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Odisha CHSE +2 Vocational EDA (Electrical Domestic Appliances) study materials
Odisha CHSE +2 Vocational EDA (Electrical Domestic Appliances) study resources

Odisha CHSE +2 Vocational EDA (Electrical Domestic Appliances) practice questions

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Question 1Basic Electrical Principles and Measurements

In a domestic wiring circuit, the live wire is identified by which insulation colour as per Indian convention?

  1. Red or brown Correct answer.
  2. Black
  3. Blue
  4. Green

Explanation

Indian domestic wiring convention uses red (older wiring) or brown (newer flexible cords) for the phase or live conductor. This colour coding lets a technician identify the line conductor before testing or terminating an appliance.

Question 2Basic Electrical Principles and Measurements

A heater draws 5 A from a 230 V supply. What is its power rating?

  1. 115 W
  2. 1150 W Correct answer.
  3. 2300 W
  4. 46 W

Explanation

Power in a resistive appliance equals voltage multiplied by current, so 230 V × 5 A = 1150 W. Domestic heater ratings are quoted in watts using this product.

Question 3Basic Electrical Principles and Measurements

Which instrument is connected in series with a domestic appliance to measure the current it draws?

  1. Ammeter Correct answer.
  2. Wattmeter
  3. Megger
  4. Voltmeter

Explanation

An ammeter has very low internal resistance and is connected in series so that the whole load current passes through it. Connecting it in parallel would short the supply and damage the meter.

Question 4Basic Electrical Principles and Measurements

The resistance of a conductor of uniform cross-section is directly proportional to which quantity?

  1. The square of its diameter
  2. Its length Correct answer.
  3. Its cross-sectional area
  4. The applied frequency

Explanation

Resistance equals resistivity times length divided by area, so for a fixed material and area it rises with length. This is why long appliance leads have slightly higher resistance than short ones.

Question 5Basic Electrical Principles and Measurements

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

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

Explanation

For two resistors in parallel the equivalent is the product divided by the sum: (6 × 3)/(6 + 3) = 18/9 = 2 Ω. The result is always smaller than the smallest branch resistance.

Question 6Basic Electrical Principles and Measurements

In a single-phase domestic supply, the purpose of the earth wire connected to an appliance body is to:

  1. Reduce the power consumption of the appliance
  2. Carry the normal load current back to the supply
  3. Improve the power factor of the appliance
  4. Provide a low-resistance path so that fault current trips the protective device Correct answer.

Explanation

The earth conductor bonds exposed metal to the supply earth so that a fault creates a large current which quickly operates the fuse or MCB. It does not carry normal load current or alter the appliance's power consumption.

Question 7Basic Electrical Principles and Measurements

Which of the following is a derived SI unit used in electrical measurement?

  1. Kelvin
  2. Kilogram
  3. Volt Correct answer.
  4. Second

Explanation

The volt is a derived unit defined as one joule per coulomb, formed from the base units of energy and charge. Kilogram, second and kelvin are base SI units.

Question 8Basic Electrical Principles and Measurements

A 230 V appliance has a resistance of 46 Ω. What current does it draw?

  1. 10580 A
  2. 10 A
  3. 5 A Correct answer.
  4. 0.2 A

Explanation

Ohm's law gives current as voltage divided by resistance, so 230/46 = 5 A. This current value is then used to select the correct fuse rating for the appliance.

Question 9Basic Electrical Principles and Measurements

An electric iron rated 1000 W at 230 V is used for 2 hours daily. What energy does it consume in 30 days?

  1. 2 kWh
  2. 60 kWh Correct answer.
  3. 30 kWh
  4. 120 kWh

Explanation

Daily energy is 1 kW × 2 h = 2 kWh, and over 30 days this becomes 60 kWh. Domestic tariffs are billed per unit, where one unit equals one kilowatt-hour.

Question 10Basic Electrical Principles and Measurements

A moving-coil instrument is preferred for DC measurement mainly because it:

  1. Requires no permanent magnet
  2. Works equally well on AC without a rectifier
  3. Has zero damping
  4. Has a uniform scale and high sensitivity Correct answer.

Explanation

The moving-coil movement produces a deflecting torque proportional to current, giving a linear scale with good sensitivity. It responds to the average value, so on AC without a rectifier it reads near zero.

Question 11Basic Electrical Principles and Measurements

The reading of a voltmeter connected across a 230 V supply drops noticeably when a low-resistance load is switched on. The most likely cause is:

  1. The load has a leading power factor
  2. The earth wire is disconnected
  3. The voltmeter has too high a resistance
  4. Excessive voltage drop in the supply wiring due to load current Correct answer.

Explanation

Load current flowing through the finite resistance of the supply conductors causes a voltage drop, so the terminal voltage falls below the no-load value. A high-resistance voltmeter is desirable and would not cause the drop.

Question 12Basic Electrical Principles and Measurements

Which property of a material makes it suitable for use as the heating element of a domestic electric heater?

  1. Zero temperature coefficient of resistance
  2. High resistivity and high melting point Correct answer.
  3. Low resistivity and low melting point
  4. High resistivity and low melting point

Explanation

A heating element must dissipate power without melting, so it needs high resistivity to generate heat and a high melting point to survive high temperatures. Nichrome is a common example.

Question 13Basic Electrical Principles and Measurements

Three 40 W lamps are connected in parallel across a 230 V supply. What is the total current drawn?

  1. 0.52 A Correct answer.
  2. 0.87 A
  3. 0.17 A
  4. 1.74 A

Explanation

Total power is 3 × 40 = 120 W, and current equals power divided by voltage, giving 120/230 ≈ 0.52 A. In a parallel connection each lamp receives the full supply voltage.

Question 14Basic Electrical Principles and Measurements

In a domestic circuit, a 6 A MCB protecting a lighting sub-circuit is intended mainly to:

  1. Convert alternating current to direct current
  2. Interrupt the circuit automatically on overload or short circuit Correct answer.
  3. Improve the power factor of the lamps
  4. Limit the voltage supplied to the lamps

Explanation

A miniature circuit breaker trips thermally on sustained overload and magnetically on short-circuit current, protecting the wiring. It does not regulate voltage or condition the supply.

Question 15Basic Electrical Principles and Measurements

A moving-iron instrument is used in a domestic panel ammeter. Its main advantage over a moving-coil instrument is that it:

  1. Can measure both AC and DC directly Correct answer.
  2. Has a perfectly linear scale
  3. Has higher sensitivity than a moving-coil meter
  4. Needs no damping

Explanation

The moving-iron movement responds to the RMS value of current and works on both AC and DC without a rectifier. Its scale is slightly non-uniform and its sensitivity is lower than that of a moving-coil meter.

Question 16Basic Electrical Principles and Measurements

The resistance of a copper conductor is 20 Ω at 20 °C. If its temperature coefficient of resistance is 0.004 per °C, what is its resistance at 70 °C?

  1. 28 Ω
  2. 24 Ω Correct answer.
  3. 22 Ω
  4. 20 Ω

Explanation

The rise is 50 °C, so the increase is 20 × 0.004 × 50 = 4 Ω, giving 24 Ω. Copper has a positive temperature coefficient, so its resistance rises with temperature.

Question 17Basic Electrical Principles and Measurements

A wattmeter in a domestic single-phase circuit has its current coil connected in series with the load and its voltage coil in parallel. This arrangement ensures that the instrument measures:

  1. The reactive power only
  2. The supply voltage only
  3. The load current only
  4. The product of load current and supply voltage, giving power Correct answer.

Explanation

The current coil carries the load current while the voltage coil carries a current proportional to supply voltage, so the deflecting torque is proportional to their product. That product, with the cosine of the phase angle, is the active power.

Question 18Basic Electrical Principles and Measurements

A 1500 W geyser is connected to a 230 V supply through a circuit protected by a 6 A MCB. What happens when the geyser is switched on?

  1. It runs normally because 6 A is above its current
  2. The MCB trips because the geyser draws about 6.5 A Correct answer.
  3. The voltage rises to compensate for the load
  4. The geyser draws only 0.15 A and runs safely

Explanation

The geyser current is 1500/230 ≈ 6.5 A, which exceeds the 6 A rating of the breaker. A sustained overload of this kind operates the thermal element and trips the MCB.

Question 19Basic Electrical Principles and Measurements

Two identical 100 W lamps are connected in series across a 230 V supply. What is the total power consumed, assuming constant resistance?

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

Explanation

Each lamp receives half the supply voltage, so each dissipates one quarter of its rated power, giving 25 W each and 50 W total. This is why lamps in series glow dimly.

Question 20Basic Electrical Principles and Measurements

A domestic energy meter with a meter constant of 600 revolutions per kWh makes 30 revolutions in 3 minutes. What is the connected load in kW?

  1. 2 kW
  2. 0.1 kW
  3. 1 kW Correct answer.
  4. 0.5 kW

Explanation

Energy registered is 30/600 = 0.05 kWh over 3 minutes, which is 0.05 h. Dividing energy by time gives 0.05/0.05 = 1 kW.

Question 21Basic Electrical Principles and Measurements

A voltmeter of 1000 Ω resistance is connected across a 100 kΩ resistor carrying current in a circuit. What is the main effect on the measurement?

  1. The resistor burns out immediately
  2. The reading is accurate because the voltmeter resistance is high
  3. The voltmeter loads the circuit and reads much less than the true voltage Correct answer.
  4. The voltmeter reads a higher voltage than the true value

Explanation

A voltmeter of 1000 Ω placed across 100 kΩ draws significant current and forms a parallel path that lowers the effective resistance. The measured voltage is therefore much lower than the true value, showing why voltmeters need very high resistance.

Question 22Basic Electrical Principles and Measurements

A coil of resistance 20 Ω and inductive reactance 15 Ω is connected to a 230 V AC supply. What is the impedance and current?

  1. 25 Ω and about 5.8 A
  2. 5 Ω and 46 A
  3. 35 Ω and about 6.6 A
  4. 25 Ω and about 9.2 A Correct answer.

Explanation

Impedance is the vector sum of resistance and reactance: the square root of (20² + 15²) = 25 Ω. Current is then 230/25 ≈ 9.2 A.

Question 23Basic Electrical Principles and Measurements

A moving-coil ammeter has a full-scale current of 1 mA and a resistance of 100 Ω. What shunt resistance is needed to extend its range to 1 A?

  1. About 0.1 Ω Correct answer.
  2. About 1000 Ω
  3. About 100 Ω
  4. About 10 Ω

Explanation

The shunt must carry 0.999 A while the meter carries 0.001 A at full scale, so the shunt is about 1/999 of the meter resistance. That gives roughly 0.1 Ω.

Question 24Basic Electrical Principles and Measurements

In a series circuit containing a resistor, an inductor and a capacitor at resonance, which statement describes the circuit behaviour?

  1. Impedance is maximum and current is minimum
  2. Impedance is minimum and current is maximum Correct answer.
  3. The capacitor carries no current
  4. The power factor is zero

Explanation

At series resonance the inductive and capacitive reactances cancel, leaving only resistance, so impedance is at its minimum and current at its maximum. The power factor is then unity, not zero.

Question 25Electrical Materials, Wiring Accessories and Safety

In a domestic wiring installation, which conductor colour conventionally identifies the earth (protective) conductor in a flexible three-core cable?

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

Explanation

Standard flexible-cable colour coding reserves green/yellow for the protective earth conductor so that it can never be confused with a live or neutral core. Brown is used for the phase (live) conductor and blue for the neutral conductor in modern harmonised wiring. The earth conductor is connected to the metal enclosure and to the earth pin of the socket.

Question 26Electrical Materials, Wiring Accessories and Safety

A fuse in a domestic appliance circuit performs which primary protective function?

  1. It limits the voltage reaching the appliance to 230 V
  2. It interrupts the circuit when current exceeds its rated value Correct answer.
  3. It converts alternating current into direct current
  4. It balances the load between phase and neutral

Explanation

A fuse element is a calibrated metallic strip or wire that melts when the current exceeds its rating, thereby opening the circuit and protecting wiring and equipment from overheating. It responds to overcurrent, whether caused by overload or short circuit. It does not regulate voltage, rectify current, or balance loads.

Question 27Electrical Materials, Wiring Accessories and Safety

Which material is most commonly used for the current-carrying element of a domestic fuse because of its low melting point and predictable fusing characteristic?

  1. Silver
  2. Tinned copper alloy Correct answer.
  3. Copper
  4. Aluminium

Explanation

Fuse elements are made from alloys such as tinned copper or zinc-based alloys chosen so that the element melts reliably at a defined current-time characteristic. Pure copper and silver have high melting points and are used for conductors, not fuse elements. Aluminium is used for heavy distribution conductors rather than small appliance fuses.

Question 28Electrical Materials, Wiring Accessories and Safety

A 2.5 mm² copper conductor is used on a domestic lighting circuit rated at 6 A. Which property of copper makes it the preferred conductor material for such wiring?

  1. Very high melting point with low conductivity
  2. High magnetic permeability
  3. High electrical conductivity with good ductility Correct answer.
  4. High resistivity with low cost

Explanation

Copper combines high electrical conductivity (low resistivity) with good ductility, so it can be drawn into wires and bent during installation without cracking. Low resistivity keeps voltage drop and heating within limits for a given cross-section. Magnetic permeability and very high melting point are not the reasons copper is chosen for wiring.

Question 29Electrical Materials, Wiring Accessories and Safety

In a domestic wiring system, the purpose of earthing the metal body of an appliance is to:

  1. Increase the current-carrying capacity of the live conductor
  2. Convert the appliance to a double-insulated design
  3. Reduce the electricity bill by improving power factor
  4. Provide a low-resistance path so that fault current trips the protective device Correct answer.

Explanation

Earthing connects exposed metalwork to the general mass of earth through a low-resistance path. If a live conductor touches the metal body, a large fault current flows and quickly operates the fuse or MCB, disconnecting the supply before a person can be electrocuted. Earthing does not affect billing, conductor rating, or insulation class.

Question 30Electrical Materials, Wiring Accessories and Safety

Which wiring accessory is used to connect a flexible cord of an appliance to the fixed installation in a way that allows easy disconnection without tools?

  1. A conduit coupler
  2. A junction box
  3. A plug and socket outlet Correct answer.
  4. A ceiling rose

Explanation

A plug and socket outlet provides a demountable connection between the flexible cord of an appliance and the fixed wiring, allowing the appliance to be plugged in and removed without tools. A ceiling rose is a fixed termination for a luminaire, and a junction box is for permanent joints. A conduit coupler only joins lengths of conduit.

Question 31Electrical Materials, Wiring Accessories and Safety

A socket outlet in a bathroom is protected by a 30 mA residual current device. What does this device detect?

  1. An excessive voltage between phase and neutral
  2. An overload of the neutral conductor only
  3. An imbalance between the phase and neutral currents Correct answer.
  4. A reversal of the phase and earth connections

Explanation

An RCD continuously compares the current flowing in the phase and neutral conductors through a toroidal core. Any difference, such as current leaking to earth through a person or wet surface, produces a magnetic imbalance that trips the device at its rated residual current. It does not respond directly to overvoltage, neutral overload alone, or polarity reversal.

Question 32Electrical Materials, Wiring Accessories and Safety

Which type of wiring system is most suitable for concealed installation in the walls of a modern domestic building?

  1. Cleat wiring
  2. Batton wiring
  3. Casing and capping wiring
  4. Conduit wiring Correct answer.

Explanation

Conduit wiring allows insulated conductors to be drawn through tubes embedded in plaster or laid in the wall, giving mechanical protection and permitting later replacement of conductors. Cleat and batton wiring are surface methods, and casing and capping is also surface-mounted. Concealed conduit is therefore the standard choice for modern domestic construction.

Question 33Electrical Materials, Wiring Accessories and Safety

A domestic circuit uses PVC-insulated copper conductors. What is the main reason PVC is chosen as the insulation?

  1. It has high thermal conductivity
  2. It is a good conductor of electricity at low voltages
  3. It is a good electrical insulator and is flexible and moisture-resistant Correct answer.
  4. It has a very high melting point above 500 °C

Explanation

PVC is selected because it has high dielectric strength, is flexible enough for bending and drawing into conduit, and resists moisture and many chemicals. Its working temperature is limited to about 70 °C, so it is not chosen for high-temperature duty. It is an insulator and does not conduct electricity.

Question 34Electrical Materials, Wiring Accessories and Safety

A 230 V, 1000 W electric iron is connected to a domestic socket. What current does it draw, and which fuse rating is appropriate?

  1. About 10 A, so a 10 A fuse
  2. About 4.3 A, so a 5 A fuse Correct answer.
  3. About 2.3 A, so a 2 A fuse
  4. About 0.23 A, so a 0.5 A fuse

Explanation

Current equals power divided by voltage, so 1000 W divided by 230 V gives about 4.35 A. A 5 A fuse is the smallest standard rating above this value, giving normal operation without nuisance blowing while still protecting the circuit. Ratings below the load current would blow in normal use, and a much larger fuse gives poorer protection.

Question 35Electrical Materials, Wiring Accessories and Safety

Why is it dangerous to replace a blown 5 A fuse in a plug with a piece of thick copper wire?

  1. The copper wire will act as an insulator and stop the current
  2. The copper wire will reduce the supply voltage
  3. The copper wire will not melt at the intended current, so the circuit is left unprotected Correct answer.
  4. The copper wire has too much resistance and will overheat

Explanation

A fuse protects a circuit because its element melts at a defined current. A thick copper wire has a much higher melting point and lower resistance, so it will carry a large fault current without melting, leaving the appliance and wiring unprotected. This practice has caused many fires and defeats the purpose of the fuse.

Question 36Electrical Materials, Wiring Accessories and Safety

Which of these is the correct sequence of connections when wiring a three-pin plug?

  1. Live to brown, neutral to green/yellow, earth to blue
  2. Live to green/yellow, neutral to blue, earth to brown
  3. Live to brown, neutral to blue, earth to green/yellow Correct answer.
  4. Live to blue, neutral to brown, earth to green/yellow

Explanation

In the harmonised colour code the phase (live) conductor is brown, the neutral is blue, and the protective earth is green with a yellow stripe. These must be connected to the corresponding terminals marked L, N and E inside the plug. Reversing live and neutral, or connecting earth to any other colour, creates a serious shock hazard.

Question 37Electrical Materials, Wiring Accessories and Safety

A miniature circuit breaker (MCB) is preferred over a rewirable fuse in modern domestic distribution boards mainly because:

  1. It works without any supply voltage
  2. It is cheaper to manufacture than a fuse
  3. It can be reset after operation and gives more consistent tripping Correct answer.
  4. It eliminates the need for earthing

Explanation

An MCB trips by a calibrated thermal and magnetic mechanism, so its characteristic is more consistent than a rewirable fuse, and it can be reset after clearing the fault. It is generally more expensive than a simple fuse, still requires supply voltage to operate its trip coil, and does not remove the need for earthing.

Question 38Electrical Materials, Wiring Accessories and Safety

In a domestic installation, what is the function of a distribution board?

  1. To divide the supply into separate final circuits each with its own protective device Correct answer.
  2. To measure the energy consumed by the whole house
  3. To step down the supply voltage to 12 V
  4. To convert direct current into alternating current

Explanation

A distribution board receives the incoming supply and splits it into a number of final circuits, each protected by its own fuse or MCB. This allows a fault on one circuit to be isolated without disconnecting the whole installation. Voltage transformation, inversion and energy measurement are performed by other equipment.

Question 39Electrical Materials, Wiring Accessories and Safety

A metal conduit used to carry domestic wiring must be earthed. What is the main reason?

  1. To prevent the conduit from becoming live if a conductor inside develops a fault Correct answer.
  2. To improve the appearance of the installation
  3. To increase the current-carrying capacity of the cables
  4. To reduce the resistance of the live conductor

Explanation

If a conductor inside the conduit chafes through its insulation and touches the metal, the conduit becomes live. Earthing the conduit ensures that fault current flows to earth and operates the protective device, so the metalwork cannot remain at a dangerous potential. Earthing does not change conductor resistance, current rating or appearance.

Question 40Electrical Materials, Wiring Accessories and Safety

Which of the following is a property of a good insulating material used in domestic appliances?

  1. High electrical conductivity and low melting point
  2. Low dielectric strength and high moisture absorption
  3. High magnetic permeability and low resistivity
  4. High dielectric strength and high insulation resistance Correct answer.

Explanation

An insulator must withstand the applied voltage without breakdown, which means high dielectric strength, and must resist leakage current, which means high insulation resistance. It should also resist moisture, since water greatly reduces insulation resistance. High conductivity, low melting point and high permeability are properties of conductors or magnetic materials, not insulators.

Question 41Electrical Materials, Wiring Accessories and Safety

An electrician finds that the earth pin of a socket outlet is not connected to the earth bar in the distribution board. What is the most serious consequence?

  1. The appliance will run at a lower voltage
  2. The neutral conductor will overheat
  3. The appliance will consume more power
  4. A faulty appliance with a live body will not trip the protective device, risking electrocution Correct answer.

Explanation

Without a continuous earth path, a fault that makes the metal body live will not produce enough fault current to blow the fuse or trip the MCB. The body remains at dangerous potential until someone touches it, causing severe shock. Voltage, power consumption and neutral heating are not the primary consequence of a missing earth.

Question 42Electrical Materials, Wiring Accessories and Safety

A domestic circuit is protected by a 16 A MCB and wired with 1.5 mm² copper conductors. Why is this combination considered unsafe?

  1. The MCB will trip too quickly during normal load
  2. The conductor is too thick for the MCB to detect faults
  3. The conductor will act as a fuse and melt at 16 A
  4. The MCB rating is higher than the current-carrying capacity of the conductor, so the cable may overheat before the MCB trips Correct answer.

Explanation

Protective devices must be selected so that their rated current does not exceed the current-carrying capacity of the smallest conductor they protect. A 1.5 mm² conductor has a lower capacity than 16 A under typical installation conditions, so sustained overload could overheat the cable without tripping the MCB. Correct coordination of conductor size and protective device rating is essential.

Question 43Electrical Materials, Wiring Accessories and Safety

Which material is commonly used for the contacts of domestic switches and socket outlets because it resists arcing and oxidation?

  1. Aluminium
  2. Carbon
  3. Silver alloy Correct answer.
  4. Soft iron

Explanation

Switch and socket contacts are usually made from silver alloys or silver-plated copper because silver has low contact resistance and resists oxidation and arcing damage. Soft iron corrodes easily, carbon has high resistance, and aluminium forms an insulating oxide layer that increases contact resistance. Reliable low-resistance contacts are essential for safety and long life.

Question 44Electrical Materials, Wiring Accessories and Safety

A household has a total connected load of 5 kW at 230 V. What is the approximate total current, and why is diversity applied when sizing the main switch?

  1. About 11.5 A; diversity is applied to increase the supply voltage
  2. About 2.2 A; diversity is applied to lower the fuse rating
  3. About 43 A; diversity is applied to reduce the earth resistance
  4. About 21.7 A; diversity is applied because not all appliances operate simultaneously Correct answer.

Explanation

Total current is 5000 W divided by 230 V, which is about 21.7 A. In practice not every appliance runs at once, so a diversity factor is applied to arrive at a realistic maximum demand and a suitable main switch and cable size. Diversity does not change voltage, earth resistance or fuse rating directly.

Question 45Domestic Wiring Systems, Circuits and Protection

In a domestic single-phase wiring system, which conductor is connected to the earth pit through the earth electrode?

  1. The live conductor feeding the fan regulator
  2. The green-yellow earth continuity conductor Correct answer.
  3. The black neutral conductor
  4. The red phase conductor

Explanation

The protective earth conductor is deliberately connected to the earth electrode so that exposed metal parts of appliances remain at earth potential. It carries current only under fault conditions. Phase and neutral conductors carry the operating current and must never be bonded to the earth pit.

Question 46Domestic Wiring Systems, Circuits and Protection

A 1.5 mm² copper conductor is commonly selected for which circuit in a typical Indian house?

  1. The earthing lead to the earth pit
  2. The main incoming service cable from the meter
  3. The 15 A power circuit feeding a geyser
  4. Lighting sub-circuits feeding lamps and fans Correct answer.

Explanation

Lighting sub-circuits carry small currents, so 1.5 mm² copper is the usual size, protected by a 6 A to 10 A device. Larger loads such as geysers need 2.5 mm² or more, and service cables are much heavier still.

Question 47Domestic Wiring Systems, Circuits and Protection

Which protective device operates by sensing the difference between the current in the phase and the current in the neutral?

  1. Miniature circuit breaker
  2. Rewirable fuse
  3. Cartridge fuse
  4. Residual current device Correct answer.

Explanation

A residual current device uses a toroidal current transformer to compare phase and neutral currents. When the difference exceeds the sensitivity setting, the trip coil opens the contacts. Fuses and MCBs respond only to overcurrent and cannot detect this imbalance.

Question 48Domestic Wiring Systems, Circuits and Protection

Which colour code identifies the neutral conductor in a modern Indian domestic flexible cord?

  1. Black or blue Correct answer.
  2. Red
  3. Green with yellow stripe
  4. White with a red stripe

Explanation

Indian practice follows the convention of black or blue for neutral, with brown or red for phase and green-yellow for earth. Using the correct colour prevents accidental cross-connection at accessories. Earth conductors must never be used as neutral.

Question 49Domestic Wiring Systems, Circuits and Protection

What is the primary function of a fuse in a domestic distribution board?

  1. To melt and open the circuit on excessive current Correct answer.
  2. To improve the power factor of inductive loads
  3. To limit the supply voltage to each sub-circuit
  4. To convert alternating current into direct current

Explanation

A fuse is a sacrificial element whose metal link melts when current exceeds its rating, isolating the faulty circuit. It protects conductors and equipment from overheating and fire. It does not regulate voltage, correct power factor, or rectify current.

Question 50Domestic Wiring Systems, Circuits and Protection

Why is a two-way switch arrangement used on a staircase lighting circuit?

  1. To provide a second earth connection near the staircase
  2. To allow the lamp to be switched from either the top or the bottom of the stairs Correct answer.
  3. To protect the lamp from voltage surges during switching
  4. To reduce the current drawn by the lamp when it is switched on

Explanation

Two two-way switches are interconnected by strapper wires so that either switch can complete or break the circuit independently. This gives control of one lamp from two positions. It does not change current, earthing, or surge protection.