 2 C
  3. 5000 C
  4. 0.5 C

Explanation

Charge equals capacitance multiplied by voltage. Converting 100 microfarads to 0.0001 farad and multiplying by 50 volts gives 0.005 coulomb.

Question 12Electrical Theory, Circuits, and Calculations

What happens to the total resistance of a circuit when an additional resistor is connected in parallel with an existing one?

  1. The total resistance increases.
  2. The total resistance stays the same.
  3. The total resistance becomes zero.
  4. The total resistance decreases. Correct answer.

Explanation

Adding a parallel path increases the total conductance, so the equivalent resistance falls below the smallest individual branch resistance. The supply current therefore increases for a fixed source voltage.

Question 13Electrical Theory, Circuits, and Calculations

A transformer has 400 primary turns and 100 secondary turns. If the primary is supplied at 240 volts, what is the secondary voltage?

  1. 120 V
  2. 480 V
  3. 960 V
  4. 60 V Correct answer.

Explanation

The voltage ratio equals the turns ratio, so the secondary voltage is the primary voltage multiplied by the secondary turns divided by the primary turns. That is 240 times 100 divided by 400, or 60 volts.

Question 14Electrical Theory, Circuits, and Calculations

In a three-phase star-connected system with a line voltage of 400 volts, what is the phase voltage?

  1. 231 V Correct answer.
  2. 693 V
  3. 200 V
  4. 400 V

Explanation

In a star connection the phase voltage equals the line voltage divided by the square root of 3. Dividing 400 volts by 1.732 gives approximately 231 volts.

Question 15Electrical Theory, Circuits, and Calculations

What is the primary function of a diode in a rectifier circuit?

  1. To allow current to flow in one direction only Correct answer.
  2. To store electrical energy
  3. To oppose changes in current
  4. To amplify the signal

Explanation

A diode conducts readily in the forward direction and blocks current in reverse, so it converts alternating current into pulsating direct current. This one-way conduction is the basis of rectification.

Question 16Electrical Theory, Circuits, and Calculations

A 2-kilowatt heater runs continuously for 3 hours. How much energy does it consume?

  1. 1.5 kWh
  2. 600 kWh
  3. 0.67 kWh
  4. 6 kWh Correct answer.

Explanation

Energy in kilowatt-hours equals power in kilowatts multiplied by time in hours. Two kilowatts times three hours gives six kilowatt-hours.

Question 17Electrical Theory, Circuits, and Calculations

Which statement correctly describes conventional current flow?

  1. It alternates direction in a DC circuit.
  2. It flows from positive to negative within the external circuit. Correct answer.
  3. It flows from negative to positive within the external circuit.
  4. It flows only in conductors containing free electrons.

Explanation

Conventional current is defined as flowing from the positive terminal through the external circuit to the negative terminal, opposite to electron drift. This convention predates the discovery of the electron and remains standard in circuit analysis.

Question 18Electrical Theory, Circuits, and Calculations

A series circuit contains a 6-volt battery and two resistors of 2 ohms and 4 ohms. What current flows?

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

Explanation

The total series resistance is 6 ohms, and Ohm's law gives current as voltage divided by resistance. Six volts divided by six ohms is 1 ampere.

Question 19Electrical Theory, Circuits, and Calculations

What is the power factor of a circuit in which the true power is 800 watts and the apparent power is 1000 volt-amperes?

  1. 0.6
  2. 0.2
  3. 0.8 Correct answer.
  4. 1.25

Explanation

Power factor is the ratio of true power to apparent power. Dividing 800 watts by 1000 volt-amperes gives 0.8, which corresponds to a phase angle of about 37 degrees.

Question 20Electrical Theory, Circuits, and Calculations

Which law states that the algebraic sum of the currents entering and leaving a junction is zero?

  1. Kirchhoff's current law Correct answer.
  2. Lenz's law
  3. Faraday's law
  4. Kirchhoff's voltage law

Explanation

Kirchhoff's current law expresses conservation of charge at a node, so the sum of currents entering equals the sum leaving. Faraday's and Lenz's laws concern induced electromotive force.

Question 21Electrical Theory, Circuits, and Calculations

A conductor carries 5 amperes for 120 seconds. How much charge passes a point in the conductor?

  1. 600 C Correct answer.
  2. 24 C
  3. 125 C
  4. 0.042 C

Explanation

Charge equals current multiplied by time. Five amperes times 120 seconds gives 600 coulombs, since one ampere is one coulomb per second.

Question 22Electrical Theory, Circuits, and Calculations

An inductor of 0.5 henry carries a current changing at 4 amperes per second. What is the induced EMF?

  1. 0.125 V
  2. 8 V Correct answer.
  3. 2 V
  4. 0.5 V

Explanation

The induced EMF equals inductance multiplied by the rate of change of current. Half a henry times 4 amperes per second gives 2 volts, not 8; the correct product is 2 V.

Question 23Electrical Theory, Circuits, and Calculations

What is the phase relationship between voltage and current in a purely resistive AC circuit?

  1. Current leads voltage by 90 degrees.
  2. They are exactly in phase. Correct answer.
  3. Voltage lags current by 45 degrees.
  4. Voltage leads current by 90 degrees.

Explanation

Resistance dissipates energy without storing it, so the voltage across a resistor and the current through it reach their peaks at the same instant. They are therefore in phase, giving a power factor of unity.

Question 24Electrical Theory, Circuits, and Calculations

A circuit draws 10 amperes at a power factor of 0.75 from a 240-volt supply. What is the apparent power?

  1. 3200 VA
  2. 2400 VA Correct answer.
  3. 2400 W
  4. 1800 VA

Explanation

Apparent power equals voltage multiplied by current, independent of power factor. Multiplying 240 volts by 10 amperes gives 2400 volt-amperes; the true power would be 2400 times 0.75, or 1800 watts.

Question 25Electrical Theory, Circuits, and Calculations

Which effect explains why the resistance of most metallic conductors increases as temperature rises?

  1. Reduction in the applied voltage
  2. Increased lattice vibration scattering the charge carriers Correct answer.
  3. Increased number of free electrons
  4. Decreased atomic spacing

Explanation

As temperature rises, the metal lattice vibrates more vigorously and scatters drifting electrons more frequently, so resistance increases. This temperature coefficient is positive for most metals.

Question 26Electrical Theory, Circuits, and Calculations

Which quantity is the same for every component connected in a parallel branch of a DC circuit?

  1. The resistance of each branch
  2. The voltage across each branch Correct answer.
  3. The current through each branch
  4. The power dissipated in each branch

Explanation

In a parallel connection all branch ends are joined to the same two nodes, so each branch experiences the identical potential difference supplied by those nodes. Current, resistance, and power may each differ between branches because they depend on the individual branch values.

Question 27Electrical Theory, Circuits, and Calculations

A 12-volt battery supplies a circuit whose total resistance is 4 ohms. What current flows in the circuit?

  1. 16 amperes
  2. 3 amperes Correct answer.
  3. 48 amperes
  4. 0.33 ampere

Explanation

Ohm's law states that current equals voltage divided by resistance, so 12 volts divided by 4 ohms gives 3 amperes. The result is a direct application of the relationship among voltage, current, and resistance in a simple DC circuit.

Question 28Electrical Theory, Circuits, and Calculations

A 240-volt single-phase load draws 15 amperes at a power factor of 0.8. What is the true power consumed by the load?

  1. 4500 watts
  2. 2880 watts Correct answer.
  3. 3600 watts
  4. 1800 watts

Explanation

Apparent power is voltage multiplied by current, giving 240 times 15, or 3600 volt-amperes. True power is apparent power multiplied by the power factor, so 3600 times 0.8 equals 2880 watts.

Question 29Electrical Theory, Circuits, and Calculations

Two capacitors of 6 microfarads and 3 microfarads are connected in series. What is the equivalent capacitance of the combination?

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

Explanation

Capacitors in series combine like resistors in parallel, so the reciprocal of the total equals the sum of the reciprocals of the individual values. Here 1/6 plus 1/3 equals 1/2, whose reciprocal is 2 microfarads.

Question 30Electrical Theory, Circuits, and Calculations

A series RLC circuit has a resistance of 30 ohms and equal inductive and capacitive reactances of 40 ohms each. What is the impedance of the circuit?

  1. 50 ohms
  2. 10 ohms
  3. 30 ohms Correct answer.
  4. 110 ohms

Explanation

In series, the net reactance is the inductive reactance minus the capacitive reactance, and equal values cancel to zero. The impedance therefore reduces to the resistance alone, which is 30 ohms, and the circuit behaves resistively at that frequency.

Question 31Wiring Methods, Materials, and Installation Standards

Which conductor material is most commonly used for branch-circuit wiring because of its high conductivity and moderate cost?

  1. Silver
  2. Iron
  3. Aluminum
  4. Copper Correct answer.

Explanation

Copper is the standard branch-circuit conductor because it combines high electrical conductivity with reasonable cost and good mechanical strength at terminations. Silver conducts better but is far too expensive for general wiring. Aluminum is used for larger feeders but requires special termination methods.

Question 32Wiring Methods, Materials, and Installation Standards

A conductor with a larger cross-sectional area, all else equal, will have which effect on voltage drop along a run?

  1. It has no effect on voltage drop
  2. It reduces voltage drop Correct answer.
  3. It increases voltage drop
  4. It reverses the current direction

Explanation

Resistance is inversely proportional to cross-sectional area, so a larger conductor lowers resistance and therefore lowers voltage drop for a given load current. This is why long runs often require upsized conductors to keep voltage drop within acceptable limits.

Question 33Wiring Methods, Materials, and Installation Standards

In a standard nonmetallic-sheathed cable assembly, what is the function of the bare conductor run with the insulated circuit conductors?

  1. It carries the unbalanced neutral current
  2. It serves as the equipment grounding conductor Correct answer.
  3. It shields the cable from radio interference
  4. It provides a spare phase conductor

Explanation

The bare conductor in nonmetallic-sheathed cable is the equipment grounding conductor that bonds metal enclosures and grounding terminals back to the service. It normally carries no current except during a fault. The insulated white conductor is the grounded neutral.

Question 34Wiring Methods, Materials, and Installation Standards

Which box type is designed for installation in a finished wall so that the box front sits flush with the wall surface?

  1. Octagon box
  2. Old-work (remodel) box Correct answer.
  3. Masonry box
  4. Handhole enclosure

Explanation

Old-work or remodel boxes are made to be inserted through an opening in an existing finished wall and secured to the wallboard. Octagon boxes are typically used for ceiling fixtures, and masonry boxes are set into concrete or block during construction.

Question 35Wiring Methods, Materials, and Installation Standards

What does the term 'ampacity' describe for a conductor?

  1. The maximum voltage it can withstand before insulation breakdown
  2. The mechanical pull strength of the conductor
  3. The total length of conductor permitted in a raceway
  4. The maximum current it can carry continuously under stated conditions without exceeding its temperature rating Correct answer.

Explanation

Ampacity is the current-carrying capacity of a conductor under specified installation conditions, limited by the allowable conductor temperature. It depends on conductor size, insulation type, ambient temperature, and the number of current-carrying conductors bundled together.

Question 36Wiring Methods, Materials, and Installation Standards

A standard straight-blade 15-ampere, 125-volt receptacle has which blade configuration characteristic?

  1. Four round pins in a square pattern
  2. Two parallel flat blades plus a round or U-shaped grounding pin Correct answer.
  3. Three flat blades arranged in a triangle
  4. Two flat blades of unequal width with no grounding pin

Explanation

The common 15-ampere 125-volt receptacle has two parallel flat current-carrying slots and a grounding contact, which may be round or U-shaped. The wider neutral slot distinguishes it from the narrower hot slot. Configurations with different geometry belong to other ratings or to special-purpose receptacles.

Question 37Wiring Methods, Materials, and Installation Standards

Why must electrical nonmetallic tubing be installed only where it is protected from physical damage or where the building construction permits its use?

  1. Because it cannot be bent to form bends
  2. Because it is a flexible plastic raceway with limited resistance to impact and heat Correct answer.
  3. Because it conducts electricity like a metal raceway
  4. Because it is only permitted outdoors

Explanation

Nonmetallic tubing is a flexible plastic raceway, so it lacks the impact resistance of rigid metal and can be damaged by heat or sharp objects. Installation rules therefore restrict it to concealed or protected locations and buildings of permitted construction types.

Question 38Wiring Methods, Materials, and Installation Standards

What is the primary purpose of a locknut when terminating rigid metal conduit at a box?

  1. To seal the conduit against water entry
  2. To secure the conduit fitting tightly to the enclosure and ensure electrical continuity Correct answer.
  3. To reduce the inside diameter of the conduit
  4. To provide a bonding jumper around the box

Explanation

A locknut threads onto the conduit or fitting and clamps the enclosure wall between itself and another locknut or bushing, mechanically securing the connection and maintaining metal-to-metal contact for grounding continuity. Sealing against moisture requires separate sealing fittings.

Question 39Wiring Methods, Materials, and Installation Standards

A 20-ampere branch circuit feeding general-use receptacles in a commercial area uses copper conductors. Which minimum conductor size is generally required?

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

Explanation

Copper 14 AWG is limited to 15-ampere circuits, so a 20-ampere branch circuit requires at least 12 AWG copper. Sizes 16 and 18 AWG are not permitted for general branch-circuit power wiring. The overcurrent device must also match the conductor ampacity.

Question 40Wiring Methods, Materials, and Installation Standards

When multiple current-carrying conductors are bundled together in a raceway, what adjustment must generally be applied to their ampacity?

  1. The ampacity is increased because conductors share the load
  2. No change is needed because the raceway dissipates heat
  3. The ampacity is halved regardless of conductor count
  4. A derating factor is applied because heat dissipation is reduced Correct answer.

Explanation

Bundled conductors cannot dissipate heat as readily as isolated ones, so the allowable ampacity is reduced by a derating factor that depends on the number of current-carrying conductors. The grounded neutral may or may not count, depending on circuit characteristics.

Question 41Wiring Methods, Materials, and Installation Standards

A metal raceway system must be electrically continuous throughout. Which practice best ensures this continuity at joints?

  1. Wrapping joints with insulating tape
  2. Tightening couplings and fittings to bare metal and using listed bonding fittings where required Correct answer.
  3. Inserting plastic bushings between couplings
  4. Painting each coupling after assembly

Explanation

Electrical continuity in metal raceways depends on clean, tight metal-to-metal connections at couplings and fittings, supplemented by listed bonding means such as bonding jumpers around expansion fittings. Insulating or coating joints defeats the grounding path.

Question 42Wiring Methods, Materials, and Installation Standards

Which installation method is appropriate for supporting nonmetallic-sheathed cable in a basement ceiling?

  1. Fastening the cable at intervals with staples or straps that do not damage the sheath Correct answer.
  2. Hanging the cable from pipes with wire ties
  3. Laying it directly on a suspended ceiling grid
  4. Running it inside a metal duct

Explanation

Nonmetallic-sheathed cable must be secured with staples, straps, or similar fasteners at required intervals and within a specified distance of boxes, using fasteners that do not cut or crush the sheath. Support from piping or ducts is not permitted.

Question 43Wiring Methods, Materials, and Installation Standards

What is the main reason junction boxes must be sized according to the number and size of conductors and devices they contain?

  1. To increase the circuit voltage
  2. To provide enough free space to prevent overheating and insulation damage Correct answer.
  3. To reduce the number of required supports
  4. To make the box easier to paint

Explanation

Box fill limits ensure adequate free space so conductors and splices do not overheat and insulation is not damaged during installation. Each conductor, device, and fitting contributes a calculated volume to the required box size.

Question 44Wiring Methods, Materials, and Installation Standards

A rigid metal conduit run passes through a building expansion joint where movement is expected. What is the appropriate provision?

  1. Replace the rigid conduit with flexible cord
  2. Weld the conduit solidly across the joint
  3. Cut the conduit and leave the ends open
  4. Install an expansion fitting designed to accommodate movement while maintaining continuity Correct answer.

Explanation

Expansion fittings allow the conduit to move with the building while preserving electrical continuity through an internal bonding jumper. Welding would transfer stress and crack the conduit, and an open cut would break both the raceway and the grounding path.

Question 45Wiring Methods, Materials, and Installation Standards

In a wet location, which characteristic is most important when selecting a conduit body?

  1. It uses the fewest possible set screws
  2. It has the largest possible internal volume
  3. It is painted a bright color
  4. It is listed and marked for use in wet locations Correct answer.

Explanation

Conduit bodies installed in wet locations must be listed and marked for that environment, often requiring gasketed covers and drainage provisions. Ordinary conduit bodies may collect water and are unsuitable outdoors or in damp areas.

Question 46Wiring Methods, Materials, and Installation Standards

A luminaire is to be installed in a location subject to dampness but not direct water contact. Which marking should the luminaire carry?

  1. A marking indicating it is for dry locations only
  2. No marking is necessary
  3. A marking indicating it is suitable for damp locations Correct answer.
  4. A marking indicating it is for hazardous locations only

Explanation

Luminaires are marked for dry, damp, or wet locations, and a damp location requires a fixture listed and marked for damp use. A dry-location fixture could corrode or fail where moisture is present. Hazardous-location marking addresses flammable atmospheres, not ordinary moisture.

Question 47Wiring Methods, Materials, and Installation Standards

Which factor most directly determines the minimum bending radius permitted for a given conduit installation?

  1. The color of the conduit
  2. The number of couplings used
  3. The voltage of the circuit
  4. The conduit trade size and type, as specified in installation standards Correct answer.

Explanation

Minimum bending radius depends on the conduit size and type because bends must not kink the raceway or damage conductors during pulling. Standards specify minimum radii for each trade size. Circuit voltage and fitting count do not set the bend radius.

Question 48Wiring Methods, Materials, and Installation Standards

A metal-sheathed cable is used to supply a motor in an area exposed to physical abuse. Which installation approach is most appropriate?

  1. Use bare conductors in surface-mounted cleats
  2. Use nonmetallic-sheathed cable without additional protection
  3. Use a cable type with an interlocking metal armor that provides mechanical protection Correct answer.
  4. Use flexible cord stapled to the wall

Explanation

Where physical abuse is a concern, a cable with interlocking metal armor provides mechanical protection while remaining flexible. Nonmetallic sheathed cable lacks that armor, and flexible cord or bare conductors are not permitted as fixed wiring methods in this application.

Question 49Wiring Methods, Materials, and Installation Standards

A feeder is installed in a location where it must resist corrosion from soil. Which conductor characteristic should be verified?

  1. The conductor is color-coded red
  2. The conductor has the highest possible ampacity
  3. The conductor is the smallest size permitted by ampacity
  4. The conductor and jacket are listed for direct burial or the raceway is corrosion-resistant Correct answer.

Explanation

Underground and soil-exposed installations require conductors or raceways listed and identified for direct burial or otherwise protected against corrosion. Ampacity and color coding do not address corrosion resistance.

Question 50Wiring Methods, Materials, and Installation Standards

When installing a surface metal raceway, what must be done at each end to maintain the grounding path?

  1. Leave the end open for ventilation
  2. Fill the end with sealing compound
  3. Insert a plastic end cap
  4. Bond the raceway to the enclosure or grounding conductor with a listed fitting Correct answer.

Explanation

Surface metal raceways must be electrically continuous and bonded to enclosures and the equipment grounding system at terminations. Open ends or insulating caps would interrupt the conductive path.