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Odisha CHSE +2 VOC-ITV Wireman Control Panel study materials
Odisha CHSE +2 VOC-ITV Wireman Control Panel study resources

Odisha CHSE +2 VOC-ITV Wireman Control Panel practice questions

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Question 1Electrical Fundamentals and Circuit Theory

In a wireman control panel, which material is normally used for the conductor of a current-carrying circuit because of its low resistivity?

  1. Nichrome
  2. Copper Correct answer.
  3. Carbon
  4. Tungsten

Explanation

Copper has very low resistivity, about 1.7 × 10⁻⁸ ohm-metre, so it carries current with small voltage drop and low heating. That is why panel wiring and busbars are usually made of copper. Nichrome and tungsten are chosen for high resistance or heat, not for ordinary conductors.

Question 2Electrical Fundamentals and Circuit Theory

A control panel resistor has a colour code of brown, black, red and gold. What is its resistance and tolerance?

  1. 10 Ω ± 5%
  2. 100 Ω ± 5%
  3. 120 Ω ± 10%
  4. 1000 Ω ± 5% Correct answer.

Explanation

Brown is 1, black is 0 and red is a multiplier of 100, giving 10 × 100 = 1000 Ω. Gold in the fourth band means ±5% tolerance. Reading the multiplier band as 10 or 1 is the usual error.

Question 3Electrical Fundamentals and Circuit Theory

Two resistors of 6 Ω and 3 Ω are connected in parallel across a 12 V supply in a panel circuit. What current does the supply deliver?

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

Explanation

The parallel equivalent is (6 × 3)/(6 + 3) = 2 Ω. Supply current is V/R = 12/2 = 6 A. Adding the branch currents directly also gives 2 A + 4 A = 6 A.

Question 4Electrical Fundamentals and Circuit Theory

Which instrument connection is correct when a wireman measures the current in a panel branch circuit?

  1. Megger connected across the live and neutral terminals
  2. Voltmeter connected in series with the branch
  3. Ammeter connected in parallel with the branch
  4. Ammeter connected in series with the branch Correct answer.

Explanation

An ammeter must carry the branch current, so it is connected in series and has very low internal resistance. A voltmeter is connected in parallel because it must sense voltage with high resistance. A megger is for insulation testing and must never be used on a live circuit.

Question 5Electrical Fundamentals and Circuit Theory

What is the effective value (RMS value) of a sinusoidal supply whose peak value is 325 V, as found at a panel busbar?

  1. 650 V
  2. 325 V
  3. 230 V Correct answer.
  4. 460 V

Explanation

For a sine wave, RMS value equals peak value divided by √2, that is 325/1.414 ≈ 230 V. This is the standard single-phase supply voltage. The peak is not the value read by an ordinary voltmeter.

Question 6Electrical Fundamentals and Circuit Theory

Which statement describes the function of a fuse in a control panel?

  1. It converts alternating current into direct current
  2. It improves the power factor of an inductive load
  3. It opens the circuit by melting when current exceeds its rating Correct answer.
  4. It limits the voltage reaching the load to a fixed value

Explanation

A fuse element is designed to melt and interrupt the circuit when current exceeds the rated value for a certain time. It is a protective device against overload and short circuit. Voltage regulation, rectification and power-factor correction are done by other devices.

Question 7Electrical Fundamentals and Circuit Theory

A panel lamp rated 60 W at 230 V is used on a 230 V supply. What current does it draw?

  1. 0.26 A Correct answer.
  2. 2.6 A
  3. 3.8 A
  4. 0.38 A

Explanation

Power equals voltage times current, so I = P/V = 60/230 ≈ 0.26 A. This is a simple application of the power formula to a resistive lamp load. Multiplying instead of dividing gives the wrong answers.

Question 8Electrical Fundamentals and Circuit Theory

In a DC series circuit inside a panel, a 12 V battery feeds three resistors of 2 Ω, 3 Ω and 7 Ω. What is the voltage across the 3 Ω resistor?

  1. 3 V Correct answer.
  2. 12 V
  3. 4 V
  4. 6 V

Explanation

Total resistance is 2 + 3 + 7 = 12 Ω, so current is 12/12 = 1 A. The voltage across the 3 Ω resistor is IR = 1 × 3 = 3 V. In a series circuit the current is common and voltage divides in proportion to resistance.

Question 9Electrical Fundamentals and Circuit Theory

A coil in a contactor has an inductive reactance of 40 Ω and a resistance of 30 Ω. What is its impedance?

  1. 1200 Ω
  2. 70 Ω
  3. 50 Ω Correct answer.
  4. 10 Ω

Explanation

For a series R-L circuit, impedance Z = √(R² + X²) = √(30² + 40²) = √2500 = 50 Ω. Resistance and reactance add vectorially, not arithmetically. This 3-4-5 relationship is common in panel coil calculations.

Question 10Electrical Fundamentals and Circuit Theory

A wireman needs to find the resistance of a coil whose temperature rises during operation. Which effect explains why the measured resistance increases?

  1. Reduction of the coil inductance with heat
  2. Negative temperature coefficient of the copper winding
  3. Positive temperature coefficient of the copper winding Correct answer.
  4. Increase of supply frequency with heat

Explanation

Copper has a positive temperature coefficient, so its resistance rises as temperature rises. This is why hot resistance readings are higher than cold readings. Inductance and supply frequency are not increased by heating the winding.

Question 11Electrical Fundamentals and Circuit Theory

In an AC panel circuit, the current lags the voltage by 90°. Which element is the load?

  1. A pure inductor Correct answer.
  2. A pure capacitor
  3. A pure resistor
  4. An open circuit

Explanation

In a pure inductor the current lags the applied voltage by exactly 90°. A pure resistor has current in phase, and a pure capacitor has current leading by 90°. The stated phase relationship identifies an inductive load.

Question 12Electrical Fundamentals and Circuit Theory

A single-phase panel load draws 10 A at 230 V with a power factor of 0.8. What is the active power consumed?

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

Explanation

Active power P = V × I × cos φ = 230 × 10 × 0.8 = 1840 W. The product VI alone gives apparent power in volt-amperes. Power factor reduces apparent power to the real power actually consumed.

Question 13Electrical Fundamentals and Circuit Theory

A 3-phase balanced load of 5 kW operates at 415 V with a power factor of 0.85. What is the line current approximately?

  1. 14.2 A
  2. 12.0 A
  3. 8.2 A Correct answer.
  4. 6.9 A

Explanation

For a balanced three-phase load, P = √3 × V × I × cos φ, so I = 5000/(1.732 × 415 × 0.85) ≈ 8.2 A. The √3 factor appears because the three phases share the total power. Omitting it gives an inflated current.

Question 14Electrical Fundamentals and Circuit Theory

Why is a capacitor bank connected across an inductive panel load?

  1. To increase the active power consumed by the load
  2. To convert the supply from AC to DC
  3. To supply reactive power and improve the power factor Correct answer.
  4. To step up the supply voltage to the panel

Explanation

An inductive load draws lagging reactive power. A parallel capacitor supplies leading reactive power locally, reducing the total line current and improving the power factor. It does not create active power or change the supply voltage.

Question 15Electrical Fundamentals and Circuit Theory

Two 100 W lamps, one rated 230 V and the other rated 115 V, are each operated at their rated voltage. How do their resistances compare?

  1. The 115 V lamp has one quarter the resistance of the 230 V lamp Correct answer.
  2. The 115 V lamp has four times the resistance of the 230 V lamp
  3. The 115 V lamp has half the resistance of the 230 V lamp
  4. The two lamps have equal resistance

Explanation

Resistance from ratings is R = V²/P. For 230 V, R = 230²/100 = 529 Ω; for 115 V, R = 115²/100 = 132.25 Ω, which is one quarter. The same wattage at half the voltage needs a quarter of the resistance.

Question 16Electrical Fundamentals and Circuit Theory

A wireman uses a megger to test a panel circuit. What does the instrument measure?

  1. Voltage between phases during operation
  2. Current drawn by the connected load
  3. Insulation resistance between conductors and earth Correct answer.
  4. Earth loop current during a fault

Explanation

A megger applies a high DC test voltage and measures insulation resistance, typically in megohms. It is used on de-energised circuits to check insulation health. It does not measure load current, operating voltage, or fault current.

Question 17Electrical Fundamentals and Circuit Theory

In a control panel, a relay coil rated 24 V DC is to be energised from a 24 V DC supply. Which protective device is placed in series to protect the coil against overcurrent?

  1. A capacitor across the supply
  2. A fuse of suitable current rating Correct answer.
  3. A voltmeter in series
  4. An ammeter in parallel

Explanation

A fuse in series with the coil opens the circuit if the current exceeds its rating, protecting the coil and wiring. Capacitors and meters do not provide overcurrent protection. Meters must also be connected correctly, not used as protective devices.

Question 18Electrical Fundamentals and Circuit Theory

A 2 kW heater and a 1 kW motor are connected to the same 230 V panel supply. Which statement about the current drawn is correct?

  1. The heater draws more current because its power factor is unity Correct answer.
  2. The motor draws more current because it has a lower power factor
  3. The motor draws no current because it is inductive
  4. Both draw the same current because they are on the same supply

Explanation

For the heater, I = 2000/230 ≈ 8.7 A with unity power factor. For the motor, I = 1000/(230 × power factor), which is smaller even with a power factor below one. The heater therefore draws more current.

Question 19Electrical Fundamentals and Circuit Theory

A cable in a panel has a resistance of 0.5 Ω per conductor and carries 20 A. What is the total power loss in the live and neutral conductors together?

  1. 200 W
  2. 10 W
  3. 400 W Correct answer.
  4. 800 W

Explanation

Each conductor dissipates I²R = 20² × 0.5 = 200 W. With two conductors, live and neutral, the total loss is 400 W. Using only one conductor gives half the loss.

Question 20Electrical Fundamentals and Circuit Theory

A wireman measures 0 V across a closed push button in a live control circuit while the contactor does not operate. What is the most likely conclusion?

  1. The contact is closed, so the fault lies elsewhere in the circuit Correct answer.
  2. The contact is open, so the button must be replaced
  3. The supply voltage has failed completely
  4. The meter is reading the contactor coil voltage

Explanation

A closed contact has almost no voltage across it, so 0 V indicates the contact is closed and conducting. If the contactor still does not operate, the fault is elsewhere, such as the coil or supply. An open contact would show full supply voltage across it.

Question 21Electrical Fundamentals and Circuit Theory

In a series RLC circuit at resonance, which condition holds?

  1. Capacitive reactance is twice the inductive reactance
  2. Resistance equals inductive reactance, so impedance is zero
  3. Inductive reactance equals capacitive reactance, so impedance is purely resistive Correct answer.
  4. Impedance reaches its maximum value at resonance

Explanation

At resonance, X_L = X_C, so the two reactances cancel and the impedance is just the resistance. The current is at its maximum and in phase with the voltage. Impedance is minimum, not maximum, at series resonance.

Question 22Electrical Fundamentals and Circuit Theory

A 230 V panel supply feeds a load through a cable of total loop resistance 0.4 Ω. The load draws 25 A. What is the approximate voltage at the load terminals?

  1. 210 V
  2. 230 V
  3. 220 V Correct answer.
  4. 240 V

Explanation

The voltage drop in the loop is I × R = 25 × 0.4 = 10 V. Subtracting this from the supply gives 230 − 10 = 220 V at the load. Adding the drop instead of subtracting is a common error.

Question 23Electrical Fundamentals and Circuit Theory

A balanced star-connected load of 10 Ω per phase is connected to a 415 V three-phase supply. What is the phase voltage approximately?

  1. 240 V Correct answer.
  2. 415 V
  3. 720 V
  4. 208 V

Explanation

In a star connection, phase voltage is line voltage divided by √3, so 415/1.732 ≈ 240 V. The line voltage equals √3 times the phase voltage. Treating the line voltage as the phase voltage is incorrect.

Question 24Electrical Fundamentals and Circuit Theory

A 100 Ω resistor, a 0.1 H inductor and a 10 µF capacitor are in series across a 230 V, 50 Hz supply. What is the approximate impedance?

  1. About 300 Ω Correct answer.
  2. About 400 Ω
  3. About 210 Ω
  4. About 100 Ω

Explanation

X_L = 2πfL ≈ 31.4 Ω and X_C = 1/(2πfC) ≈ 318 Ω, so net reactance is about 287 Ω. Combining with R = 100 Ω gives Z = √(100² + 287²) ≈ 304 Ω, close to 300 Ω. The reactances must be subtracted before combining with resistance.

Question 25Wiring Materials, Conductors and Accessories

In a wireman's control panel, which conductor colour is conventionally used for the protective earth (PE) connection?

  1. Green with a yellow stripe Correct answer.
  2. Solid blue
  3. Solid black
  4. Brown

Explanation

Protective earth conductors are identified by the green-and-yellow combination so that the safety connection can never be confused with a live or neutral conductor. This colour code is followed in Indian wiring practice under the relevant IS/IEC conventions.

Question 26Wiring Materials, Conductors and Accessories

A control panel wire is marked '1.5 sq mm FR'. What does the 'FR' suffix indicate about the wire?

  1. It is flame retardant Correct answer.
  2. It is fire resistant for two hours
  3. It is fitted with a fuse-rated lug
  4. It is flexible rubber insulated

Explanation

FR on Indian house and panel wiring cable means the insulation is flame retardant, i.e. it resists propagation of flame after the ignition source is removed. It does not mean fire resistant or rubber insulated.

Question 27Wiring Materials, Conductors and Accessories

Which accessory is used to join two conductors permanently and provide good electrical and mechanical continuity inside a junction box?

  1. Cable gland
  2. Crimp-type joint / connector Correct answer.
  3. Thimble
  4. Ferrule

Explanation

A crimp-type connector or joint is compressed onto the conductors to form a permanent low-resistance joint. Cable glands secure cable entries, ferrules identify cores, and thimbles protect conductor strands at terminals.

Question 28Wiring Materials, Conductors and Accessories

What is the primary purpose of using lugs (cable thimbles) on the ends of panel wiring conductors?

  1. To provide a clean, low-resistance termination and prevent strand damage under the screw Correct answer.
  2. To identify the circuit by colour
  3. To increase the current rating of the conductor
  4. To insulate the conductor end from the terminal block

Explanation

A lug consolidates the strands into a solid termination, giving reliable contact pressure and preventing strands from spreading or breaking under the terminal screw. It does not change the conductor's current rating or insulate the end.

Question 29Wiring Materials, Conductors and Accessories

In a control panel, which wiring method gives the neatest and most maintainable result for inter-panel component connections?

  1. Wires laid loosely across components
  2. Wiring routed in PVC channels/wire ducts with ferrules Correct answer.
  3. Random point-to-point wiring
  4. Twisted bare wires stapled to the panel

Explanation

Routing conductors through slotted PVC ducts and terminating them with ferrules keeps wiring organised, protects insulation, and makes fault tracing easy. Loose or random wiring increases the risk of mechanical damage and misidentification.

Question 30Wiring Materials, Conductors and Accessories

Which material is most commonly used as the conductor in control panel wiring because of its high conductivity and ductility?

  1. Aluminium
  2. Iron
  3. Brass
  4. Copper Correct answer.

Explanation

Annealed copper offers very high electrical conductivity, good ductility for bending in tight panel spaces, and reliable behaviour at terminals. Aluminium and its alloys have lower conductivity and poorer bend/termination characteristics at small sizes.

Question 31Wiring Materials, Conductors and Accessories

A 2.5 sq mm copper conductor carries 18 A in a panel. If it is replaced by a 1.5 sq mm conductor of the same material and insulation, what is the practical consequence?

  1. Insulation class automatically increases
  2. Current capacity rises because resistance falls
  3. Current capacity falls and conductor heating rises Correct answer.
  4. Current capacity stays the same because voltage is unchanged

Explanation

Current-carrying capacity depends on cross-sectional area; reducing the area from 2.5 to 1.5 sq mm lowers the safe current and raises resistive heating for the same load. Voltage and insulation class are not determined by the conductor size change in this way.

Question 32Wiring Materials, Conductors and Accessories

Why is it important to match the cable gland size to the cable outer diameter in a control panel?

  1. To increase the insulation resistance of the cable
  2. To change the conductor colour code
  3. To ensure a proper seal and mechanical grip on the cable sheath Correct answer.
  4. To set the correct current rating of the cable

Explanation

A gland of the correct size compresses its seal around the cable sheath, giving strain relief and maintaining the enclosure's ingress protection. A mismatched gland either crushes the cable or leaves it loose and unsealed.

Question 33Wiring Materials, Conductors and Accessories

A wireman needs to connect a stranded flexible conductor to a screw terminal block. Which combination gives the most reliable connection?

  1. Soldering the strands and clamping the solder blob
  2. Crimped ferrule or lug on the conductor before tightening the screw Correct answer.
  3. Folding the strands back over the insulation
  4. Bare stranded wire twisted and inserted directly

Explanation

A crimped ferrule or lug consolidates the strands so the terminal screw clamps a solid mass, preventing strand breakage and loose contact. Bare twisted strands tend to spread and fatigue under the screw.

Question 34Wiring Materials, Conductors and Accessories

What is the function of a terminal block (connector strip) in a control panel?

  1. To suppress electromagnetic interference
  2. To step down the supply voltage
  3. To provide a safe, organised point for joining and distributing conductors Correct answer.
  4. To measure the current in a circuit

Explanation

Terminal blocks give a mechanical and electrical junction where incoming and outgoing conductors meet in an organised, testable way. They do not transform voltage, filter interference, or measure current.

Question 35Wiring Materials, Conductors and Accessories

A panel uses PVC conduit to route control wiring between sections. Which practice best preserves the wiring's insulation life?

  1. Leave conduit ends open to allow ventilation
  2. Pull wires with sharp bends at every corner
  3. Fill the conduit to more than 60 percent of its cross-section
  4. Deburr conduit ends and use bushings before pulling wires Correct answer.

Explanation

Sharp conduit ends and burrs cut into insulation during pulling, so deburring and fitting bushings protects the conductors. Conduit fill should also be limited so wires can be pulled without excessive friction.

Question 36Wiring Materials, Conductors and Accessories

Which type of cable is most suitable for a control panel connection that must remain functional for a short period during a fire?

  1. Fire-resistant (FR/FS or fire-survival) cable Correct answer.
  2. Ordinary PVC-insulated cable
  3. FR (flame retardant) cable
  4. Flexible single-core hook-up wire

Explanation

Fire-survival cable is designed with a mica or ceramic barrier so the circuit keeps working for a defined period during a fire, which is required for certain safety circuits. Standard flame-retardant PVC cable only limits flame spread and does not guarantee continued operation.

Question 37Wiring Materials, Conductors and Accessories

In a control panel, why are control wires sometimes run in a separate duct from power wires?

  1. To increase the voltage rating of control wires
  2. To save the cost of ferrules
  3. To reduce electromagnetic interference coupling into control signals Correct answer.
  4. To allow control wires to carry more current

Explanation

Separating signal/control wiring from power wiring reduces inductive and capacitive coupling of switching noise into sensitive control circuits. It has no bearing on ferrule cost, voltage rating, or current capacity.

Question 38Wiring Materials, Conductors and Accessories

A wireman must select the conductor size for a control circuit that draws 5 A over a 20 m run, keeping voltage drop below 2 percent at 24 V DC. Which approach is correct?

  1. Select wire based only on insulation colour
  2. Assume any 1.5 sq mm wire is always adequate
  3. Choose the smallest wire that physically fits the terminal
  4. Calculate the resistance of the run using resistivity and cross-section, then check the drop Correct answer.

Explanation

Voltage drop equals current times the total loop resistance, and resistance is resistivity times length divided by cross-sectional area, so the run length and area must be calculated. Terminal fit or colour alone cannot guarantee the 2 percent limit.

Question 39Wiring Materials, Conductors and Accessories

A control panel shows intermittent faults that disappear when wiring is disturbed. Which wiring-material cause is most likely?

  1. Conduit painted in the wrong colour
  2. Use of green-yellow earth wire
  3. Incorrect ferrule numbering
  4. A loose termination or damaged lug at a terminal Correct answer.

Explanation

Intermittent faults that change when wiring is moved point to a mechanical connection problem such as a loose screw, a poorly crimped lug, or a broken strand at a terminal. Identification or cosmetic issues do not cause intermittent electrical faults.

Question 40Wiring Materials, Conductors and Accessories

Why should the earth continuity conductor in a control panel be bonded to the metal enclosure at a dedicated earthing stud?

  1. To provide a low-impedance fault path so protective devices operate quickly Correct answer.
  2. To serve as a neutral return path
  3. To increase the panel's current rating
  4. To reduce the panel's power consumption

Explanation

Bonding the enclosure to earth creates a low-impedance path so that a fault current trips the protective device rapidly and touch voltage stays safe. The earth conductor is not a load or neutral return and does not affect power consumption.

Question 41Wiring Materials, Conductors and Accessories

Which accessory is used to protect a cable where it passes through a metal panel wall?

  1. Ferrule
  2. Thimble
  3. Grommet or cable bushing Correct answer.
  4. Terminal block

Explanation

A grommet or bushing lines the hole so the sharp metal edge cannot cut into the cable sheath as it passes through. Ferrules, thimbles, and terminal blocks serve different functions at the conductor end.

Question 42Wiring Materials, Conductors and Accessories

A control panel wire is specified as '1.0 sq mm, 1100 V grade, PVC insulated'. What does the 1100 V figure represent?

  1. The supply voltage required to operate the panel
  2. The maximum current the wire can carry
  3. The test voltage applied to the panel during commissioning
  4. The voltage grade of the insulation between conductor and earth Correct answer.

Explanation

The voltage grade states the insulation's rated voltage to earth, indicating the supply systems for which the cable is suitable. It is not a current rating, an operating voltage, or a commissioning test value.

Question 43Wiring Materials, Conductors and Accessories

In a panel with many identical control wires, what is the main benefit of fitting numbered ferrules at both ends of every core?

  1. It allows any core to be traced to its source during maintenance Correct answer.
  2. It raises the insulation resistance of the wiring
  3. It removes the need for terminal blocks
  4. It increases the current capacity of the core

Explanation

Matching ferrule numbers at both ends let a technician identify a conductor's origin and destination without physically tracing it through ducts. Ferrules are identification aids and do not change electrical characteristics.

Question 44Wiring Materials, Conductors and Accessories

A wireman finds that a copper conductor has turned black and brittle at a terminal after some months. Which cause best explains this?

  1. Use of a green-yellow earth sleeve
  2. Correct crimping of the lug
  3. Overheating from a loose, high-resistance joint Correct answer.
  4. Routing the wire through a PVC duct

Explanation

A loose joint raises contact resistance, causing local heating that oxidises and embrittles the copper over time. Correct crimping, proper sleeving, and duct routing do not produce blackened, brittle conductor ends.

Question 45Domestic and Industrial Wiring Installation

In a domestic single-phase installation, which conductor colour identifies the protective earth (PE) conductor of a three-core flexible cable?

  1. Brown
  2. Solid black
  3. Solid blue
  4. Green with a yellow stripe Correct answer.

Explanation

Indian wiring practice follows the green-and-yellow combination for the protective conductor so it can never be confused with a live or neutral core. Black and blue are used for neutral in different conventions, and brown is a phase colour. The earth core must remain identifiable along the whole length of the cable.

Question 46Domestic and Industrial Wiring Installation

A control panel for a 3 kW single-phase motor is to be wired. Which protective device selection gives overload protection to the motor winding?

  1. A thermal overload relay set to the motor full-load current Correct answer.
  2. A no-volt release coil in the contactor
  3. A residual current circuit breaker of 30 mA sensitivity
  4. A 63 A miniature circuit breaker on the incoming supply

Explanation

Overload protection must respond to a sustained current slightly above the rated full-load current, which a thermal overload relay with correctly set current does. An MCB rated far above the motor current protects the cable but not the winding. An RCCB protects people against earth leakage, and a no-volt coil only prevents automatic restart.

Question 47Domestic and Industrial Wiring Installation

Which accessory is used to make a straight-through joint in a domestic lighting circuit concealed inside a PVC conduit?

  1. A modular switch plate
  2. A PVC through box with a closed lid Correct answer.
  3. A porcelain ceiling rose
  4. A batten holder

Explanation

A through box (coupler box) provides a closed enclosure where conductors are joined inside a conduit run, keeping the joint accessible and protected. Ceiling roses and batten holders are luminaire accessories, and switch plates terminate switch wiring. Joints must never be buried in the conduit itself without an accessible box.

Question 48Domestic and Industrial Wiring Installation

What is the main purpose of an earth continuity conductor run from the metal enclosure of a control panel back to the main earthing terminal?

  1. To provide a low-impedance fault path that operates the protective device Correct answer.
  2. To carry the normal load current of the panel
  3. To reduce the voltage drop on the phase conductor
  4. To balance the load between phases

Explanation

Bonding the metal enclosure to the earthing terminal gives fault current a low-impedance return route so the fuse or circuit breaker clears the fault quickly. It does not carry load current under healthy conditions. Voltage drop and load balance are separate design issues.

Question 49Domestic and Industrial Wiring Installation

In an industrial wiring installation, why is stranded copper conductor preferred over a single solid conductor for panel internal wiring?

  1. It has lower resistance per unit length than solid copper
  2. It eliminates the need for cable glands
  3. It needs no termination ferrules
  4. It withstands repeated bending and vibration without cracking Correct answer.

Explanation

Stranded conductors flex repeatedly without work-hardening and cracking, which suits panel doors, DIN-rail terminations and vibrating machinery. Resistance depends on total cross-section, not stranding, and stranded ends actually need ferrules or crimp lugs. Cable glands are still required at enclosure entries.

Question 50Domestic and Industrial Wiring Installation

A domestic ring main is protected by a 32 A MCB. Which conductor size is normally used for the phase and neutral of this ring circuit?

  1. 0.75 mm² copper
  2. 6 mm² aluminium
  3. 10 mm² copper
  4. 2.5 mm² copper Correct answer.

Explanation

A 32 A ring final circuit is conventionally wired in 2.5 mm² copper, because two parallel paths share the load and the cable is derated accordingly. A 0.75 mm² flexible conductor is far too small for socket outlets. Six square millimetre aluminium and 10 mm² copper would be used for larger radial or submain circuits.