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Maharashtra SSC Electrical Technology Pre-Voc/NSQF study materials
Maharashtra SSC Electrical Technology Pre-Voc/NSQF study resources

Maharashtra SSC Electrical Technology Pre-Voc/NSQF practice questions

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Question 1Basic Electrical Principles and Safety

In a typical Indian household wiring system, which conductor is connected to the earth pit through a green or green-yellow insulated wire?

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

Explanation

The earth (ground) wire provides a low-resistance path to the earth electrode so that fault current trips the protective device and exposed metal stays near earth potential. Standard Indian practice identifies it by green or green-yellow insulation. Phase is red/brown/yellow/blue and neutral is black or light blue depending on the code followed.

Question 2Basic Electrical Principles and Safety

Which safety device operates by detecting the difference between the current leaving through the phase and returning through the neutral?

  1. Metal oxide varistor
  2. Rewirable fuse
  3. Miniature circuit breaker
  4. Earth leakage circuit breaker Correct answer.

Explanation

An ELCB or RCCB compares phase and neutral currents through a toroidal core; any imbalance means current is leaking to earth, and the trip coil opens the circuit, usually within 30 mA and 30 ms for personnel protection. A fuse and an MCB respond only to overcurrent, not to small earth leakage.

Question 3Basic Electrical Principles and Safety

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

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

Explanation

Resistance is given by R = ρL/A, so for a fixed material and cross-section it rises linearly with length. Doubling the length doubles the resistance, while increasing area reduces it. Frequency has no first-order effect on DC resistance of a copper conductor.

Question 4Basic Electrical Principles and Safety

What is the SI unit of electric current, defined as the flow of one coulomb of charge per second?

  1. Watt
  2. Ampere Correct answer.
  3. Volt
  4. Ohm

Explanation

One ampere equals one coulomb per second, so current is the rate of charge flow. The volt is the unit of potential difference, the ohm of resistance, and the watt of power. This definition underpins every current rating printed on Indian switchgear and cable.

Question 5Basic Electrical Principles and Safety

A 100 W lamp is connected to a 230 V supply. What current does it draw, approximately?

  1. 0.43 A Correct answer.
  2. 0.23 A
  3. 4.3 A
  4. 2.3 A

Explanation

Using P = VI, current I = P/V = 100/230 ≈ 0.435 A. This is the figure used when selecting the correct fuse or MCB rating for the lamp circuit. The answer is close to half an ampere, not a quarter or several amperes.

Question 6Basic Electrical Principles and Safety

Which of the following is the correct first action when a person is found in contact with a live conductor and cannot let go?

  1. Pour water on the conductor to cool it
  2. Switch off the supply or isolate the circuit Correct answer.
  3. Pull the person away with bare hands
  4. Wait for the person to release the conductor

Explanation

The rescuer must first isolate the supply at the switch, MCB or main, because touching the victim while the conductor is live makes the rescuer a second victim. Only after isolation should first aid and artificial respiration be started if needed.

Question 7Basic Electrical Principles and Safety

Which material is used for the heating element of an electric iron because of its high resistivity and oxidation resistance?

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

Explanation

Nichrome, an alloy of nickel and chromium, has high resistivity and withstands high temperature without rapid oxidation, so it converts electrical energy into heat efficiently. Copper, silver and aluminium have low resistivity and are used for conductors, not heating elements.

Question 8Basic Electrical Principles and Safety

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

  1. 4 A
  2. 1.33 A
  3. 6 A Correct answer.
  4. 9 A

Explanation

The parallel equivalent is (6 × 3)/(6 + 3) = 2 Ω, so total current is 12/2 = 6 A. Equivalently, branch currents are 2 A and 4 A, summing to 6 A. Parallel branches share current, so the total is larger than either branch current alone.

Question 9Basic Electrical Principles and Safety

Three 4 Ω resistors are connected in series. What is the total resistance of the combination?

  1. 8 Ω
  2. 4 Ω
  3. 12 Ω Correct answer.
  4. 1.33 Ω

Explanation

In a series circuit the resistances add directly, so 4 + 4 + 4 = 12 Ω. The same current passes through every element, and the total voltage is the sum of the individual drops. Series connection always gives a total larger than the largest single resistor.

Question 10Basic Electrical Principles and Safety

A copper conductor has resistance 2 Ω at 20 °C. If its length is doubled and its cross-sectional area is also doubled, what is the new resistance?

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

Explanation

From R = ρL/A, doubling the length doubles R while doubling the area halves it, so the two effects cancel and the resistance stays at 2 Ω. This is why a longer run needs a thicker conductor to keep voltage drop within limits.

Question 11Basic Electrical Principles and Safety

What is the primary function of a fuse in an electrical circuit?

  1. To convert alternating current to direct current
  2. To store energy for the load
  3. To regulate the supply voltage
  4. To melt and open the circuit on excessive current Correct answer.

Explanation

The fuse element is a calibrated wire that melts when current exceeds its rating, opening the circuit before conductors overheat. It protects the wiring and equipment against overload and short circuit. It does not regulate voltage, store energy or rectify current.

Question 12Basic Electrical Principles and Safety

A fuse rated for a lighting circuit must be selected mainly on the basis of which quantity?

  1. The rated current of the circuit it protects Correct answer.
  2. The supply voltage only
  3. The colour of the fuse carrier
  4. The length of the wiring run

Explanation

A fuse is chosen so that its current rating is above the normal load current but below the current-carrying capacity of the cable, so it melts before the conductor is damaged. Voltage rating must also be adequate, but it is not the main selection basis. Colour and cable length are not selection parameters.

Question 13Basic Electrical Principles and Safety

Why is earthing of the metallic body of an electric appliance essential?

  1. To improve the power factor of the load
  2. To provide a return path that keeps the body at earth potential during a fault Correct answer.
  3. To increase the current drawn by the appliance
  4. To reduce the electricity bill

Explanation

If a live conductor touches the metal body, the earth connection provides a low-resistance path so fault current flows and the fuse or MCB operates quickly. Meanwhile the body stays near earth potential, protecting the user. Earthing has no effect on billing, load current or power factor.

Question 14Basic Electrical Principles and Safety

Which effect of electric current is used in an electric bell?

  1. Magnetic effect Correct answer.
  2. Chemical effect
  3. Photoelectric effect
  4. Heating effect

Explanation

Current through the bell coil magnetises an electromagnet that pulls the hammer, and the contact break repeats the action to give the ringing. The heating effect is used in irons and heaters, and the chemical effect in electroplating.

Question 15Basic Electrical Principles and Safety

A 2 kW water heater runs for 3 hours a day. How many units (kWh) does it consume in 30 days?

  1. 120 units
  2. 180 units Correct answer.
  3. 60 units
  4. 240 units

Explanation

Energy per day is 2 kW × 3 h = 6 kWh, and over 30 days this is 6 × 30 = 180 kWh, that is, 180 units. One unit is one kilowatt-hour, the billing unit used by Indian utilities. Multiplying power by time in hours is the standard method.

Question 16Basic Electrical Principles and Safety

In a three-pin plug used in Indian domestic circuits, what is the purpose of the longer earth pin?

  1. It carries the neutral return current
  2. It carries the phase supply to the appliance
  3. It ensures the earth connection is made before the live connection Correct answer.
  4. It operates as a fuse inside the plug

Explanation

The earth pin is longer and thicker so that it enters the socket first, earthing the appliance frame before phase and neutral make contact, and it is the last to disconnect. This sequencing protects the user during plugging and unplugging. It carries no normal load current.

Question 17Basic Electrical Principles and Safety

Which condition causes a short circuit in a domestic installation?

  1. Direct contact between phase and neutral conductors Correct answer.
  2. An appliance drawing its normal rated current
  3. A switch left on for a long time
  4. A loose lamp holder screw

Explanation

A short circuit occurs when phase and neutral touch directly through a low-resistance path, so a very large current flows and the fuse or MCB operates. Normal rated current and a switch left on do not create a short. A loose screw is a poor contact, which causes local heating rather than a dead short.

Question 18Basic Electrical Principles and Safety

What is the effect on the total resistance of a circuit when an additional resistor is connected in parallel with an existing resistor?

  1. The total resistance increases
  2. The total resistance becomes zero
  3. The total resistance decreases Correct answer.
  4. The total resistance remains unchanged

Explanation

Adding a parallel path gives current an extra route, so the equivalent resistance falls below the smallest branch resistance. The reciprocal formula 1/R = 1/R1 + 1/R2 shows the total always decreasing as branches are added. This is why parallel loads increase the current drawn from the supply.

Question 19Basic Electrical Principles and Safety

A 230 V, 5 A socket outlet is protected by a 6 A MCB. A 2 kW heater is plugged in. What is the most likely result?

  1. The MCB trips because the current exceeds 5 A Correct answer.
  2. The heater draws exactly 5 A
  3. The heater works normally at reduced voltage
  4. The earth wire carries the excess current

Explanation

The heater current is 2000/230 ≈ 8.7 A, which exceeds both the 5 A socket rating and the 6 A MCB rating, so the breaker trips. A load must never exceed the rating of the outlet or the protective device. The earth conductor carries current only during a fault, not normal overload.

Question 20Basic Electrical Principles and Safety

Which statement correctly distinguishes an MCB from a rewirable fuse?

  1. An MCB provides no short-circuit protection
  2. An MCB works only on DC circuits
  3. An MCB can be reset and reused after tripping, while a fuse must be replaced Correct answer.
  4. A fuse has a higher breaking capacity than any MCB

Explanation

An MCB trips by thermal-magnetic action and can be reset once the fault is cleared, whereas a fuse element melts and must be replaced. MCBs work on AC and DC and provide both overload and short-circuit protection. Modern MCBs are available with breaking capacities comparable to or better than many small fuses.

Question 21Basic Electrical Principles and Safety

In a series circuit, if one of three identical lamps fails open, what happens to the other two?

  1. They flicker but stay lit
  2. They go out because the circuit is broken Correct answer.
  3. They glow brighter
  4. They continue glowing normally

Explanation

A series circuit has only one path for current, so an open filament breaks the path and no current flows anywhere. All lamps therefore go out. This is a known drawback of series-connected lamps compared with parallel connection.

Question 22Basic Electrical Principles and Safety

A 10 Ω resistor and a 20 Ω resistor are in series across a 60 V supply. What is the voltage across the 20 Ω resistor?

  1. 60 V
  2. 40 V Correct answer.
  3. 20 V
  4. 30 V

Explanation

The total resistance is 30 Ω, so the current is 60/30 = 2 A. The drop across the 20 Ω resistor is 2 × 20 = 40 V, and 20 V appears across the 10 Ω resistor. In series, voltage divides in proportion to resistance.

Question 23Basic Electrical Principles and Safety

An electric shock of 30 mA through the human body can be dangerous mainly because it can cause:

  1. Muscular contraction and interference with the heart rhythm Correct answer.
  2. Permanent deafness
  3. Damage to the skin only
  4. Loss of eyesight

Explanation

Currents of the order of 30 mA can cause muscular tetany that prevents letting go, and higher currents can disturb the heart rhythm, leading to ventricular fibrillation. The danger is a function of current through the body and its path, especially through the chest. Skin burns alone do not explain the fatality risk.

Question 24Basic Electrical Principles and Safety

A 1.5 kW load is supplied through a cable whose round-trip resistance is 0.5 Ω at 230 V. What is the approximate power wasted in the cable?

  1. About 112 W
  2. About 21 W Correct answer.
  3. About 47 W
  4. About 3.3 W

Explanation

The load current is 1500/230 ≈ 6.52 A, and the copper loss is I²R = 6.52² × 0.5 ≈ 21 W. This loss heats the cable and lowers the voltage at the load, which is why long runs need thicker conductors. The loss rises with the square of the current.

Question 25Electrical Materials, Tools and Measuring Instruments

In an electrical workshop, which tool is specifically designed for gripping, twisting and cutting wires while its insulated handles protect the user from shock?

  1. Steel rule
  2. Combination pliers Correct answer.
  3. Ball-peen hammer
  4. Try square

Explanation

Combination pliers have serrated jaws for gripping and twisting conductors plus a cutting edge near the pivot. Insulated handles make them suitable for live-adjacent wiring work in the workshop. The other listed tools perform measuring, marking or striking duties and cannot grip or cut wire.

Question 26Electrical Materials, Tools and Measuring Instruments

A technician needs to measure the diameter of a bare copper conductor to an accuracy of 0.01 mm. Which measuring instrument is most appropriate?

  1. Spirit level
  2. Try square
  3. Tailor's tape
  4. Micrometer screw gauge Correct answer.

Explanation

A micrometer screw gauge has a calibrated thimble that reads fractions of a millimetre, typically to 0.01 mm, and its flat anvils suit small round conductors. The other instruments measure length, squareness or level and cannot resolve 0.01 mm on a wire.

Question 27Electrical Materials, Tools and Measuring Instruments

Which material is chosen for the conductor of a domestic wiring cable because of its high electrical conductivity and low cost?

  1. Bakelite
  2. Hard rubber
  3. Mica
  4. Electrolytic copper Correct answer.

Explanation

Electrolytic copper offers very low resistivity, good ductility and reasonable cost, so it is the standard conductor in domestic wiring. Rubber, Bakelite and mica are insulators used around or instead of conductors, not for carrying current.

Question 28Electrical Materials, Tools and Measuring Instruments

The least count of a vernier calliper is 0.02 mm. The main scale reads 24 mm and the 7th vernier division coincides with a main scale line. What is the measured length?

  1. 24.14 mm Correct answer.
  2. 24.07 mm
  3. 25.40 mm
  4. 24.70 mm

Explanation

Vernier reading equals main scale reading plus (vernier coincidence × least count). Here 24 mm + (7 × 0.02 mm) = 24 mm + 0.14 mm = 24.14 mm. Adding the vernier count as whole millimetres or reversing the multiplication gives the wrong values.

Question 29Electrical Materials, Tools and Measuring Instruments

Why is a megger used instead of an ordinary multimeter when testing a new installation?

  1. It records the load current over 24 hours
  2. It applies a high DC test voltage and measures very high insulation resistance Correct answer.
  3. It checks the phase sequence of a three-phase supply
  4. It measures earth loop impedance directly

Explanation

A megger (insulation resistance tester) injects a high DC voltage, commonly 500 V or 1000 V, and reads resistance in megohms. That stress reveals weak or damp insulation that a low-voltage ohmmeter cannot detect. It is not a current recorder, phase-sequence meter or loop-impedance instrument.

Question 30Electrical Materials, Tools and Measuring Instruments

A fuse in a circuit is described as having a rating of 6 A. What does this rating specify?

  1. The resistance of the fuse element in ohms
  2. The time in seconds for which the fuse survives a short circuit
  3. The voltage at which the fuse element melts
  4. The maximum current the fuse element can carry continuously without melting Correct answer.

Explanation

The current rating of a fuse is the continuous current its element can carry without overheating and melting under normal conditions. Above this value the element heats and ruptures, clearing the circuit. It is not a voltage, resistance or time value.

Question 31Electrical Materials, Tools and Measuring Instruments

Which property makes PVC the preferred insulation for general-purpose domestic wiring cables?

  1. It is a tough thermoplastic with good dielectric strength and flame-retardant behaviour Correct answer.
  2. It is a good conductor of heat for dissipating cable losses
  3. It has very low resistivity so it assists current flow
  4. It becomes permanently hard on first heating

Explanation

PVC is a thermoplastic insulator with high dielectric strength, mechanical toughness and additives that resist flame propagation, which suits fixed domestic wiring. It is an insulator, not a conductor, and being thermoplastic it softens on heating rather than hardening permanently.

Question 32Electrical Materials, Tools and Measuring Instruments

A wire stripper is preferred over a knife for removing insulation from a small conductor. What is the main technical reason?

  1. It removes insulation without nicking or cutting the conductor strands Correct answer.
  2. It can be used to measure the conductor diameter
  3. It insulates the joint after stripping
  4. It tests continuity of the conductor

Explanation

A wire stripper has shaped blades and a stop that cut only the insulation, so the copper strands remain uncut and the conductor keeps its full cross-section. A knife cut depends on hand pressure and often nicks strands, creating a weak point that can overheat. Strippers do not measure, insulate joints or test continuity.

Question 33Electrical Materials, Tools and Measuring Instruments

Which instrument would a technician use to measure the current in a live single-core cable without breaking the circuit?

  1. Earth tester
  2. Wheatstone bridge
  3. Megger
  4. Clamp meter Correct answer.

Explanation

A clamp meter has a split magnetic core that is closed around one conductor and senses the magnetic field produced by the current, so no disconnection is needed. Meggers, bridges and earth testers measure insulation resistance, resistance and earth resistance respectively.

Question 34Electrical Materials, Tools and Measuring Instruments

A copper conductor of length 50 m and cross-sectional area 1 mm² has resistivity 0.0175 ohm-mm²/m. What is its resistance?

  1. 1.75 ohm
  2. 0.875 ohm Correct answer.
  3. 8.75 ohm
  4. 0.35 ohm

Explanation

Resistance equals resistivity times length divided by area: 0.0175 × 50 ÷ 1 = 0.875 ohm. The area of 1 mm² makes the numerical calculation direct. Errors arise from multiplying by area instead of dividing or from misplacing the decimal point.

Question 35Electrical Materials, Tools and Measuring Instruments

Which material is used for the heating element of an electric iron because it withstands high temperature without oxidising rapidly?

  1. Aluminium foil
  2. Annealed copper
  3. Nichrome Correct answer.
  4. Soft solder

Explanation

Nichrome, an alloy of nickel and chromium, has relatively high resistivity and resists oxidation at red heat, so it is used for heating elements. Copper, solder and aluminium foil are low-resistance conductors that would not generate controlled heat and would oxidise or melt.

Question 36Electrical Materials, Tools and Measuring Instruments

An earth tester using the three-electrode method gives a reading that fluctuates whenever the auxiliary spikes are moved. What is the most likely cause?

  1. High resistance between the potential or current spikes and the surrounding soil Correct answer.
  2. The electrode under test is made of copper
  3. The test leads are shorter than one metre
  4. The instrument battery is fully charged

Explanation

The three-electrode method depends on good contact between the auxiliary current and potential spikes and moist soil. Dry, rocky or loose soil raises spike resistance and makes the reading unstable or falsely high. Battery condition, electrode metal and short leads are not the cause described.

Question 37Electrical Materials, Tools and Measuring Instruments

What is the function of the ratchet (friction) stop on a micrometer screw gauge?

  1. It limits tightening force so the anvils do not compress the workpiece or damage the thread Correct answer.
  2. It locks the spindle after a reading is taken
  3. It converts rotary motion into a linear scale reading
  4. It zeroes the instrument automatically

Explanation

The ratchet slips at a set torque so the user applies consistent, light pressure on the workpiece. This prevents over-tightening that would compress soft material, damage the precision thread and give a false small reading. It does not lock the spindle, produce the scale reading or zero the gauge.

Question 38Electrical Materials, Tools and Measuring Instruments

Which type of cable is most suitable for a wet underground duct where mechanical protection and moisture resistance are both required?

  1. Fabric-braided instrument wire
  2. Flat twin bell wire
  3. Steel wire armoured PVC-insulated cable Correct answer.
  4. Single-core flexible appliance cord

Explanation

Steel wire armour provides mechanical protection against damage in ducts and soil, while the PVC insulation and bedding resist moisture. Flexible cords, bell wire and braided instrument wire lack the armour and moisture barrier needed underground.

Question 39Electrical Materials, Tools and Measuring Instruments

A fuse wire of a given material must be replaced by one of the same rating but half the diameter. How must the length be changed if the same material and current rating are to be kept?

  1. The length must be doubled
  2. The length must be increased four times
  3. The length must be halved
  4. The length must be reduced to one quarter Correct answer.

Explanation

For a given current the heat produced per unit length depends on resistance per unit length, which rises as area falls. Halving the diameter reduces area to one quarter, so resistance per metre becomes four times larger; the length must therefore be cut to one quarter to keep total resistance and heat balance the same. Doubling or increasing the length would raise total resistance further and lower the fusing current.

Question 40Electrical Materials, Tools and Measuring Instruments

A coil of annealed copper wire measures 2.0 ohm at 20 degrees Celsius. Taking the temperature coefficient of copper as 0.004 per degree Celsius at 20 degrees Celsius, what is its resistance at 70 degrees Celsius?

  1. 1.60 ohm
  2. 2.56 ohm
  3. 2.40 ohm Correct answer.
  4. 2.08 ohm

Explanation

Resistance rises linearly over this range: R = R20[1 + alpha(t − 20)] = 2.0[1 + 0.004 × 50] = 2.0 × 1.20 = 2.40 ohm. The 50-degree rise multiplied by 0.004 gives a 20 per cent increase. Using the wrong temperature difference or subtracting the correction produces the other values.

Question 41Electrical Materials, Tools and Measuring Instruments

Why are silver contacts used in precision relays even though silver is more expensive than copper?

  1. Silver is a thermosetting insulator
  2. Silver has the lowest contact resistance among common metals and resists oxidation films at low currents Correct answer.
  3. Silver has the highest resistivity of the common metals
  4. Silver has the highest melting point of all metals

Explanation

Silver offers the lowest contact resistance of the common contact metals, and its oxide is comparatively conductive, so low-level signals pass reliably. That matters in precision relays where a thin film would cause intermittent operation. Silver is not the highest-melting metal, is a conductor rather than an insulator, and has low not high resistivity.

Question 42Electrical Materials, Tools and Measuring Instruments

Two identical insulation resistance readings of 50 megohm are obtained on a long cable, one with a 500 V megger and one with a 1000 V megger. What does this indicate about the insulation?

  1. The 1000 V reading must be wrong because resistance always halves
  2. The cable has a short circuit between conductors
  3. The insulation is damp because resistance did not fall with voltage
  4. The insulation is sound because the resistance is largely independent of the applied test voltage Correct answer.

Explanation

Good, dry insulation behaves nearly as a linear dielectric, so the measured resistance stays roughly the same when the test voltage is doubled. A pronounced fall at the higher voltage would suggest moisture, tracking or degradation. Equal readings therefore support a healthy insulation, not a fault.

Question 43Electrical Materials, Tools and Measuring Instruments

Which tool is used to cut a wide rectangular opening in a sheet-metal switchboard panel with clean edges?

  1. Cold chisel
  2. Centre punch
  3. Hacksaw
  4. Tin snips Correct answer.

Explanation

Tin snips are lever-type shears designed for cutting sheet metal along marked lines and leave a reasonably clean edge. A cold chisel is for chipping thicker metal, a hacksaw for bar and pipe, and a centre punch only marks a drilling point.

Question 44Electrical Materials, Tools and Measuring Instruments

What is the purpose of tinning the tip of a soldering iron before use?

  1. To improve heat transfer and protect the copper bit from oxidation Correct answer.
  2. To increase the electrical resistance of the bit
  3. To insulate the bit from the mains supply
  4. To lower the melting point of the solder alloy

Explanation

A thin film of solder on the bit gives good thermal contact with the joint and shields the copper from oxidation, which otherwise reduces heat flow. Tinning does not change the bit resistance, insulate it or alter the solder alloy's melting point.

Question 45Electrical Materials, Tools and Measuring Instruments

Which instrument is used to check the continuity of a winding when no supply is available at the site?

  1. Series test lamp with battery Correct answer.
  2. Clip-on ammeter
  3. Megger
  4. Frequency meter

Explanation

A battery-and-lamp continuity tester needs no mains supply and lights when a low-resistance path exists through the winding. A megger needs its own high-voltage source and is for insulation, while a clip-on ammeter and frequency meter require a live circuit.

Question 46Electrical Materials, Tools and Measuring Instruments

A cable is marked 3 × 2.5 mm². What does the marking convey?

  1. Three cores, each of 2.5 mm² nominal cross-sectional area Correct answer.
  2. Three amperes rating at 2.5 kilovolts
  3. Three cores of 2.5 mm overall diameter
  4. A 3 mm insulation thickness on a 2.5 mm conductor

Explanation

The first figure gives the number of cores and the second the nominal cross-sectional area of each conductor in square millimetres. This area determines current-carrying capacity and voltage drop. The marking does not give overall diameter, insulation thickness or a current-voltage rating.

Question 47Electrical Materials, Tools and Measuring Instruments

A technician must check that a newly installed earthing conductor has low resistance to the general mass of earth. Which instrument is designed for this test?

  1. Multimeter on the volt range
  2. Wattmeter
  3. Insulation resistance megger
  4. Earth electrode tester Correct answer.

Explanation

An earth electrode tester injects a current through auxiliary spikes and measures the resulting potential to compute electrode resistance. A megger measures insulation, a voltmeter reads potential difference and a wattmeter measures power, so none of them gives earth resistance directly.

Question 48Electrical Materials, Tools and Measuring Instruments

Why is an aluminium conductor often used for overhead transmission lines although copper has better conductivity?

  1. Aluminium melts at a higher temperature than copper
  2. Aluminium has higher conductivity than copper
  3. Aluminium has a much lower mass per unit length for the same conductance, reducing tower loading Correct answer.
  4. Aluminium needs no support insulators

Explanation

Aluminium is lighter and cheaper per unit of conductance, so a larger aluminium conductor can match copper conductance while imposing far less mechanical load on towers and spans. It does not have higher conductivity or a higher melting point than copper, and it still requires insulators.

Question 49Wiring Systems, Accessories and Installation Practice

In a domestic single-phase installation, which conductor colour is used for the earth (protective) wire as per Indian wiring convention?

  1. Green or green with yellow stripe Correct answer.
  2. Yellow
  3. Black
  4. Red

Explanation

The protective earth conductor is identified by green or green-with-yellow-stripe insulation so that it can never be confused with a live or neutral conductor. This colour coding is a safety requirement, because the earth wire must be instantly recognisable at every point of the circuit. Black, red and yellow are all reserved for live or neutral functions in standard practice.

Question 50Wiring Systems, Accessories and Installation Practice

Which wiring system uses porcelain cleats to hold the conductors at a fixed spacing along walls and ceilings?

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

Explanation

Cleat wiring is the oldest surface system, in which VIR or PVC cables are gripped by two-piece porcelain cleats screwed to the wall at regular intervals. The cleats keep the conductors separated and support them mechanically. Casing-capping, conduit and batton systems all enclose or mount the cable differently.