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SG PPE Electrical practice questions

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Question 1Electrical theory and circuit fundamentals

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

  1. Lagging the voltage by 90 degrees
  2. Leading the voltage by 90 degrees
  3. Lagging the voltage by 45 degrees
  4. In phase with the voltage Correct answer.

Explanation

Resistance dissipates energy without storing it, so current rises and falls in step with voltage. Phase shift requires reactive elements such as inductors or capacitors.

Question 2Electrical theory and circuit fundamentals

A 12-volt battery is connected across a 4-ohm resistor. What current flows through the resistor?

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

Explanation

Ohm's law states that current equals voltage divided by resistance. Dividing 12 volts by 4 ohms gives 3 amperes.

Question 3Electrical theory and circuit fundamentals

Which quantity is measured in coulombs?

  1. Capacitance
  2. Electric power
  3. Resistance
  4. Electric charge Correct answer.

Explanation

The coulomb is the SI unit of electric charge, equal to one ampere-second. Capacitance is measured in farads, power in watts, and resistance in ohms.

Question 4Electrical theory and circuit fundamentals

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

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

Explanation

For two parallel resistors, the equivalent resistance is the product divided by the sum. Multiplying 6 by 3 gives 18, and dividing by 9 gives 2 ohms.

Question 5Electrical theory and circuit fundamentals

In a series circuit containing three resistors, which statement about current is true?

  1. The current divides in proportion to resistance
  2. The current is largest through the smallest resistor
  3. The current is zero between resistors
  4. The current is the same through every resistor Correct answer.

Explanation

A series circuit provides only one path, so the same current must pass through each element. Voltage, not current, divides among series resistors.

Question 6Electrical theory and circuit fundamentals

What is the total capacitance of two 10-microfarad capacitors connected in parallel?

  1. 10 microfarads
  2. 100 microfarads
  3. 20 microfarads Correct answer.
  4. 5 microfarads

Explanation

Capacitors in parallel add directly because their plates are effectively joined, increasing total plate area. The sum of 10 and 10 microfarads is 20 microfarads.

Question 7Electrical theory and circuit fundamentals

Which material is classified as a good conductor of electricity?

  1. Glass
  2. Rubber
  3. Dry wood
  4. Copper Correct answer.

Explanation

Conductors have many free electrons that move easily under an applied voltage; copper is a metal with abundant free electrons. Glass, rubber, and dry wood are insulators with tightly bound electrons.

Question 8Electrical theory and circuit fundamentals

A circuit has a 24-volt source and draws 2 amperes. What power is delivered to the circuit?

  1. 48 watts Correct answer.
  2. 26 watts
  3. 96 watts
  4. 12 watts

Explanation

Power equals voltage multiplied by current. Multiplying 24 volts by 2 amperes yields 48 watts.

Question 9Electrical theory and circuit fundamentals

Three 12-ohm resistors are connected in series across a 36-volt supply. What is the current in the circuit?

  1. 3 amperes
  2. 0.33 amperes
  3. 1 ampere Correct answer.
  4. 12 amperes

Explanation

Series resistances add, giving 36 ohms total. Dividing the 36-volt supply by 36 ohms yields 1 ampere.

Question 10Electrical theory and circuit fundamentals

A 100-ohm resistor carries 0.5 amperes. What is the voltage drop across it?

  1. 50 volts Correct answer.
  2. 0.005 volts
  3. 200 volts
  4. 25 volts

Explanation

Ohm's law gives voltage as current times resistance. Multiplying 0.5 amperes by 100 ohms yields 50 volts.

Question 11Electrical theory and circuit fundamentals

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

  1. 0.5 amperes Correct answer.
  2. 7200 amperes
  3. 2 amperes
  4. 60 amperes

Explanation

Rearranging the power equation gives current equal to power divided by voltage. Dividing 60 watts by 120 volts yields 0.5 amperes.

Question 12Electrical theory and circuit fundamentals

A parallel circuit has two branches of 4 ohms and 12 ohms across a 24-volt source. What current flows through the 12-ohm branch?

  1. 8 amperes
  2. 2 amperes Correct answer.
  3. 6 amperes
  4. 1.5 amperes

Explanation

In a parallel circuit each branch sees the full source voltage. Dividing 24 volts by 12 ohms gives 2 amperes in that branch.

Question 13Electrical theory and circuit fundamentals

Which statement correctly describes the voltage across components connected in parallel?

  1. It equals the source voltage on each branch Correct answer.
  2. It sums to the source voltage across the branches
  3. It is zero on the lowest-resistance branch
  4. It is inversely proportional to branch resistance

Explanation

Parallel branches share the same two nodes, so each branch experiences the full source voltage. Branch resistance affects branch current, not branch voltage.

Question 14Electrical theory and circuit fundamentals

An inductor is connected to an AC source. How does its inductive reactance change if the frequency is doubled?

  1. It halves
  2. It stays the same
  3. It falls to zero
  4. It doubles Correct answer.

Explanation

Inductive reactance equals two pi times frequency times inductance, so it is directly proportional to frequency. Doubling the frequency therefore doubles the reactance.

Question 15Electrical theory and circuit fundamentals

How does capacitive reactance respond to an increase in frequency?

  1. It remains constant
  2. It becomes infinite
  3. It decreases Correct answer.
  4. It increases proportionally

Explanation

Capacitive reactance equals one divided by two pi times frequency times capacitance. Because frequency is in the denominator, raising frequency lowers the reactance.

Question 16Electrical theory and circuit fundamentals

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

  1. 170 volts
  2. 85 volts
  3. 120 volts Correct answer.
  4. 340 volts

Explanation

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

Question 17Electrical theory and circuit fundamentals

In a series RLC circuit at resonance, which condition is true?

  1. The voltage leads the current by 90 degrees
  2. Inductive reactance equals capacitive reactance Correct answer.
  3. The current is at a minimum
  4. Resistance equals zero

Explanation

Resonance occurs when inductive and capacitive reactances are equal in magnitude, so they cancel. The circuit then behaves resistively with current in phase with voltage.

Question 18Electrical theory and circuit fundamentals

A 10-microfarad capacitor is charged to 50 volts. How much charge is stored?

  1. 5 microcoulombs
  2. 0.2 microcoulombs
  3. 500 microcoulombs Correct answer.
  4. 50 microcoulombs

Explanation

Charge equals capacitance multiplied by voltage. Multiplying 10 microfarads by 50 volts gives 500 microcoulombs.

Question 19Electrical theory and circuit fundamentals

Two batteries of 9 volts and 6 volts are connected in series aiding. What is the total source voltage?

  1. 54 volts
  2. 3 volts
  3. 15 volts Correct answer.
  4. 7.5 volts

Explanation

Series-aiding voltage sources add their potentials because their polarities reinforce each other. The sum of 9 volts and 6 volts is 15 volts.

Question 20Electrical theory and circuit fundamentals

A circuit drawing 4 amperes has a total resistance of 15 ohms. What power is dissipated?

  1. 3.75 watts
  2. 30 watts
  3. 60 watts
  4. 240 watts Correct answer.

Explanation

Power can be found as current squared times resistance. Squaring 4 amperes gives 16, and multiplying by 15 ohms yields 240 watts.

Question 21Electrical theory and circuit fundamentals

A 120-volt source feeds a series circuit of 30 ohms and 10 ohms. What is the voltage across the 10-ohm resistor?

  1. 30 volts Correct answer.
  2. 120 volts
  3. 10 volts
  4. 90 volts

Explanation

Total resistance is 40 ohms, so current is 120 divided by 40, or 3 amperes. The 10-ohm resistor then drops 3 amperes times 10 ohms, which is 30 volts.

Question 22Electrical theory and circuit fundamentals

A circuit has a resistive load of 8 ohms in series with an inductive reactance of 6 ohms. What is the impedance magnitude?

  1. 2 ohms
  2. 10 ohms Correct answer.
  3. 48 ohms
  4. 14 ohms

Explanation

Impedance magnitude combines resistance and reactance as the square root of the sum of their squares. The square root of 64 plus 36 is the square root of 100, or 10 ohms.

Question 23Electrical theory and circuit fundamentals

In a series RC circuit, how does the current relate to the source voltage?

  1. Current leads voltage by an angle between 0 and 90 degrees Correct answer.
  2. Current lags voltage by an angle between 0 and 90 degrees
  3. Current is exactly in phase with voltage
  4. Current lags voltage by exactly 90 degrees

Explanation

Capacitive current leads voltage, and the series resistance limits the phase angle to less than 90 degrees. The exact lead angle depends on the ratio of reactance to resistance.

Question 24Electrical theory and circuit fundamentals

A 10-ohm resistor carries 3 amperes. How much energy does it dissipate in 20 seconds?

  1. 1800 joules Correct answer.
  2. 90 joules
  3. 600 joules
  4. 30 joules

Explanation

Power equals current squared times resistance, giving 9 times 10, or 90 watts. Energy is power times time, so 90 watts times 20 seconds yields 1800 joules.

Question 25Electrical theory and circuit fundamentals

A parallel circuit has a 6-ohm and a 3-ohm branch across a 12-volt source. What total current does the source supply?

  1. 2 amperes
  2. 6 amperes Correct answer.
  3. 4 amperes
  4. 1.33 amperes

Explanation

Each branch sees 12 volts, giving 2 amperes through 6 ohms and 4 amperes through 3 ohms. The source supplies the sum, which is 6 amperes.

Question 26Electrical theory and circuit fundamentals

Which quantity is defined as the rate at which electrical charge flows past a point in a circuit?

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

Explanation

Current is the rate of charge flow, measured in amperes, where one ampere equals one coulomb per second. Voltage is a potential difference, resistance opposes flow, and power is the rate of energy transfer.

Question 27Electrical theory and circuit fundamentals

Which property of a circuit element describes its ability to store energy in an electric field?

  1. Reactance
  2. Conductance
  3. Capacitance Correct answer.
  4. Inductance

Explanation

Capacitance is the property that stores energy in an electric field between two conductors separated by a dielectric. Inductance stores energy in a magnetic field, conductance describes ease of current flow, and reactance is opposition to AC current.

Question 28Electrical theory and circuit fundamentals

A resistor of 50 ohms is connected across a 10-volt source. What current flows through the resistor?

  1. 5.0 amperes
  2. 500 amperes
  3. 0.2 amperes Correct answer.
  4. 0.5 amperes

Explanation

Ohm's law states that current equals voltage divided by resistance. Dividing 10 volts by 50 ohms gives 0.2 amperes.

Question 29Electrical theory and circuit fundamentals

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

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

Explanation

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

Question 30Electrical theory and circuit fundamentals

A sinusoidal alternating current has a peak value of 20 amperes. What is its average value over one complete cycle?

  1. 0 amperes Correct answer.
  2. 6.37 amperes
  3. 12.7 amperes
  4. 20 amperes

Explanation

A sine wave is symmetrical about zero, so its positive half-cycle area exactly cancels its negative half-cycle area over a full period. The average over one complete cycle is therefore zero. The value 12.7 amperes is the half-cycle average, not the full-cycle average.

Question 31Wiring systems, cables and accessories

Which British Standard applies to the general requirements for electrical installations in domestic and similar premises?

  1. BS EN 61386
  2. BS 1363
  3. BS EN 60898
  4. BS 7671 Correct answer.

Explanation

BS 7671 is the IET Wiring Regulations and sets out the general requirements for the design, erection and verification of electrical installations. The other standards cover products such as circuit breakers, conduit and plugs.

Question 32Wiring systems, cables and accessories

What does the csa of a cable conductor refer to?

  1. The cross-sectional area of the conductive metal Correct answer.
  2. The thickness of the insulation wall
  3. The overall diameter of the sheathed cable
  4. The length of cable on a drum

Explanation

Cross-sectional area (csa) is the area of the metal conductor measured in square millimetres and determines current-carrying capacity. It is not a measure of insulation, overall diameter or cable length.

Question 33Wiring systems, cables and accessories

Which colour identifies the line conductor of a single-phase circuit in a modern harmonised cable?

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

Explanation

Under harmonised colour coding, brown is the line conductor, blue is neutral and green/yellow is protective earth. Grey is used as a line or phase conductor in three-phase arrangements.

Question 34Wiring systems, cables and accessories

What is the primary purpose of a ring final circuit in a domestic installation?

  1. To provide a dedicated supply to a shower unit
  2. To share load current around two paths back to the origin Correct answer.
  3. To allow each socket to have its own fuse
  4. To limit the circuit to lighting loads only

Explanation

A ring final circuit loops the conductors so that current can travel to the origin by two paths, allowing a smaller cable csa to serve multiple socket-outlets. It is not a radial dedicated supply and does not fuse each socket individually.

Question 35Wiring systems, cables and accessories

Which accessory is designed to isolate a circuit locally for maintenance?

  1. A double-pole isolator switch Correct answer.
  2. A cable gland
  3. A ceiling rose
  4. A fused connection unit

Explanation

A double-pole isolator switch disconnects both line and neutral to provide local isolation for maintenance. A ceiling rose is a termination point, an FCU provides fusing and a gland provides mechanical termination.

Question 36Wiring systems, cables and accessories

What does the term 'sheath' describe on a typical twin and earth cable?

  1. The terminal block inside an accessory
  2. The copper conductors
  3. The earth conductor itself
  4. The outer protective covering over the insulated cores Correct answer.

Explanation

The sheath is the outer covering that protects the insulated cores from mechanical damage and moisture. It is distinct from the core insulation and from the conductors.

Question 37Wiring systems, cables and accessories

Why is a cable derating factor applied when cables are bunched together?

  1. To allow smaller protective devices to be used
  2. To compensate for voltage drop over long runs
  3. To increase the current-carrying capacity for grouped cables
  4. To account for reduced heat dissipation between adjacent cables Correct answer.

Explanation

Grouped cables cannot dissipate heat as effectively, so their current-carrying capacity is reduced by a grouping factor. Voltage drop and protective device selection are handled separately.

Question 38Wiring systems, cables and accessories

What is the function of a cable clip when installing surface wiring?

  1. To insulate exposed conductors
  2. To support and secure the cable to the structure Correct answer.
  3. To join two lengths of cable together
  4. To provide an earth connection

Explanation

Cable clips mechanically support the cable and keep it secure against the building structure. They do not provide electrical connection or insulation.

Question 39Wiring systems, cables and accessories

A 2.5 mm² copper conductor is to be selected for a 20 A radial socket circuit. Which property most directly determines whether the cable can carry the load current?

  1. Its current-carrying capacity after applying correction factors Correct answer.
  2. Its insulation colour
  3. Its overall sheath diameter
  4. Its resistance per metre only

Explanation

The cable's tabulated current-carrying capacity, corrected for installation method and grouping, must be at least the design current. Colour, diameter and resistance alone do not determine thermal adequacy.

Question 40Wiring systems, cables and accessories

Which installation method generally gives a cable the lowest current-carrying capacity?

  1. On a perforated cable tray in free air
  2. Enclosed in thermal insulation Correct answer.
  3. Buried in free-draining soil
  4. Clipped direct to a surface

Explanation

Cables surrounded by thermal insulation cannot dissipate heat readily, so their capacity is significantly reduced. Surface clipping, burial and tray installation allow better heat transfer.

Question 41Wiring systems, cables and accessories

A circuit has a design current of 18 A and the selected cable has a corrected capacity of 20 A. Which protective device rating is most appropriate?

  1. A 32 A device
  2. A 6 A device
  3. A 20 A device Correct answer.
  4. A 45 A device

Explanation

The protective device rating must be at least the design current but not exceed the corrected cable capacity, so 20 A satisfies both conditions. Larger devices would not protect the cable and a 6 A device would not carry the load.

Question 42Wiring systems, cables and accessories

Why must the neutral conductor of a single-phase final circuit be sized to match the line conductor in most socket circuits?

  1. Because the neutral carries the same current as the line in normal operation Correct answer.
  2. Because the neutral must be smaller to limit fault current
  3. Because the neutral is only used during faults
  4. Because the neutral is always at a higher potential

Explanation

In a single-phase circuit the neutral carries the same current as the line during normal balanced operation, so it must be sized accordingly. It is not a fault-only conductor and is not deliberately made smaller.

Question 43Wiring systems, cables and accessories

Which type of cable is most suitable for direct burial without additional protection?

  1. Flexible cord with a textile braid
  2. Steel wire armoured cable Correct answer.
  3. Single-insulated panel wire
  4. Flat twin and earth PVC cable

Explanation

Steel wire armoured cable provides mechanical protection suitable for direct burial. Flat twin and earth, flexible cord and single-insulated wire lack the necessary mechanical protection.

Question 44Wiring systems, cables and accessories

What is the main reason for using a fused connection unit on a fixed appliance spur?

  1. To act as an earth electrode
  2. To protect the appliance and its flexible cable with a suitable fuse Correct answer.
  3. To increase the circuit's current rating
  4. To provide additional socket-outlets

Explanation

A fused connection unit contains a fuse chosen to protect the appliance and its flexible cord, which may be smaller than the circuit cable. It does not add socket-outlets or increase circuit rating.

Question 45Wiring systems, cables and accessories

Which factor must be considered when determining the minimum bending radius of a cable?

  1. The colour of the sheath
  2. The rating of the protective device
  3. The cable's overall diameter and construction Correct answer.
  4. The number of socket-outlets on the circuit

Explanation

Minimum bending radius is expressed as a multiple of the cable's overall diameter and depends on its construction, since excessive bending can damage insulation or conductors. Colour, device rating and outlet count do not determine it.

Question 46Wiring systems, cables and accessories

In a three-phase distribution board, which conductor colour is conventionally used for phase L2 in harmonised coding?

  1. Grey
  2. Blue
  3. Brown
  4. Black Correct answer.

Explanation

Harmonised three-phase coding uses brown for L1, black for L2 and grey for L3, with blue as neutral. Brown is L1, grey is L3 and blue is neutral.

Question 47Wiring systems, cables and accessories

A cable passes through a fire-rated wall. Which accessory is used to maintain the fire resistance of the penetration?

  1. A junction box
  2. A fire-stop sealing system Correct answer.
  3. A conduit coupler
  4. A cable tie

Explanation

A fire-stop sealing system restores the fire resistance of a wall or floor where services penetrate it. Cable ties, junction boxes and couplers do not provide fire sealing.

Question 48Wiring systems, cables and accessories

Which of the following best describes the purpose of a consumer unit's main switch?

  1. To limit current on a single circuit
  2. To measure energy consumption
  3. To isolate all final circuits from the supply Correct answer.
  4. To provide earth fault protection

Explanation

The main switch isolates the entire installation from the supply for maintenance or emergency. Earth fault protection is provided by RCDs, individual circuits are limited by MCBs or fuses, and metering is separate.

Question 49Wiring systems, cables and accessories

A 10 mm² cable is to be replaced by a cable of the same type but with a longer route. Which design consideration is most likely to become the limiting factor?

  1. Fuse colour coding
  2. Sheath colour
  3. Voltage drop Correct answer.
  4. Cable clip spacing

Explanation

Longer cable runs increase voltage drop, which can become the limiting design factor even when current-carrying capacity is adequate. Colour, clip spacing and fuse coding do not depend on route length in this way.

Question 50Wiring systems, cables and accessories

Which of these is a recognised method of protecting a cable installed in a stud wall from nail penetration?

  1. Increasing the fuse rating
  2. Using a cable with a metallic covering or installing a protective plate Correct answer.
  3. Reducing the cable csa
  4. Painting the cable a warning colour

Explanation

Mechanical protection such as a metallic covering or steel plate prevents nails and screws from damaging concealed cables. Reducing csa, increasing fuse rating or painting do not provide mechanical protection.