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NSW Electrical Licence practice questions

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Question 1Electrical principles and theory

Which quantity is measured in coulombs?

  1. Electric charge Correct answer.
  2. Electromotive force
  3. Power
  4. Resistance

Explanation

The coulomb is the SI unit of electric charge, defined as the charge carried by a steady current of one ampere for one second. Voltage, power and resistance all have their own separate units, being the volt, watt and ohm.

Question 2Electrical principles and theory

A single-phase circuit draws 10 A at 240 V. What is the apparent power?

  1. 24 VA
  2. 2400 VA Correct answer.
  3. 240 VA
  4. 24000 VA

Explanation

Apparent power in a single-phase circuit is the product of voltage and current, so 240 V multiplied by 10 A gives 2400 VA. Apparent power is expressed in volt-amperes because it ignores any phase difference between voltage and current.

Question 3Electrical principles and theory

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

  1. In phase with the voltage Correct answer.
  2. Lagged by 90 degrees
  3. Leading the voltage by 90 degrees
  4. Opposite in phase by 180 degrees

Explanation

Resistance dissipates energy without storing it, so voltage and current rise and fall together. The phase angle between them is therefore zero, giving a power factor of one.

Question 4Electrical principles and theory

Two 100 ohm resistors are connected in parallel. What is the total resistance?

  1. 50 ohms Correct answer.
  2. 200 ohms
  3. 100 ohms
  4. 25 ohms

Explanation

For equal resistors in parallel the total is the value of one resistor divided by the number of branches, so 100 divided by two gives 50 ohms. The reciprocal formula gives the same result because 1/100 plus 1/100 equals 1/50.

Question 5Electrical principles and theory

Which material is classed as a semiconductor?

  1. Copper
  2. Mica
  3. Nichrome
  4. Silicon Correct answer.

Explanation

Silicon has four valence electrons and its conductivity lies between that of conductors and insulators, which is the defining property of a semiconductor. Copper is a conductor, mica an insulator and nichrome a resistive alloy.

Question 6Electrical principles and theory

What is the RMS value of a sinusoidal voltage that has a peak value of 340 V?

  1. 240 V Correct answer.
  2. 480 V
  3. 340 V
  4. 170 V

Explanation

The RMS value of a sine wave is the peak value divided by the square root of two, that is multiplied by about 0.707. Applying this to 340 V gives approximately 240 V, which matches a standard low voltage supply.

Question 7Electrical principles and theory

Which statement correctly describes conventional current flow?

  1. It does not flow in an open circuit
  2. It moves from positive to negative through the external circuit Correct answer.
  3. It moves from negative to positive internally in a source
  4. It flows only in conductors carrying alternating current

Explanation

Conventional current is defined as flowing from the positive terminal to the negative terminal through the external circuit. Electron flow is in the opposite direction, from negative to positive externally.

Question 8Electrical principles and theory

A 12 V battery is connected across a 6 ohm resistor. What current flows?

  1. 18 A
  2. 2 A Correct answer.
  3. 72 A
  4. 0.5 A

Explanation

Ohm's law states that current equals voltage divided by resistance. Dividing 12 V by 6 ohms gives 2 A.

Question 9Electrical principles and theory

A cable carries 8 A and has a resistance of 0.5 ohm over its length. What power is dissipated in the cable?

  1. 64 W
  2. 4 W
  3. 32 W Correct answer.
  4. 16 W

Explanation

Power loss in a conductor is found with the relationship I squared multiplied by R. Squaring 8 A gives 64, and multiplying by 0.5 ohm gives 32 W.

Question 10Electrical principles and theory

Three resistors of 4, 6 and 10 ohms are connected in series across a 20 V supply. What is the voltage across the 10 ohm resistor?

  1. 10 V Correct answer.
  2. 6 V
  3. 4 V
  4. 12 V

Explanation

The total series resistance is 20 ohms, so the current is 20 V divided by 20 ohms, which is 1 A. The voltage across the 10 ohm resistor is therefore 1 A multiplied by 10 ohms, giving 10 V.

Question 11Electrical principles and theory

A circuit has a power factor of 0.8 and draws 5 kW of active power. What is the apparent power?

  1. 8 kVA
  2. 5.8 kVA
  3. 4 kVA
  4. 6.25 kVA Correct answer.

Explanation

Apparent power equals active power divided by power factor. Dividing 5 kW by 0.8 gives 6.25 kVA, which is always larger than the active power when the power factor is below one.

Question 12Electrical principles and theory

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

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

Explanation

Impedance in a series resistance-inductance circuit is the square root of the sum of the squares of resistance and reactance. The square root of 1600 plus 900 is the square root of 2500, which is 50 ohm.

Question 13Electrical principles and theory

How are the line and phase voltages related in a balanced star-connected three-phase system?

  1. Line voltage equals phase voltage multiplied by three
  2. Line voltage equals phase voltage multiplied by the square root of three Correct answer.
  3. Line voltage equals phase voltage divided by the square root of three
  4. Line voltage equals phase voltage

Explanation

In a star connection each line voltage is the phasor difference of two phase voltages displaced by 120 degrees. This gives a line voltage of root three, about 1.732, times the phase voltage.

Question 14Electrical principles and theory

A transformer has 500 turns on the primary and 100 turns on the secondary. If the primary voltage is 240 V, what is the secondary voltage?

  1. 48 V Correct answer.
  2. 60 V
  3. 1200 V
  4. 24 V

Explanation

The voltage ratio equals the turns ratio, so the secondary voltage is the primary voltage multiplied by secondary turns divided by primary turns. Multiplying 240 V by 100/500 gives 48 V.

Question 15Electrical principles and theory

Which effect explains why a capacitor opposes changes in voltage across it?

  1. It stores energy in an electric field Correct answer.
  2. It stores energy in a magnetic field
  3. It dissipates energy as heat
  4. It converts energy to mechanical work

Explanation

A capacitor stores charge and energy in the electric field between its plates. Because the stored charge takes time to build up or discharge, the voltage across the capacitor cannot change instantaneously.

Question 16Electrical principles and theory

A 100 microfarad capacitor is connected to a 50 Hz supply. What is its capacitive reactance, approximately?

  1. 318 ohm
  2. 3.18 ohm
  3. 31.8 ohm Correct answer.
  4. 63.7 ohm

Explanation

Capacitive reactance equals one divided by two pi times frequency times capacitance. Using 2 pi times 50 times 0.0001 gives a denominator of about 0.0314, so the reactance is approximately 31.8 ohm.

Question 17Electrical principles and theory

A 10 ohm resistor and a 30 ohm inductive reactance are in parallel. Which statement best describes the total impedance?

  1. It is greater than 30 ohm
  2. It lies between 10 and 30 ohm
  3. It is exactly 40 ohm
  4. It is less than 10 ohm Correct answer.

Explanation

When a resistance and a reactance are in parallel, the resultant impedance is always lower than the smallest of the branch impedances. The two branch currents are out of phase, so the total current exceeds the current in either branch.

Question 18Electrical principles and theory

A sinusoidal current has an RMS value of 10 A. What is its peak value?

  1. 14.14 A Correct answer.
  2. 10 A
  3. 20 A
  4. 7.07 A

Explanation

Peak value equals RMS value multiplied by the square root of two, about 1.414. Multiplying 10 A by 1.414 gives approximately 14.14 A.

Question 19Electrical principles and theory

Which statement about energy and power is correct?

  1. Power is the rate at which energy is transferred Correct answer.
  2. Energy is measured in watts
  3. Power is energy multiplied by time
  4. Power is measured in joules

Explanation

Power is the rate of doing work or transferring energy, so one watt equals one joule per second. Energy is the quantity transferred, while power describes how quickly the transfer occurs.

Question 20Electrical principles and theory

A conductor of uniform material has its length doubled while its cross-sectional area stays the same. How does its resistance change?

  1. It halves
  2. It doubles Correct answer.
  3. It increases four times
  4. It stays the same

Explanation

Resistance is directly proportional to length and inversely proportional to cross-sectional area. Doubling the length while keeping the area constant therefore doubles the resistance.

Question 21Electrical principles and theory

A 240 V single-phase circuit supplies a 3 kW heating load. What current does it draw, assuming unity power factor?

  1. 12.5 A Correct answer.
  2. 7.2 A
  3. 80 A
  4. 0.08 A

Explanation

For a resistive load the current equals power divided by voltage. Dividing 3000 W by 240 V gives 12.5 A.

Question 22Electrical principles and theory

In a series resonance circuit, which condition occurs at the resonant frequency?

  1. Total impedance reaches its maximum value
  2. Inductive and capacitive reactances are equal and cancel Correct answer.
  3. Capacitive reactance exceeds inductive reactance
  4. Inductive reactance exceeds capacitive reactance

Explanation

At resonance the inductive and capacitive reactances are equal in magnitude but opposite in phase, so they cancel. The circuit impedance then reduces to resistance alone and the current reaches its maximum.

Question 23Electrical principles and theory

A 400 V three-phase motor draws a line current of 10 A at a power factor of 0.85. What is the active power input, approximately?

  1. 1.7 kW
  2. 10.2 kW
  3. 3.4 kW
  4. 5.9 kW Correct answer.

Explanation

Three-phase active power equals root three times line voltage times line current times power factor. Multiplying 1.732 by 400 by 10 by 0.85 gives approximately 5.9 kW.

Question 24Electrical principles and theory

A 20 ohm resistor is connected in series with a coil having 15 ohm resistance and 20 ohm inductive reactance. What is the phase angle of the total impedance?

  1. About 53 degrees, current lagging
  2. About 37 degrees, current leading
  3. About 45 degrees, current leading
  4. About 33 degrees, current lagging Correct answer.

Explanation

The total resistance is 35 ohm and the total reactance is 20 ohm, so the tangent of the phase angle is 20 divided by 35, about 0.571. This gives an angle of roughly 30 to 33 degrees, and because the reactance is inductive the current lags the voltage.

Question 25Electrical principles and theory

A transformer delivers 2.4 kW to a load at 80 percent efficiency. What is the input power?

  1. 2.88 kW
  2. 3.0 kW Correct answer.
  3. 1.92 kW
  4. 3.2 kW

Explanation

Efficiency equals output power divided by input power, so input power equals output divided by efficiency. Dividing 2.4 kW by 0.8 gives 3.0 kW.

Question 26Electrical principles and theory

A resistor has a conductance of 0.05 siemens. What is its resistance?

  1. 5 ohm
  2. 0.05 ohm
  3. 50 ohm
  4. 20 ohm Correct answer.

Explanation

Conductance is the reciprocal of resistance, so resistance equals one divided by the conductance in siemens. Dividing 1 by 0.05 gives 20 ohm. The relationship is inverse, so higher conductance always means lower resistance.

Question 27Electrical principles and theory

Two resistors of 6 ohm and 3 ohm are connected in parallel. What is the equivalent resistance?

  1. 1.5 ohm
  2. 2 ohm Correct answer.
  3. 4.5 ohm
  4. 9 ohm

Explanation

For two resistors in parallel the equivalent resistance is the product divided by the sum, so 6 times 3 divided by 9 equals 2 ohm. The result must always be smaller than the smallest branch resistance, which confirms 2 ohm is sensible.

Question 28Electrical principles and theory

Which statement correctly describes the magnetic field produced by a current-carrying straight conductor?

  1. It forms concentric circles around the conductor Correct answer.
  2. It exists only at the ends of the conductor
  3. It runs parallel to the conductor along its length
  4. It alternates direction regardless of current direction

Explanation

A current in a straight conductor produces a magnetic field whose flux lines form concentric circles around the conductor. The direction of these circles reverses when the current direction reverses, following the right-hand grip rule. The field strength falls with distance from the conductor.

Question 29Electrical principles and theory

A 240 V supply is applied to a coil with 60 ohm resistance and 80 ohm inductive reactance in series. What current flows?

  1. 1.92 A
  2. 4.0 A
  3. 3.0 A
  4. 2.4 A Correct answer.

Explanation

Series impedance is the square root of resistance squared plus reactance squared, giving the square root of 3600 plus 6400, which is 100 ohm. Dividing 240 V by 100 ohm gives 2.4 A. Using resistance alone would overstate the current.

Question 30Electrical principles and theory

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

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

Explanation

In a pure capacitance the current reaches its maximum before the voltage does, so current leads voltage by a quarter cycle, or 90 degrees. This happens because the capacitor charges fastest when the voltage is changing most rapidly. Inductance produces the opposite relationship.

Question 31Electrical principles and theory

A single-phase load draws 10 A at 240 V with a power factor of 0.6 lagging. What reactive power does it consume?

  1. 1.92 kvar Correct answer.
  2. 1.44 kvar
  3. 2.4 kvar
  4. 0.96 kvar

Explanation

Apparent power is 240 V times 10 A, which is 2400 VA. The reactive power equals apparent power times the sine of the phase angle; with a power factor of 0.6 the sine is 0.8, giving 1920 var or 1.92 kvar. Active power would be 1.44 kW.

Question 32Electrical principles and theory

A transformer has a primary winding of 800 turns and a secondary of 200 turns. What type of transformer is it and what is the turns ratio?

  1. Step-down with a ratio of 1 to 4
  2. Step-up with a ratio of 1 to 4
  3. Step-down with a ratio of 4 to 1 Correct answer.
  4. Step-up with a ratio of 4 to 1

Explanation

The turns ratio is the primary turns divided by the secondary turns, so 800 divided by 200 gives 4 to 1. Because the secondary has fewer turns, the secondary voltage is lower, making it a step-down transformer. The current ratio is the inverse of the voltage ratio.

Question 33Electrical principles and theory

Which material property determines how much magnetic flux a core carries for a given magnetising force?

  1. Permeability Correct answer.
  2. Temperature coefficient
  3. Resistivity
  4. Dielectric strength

Explanation

Permeability expresses how readily a material supports the establishment of magnetic flux, so a high-permeability core carries more flux for the same magnetising force. Resistivity and dielectric strength relate to electrical conduction and insulation respectively, not to magnetic behaviour.

Question 34Electrical principles and theory

A 2 kW load runs for 3 hours each day. How much energy does it consume over 30 days?

  1. 600 kWh
  2. 60 kWh
  3. 180 kWh Correct answer.
  4. 18 kWh

Explanation

Energy equals power multiplied by time, so 2 kW for 3 hours gives 6 kWh per day. Multiplying by 30 days gives 180 kWh. Keeping the units consistent in kilowatts and hours avoids conversion errors.

Question 35Electrical principles and theory

A balanced delta-connected load has a phase current of 10 A. What is the line current?

  1. 10 A
  2. 17.3 A Correct answer.
  3. 5.77 A
  4. 30 A

Explanation

In a delta connection the line current is the square root of three times the phase current, so 1.732 times 10 A gives about 17.3 A. The line voltage equals the phase voltage in delta, which is why the current relationship differs from a star connection.

Question 36Electrical principles and theory

A coil with negligible resistance is connected across a DC supply and then across an AC supply of the same RMS voltage. What is observed?

  1. The DC current is much larger because inductive reactance is zero at zero frequency Correct answer.
  2. The AC current is larger because the coil stores energy each cycle
  3. The current is the same in both cases
  4. The DC current is zero because the coil blocks direct current

Explanation

Inductive reactance equals two pi times frequency times inductance, so at zero frequency the reactance is effectively zero and only the small winding resistance limits current. On AC the reactance opposes current, so the RMS current is smaller. This is why transformers cannot operate on steady DC.

Question 37Electrical principles and theory

A capacitor and a resistor are connected in series across an AC supply. As frequency is increased, what happens to the total impedance?

  1. It decreases towards the resistance value Correct answer.
  2. It increases towards the resistance value
  3. It falls to zero at high frequency
  4. It remains constant at the resistance value

Explanation

Capacitive reactance equals one divided by two pi times frequency times capacitance, so it falls as frequency rises. The total impedance, the vector sum of resistance and reactance, therefore decreases and approaches the resistance value but never falls below it.

Question 38Electrical principles and theory

A series RLC circuit has 10 ohm resistance, 20 ohm inductive reactance and 20 ohm capacitive reactance. What are the total impedance and the circuit phase relationship?

  1. 10 ohm with current leading voltage
  2. 50 ohm with current lagging voltage
  3. 28.3 ohm with current leading voltage
  4. 10 ohm with current in phase with voltage Correct answer.

Explanation

The inductive and capacitive reactances are equal and opposite in series, so they cancel, leaving only the 10 ohm resistance. The circuit is at resonance, so the current is in phase with the supply voltage and impedance is at its minimum.

Question 39Electrical principles and theory

Two identical 100 W lamps rated at 240 V are connected in series across a 240 V supply. What total power do they consume, assuming constant resistance?

  1. 200 W
  2. 50 W Correct answer.
  3. 100 W
  4. 25 W

Explanation

Each lamp has a resistance of 240 squared divided by 100, which is 576 ohm, so the series pair totals 1152 ohm. The current is 240 divided by 1152, about 0.208 A, and total power is 240 times that current, roughly 50 W. Each lamp therefore runs at about one quarter of its rated power.

Question 40Electrical principles and theory

A 12 V battery is connected across three resistors of 4 ohm, 6 ohm and 12 ohm joined in parallel. What is the total current drawn from the battery?

  1. 1.5 A
  2. 6 A Correct answer.
  3. 3 A
  4. 0.5 A

Explanation

For parallel branches the reciprocal of the total resistance equals the sum of the reciprocals of the individual resistances, so 1/R = 1/4 + 1/6 + 1/12 = 3/12 + 2/12 + 1/12 = 6/12, giving R = 2 ohm. Applying Ohm's law to the whole circuit, I = V/R = 12/2 = 6 A. Equivalently, the branch currents of 3 A, 2 A and 1 A add to 6 A.

Question 41Wiring systems and installation practices

What is the primary purpose of a circuit protective device installed in a final subcircuit?

  1. To limit the total energy consumed by the installation
  2. To automatically disconnect the supply when fault current or overload occurs Correct answer.
  3. To regulate the voltage supplied to connected equipment
  4. To improve the power factor of inductive loads

Explanation

Circuit protective devices such as circuit breakers and fuses exist to automatically interrupt the circuit when current exceeds safe levels due to overload or fault, protecting conductors and people. They do not regulate voltage, correct power factor, or meter energy.

Question 42Wiring systems and installation practices

Which conductor colour identifies the active conductor in a typical single-phase flexible cord to AS/NZS 3191?

  1. Black
  2. Green/yellow
  3. Brown Correct answer.
  4. Blue

Explanation

In flexible cords to the Australian standard, brown identifies the active, blue identifies the neutral, and green/yellow identifies the protective earth. Black is used for active in some fixed wiring, so colour interpretation depends on the cable type.

Question 43Wiring systems and installation practices

Why must cables be derated when several are bunched together and enclosed in thermal insulation?

  1. Bunching reduces the voltage drop along each cable
  2. Heat cannot dissipate readily, so the conductors run hotter for a given current Correct answer.
  3. Enclosure increases the mechanical stress on the conductors
  4. The insulation adds capacitance that increases charging current

Explanation

Each current-carrying conductor produces heat, and grouping or enclosing cables traps that heat so the conductors reach a higher temperature for the same current. Ratings must therefore be reduced to keep conductor temperature within the insulation limit.

Question 44Wiring systems and installation practices

What is the minimum requirement for a main earthing conductor connection at the switchboard?

  1. It must be connected to the main earthing terminal with a reliable, low-resistance joint Correct answer.
  2. It may be joined to the neutral bar to save a terminal
  3. It may be connected to any convenient metal enclosure panel
  4. It can be left disconnected if residual current devices are installed

Explanation

The main earthing conductor must terminate at the main earthing terminal, which provides a dedicated, reliable and low-resistance connection point. Earthing must never be combined with the neutral bar except at the defined MEN point, and RCDs do not remove the need for earthing.

Question 45Wiring systems and installation practices

A socket-outlet is installed in a residential bathroom. Which protective measure is required for the final subcircuit supplying it?

  1. A voltage-operated earth leakage device
  2. Additional protection by a 30 mA residual current device Correct answer.
  3. A dedicated isolating transformer for each outlet
  4. Double insulation of the entire switchboard

Explanation

Socket-outlets in wet or damp areas such as bathrooms require additional protection by a residual current device with a rated residual operating current not exceeding 30 mA. This limits the duration of a shock should contact occur.

Question 46Wiring systems and installation practices

Which wiring method is generally acceptable for installing cables in a ceiling space that is regularly accessed?

  1. Resting directly on the ceiling insulation
  2. Supported on cable trays or saddled clear of walkways and heat sources Correct answer.
  3. Run through the roof cavity without any support
  4. Laid loosely across the ceiling battens

Explanation

Cables in accessible ceiling spaces must be supported and protected from mechanical damage and heat, so trays or saddles keeping them clear of walkways and heat sources are appropriate. Loose, unsupported, or insulation-buried cables risk damage and overheating.

Question 47Wiring systems and installation practices

What does the term 'MEN' refer to in an electrical installation?

  1. Multiple earthed neutral system linking earth and neutral at the supply point Correct answer.
  2. Minimum energy network used for load shedding
  3. Main equipment neutral used for switching
  4. Mandatory earthing node fitted at each outlet

Explanation

MEN stands for Multiple Earthed Neutral, a system where the neutral is connected to earth at the supply transformer and at each installation's main earthing point. This arrangement ensures fault current returns via a low-impedance path to operate protective devices.

Question 48Wiring systems and installation practices

Why is a switch required to be placed in the active conductor rather than the neutral?

  1. So the switch can carry a higher current rating
  2. So the earth conductor can be switched simultaneously
  3. So the equipment is isolated from the supply when the switch is open Correct answer.
  4. So the neutral current is reduced during operation

Explanation

Switching the active ensures that, when open, the equipment and its wiring are isolated from the live supply, preventing shock during maintenance. A neutral-only switch leaves the equipment live even though it appears off.

Question 49Wiring systems and installation practices

A 2.5 mm² copper conductor carries 20 A over a 30 m run. Which factor most directly determines whether the voltage drop is acceptable?

  1. The calculated drop compared with the maximum permitted percentage of supply voltage Correct answer.
  2. The number of cable saddles used along the run
  3. The brand of the circuit breaker protecting the circuit
  4. The colour of the conductor insulation

Explanation

Voltage drop is calculated from current, conductor length and impedance, then compared with the maximum percentage permitted for the installation. If the calculated drop exceeds the limit, the conductor size must be increased.

Question 50Wiring systems and installation practices

Which condition requires the use of a cable with a higher temperature rating in a roof space?

  1. Ambient temperature in the space exceeds the assumed reference value Correct answer.
  2. The roof space contains timber framing
  3. The cable is fixed with plastic saddles
  4. The circuit is protected by a circuit breaker

Explanation

Cable current ratings are based on a reference ambient temperature, so if the actual ambient is higher the cable must be derated or a higher-temperature-rated cable selected. Saddles, breaker type and framing material do not by themselves raise conductor temperature.