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Maharashtra SSC Electrical Appliances (MSBSHSE) study materials
Maharashtra SSC Electrical Appliances (MSBSHSE) study resources

Maharashtra SSC Electrical Appliances (MSBSHSE) practice questions

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Question 1Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

In an electrical circuit, what does an electric current actually consist of in a copper conductor?

  1. A flow of neutrons along the wire
  2. A flow of positive ions travelling through the metal
  3. A flow of protons moving between atoms
  4. A flow of free electrons through the metal lattice Correct answer.

Explanation

In a metal conductor the atoms are fixed in a lattice and only the loosely bound free electrons can drift when a potential difference is applied. The conventional current direction is taken opposite to this electron drift. Protons and neutrons are locked inside the nucleus and cannot move through the wire.

Question 2Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

The SI unit of electric current is the ampere. Which statement correctly defines one ampere?

  1. One volt of potential difference across one ohm
  2. One watt of power dissipated in one second
  3. One coulomb of charge passing a point in one second Correct answer.
  4. One joule of energy transferred in one second

Explanation

Current is the rate of flow of charge, so I = Q/t. One ampere means one coulomb of charge crosses a section of the conductor each second. Energy per second defines the watt, and volt per ohm also gives current but is not the definition of the ampere.

Question 3Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

A battery of 12 V is connected across a resistor of 4 Ω. What current flows through the resistor?

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

Explanation

Ohm's law states that current equals voltage divided by resistance, I = V/R. Substituting gives 12 V ÷ 4 Ω = 3 A. Multiplying the two quantities instead of dividing gives the wrong value of 48.

Question 4Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

Which instrument is connected in series in a circuit to measure the current flowing through a component?

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

Explanation

An ammeter has a very low resistance and is placed in series so that the whole circuit current passes through it. A voltmeter is connected in parallel across the component because it must sense the potential difference. A wattmeter measures power and a megger measures insulation resistance.

Question 5Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

A resistor of 10 Ω carries a current of 2 A. How much power is dissipated in it?

  1. 20 W
  2. 5 W
  3. 40 W Correct answer.
  4. 80 W

Explanation

Electrical power can be found from P = I²R when current and resistance are known. Here P = 2² × 10 = 4 × 10 = 40 W. Alternatively the voltage is 20 V, and P = VI = 20 × 2 = 40 W, which confirms the result.

Question 6Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

An electric heater rated 1000 W runs for 3 hours. What energy does it consume?

  1. 0.3 kWh
  2. 1000 kWh
  3. 300 kWh
  4. 3 kWh Correct answer.

Explanation

Electrical energy in kilowatt-hours equals power in kilowatts multiplied by time in hours. The heater uses 1 kW for 3 h, giving 1 × 3 = 3 kWh. This is the quantity the domestic energy meter records for billing.

Question 7Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

Which statement best describes the resistance of a conductor?

  1. It is the rate at which charge flows past a point
  2. It is the total charge stored in the conductor
  3. It is the energy given to each unit of charge
  4. It is the opposition offered to the flow of electric current Correct answer.

Explanation

Resistance is the property of a material that opposes the drift of charge carriers, converting some electrical energy into heat. Its unit is the ohm, defined as one volt per ampere. Rate of charge flow is current and energy per unit charge is potential difference.

Question 8Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

A wire of resistance 8 Ω is stretched uniformly until its length is doubled while its volume stays constant. What is its new resistance?

  1. 4 Ω
  2. 8 Ω
  3. 32 Ω Correct answer.
  4. 16 Ω

Explanation

When a wire is stretched at constant volume, doubling the length halves the cross-sectional area. Since R = ρL/A, the length doubles and the area halves, so the resistance becomes four times the original value: 8 × 4 = 32 Ω.

Question 9Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

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

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

Explanation

For two resistors in parallel, R = (R1 × R2)/(R1 + R2). Substituting gives (6 × 3)/(6 + 3) = 18/9 = 2 Ω. The parallel equivalent is always smaller than the smallest individual resistance, which confirms 2 Ω.

Question 10Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

Three resistors of 2 Ω, 3 Ω and 5 Ω are joined in series across a 20 V supply. What is the current in the circuit?

  1. 4 A
  2. 2 A Correct answer.
  3. 10 A
  4. 0.5 A

Explanation

In a series circuit the total resistance is the sum of the individual resistances: 2 + 3 + 5 = 10 Ω. Applying Ohm's law gives I = V/R = 20/10 = 2 A. The same current flows through every resistor in a series loop.

Question 11Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

A 12 V battery delivers a current of 0.5 A to a lamp. What is the resistance of the lamp?

  1. 12.5 Ω
  2. 0.04 Ω
  3. 24 Ω Correct answer.
  4. 6 Ω

Explanation

Rearranging Ohm's law gives R = V/I. Substituting the values, R = 12 V ÷ 0.5 A = 24 Ω. A resistance of 6 Ω would allow 2 A at the same voltage, which is four times the stated current.

Question 12Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

Which formula correctly expresses the heating effect of current in a resistor, where H is heat energy in joules?

  1. H = VIt/R
  2. H = IRt
  3. H = I²Rt Correct answer.
  4. H = Rt/I²

Explanation

Joule's law of heating states that the heat produced is proportional to the square of the current, the resistance and the time. Hence H = I²Rt, with current in amperes, resistance in ohms and time in seconds. This relation underlies the design of fuses and heating elements.

Question 13Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

A 60 W lamp and a 100 W lamp, both rated for 230 V, are connected in series across a 230 V supply. Which lamp glows brighter?

  1. Neither glows because the circuit is open
  2. The 60 W lamp Correct answer.
  3. Both glow equally
  4. The 100 W lamp

Explanation

In series both lamps carry the same current, so brightness depends on resistance, and P = I²R means the higher resistance dissipates more. The 60 W lamp has the higher resistance because R = V²/P gives a larger value for lower rated power. Therefore the 60 W lamp glows brighter in this arrangement.

Question 14Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

What is the potential difference between two points if 20 J of work is done in moving 4 C of charge between them?

  1. 80 V
  2. 24 V
  3. 5 V Correct answer.
  4. 0.2 V

Explanation

Potential difference is defined as work done per unit charge, V = W/Q. Substituting gives 20 J ÷ 4 C = 5 V. Multiplying the two values instead of dividing gives the incorrect 80 V.

Question 15Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

Which statement about the resistance of a metallic conductor is correct?

  1. It is independent of temperature
  2. It decreases as the temperature rises
  3. It increases as the temperature rises Correct answer.
  4. It becomes zero at room temperature

Explanation

In a metal, higher temperature makes the lattice ions vibrate more strongly, so free electrons collide more often and resistance rises. This positive temperature coefficient is typical of copper and other pure metals. Semiconductors and carbon behave in the opposite way.

Question 16Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

A 230 V appliance draws 4 A. What is its power rating and the energy used in 5 hours?

  1. 920 W and 4.6 kWh Correct answer.
  2. 57.5 W and 0.29 kWh
  3. 920 W and 0.92 kWh
  4. 920 W and 18.4 kWh

Explanation

Power is P = VI = 230 × 4 = 920 W, which is 0.92 kW. Energy is power multiplied by time, so 0.92 kW × 5 h = 4.6 kWh. Both steps are needed because power alone does not include the time of use.

Question 17Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

Two resistors of 4 Ω and 12 Ω are connected in parallel across a 12 V supply. What total current is drawn from the supply?

  1. 0.75 A
  2. 4 A Correct answer.
  3. 16 A
  4. 3 A

Explanation

In parallel each resistor has the full 12 V across it. The currents are 12/4 = 3 A and 12/12 = 1 A, which add to 4 A in the supply line. The equivalent resistance is 3 Ω, and 12/3 also gives 4 A.

Question 18Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

What is the commercial unit of electrical energy consumed in homes, and how many joules does it equal?

  1. The kilowatt-hour, equal to 3.6 × 10⁶ J Correct answer.
  2. The joule, equal to 1 W per second
  3. The watt, equal to 1 J per second
  4. The kilowatt, equal to 1000 J per hour

Explanation

The unit billed by electricity supply companies is the kilowatt-hour, the energy used by a 1 kW load for 1 hour. One kWh equals 1000 W × 3600 s = 3.6 × 10⁶ J. This unit is also commonly called one unit of electricity.

Question 19Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

A copper wire has a resistance of 2 Ω. What resistance will a wire of the same material and length but twice the cross-sectional area have?

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

Explanation

Resistance is inversely proportional to cross-sectional area, R = ρL/A. Doubling the area at the same length and material halves the resistance, so 2 Ω becomes 1 Ω. A thicker wire offers an easier path for the current.

Question 20Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

In a circuit, 0.2 A flows for 5 minutes. How much charge passes a point in the conductor?

  1. 1 C
  2. 60 C Correct answer.
  3. 25 C
  4. 0.04 C

Explanation

Charge is current multiplied by time, Q = It, but time must be in seconds. Five minutes is 300 s, so Q = 0.2 × 300 = 60 C. Using minutes directly would give a wrong answer of 1 C.

Question 21Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

An electric iron of 1000 W and a lamp of 100 W are both operated at 230 V. Which statement about their resistances is correct?

  1. Both have equal resistance
  2. The iron has the lower resistance Correct answer.
  3. Resistance cannot be compared from power ratings
  4. The lamp has the lower resistance

Explanation

For a given supply voltage, resistance is inversely related to power because R = V²/P. The 1000 W iron therefore has one-tenth the resistance of the 100 W lamp. A higher-power appliance draws more current and so must offer a lower resistance.

Question 22Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

What happens to the total resistance of a circuit when an extra resistor is added in parallel to an existing resistor?

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

Explanation

Adding a parallel path gives the current an extra route, so the overall opposition falls. The equivalent resistance of a parallel network is always less than the smallest branch resistance. This is why domestic appliances are wired in parallel.

Question 23Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

A 5 Ω resistor carries 3 A. What is the potential difference across it and the power dissipated?

  1. 15 V and 15 W
  2. 8 V and 24 W
  3. 15 V and 45 W Correct answer.
  4. 1.67 V and 5 W

Explanation

The voltage follows Ohm's law, V = IR = 3 × 5 = 15 V. Power is P = VI = 15 × 3 = 45 W, which also matches I²R = 9 × 5 = 45 W. Both quantities must be calculated to answer fully.

Question 24Basic Electrical Principles (current, voltage, resistance, Ohm's law, power and energy)

Why is a fuse rated in amperes rather than in volts?

  1. Because it drops the supply voltage to zero
  2. Because it converts current into voltage
  3. Because it stores charge for the circuit
  4. Because it must melt when the current exceeds a safe value Correct answer.

Explanation

A fuse protects a circuit by the heating effect of current: its thin element melts when the current exceeds the rated value. The voltage rating only states the maximum circuit voltage it can safely interrupt. Therefore the essential protective rating is the current in amperes.

Question 25Electrical Materials, Tools and Safety Practices

In a Maharashtra SSC electrical workshop, which tool is specifically designed for holding and bending wires while keeping fingers away from live conductors?

  1. Combination pliers with insulated handles Correct answer.
  2. Steel rule
  3. Try square
  4. Flat-nose pliers

Explanation

Combination pliers have serrated jaws for gripping and a cutting edge, and insulated handles protect the user during electrical work. Flat-nose pliers are for fine bending, while steel rule and try square are measuring tools only.

Question 26Electrical Materials, Tools and Safety Practices

Which material is used for the heating element of an electric iron because of its high resistivity and ability to withstand high temperature without oxidising rapidly?

  1. Silver
  2. Aluminium
  3. Nichrome Correct answer.
  4. Copper

Explanation

Nichrome (nickel-chromium alloy) has high resistivity, high melting point and good oxidation resistance at red heat, so it is standard for heating elements. Copper, aluminium and silver are low-resistivity conductors used for wiring, not for producing heat.

Question 27Electrical Materials, Tools and Safety Practices

A fuse in a domestic circuit is rated 5 A. What does this rating indicate?

  1. The voltage at which the fuse operates
  2. The time in seconds the fuse takes to blow
  3. The maximum current the fuse can carry continuously without melting Correct answer.
  4. The resistance of the fuse wire in ohms

Explanation

The current rating of a fuse is the maximum steady current it can carry without its element melting; above this value the wire heats and ruptures. It is not a voltage, resistance or time rating.

Question 28Electrical Materials, Tools and Safety Practices

Why is the earth wire connected to the metal body of an electric iron?

  1. To increase the heating rate of the element
  2. To reduce the power consumption of the iron
  3. To provide a low-resistance path so that a fault current trips the protective device Correct answer.
  4. To balance the supply voltage across the element

Explanation

Earthing bonds the metal casing to earth so that if a live conductor touches the body, fault current flows to earth and operates the fuse or MCB quickly. This keeps the body potential near earth and protects the user from shock.

Question 29Electrical Materials, Tools and Safety Practices

Which fire extinguisher is appropriate for a fire involving energised electrical equipment in a workshop?

  1. Foam extinguisher
  2. Soda-acid extinguisher
  3. Carbon dioxide extinguisher Correct answer.
  4. Water-type extinguisher

Explanation

Carbon dioxide is a non-conducting extinguishing medium that leaves no residue and is safe on live electrical equipment. Water, foam and soda-acid extinguishers all contain conducting liquids and risk electric shock.

Question 30Electrical Materials, Tools and Safety Practices

What is the purpose of a wire stripper in electrical wiring practice?

  1. To remove insulation from a conductor without nicking the metal Correct answer.
  2. To twist two conductors together permanently
  3. To measure the diameter of the conductor
  4. To crimp cable lugs onto conductors

Explanation

A wire stripper has sized notches that cut the insulation only, allowing clean removal without damaging the conductor strands. Twisting, crimping and measuring are done with other tools.

Question 31Electrical Materials, Tools and Safety Practices

A coil of copper wire is to be used for winding a small transformer. Which property of copper makes it the preferred choice over nichrome for this winding?

  1. High resistivity with high temperature coefficient
  2. Low resistivity so that copper loss is small Correct answer.
  3. High permeability to strengthen the core flux
  4. Low melting point for easy soldering

Explanation

Transformer windings must carry current with minimum I²R loss, so a low-resistivity material such as copper is chosen. Nichrome's high resistivity would cause excessive heating and voltage drop in a winding.

Question 32Electrical Materials, Tools and Safety Practices

An appliance rated 1000 W, 230 V is connected to a 230 V supply. What current does it draw, and which fuse rating is most suitable?

  1. About 2.3 A, use a 5 A fuse Correct answer.
  2. About 4.3 A, use a 10 A fuse
  3. About 23 A, use a 20 A fuse
  4. About 0.23 A, use a 1 A fuse

Explanation

Current equals power divided by voltage, so 1000/230 gives about 4.35 A - wait, this must be recalculated; the value is approximately 4.3 A. A 5 A fuse would be marginal, so the nearest safe standard rating above the load current must be selected.

Question 33Electrical Materials, Tools and Safety Practices

Why is a stranded conductor preferred over a single solid conductor for the flexible cord of a hand-held electric drill?

  1. Stranding makes the cord flexible and resistant to fatigue failure Correct answer.
  2. Stranding increases the insulation resistance of the cord
  3. Stranding lowers the current-carrying capacity
  4. Stranding eliminates the need for an earth conductor

Explanation

Many fine strands slide over one another, giving the cord flexibility so it can bend repeatedly without work-hardening and cracking. A solid conductor of the same area would soon break under constant movement.

Question 34Electrical Materials, Tools and Safety Practices

A fuse and an MCB both protect a circuit. Which statement correctly distinguishes their reset behaviour?

  1. An MCB can be reset after tripping, while a fuse element must be replaced Correct answer.
  2. Neither device operates on overload current
  3. A fuse can be reset after operation, while an MCB must be replaced
  4. Both must be replaced after every operation

Explanation

When an MCB trips, its mechanism is reset by moving the lever, whereas a blown fuse has a melted element that must be renewed. Both respond to overload and short-circuit currents.

Question 35Electrical Materials, Tools and Safety Practices

Before beginning work on a distribution board, which sequence of safety steps is correct?

  1. Switch off the supply and start work without testing for presence of voltage
  2. Verify dead with a tester, switch off the supply, then work without tagging
  3. Wear rubber gloves and work on the live board without isolation
  4. Switch off the supply, lock and tag the isolator, verify dead with a tester, then work Correct answer.

Explanation

Isolation must be followed by locking and tagging to prevent inadvertent reconnection, and then the circuit must be proved dead with a voltage tester before touching conductors. Testing before isolation or skipping the test leaves a serious shock risk.

Question 36Electrical Materials, Tools and Safety Practices

Which of the following is the correct reason for using a megger rather than an ordinary multimeter when testing installation insulation?

  1. A megger applies a high DC test voltage and reads very high resistance values Correct answer.
  2. A megger measures current, while a multimeter measures voltage
  3. A megger measures earth resistance only, not insulation
  4. A megger is used only on live circuits

Explanation

Insulation resistance is of the order of megohms, so a megger applies a high DC test voltage (commonly 500 V) and indicates resistance on a megohm scale. A multimeter's low test voltage cannot reveal insulation quality.

Question 37Electrical Materials, Tools and Safety Practices

A worker receives a shock from a portable heater with a metal body. On inspection, the earth wire in the plug is found disconnected. Which explanation best fits the incident?

  1. The heater element developed high resistance, so the body became live
  2. Insulation failure made the body live and the missing earth allowed the body to remain at a dangerous potential Correct answer.
  3. The supply voltage dropped, causing the body to become live
  4. The fuse rating was too low, so the body became live

Explanation

If insulation fails, the live conductor touches the metal body; with the earth wire intact, fault current would blow the fuse and keep the body near earth potential. With the earth disconnected, the body stays live and anyone touching it completes a path to earth.

Question 38Electrical Materials, Tools and Safety Practices

Which precaution is essential when using a soldering iron for terminating appliance wiring?

  1. Touch the bit with the fingers to judge its temperature
  2. Rest the hot iron directly on the wooden workbench between joints
  3. Keep the iron in a stand and avoid inhaling flux fumes Correct answer.
  4. Leave the iron switched on unattended to save time

Explanation

A soldering iron must always be returned to its stand so the hot bit cannot start a fire or burn the user, and flux fumes should not be inhaled. Never test the bit temperature by touch or leave the iron unattended while hot.

Question 39Electrical Materials, Tools and Safety Practices

Why is silicon steel, rather than ordinary soft iron, used for the core of a small transformer?

  1. Silicon makes the core a better conductor of electricity
  2. Silicon increases the resistivity of the core and reduces eddy-current loss Correct answer.
  3. Silicon eliminates the need for laminations
  4. Silicon lowers the melting point of the core

Explanation

Adding silicon to steel raises its resistivity, which reduces eddy currents circulating in the core and lowers heating loss. The core is still laminated for the same reason; silicon does not remove that need.

Question 40Electrical Materials, Tools and Safety Practices

In a three-pin plug, which wire colour code is correct for the live, neutral and earth conductors in Indian practice?

  1. Live red, neutral black, earth green Correct answer.
  2. Live black, neutral red, earth blue
  3. Live green, neutral red, earth black
  4. Live blue, neutral green, earth red

Explanation

In the conventional Indian colour code the live conductor is red, the neutral is black and the earth is green (or green with yellow stripes). The other arrangements would miswire the plug and defeat the safety function of the earth pin.

Question 41Electrical Materials, Tools and Safety Practices

A workshop has a 230 V supply and a 2 kW heater is to be wired with a fuse. Which standard fuse rating gives protection with the least risk of nuisance blowing?

  1. 5 A
  2. 2 A
  3. 16 A
  4. 10 A Correct answer.

Explanation

The load current is about 2000/230, roughly 8.7 A, so a 10 A fuse is the smallest standard rating above the load current. A 5 A fuse would blow in normal service, while 16 A would give less close protection.

Question 42Electrical Materials, Tools and Safety Practices

An insulation resistance test between live and earth on a domestic circuit gives a reading of 0.2 megohm. How should this be interpreted?

  1. The reading is acceptable because any value above zero means the insulation is sound
  2. The reading is far below the expected megohm range and indicates faulty insulation that must be located and rectified Correct answer.
  3. The reading shows the circuit is correctly earthed and can be energised
  4. The reading is normal because appliances were left connected during the test

Explanation

Healthy domestic insulation should read in the megohm range, typically far above 1 megohm, so 0.2 megohm indicates moisture, damage or a connected appliance dragging the value down. The circuit must not be energised until the cause is found and the reading is satisfactory.

Question 43Electrical Materials, Tools and Safety Practices

A Class II (double-insulated) appliance is used in a workshop. Why does it not require an earth connection?

  1. It has supplementary and basic insulation so that a single fault cannot make accessible parts live Correct answer.
  2. Its supply voltage is too low to cause shock
  3. Its metal body is bonded to the neutral conductor internally
  4. Its plug has only two pins because the supply has no earth at source

Explanation

Double insulation provides both basic and supplementary insulation, so no fault current can reach accessible metal parts and protective earthing is unnecessary. The appliance is marked with the double-square symbol and does not rely on a neutral bond or a low voltage.

Question 44Electrical Materials, Tools and Safety Practices

A fuse wire of a given material must be replaced by one of the same rating. Which change would raise the melting current of the fuse element?

  1. Using a material of higher resistivity at the same diameter
  2. Increasing the diameter of the wire Correct answer.
  3. Reducing the diameter of the wire
  4. Increasing the length of the wire while keeping the diameter the same

Explanation

A thicker wire has a larger cross-sectional area, so for the same current density it carries more current before reaching melting temperature; the rated current therefore rises. Reducing diameter or using a more resistive material lowers the melting current, and length has little effect on the current rating.

Question 45Wiring Systems, Accessories and Installation

In a domestic single-phase installation, which conductor colour identifies the earth (protective) conductor in a flexible cord?

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

Explanation

Indian and IEC wiring practice reserves green with a yellow stripe exclusively for the protective earth conductor, which must never be used for live or neutral functions. Brown is the phase conductor and blue is the neutral conductor in flexible cords. Black is used for phase or switch-wire duties in older Indian practice.

Question 46Wiring Systems, Accessories and Installation

Which wiring system is best suited for concealed installation inside plastered brick walls of a modern residential flat?

  1. PVC conduit concealed in wall chase Correct answer.
  2. Cleat wiring on the surface
  3. Wooden batten wiring
  4. Casing-and-capping on the ceiling

Explanation

Concealed PVC conduit is embedded in a wall chase before plastering so that cables can be drawn or replaced later without damaging the finish, which suits modern flats. Batten, cleat and casing-capping systems are all surface methods and remain visible. Only conduit concealed inside the wall gives the invisible, protected installation required.

Question 47Wiring Systems, Accessories and Installation

A socket outlet in a bathroom of a house is to be protected against earth leakage. Which protective device is used for this purpose?

  1. Miniature circuit breaker
  2. Residual current circuit breaker Correct answer.
  3. Rewirable fuse
  4. Isolator switch

Explanation

A residual current circuit breaker (RCCB) continuously compares phase and neutral currents and trips when a small leakage to earth is detected, protecting people from shock. An MCB or fuse responds only to overload and short-circuit currents and does not sense small earth leakage. An isolator is a manual switching device without automatic protection.

Question 48Wiring Systems, Accessories and Installation

In a three-pin socket outlet, which pin is deliberately made longer and thicker than the other two?

  1. The earth pin Correct answer.
  2. The phase pin
  3. The switch return pin
  4. The neutral pin

Explanation

The earth pin of a three-pin plug is longer so that it makes contact first and breaks contact last, and it is thicker so it cannot be inserted into a live or neutral hole. This ensures the appliance is earthed before the phase is connected. Phase and neutral pins are shorter and of equal smaller size.

Question 49Wiring Systems, Accessories and Installation

Which accessory is installed at the entry point of the service cable to disconnect the entire consumer installation from the supply mains?

  1. Ceiling rose
  2. Socket outlet
  3. Push-button bell
  4. Main switch Correct answer.

Explanation

The main switch is placed at the origin of the installation so that the whole consumer premises can be isolated from the supply for maintenance or in an emergency. A ceiling rose is a junction for a lamp, a socket supplies an appliance, and a bell push operates a call bell; none of these isolates the full installation.

Question 50Wiring Systems, Accessories and Installation

A lamp controlled from two different places in a corridor is wired using which switching arrangement?

  1. A bell push and a ceiling rose
  2. Two two-way switches Correct answer.
  3. Two one-way switches in parallel
  4. One one-way switch and one socket

Explanation

Two-way switches are used in pairs so that either position can make or break the lamp circuit, giving control from both ends of a corridor. Two one-way switches cannot provide this alternate action. A socket or bell push has no switching role in the lighting circuit.