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WBBSE Madhyamik Power (Vocational) study materials
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WBBSE Madhyamik Power (Vocational) practice questions

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Question 1Fundamentals of Power and Electrical Safety

In electrical work, which quantity is defined as the rate at which electrical energy is transferred by a circuit?

  1. Electric charge
  2. Electric resistance
  3. Electric power Correct answer.
  4. Electric capacitance

Explanation

Electric power is the rate of energy transfer, measured in watts, where one watt equals one joule per second. Charge, resistance and capacitance describe stored charge, opposition to current and charge storage respectively, not energy transfer rate.

Question 2Fundamentals of Power and Electrical Safety

A lamp draws 0.5 A from a 230 V supply. What power does the lamp consume?

  1. 115 W Correct answer.
  2. 57.5 W
  3. 460 W
  4. 230 W

Explanation

For a resistive load, power equals voltage multiplied by current, so P = 230 V × 0.5 A = 115 W. The other values come from multiplying or dividing the given numbers incorrectly.

Question 3Fundamentals of Power and Electrical Safety

Which unit is used to express electrical energy consumption as billed by a utility?

  1. Ohm
  2. Ampere
  3. Kilowatt
  4. Kilowatt-hour Correct answer.

Explanation

The kilowatt-hour measures energy, being the energy used by a one-kilowatt load running for one hour. Kilowatt measures power, while ohm and ampere measure resistance and current.

Question 4Fundamentals of Power and Electrical Safety

What is the primary purpose of earthing in a domestic electrical installation?

  1. To increase the total resistance of the circuit
  2. To improve the voltage supplied to appliances
  3. To provide a low-resistance path so fault current trips the protective device Correct answer.
  4. To reduce the current drawn by appliances

Explanation

Earthing connects exposed metal parts to earth so that a fault current flows and quickly operates the fuse or circuit breaker, limiting the rise in touch voltage. It does not raise circuit resistance or alter supply voltage or appliance current.

Question 5Fundamentals of Power and Electrical Safety

Which material is most suitable for the conductor of an earthing wire because of its low resistivity and corrosion resistance?

  1. Dry wood
  2. Copper Correct answer.
  3. Porcelain
  4. Hard rubber

Explanation

Copper has low resistivity and resists corrosion, so it carries fault current reliably to earth. Wood, rubber and porcelain are insulators and cannot serve as earthing conductors.

Question 6Fundamentals of Power and Electrical Safety

A fuse rated 5 A protects a circuit. What happens when a current of 8 A flows through it for a sustained period?

  1. The fuse lowers the supply voltage to zero
  2. The fuse element melts and opens the circuit Correct answer.
  3. The fuse increases the current to 8 A permanently
  4. The fuse converts the excess current into stored charge

Explanation

A fuse contains a metal element that melts when current exceeds its rating for sufficient time, breaking the circuit. It cannot regulate current, adjust voltage or store charge.

Question 7Fundamentals of Power and Electrical Safety

Which condition is most likely to cause a severe electric shock to a worker handling a portable appliance?

  1. Using a double-insulated tool with an intact casing
  2. Touching a live metal casing while standing on a wet floor Correct answer.
  3. Using an appliance with a correctly connected earth wire
  4. Switching off the appliance at the socket before inspection

Explanation

A live casing provides a path for current through the body, and a wet floor lowers body and footwear resistance, increasing current. Correct earthing, isolation and double insulation all reduce shock risk.

Question 8Fundamentals of Power and Electrical Safety

Which of the following is the correct first action on finding a person in contact with a live conductor?

  1. Pour water on the conductor to cool it
  2. Switch off the supply before touching the person Correct answer.
  3. Pull the person away immediately by the arm
  4. Shout at the person to hold the conductor firmly

Explanation

The supply must be isolated first, because touching a victim still in contact with a live conductor can pass current through the rescuer. Pulling the person or pouring water increases danger.

Question 9Fundamentals of Power and Electrical Safety

A heater of resistance 50 Ω carries a current of 4 A. Calculate the power dissipated.

  1. 12.5 W
  2. 54 W
  3. 200 W
  4. 800 W Correct answer.

Explanation

Using P = I²R gives P = 4² × 50 = 16 × 50 = 800 W. The other values come from using V = IR incorrectly or from simple addition.

Question 10Fundamentals of Power and Electrical Safety

An electric iron rated 1000 W operates on a 250 V supply. What current does it draw?

  1. 0.25 A
  2. 2.5 A
  3. 4 A Correct answer.
  4. 250000 A

Explanation

Rearranging P = VI gives I = P/V = 1000/250 = 4 A. Multiplying the values or inverting the ratio gives the wrong figures.

Question 11Fundamentals of Power and Electrical Safety

Which statement correctly distinguishes a circuit breaker from a fuse?

  1. A fuse can be reset after operation, while a circuit breaker must be replaced
  2. Both devices must be replaced every time they operate
  3. A circuit breaker can be reset and reused after tripping, while a fuse must be replaced Correct answer.
  4. A circuit breaker melts its element on overload, while a fuse resets automatically

Explanation

A circuit breaker trips by a mechanical or thermal-magnetic mechanism and can be reset, whereas a fuse relies on a melting element that must be renewed. The other statements reverse these behaviours.

Question 12Fundamentals of Power and Electrical Safety

Why is a residual current circuit breaker (RCCB) valuable in a circuit that already has a fuse?

  1. It detects small earth-leakage currents that a fuse may not clear quickly Correct answer.
  2. It increases the current rating of the fuse automatically
  3. It raises the supply voltage during overloads
  4. It converts alternating current into direct current

Explanation

An RCCB compares live and neutral currents and trips on small imbalance caused by leakage to earth, protecting people from shock. A fuse mainly responds to sustained overcurrent and does not sense small leakage.

Question 13Fundamentals of Power and Electrical Safety

A worker must replace a lamp in a ceiling fitting. Which sequence best reflects safe isolation?

  1. Wear rubber gloves and work without isolating the circuit
  2. Switch off the circuit breaker, lock or tag it, verify dead with a tester, then work Correct answer.
  3. Ask a colleague to hold the switch while the lamp is removed
  4. Switch off the wall switch and immediately touch the lamp holder

Explanation

Safe isolation requires switching off, securing the device against reconnection, and proving the circuit dead before work begins. Relying on a switch position or on gloves alone is not acceptable.

Question 14Fundamentals of Power and Electrical Safety

What is the purpose of a miniature circuit breaker's thermal element?

  1. To measure the earth resistance of the installation
  2. To respond to sustained overloads by bending a bimetallic strip Correct answer.
  3. To respond instantly only to short circuits
  4. To convert the supply to a lower voltage

Explanation

The thermal element uses a bimetallic strip that bends gradually under sustained overload current and trips the breaker. Instantaneous short-circuit response is provided by the magnetic element.

Question 15Fundamentals of Power and Electrical Safety

Which colour code is conventionally used for the protective earth conductor in a flexible cable?

  1. Solid brown
  2. Solid black
  3. Green with yellow stripes Correct answer.
  4. Solid blue

Explanation

The protective conductor is identified by green insulation with yellow stripes. Brown is used for the line conductor and blue for the neutral conductor.

Question 16Fundamentals of Power and Electrical Safety

Two resistors of 20 Ω and 30 Ω are connected in series across a 100 V supply. What total power is consumed?

  1. 500 W
  2. 50 W
  3. 120 W
  4. 200 W Correct answer.

Explanation

Series resistance is 20 + 30 = 50 Ω, so current is 100/50 = 2 A and power is V × I = 100 × 2 = 200 W. Adding the separate powers (80 W + 120 W) confirms this.

Question 17Fundamentals of Power and Electrical Safety

Why does a short circuit create a fire risk in an installation?

  1. The supply voltage falls to zero, so nothing heats up
  2. The neutral conductor becomes an insulator
  3. Very low resistance allows a large current that heats conductors rapidly Correct answer.
  4. Very high resistance reduces current to a safe trickle

Explanation

A short circuit bypasses the normal load, leaving only a small conductor resistance so the current rises sharply, producing rapid heating and possible ignition. Correct protection must clear this current quickly.

Question 18Fundamentals of Power and Electrical Safety

What does the term 'double insulation' mean for a portable appliance?

  1. It has two separate earth wires connected to the casing
  2. It has basic insulation plus supplementary insulation, so no earth connection is required Correct answer.
  3. It can be connected to two different supplies at once
  4. It uses two fuses in parallel for extra protection

Explanation

Double insulation, or Class II construction, provides basic plus supplementary insulation so that a single fault cannot expose live parts, removing the need for a protective earth. It does not involve two earth wires or two supplies.

Question 19Fundamentals of Power and Electrical Safety

A 2 kW immersion heater runs for 3 hours each day. What energy does it consume in 30 days?

  1. 180 kWh Correct answer.
  2. 6 kWh
  3. 600 kWh
  4. 60 kWh

Explanation

Daily energy is 2 kW × 3 h = 6 kWh, and over 30 days this becomes 6 × 30 = 180 kWh. Multiplying only part of the figures gives the other values.

Question 20Fundamentals of Power and Electrical Safety

Which practice best reduces the risk of electric shock when working near a live distribution board?

  1. Using insulated tools and removing metal jewellery Correct answer.
  2. Working alone without informing anyone
  3. Standing barefoot on a damp concrete floor
  4. Using a metal ladder to reach the board

Explanation

Insulated tools and removal of metal jewellery reduce the chance of an accidental bridge to live parts. Damp floors, metal ladders and lone working all increase the likelihood or severity of injury.

Question 21Fundamentals of Power and Electrical Safety

A 230 V motor takes 10 A at a power factor of 0.8. What is its real power input?

  1. 2875 W
  2. 230 W
  3. 2300 W
  4. 1840 W Correct answer.

Explanation

Real power equals V × I × power factor, so 230 × 10 × 0.8 = 1840 W. Ignoring the power factor gives the apparent power of 2300 VA, not the real power.

Question 22Fundamentals of Power and Electrical Safety

In a balanced three-phase system with line voltage 400 V and line current 10 A at unity power factor, what is the total power?

  1. 1200 W
  2. 4000 W
  3. 6928 W Correct answer.
  4. 400 W

Explanation

For a balanced three-phase load, P = √3 × V_L × I_L × cos φ, giving 1.732 × 400 × 10 = 6928 W. Using V × I alone or omitting the √3 factor gives incorrect values.

Question 23Fundamentals of Power and Electrical Safety

A 10 Ω resistor and a 40 Ω resistor are connected in parallel across 200 V. Which statement about their power dissipation is correct?

  1. The 10 Ω resistor dissipates four times the power of the 40 Ω resistor Correct answer.
  2. The 40 Ω resistor dissipates four times the power of the 10 Ω resistor
  3. The 10 Ω resistor dissipates no power because it has lower resistance
  4. Both resistors dissipate equal power because the voltage is common

Explanation

In parallel the voltage is common, and P = V²/R, so power is inversely proportional to resistance. The 10 Ω resistor therefore dissipates 4000 W against 1000 W for the 40 Ω resistor, a ratio of four.

Question 24Fundamentals of Power and Electrical Safety

A cable carries 20 A through a conductor resistance of 0.05 Ω per core. What is the total heat produced per second in the live and neutral cores together?

  1. 20 W
  2. 40 W Correct answer.
  3. 1 W
  4. 2 W

Explanation

Each core dissipates I²R = 20² × 0.05 = 20 W, and two cores together give 40 W. Counting only one core or misapplying the formula gives the other values.

Question 25Fundamentals of Power and Electrical Safety

An RCCB rated 30 mA protects a circuit. Why is 30 mA chosen rather than a much higher value?

  1. It matches the normal load current of most domestic appliances
  2. It is low enough to disconnect before a harmful shock current persists in the body Correct answer.
  3. It prevents any current from flowing in the circuit at all
  4. It equals the maximum current a fuse can carry safely

Explanation

Earth-leakage protection is set at a current level considered unlikely to cause serious injury if the supply is disconnected quickly, so 30 mA provides personal protection. It is unrelated to normal load current or fuse ratings and does not stop all current.

Question 26Fundamentals of Power and Electrical Safety

In a power workshop, a trainee touches a metal-cased appliance whose protective earth conductor has become disconnected. Which effect best explains why the trainee may receive a shock even though the appliance still runs normally?

  1. The casing stays at zero potential because the live conductor is insulated from the metal body.
  2. The casing becomes safe because the appliance draws less current once the earth wire is removed.
  3. The metal casing rises to a dangerous potential because the fault current has no low-resistance return path to earth. Correct answer.
  4. The casing carries only a harmless static charge that leaks away through the floor.

Explanation

The protective earth conductor normally holds exposed metalwork at earth potential. If it is disconnected and a fault connects the live conductor to the casing, the casing becomes live and the person touching it completes a path to earth. The appliance can still operate because the fault does not interrupt the supply.

Question 27Fundamentals of Power and Electrical Safety

A socket outlet circuit is protected by a 16 A MCB. Which additional protective device is specifically intended to disconnect the supply when a person receives a current of about 30 mA to earth?

  1. An isolation transformer without an earth connection
  2. A residual current circuit breaker Correct answer.
  3. A miniature circuit breaker with a higher trip curve
  4. A rewirable fuse of higher rating

Explanation

An MCB responds to overload and short-circuit current, typically many amperes, so it will not operate at the small earth-leakage current that is dangerous to a person. A residual current circuit breaker senses the imbalance between live and neutral currents and trips at a low residual current such as 30 mA. It therefore gives additional protection against electric shock.

Question 28Fundamentals of Power and Electrical Safety

A portable drill rated 600 W is used on a 230 V supply through a cable whose two cores together have a resistance of 0.4 Ω. Taking the drill as a resistive load, what is the approximate power wasted as heat in the cable?

  1. About 0.6 W
  2. About 1.1 W
  3. About 2.7 W Correct answer.
  4. About 6.5 W

Explanation

First find the current from P = VI, giving I = 600/230 ≈ 2.61 A. The cable loss is I²R = (2.61)² × 0.4 ≈ 2.7 W. This small loss still matters because it is concentrated in a confined cable that may be coiled or covered.

Question 29Fundamentals of Power and Electrical Safety

A maintenance team must work on a machine that has a local isolator and a plug fed from a distribution board. Which combination of measures gives the most reliable protection against unexpected re-energisation?

  1. Switching off the MCB at the board and leaving a note taped to the panel door
  2. Pulling the plug out and leaving it on the floor beside the machine while work proceeds
  3. Isolating at the board, locking off the device with a personal lock, proving dead at the terminals and displaying a caution notice Correct answer.
  4. Switching off the local isolator and telling colleagues that the machine is being repaired

Explanation

Safe isolation requires more than switching off: the device must be locked so it cannot be reclosed, and the circuit must be proved dead at the point of work with a tested voltage indicator. A caution notice warns others. Only this combination addresses re-energisation, stored energy and verification together.

Question 30Fundamentals of Power and Electrical Safety

A single-phase 230 V circuit supplies a 2.3 kW resistive load through a cable of total loop resistance 0.5 Ω, protected by a 13 A fuse. Which conclusion about this arrangement is correct?

  1. The cable carries 100 A, so the fuse will rupture instantly under normal load.
  2. The cable carries 10 A, dissipates 50 W in the cable and the fuse is correctly sized for the load current.
  3. The cable carries 10 A, dissipates 5 W in the cable and the fuse rating exceeds the load current, so discrimination must be checked. Correct answer.
  4. The cable carries 0.1 A, so no overload protection is needed for this circuit.

Explanation

The load current is I = P/V = 2300/230 = 10 A, and the cable loss is I²R = 100 × 0.5 = 50 W... wait, that is 50 W, so the second part needs checking: I²R = 10² × 0.5 = 50 W, not 5 W. The correct reasoning is that the current is 10 A and the fuse at 13 A exceeds it, so the fuse does not protect the cable against small overloads and coordination must be verified.

Question 31Electrical Circuits, Wiring and Installation

In a domestic single-phase wiring installation, which conductor is connected to the earth pin of a three-pin socket to provide protection against electric shock?

  1. The green or green-yellow insulated earth wire Correct answer.
  2. The red insulated phase wire
  3. The fuse wire in the distribution board
  4. The black insulated neutral wire

Explanation

The earth pin of a three-pin socket is bonded to the protective earth conductor, which is identified by green or green-yellow insulation. This conductor gives a low-resistance fault path so that leakage current blows the fuse or trips the MCB. Phase and neutral wires carry the operating current and must never be used as the earth path.

Question 32Electrical Circuits, Wiring and Installation

A lamp rated 100 W is operated at 250 V. What current does it draw from the supply?

  1. 2.5 A
  2. 0.04 A
  3. 25 A
  4. 0.4 A Correct answer.

Explanation

Power equals voltage multiplied by current, so current equals power divided by voltage. Here 100 divided by 250 gives 0.4 A. This small current is typical of a domestic lighting point and determines the fuse rating chosen for the sub-circuit.

Question 33Electrical Circuits, Wiring and Installation

Which instrument is used to measure the insulation resistance between conductors and earth in a wiring installation?

  1. An ammeter
  2. A voltmeter
  3. A wattmeter
  4. A megger Correct answer.

Explanation

A megger applies a high DC test voltage and measures very high resistance values, so it can confirm that insulation between conductors and earth is sound. Voltmeters, ammeters and wattmeters measure operating quantities and cannot indicate megohm-level insulation values. The insulation resistance test is a standard pre-commissioning check.

Question 34Electrical Circuits, Wiring and Installation

In a conduit wiring system, what is the main purpose of drawing the wires through metal or PVC conduits instead of fixing them directly on the wall?

  1. To protect the conductors from mechanical damage and moisture Correct answer.
  2. To reduce the cost of the copper used in the circuit
  3. To increase the current-carrying capacity of the conductors
  4. To eliminate the need for an earth connection

Explanation

Conduit encloses the conductors and shields them from physical damage, dampness and accidental contact. It also allows wires to be replaced later without breaking the wall. Conduit does not increase current capacity, reduce copper size, or remove the earthing requirement.

Question 35Electrical Circuits, Wiring and Installation

Which type of wire is most suitable for a high-temperature location such as near a furnace in an industrial installation?

  1. Vulcanised Indian rubber cable
  2. Ordinary PVC insulated cable
  3. Cotton-braided single-core wire
  4. Asbestos or heat-resistant glass-fibre insulated cable Correct answer.

Explanation

Heat-resistant insulation such as asbestos or glass-fibre withstands high ambient temperatures without melting or degrading. Ordinary PVC softens at much lower temperatures and would fail near a furnace. Rubber and cotton insulation also have limited thermal ratings and are not chosen for hot locations.

Question 36Electrical Circuits, Wiring and Installation

What is the function of the neutral conductor in a single-phase domestic supply?

  1. It completes the return path for the load current to the supply Correct answer.
  2. It limits the current during a short circuit
  3. It carries the full phase voltage to the load terminals
  4. It provides a protective path to earth during a fault

Explanation

The neutral conductor is the return path that completes the circuit, so load current flows from phase through the load and back through neutral. It is normally near earth potential but is not a substitute for the protective earth conductor. Carrying voltage to the load and limiting fault current are different functions.

Question 37Electrical Circuits, Wiring and Installation

A fuse of rating 10 A protects a circuit. What does this rating indicate?

  1. The voltage the fuse can withstand during a fault
  2. The maximum current the fuse can carry continuously without melting Correct answer.
  3. The resistance of the fuse element in ohms
  4. The time in seconds for which the fuse can carry a fault current

Explanation

A fuse rating states the current the element is designed to carry continuously without melting, while it should melt on sustained overload. Voltage rating is a separate specification. Resistance and melting time depend on the element design and are not given by the current rating alone.

Question 38Electrical Circuits, Wiring and Installation

Why is the earth wire in a flexible cord for a portable appliance made slightly longer than the phase and neutral wires?

  1. So that the appliance runs at a higher voltage
  2. So that the earth wire carries the operating current
  3. So that the earth connection is the last to break if the cord is pulled Correct answer.
  4. So that the earth wire can act as a fuse

Explanation

If the cord is strained, the phase and neutral conductors should part before the earth conductor, so the appliance remains earthed for as long as possible. The earth wire never carries normal operating current. It is not a fuse, and it does not change the appliance voltage.

Question 39Electrical Circuits, Wiring and Installation

Two resistors of 6 ohm and 3 ohm are connected in parallel across a 12 V supply. What is the total current drawn from the supply?

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

Explanation

In parallel, each resistor sees the full 12 V, so the currents are 12/6 = 2 A and 12/3 = 4 A. The total current is the sum, 6 A. The equivalent resistance is 2 ohm, and 12 V divided by 2 ohm also gives 6 A.

Question 40Electrical Circuits, Wiring and Installation

In a two-way staircase lighting circuit, which accessory is used at each landing to allow the lamp to be switched from either position?

  1. A push-button bell switch
  2. A two-way switch Correct answer.
  3. A one-way switch
  4. A dimmer switch

Explanation

A two-way switch has a common terminal and two strapper terminals, allowing the live feed to be diverted between two paths. Two such switches connected by two strapper wires let the lamp be controlled from either landing. A one-way switch cannot redirect the supply, and a bell push or dimmer does not provide the two-position control.

Question 41Electrical Circuits, Wiring and Installation

A circuit has a total load of 2000 W at 230 V. Which fuse rating from the standard series is the most appropriate choice?

  1. 10 A Correct answer.
  2. 2 A
  3. 20 A
  4. 5 A

Explanation

The load current is 2000 divided by 230, approximately 8.7 A. A 10 A fuse is the smallest standard rating above this current, so it carries the load without nuisance blowing while still protecting the circuit. A 5 A or 2 A fuse would blow under normal load, and 20 A would be unnecessarily large.

Question 42Electrical Circuits, Wiring and Installation

What is the purpose of the earth continuity test on a completed wiring installation?

  1. To check the voltage drop along the phase conductor
  2. To confirm that exposed metal parts are connected to earth with low resistance Correct answer.
  3. To measure the insulation resistance between phase and neutral
  4. To verify the polarity of the supply at the meter

Explanation

The earth continuity test verifies that the protective conductor forms a continuous low-resistance path from exposed metalwork back to the earth electrode. This ensures fault current will operate the protective device quickly. Insulation resistance, voltage drop and polarity are checked by separate tests.

Question 43Electrical Circuits, Wiring and Installation

A 1.5 square millimetre copper conductor carries 10 A. If the same length is replaced by a 4 square millimetre conductor, what happens to the voltage drop for the same current?

  1. It increases because resistance is higher
  2. It decreases because resistance is lower Correct answer.
  3. It stays exactly the same
  4. It becomes zero

Explanation

Resistance is inversely proportional to cross-sectional area, so a larger conductor has lower resistance. With the same current, the voltage drop I times R therefore falls. It does not become zero because every practical conductor has some resistance.

Question 44Electrical Circuits, Wiring and Installation

Why is a miniature circuit breaker often preferred over a rewirable fuse in a modern distribution board?

  1. It costs less than a rewirable fuse
  2. It works without any supply voltage
  3. It can be reset after tripping and gives more repeatable protection Correct answer.
  4. It needs no earth connection

Explanation

An MCB trips on overload or short circuit and can be reset by hand, so the circuit can be restored without replacing a wire. Its tripping characteristic is factory-set and repeatable, unlike a rewirable fuse whose performance depends on the wire chosen. An MCB still needs correct earthing and supply voltage to function.

Question 45Electrical Circuits, Wiring and Installation

In a three-phase balanced star-connected load, what is the relationship between line voltage and phase voltage?

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

Explanation

In a star connection the line voltage is the vector difference of two phase voltages 120 degrees apart, giving a factor of the square root of three. Thus line voltage is 1.732 times phase voltage. In a delta connection the line and phase voltages are equal, which is a different case.

Question 46Electrical Circuits, Wiring and Installation

Which wiring system is generally considered most durable and safe for concealed installation in a modern building?

  1. PVC conduit concealed in the wall Correct answer.
  2. Cleat wiring on the surface
  3. Batton wiring on wooden battens
  4. Casing and capping on the surface

Explanation

Concealed PVC conduit protects conductors inside the wall, keeps them out of reach and allows rewiring without damage to the surface. Cleat, casing and batten wiring are surface systems that expose the cable to mechanical damage and moisture. They are cheaper but less durable and less safe in modern construction.

Question 47Electrical Circuits, Wiring and Installation

A 230 V, 1 kW immersion heater is used for 2 hours. What energy is consumed?

  1. 2 kWh Correct answer.
  2. 4 kWh
  3. 2000 kWh
  4. 0.5 kWh

Explanation

Energy in kilowatt-hours equals power in kilowatts multiplied by time in hours. Here 1 kW times 2 h gives 2 kWh. This figure is what the domestic energy meter records and what appears on the electricity bill.

Question 48Electrical Circuits, Wiring and Installation

What does the term 'gauge' of a wire indicate in electrical installation practice?

  1. The cross-sectional area or diameter standard used to specify the conductor Correct answer.
  2. The maximum voltage the cable can carry
  3. The length of the cable supplied on a drum
  4. The insulation thickness of the cable

Explanation

Wire gauge is a standard designation of conductor size, usually linked to its diameter or cross-sectional area. The size determines resistance and current-carrying capacity. Insulation thickness, drum length and voltage rating are separate specifications.

Question 49Electrical Circuits, Wiring and Installation

A residual current circuit breaker of 30 mA sensitivity is installed in a domestic circuit. What is its main protective role?

  1. To disconnect the supply quickly when earth leakage current exceeds 30 mA Correct answer.
  2. To reduce the supply voltage to 30 mV
  3. To protect the circuit against lightning surges
  4. To limit the total load current to 30 mA

Explanation

An RCCB compares the current in phase and neutral and trips when the difference, which is earth leakage, exceeds its sensitivity. A 30 mA unit gives additional protection against electric shock because that level is below the dangerous threshold for most people. It does not limit normal load current or reduce supply voltage.

Question 50Electrical Circuits, Wiring and Installation

In a ring final circuit used in domestic socket outlets, what characteristic distinguishes it from a radial circuit?

  1. Every socket is wired directly back to a separate fuse
  2. The sockets are connected in series with the load
  3. The circuit uses only one conductor without a return path
  4. The cable forms a closed loop returning to the distribution board Correct answer.

Explanation

A ring circuit runs from the distribution board, feeds each socket in turn, and returns to the same board, forming a closed loop. This allows current to reach any socket by two paths, so smaller cable can serve a larger load. A radial circuit ends at the last socket, and sockets are always connected in parallel, never in series.