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Maharashtra SSC Power Consumer Energy Meter Pre-Voc/NSQF study materials
Maharashtra SSC Power Consumer Energy Meter Pre-Voc/NSQF study resources

Maharashtra SSC Power Consumer Energy Meter Pre-Voc/NSQF practice questions

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Question 1Electrical Fundamentals and Safety

A consumer's single-phase energy meter records 1 unit of energy. What does one unit mean in this meter?

  1. 1 watt-hour
  2. 1 volt-ampere
  3. 1 kilowatt-hour Correct answer.
  4. 1 megawatt-hour

Explanation

In consumer billing a unit means one kilowatt-hour, the energy used by a 1000 W load running for one hour. The meter's rotating disc or digital register is calibrated so that one full unit equals 1 kWh. This unit is what appears on the bill and is multiplied by the tariff rate.

Question 2Electrical Fundamentals and Safety

Which instrument is connected in series with a domestic load to measure the current drawn by that load?

  1. Energy meter
  2. Ammeter Correct answer.
  3. Voltmeter
  4. Megger

Explanation

An ammeter measures current and must carry the load current, so it is connected in series and has very low resistance. A voltmeter is connected in parallel across the supply. An energy meter measures accumulated energy, and a megger measures insulation resistance, so neither is used as an in-line current indicator.

Question 3Electrical Fundamentals and Safety

In a single-phase energy meter, what is the function of the braking magnet?

  1. To provide a braking torque proportional to disc speed Correct answer.
  2. To stop the disc from rotating at all times
  3. To magnetise the voltage coil core
  4. To increase the driving torque of the meter

Explanation

The permanent magnet produces eddy currents in the rotating aluminium disc, giving a braking torque proportional to speed. This makes the steady disc speed proportional to the load power, which is essential for accurate registration. Without it the disc would accelerate continuously and over-register energy.

Question 4Electrical Fundamentals and Safety

A 230 V single-phase circuit supplies a 2 kW resistive heater. What current does the heater draw?

  1. 8.7 A Correct answer.
  2. 11.5 A
  3. 2.3 A
  4. 4.6 A

Explanation

For a resistive load the power factor is unity, so current equals power divided by voltage: 2000 divided by 230 gives about 8.7 A. This current value is used to select the cable size and the correct MCB rating. Using the full 2 kW value without dividing by voltage would give a wrong, much smaller figure.

Question 5Electrical Fundamentals and Safety

Which condition makes a current-carrying conductor most dangerous to a person who touches it?

  1. The conductor carries direct current only
  2. The conductor is bare and the person is standing on a wet floor Correct answer.
  3. The conductor is enclosed in a metal conduit
  4. The conductor is insulated and earthed at one end

Explanation

The danger depends on the current that flows through the body, and that current needs a return path. A bare live conductor plus a wet floor gives low body and contact resistance, so a large, potentially fatal current can flow to earth. Insulation, dry conditions, or an earthed enclosure reduce the chance of a complete circuit through the body.

Question 6Electrical Fundamentals and Safety

What is the main purpose of earthing the metal body of a domestic appliance?

  1. To stabilise the supply voltage to the appliance
  2. To increase the appliance's power factor
  3. To reduce the electricity bill by returning current
  4. To give fault current a low-resistance path so protection operates Correct answer.

Explanation

Earthing connects exposed metalwork to the earth so that a fault making the body live produces a large current. That current quickly trips the MCB or blows the fuse, disconnecting the supply before a person is shocked. Earthing does not save energy, improve power factor, or regulate voltage.

Question 7Electrical Fundamentals and Safety

Which protective device works by melting a metal element when excess current flows?

  1. Isolator
  2. Fuse Correct answer.
  3. MCB
  4. ELCB

Explanation

A fuse contains a calibrated metal wire or strip that melts when current exceeds its rating, breaking the circuit. An MCB trips by a thermal or magnetic mechanism and can be reset. An ELCB responds to earth leakage, and an isolator is only a manual switch for isolation, not automatic protection.

Question 8Electrical Fundamentals and Safety

A 1.5 kW load runs for 4 hours each day. What energy does it consume in 30 days?

  1. 18 kWh
  2. 60 kWh
  3. 180 kWh Correct answer.
  4. 600 kWh

Explanation

Daily energy is 1.5 kW times 4 h, which equals 6 kWh. Multiplying by 30 days gives 180 kWh, the monthly consumption to be billed. Multiplying power by days without the hours, or misplacing the decimal, gives the other figures.

Question 9Electrical Fundamentals and Safety

Which wiring colour is conventionally used for the neutral conductor in a single-phase Indian domestic installation?

  1. Black Correct answer.
  2. Green
  3. Red
  4. Yellow

Explanation

In the conventional Indian colour code, black identifies the neutral conductor while red is used for the phase. Green is reserved for earth, and yellow is used for phase in three-phase systems. Correct identification prevents accidental contact with a live conductor during maintenance.

Question 10Electrical Fundamentals and Safety

In a single-phase energy meter, what does the voltage coil's flux need to do for correct registration?

  1. Be independent of the supply voltage
  2. Be exactly in phase with the supply voltage Correct answer.
  3. Lead the supply voltage by 45 degrees
  4. Lag the supply voltage by exactly 90 degrees

Explanation

The driving torque depends on the phase angle between the voltage-coil flux and the current-coil flux. The voltage flux must be kept in phase with the applied voltage, and the current flux in phase with the load current, so that torque is proportional to power. Any phase error between voltage and flux causes a meter error, especially at low power factor.

Question 11Electrical Fundamentals and Safety

What is the purpose of the creep adjustment in an induction energy meter?

  1. To increase the disc speed under light load
  2. To prevent slow rotation of the disc when no current flows Correct answer.
  3. To correct the meter reading for high power factor
  4. To set the braking magnet position

Explanation

Even at no load, friction and voltage-coil effects can make the disc creep slowly and register energy that was not consumed. A small iron piece or shading loop is adjusted to create a slight counter torque so the disc stays still when only the voltage coil is energised. This protects the consumer from being billed for phantom consumption.

Question 12Electrical Fundamentals and Safety

A consumer has a connected load of 4 kW and uses it for an average of 5 hours daily. If the tariff is 8 rupees per unit, what is the approximate monthly bill for 30 days?

  1. 960 rupees
  2. 1600 rupees
  3. 4800 rupees Correct answer.
  4. 480 rupees

Explanation

Daily energy is 4 kW times 5 h, or 20 kWh, and monthly energy is 20 times 30, or 600 kWh. At 8 rupees per unit the bill is 600 times 8, which equals 4800 rupees. The other figures come from dropping a factor of 3, 10, or 5 in the calculation.

Question 13Electrical Fundamentals and Safety

Which test confirms that the insulation between a live conductor and the metal body of an appliance is sound?

  1. Insulation resistance test with a megger Correct answer.
  2. Earth loop impedance test only
  3. Continuity test with a multimeter
  4. Polarity test with a test lamp

Explanation

A megger applies a high DC test voltage and measures resistance, so it reveals degraded insulation that a low-voltage continuity test cannot. Good insulation shows a high resistance in megaohms, confirming the body is safe from the live conductor. Continuity and polarity tests check connections, not insulation quality.

Question 14Electrical Fundamentals and Safety

Why is a two-wire single-phase energy meter's current coil wound with few turns of thick wire?

  1. To carry full load current with low voltage drop Correct answer.
  2. To produce a large voltage flux in the shunt path
  3. To reduce the braking torque of the magnet
  4. To increase the resistance of the current path

Explanation

The current coil is in series with the load, so it must carry the full load current without excessive heating or voltage drop. A few turns of thick wire give the low resistance and high current capacity needed. The voltage coil, by contrast, uses many turns of thin wire to produce flux from the supply voltage.

Question 15Electrical Fundamentals and Safety

A person receives an electric shock. What is the first action to take?

  1. Switch off the supply or isolate the source Correct answer.
  2. Give the person food and drink
  3. Pour water on the person
  4. Pull the person away with bare hands

Explanation

The rescuer must first break the electrical contact safely by switching off the supply or removing the source with an insulated object. Touching the victim with bare hands can make the rescuer part of the circuit and cause a second casualty. First aid and medical help follow only after the source is isolated.

Question 16Electrical Fundamentals and Safety

What is the function of a miniature circuit breaker in a consumer's distribution board?

  1. To step down the supply voltage
  2. To measure the energy consumed
  3. To improve the power factor of the load
  4. To automatically interrupt the circuit on overload or short circuit Correct answer.

Explanation

An MCB senses overcurrent thermally and short-circuit current magnetically, then trips to protect wiring and equipment. It can be reset after the fault is cleared, unlike a fuse. It does not transform voltage, meter energy, or correct power factor.

Question 17Electrical Fundamentals and Safety

Which quantity does a consumer energy meter primarily integrate over time?

  1. Instantaneous power Correct answer.
  2. Instantaneous resistance
  3. Instantaneous current
  4. Instantaneous voltage

Explanation

Energy is the integral of power over time, so the meter multiplies voltage and current and accumulates the product. That accumulated value is what the register displays in kilowatt-hours. Voltage, current, and resistance are instantaneous quantities that the meter uses but does not bill.

Question 18Electrical Fundamentals and Safety

A meter's register advances by 10 kWh. How many revolutions would the disc make if the meter constant is 500 revolutions per kWh?

  1. 5000 Correct answer.
  2. 1000
  3. 500
  4. 50

Explanation

The meter constant states revolutions per kilowatt-hour, so total revolutions equal 500 times 10, which is 5000. This test is used to verify meter accuracy against a known load. Dividing instead of multiplying, or dropping a zero, gives the wrong figures.

Question 19Electrical Fundamentals and Safety

Which effect of electric current is used by a fuse to protect a circuit?

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

Explanation

A fuse relies on the heating effect: excess current raises the element's temperature until it melts and opens the circuit. The magnetic effect is used in relays, MCB trip coils, and meters, while the chemical effect appears in electrolysis. Correct fuse selection depends on this predictable melting behaviour.

Question 20Electrical Fundamentals and Safety

An installation has a total connected load of 5 kW. What current does it draw at 230 V assuming unity power factor?

  1. 5.0 A
  2. 21.7 A Correct answer.
  3. 43.5 A
  4. 11.5 A

Explanation

Current equals power divided by voltage for a unity power factor load: 5000 divided by 230 gives about 21.7 A. This value guides the main switch and cable rating. Doubling or halving the power, or ignoring the division, produces the other choices.

Question 21Electrical Fundamentals and Safety

What does the multiplying factor marked on a meter's dial or register mean?

  1. The tariff rate per unit
  2. The meter's rated current
  3. The factor by which the register reading is multiplied to get actual energy Correct answer.
  4. The number of phases supplied

Explanation

When a meter is used with current or voltage transformers, the register shows a scaled value, and the multiplying factor converts it to actual energy. The consumer must apply this factor before billing. It is not the tariff, the current rating, or the phase count, which are separate details.

Question 22Electrical Fundamentals and Safety

Why must the metal tank or body of a distribution transformer be earthed at the consumer's supply point?

  1. To increase the output voltage of the transformer
  2. To keep the tank cool during operation
  3. To reduce the magnetising current
  4. To prevent the tank from becoming live if a fault occurs inside Correct answer.

Explanation

If an internal fault or insulation failure makes the tank live, a person touching it could be shocked. Earthing the tank gives fault current a low-resistance path so protection operates quickly. Earthing has no role in cooling, voltage boosting, or reducing magnetising current.

Question 23Electrical Fundamentals and Safety

A consumer complains that the meter disc rotates even when all appliances are switched off but the main switch is on. Which cause is most likely?

  1. Creep due to incorrect creep adjustment Correct answer.
  2. A faulty braking magnet causing over-speed
  3. A loose meter terminal screw
  4. A reversed neutral connection

Explanation

Slow rotation with the voltage coil energised but no load current is called creeping, and it is corrected by the creep adjustment. A faulty braking magnet would make the disc run fast under load, not creep at no load. Reversed neutral or loose terminals cause other faults such as incorrect registration or heating.

Question 24Electrical Fundamentals and Safety

Which safety practice is correct before working on a domestic wiring circuit?

  1. Work with wet hands to discharge static
  2. Leave the main switch on and use insulated pliers
  3. Switch off the main switch and verify the circuit is dead Correct answer.
  4. Touch the live conductor briefly to test it

Explanation

Safe isolation means switching off the supply, locking or tagging it, and proving the circuit is dead with a tester before touching conductors. Working live, even with insulated tools, exposes the person to arc and shock hazards. Wet hands lower body resistance and increase shock severity.

Question 25Electrical Fundamentals and Safety

A 230 V appliance draws 5 A at a power factor of 0.8. What is the active power consumed?

  1. 1150 W
  2. 920 W Correct answer.
  3. 736 W
  4. 1840 W

Explanation

Active power equals voltage times current times power factor: 230 times 5 times 0.8, which gives 920 W. The product of voltage and current alone gives apparent power in volt-amperes, not active power. Multiplying by 0.8 twice or using the wrong factor leads to the other values.

Question 26Electrical Fundamentals and Safety

In a consumer energy meter installation, what is the main function of the sealing (seal wire and lead seal) applied to the meter terminal cover by the distribution utility?

  1. To keep moisture and insects out of the terminal box
  2. To prevent unauthorised tampering with the terminal connections and metering circuit Correct answer.
  3. To hold the terminal screws tightly against vibration
  4. To indicate the date on which the meter was last calibrated

Explanation

The seal is a tamper-evident device: once the utility seals the terminal cover, any attempt to loosen the incoming or outgoing connections or to bypass the current circuit breaks the seal and becomes detectable. Moisture protection and mechanical holding are incidental, and calibration dates are recorded in test records, not on the seal itself.

Question 27Electrical Fundamentals and Safety

A consumer's single-phase supply is 230 V and the main switch and wiring are rated for a safe continuous current of 20 A. Which of the following connected loads can be operated simultaneously without overloading the circuit, assuming unity power factor?

  1. A 2 kW heater and a 1.5 kW iron together Correct answer.
  2. A 3 kW water heater and a 2 kW air conditioner together
  3. A 4 kW geyser and a 1 kW room heater together
  4. A 1 kW geyser, a 1.5 kW heater and a 2 kW oven together

Explanation

The safe limit is 230 V × 20 A = 4600 W. The heater plus iron totals 3.5 kW, which is below 4600 W, so the circuit is not overloaded. Each other combination exceeds 4600 W and would trip the protective device or overheat the wiring.

Question 28Electrical Fundamentals and Safety

During a meter inspection, a technician finds the meter disc rotating slowly with the main switch ON but every appliance in the consumer's premises switched OFF. Which condition most directly explains this observation?

  1. The meter constant has been set too high by the manufacturer
  2. A leakage path or connected load exists on the consumer's side of the meter Correct answer.
  3. The supply voltage is lower than the declared 230 V
  4. The meter register is nearing its full-scale reading

Explanation

With all appliances off, an induction meter disc should be stationary (apart from negligible friction creep). Continued slow rotation means current is still flowing somewhere downstream of the meter, typically through a leakage path, a hidden load, or a neutral-to-earth fault. The other conditions do not by themselves cause the disc to rotate with no load.

Question 29Electrical Fundamentals and Safety

Which protective measure in a consumer's installation limits the duration of a fault current by automatically opening the circuit when current exceeds a preset value for a specified time?

  1. The overcurrent protective device such as an MCB Correct answer.
  2. The meter's permanent magnet damping
  3. The energy meter's creep adjustment screw
  4. Earthing of the appliance body

Explanation

An overcurrent protective device is designed to sense excess current and open the circuit within a defined time, clearing the fault before conductors are damaged. Earthing provides a low-resistance path but does not itself interrupt current, while creep adjustment and magnetic damping are metering functions, not protective ones.

Question 30Electrical Fundamentals and Safety

An induction energy meter is tested at a load of 1 kW and the disc is found to make 40 revolutions in 60 seconds. What is the meter constant in revolutions per kWh?

  1. 2400 revolutions per kWh Correct answer.
  2. 2000 revolutions per kWh
  3. 1200 revolutions per kWh
  4. 1500 revolutions per kWh

Explanation

Energy consumed in 60 seconds at 1 kW is 1 kW × (60/3600) h = 1/60 kWh. If 40 revolutions correspond to 1/60 kWh, then revolutions per kWh = 40 × 60 = 2400. The meter constant therefore works out to 2400 rev/kWh.

Question 31Power Consumer Energy Metering Concepts

A single-phase domestic consumer has a connected load of 4 kW and uses the supply for 5 hours daily. What is the monthly energy consumption in kWh (assume 30 days)?

  1. 20 kWh
  2. 3000 kWh
  3. 600 kWh Correct answer.
  4. 120 kWh

Explanation

Energy in kWh equals load in kW multiplied by hours of use. Here 4 kW × 5 h = 20 kWh per day, and 20 × 30 days gives 600 kWh for the month. Multiplying load by days only, or by hours only, gives the distractors.

Question 32Power Consumer Energy Metering Concepts

In a typical LT single-phase domestic energy meter, the meter records energy in which unit?

  1. kilowatt-hour Correct answer.
  2. volt-ampere reactive
  3. kilovolt-ampere
  4. kilowatt

Explanation

An energy meter integrates power over time, so its registered unit is the kilowatt-hour (one unit). kW and kVA are units of power, not of energy, and kVAr relates to reactive power.

Question 33Power Consumer Energy Metering Concepts

The constant marked on an energy meter as '1200 revolutions per kWh' means that the meter disc makes 1200 revolutions when the consumer uses:

  1. 1 kWh of energy Correct answer.
  2. 1 kW of power for one minute
  3. 1200 kWh of energy
  4. 1 kVAh of apparent energy

Explanation

The meter constant (rev/kWh) states how many disc revolutions correspond to one kilowatt-hour of registered energy. It is a calibration figure linking revolutions to energy, not to instantaneous power or apparent energy.

Question 34Power Consumer Energy Metering Concepts

Which type of meter is best suited for measuring energy consumed by a large industrial consumer with high load and possible reverse power flow, requiring separate import and export registers?

  1. Single-phase prepaid meter
  2. Single-phase electromechanical meter
  3. Three-phase four-wire bidirectional static meter Correct answer.
  4. Domestic LT direct-connected meter

Explanation

A three-phase four-wire bidirectional static meter handles high loads and records import and export energy separately, which suits industrial consumers with reverse power flow. Single-phase meters cannot serve three-phase high loads, and prepaid domestic meters lack bidirectional registers.

Question 35Power Consumer Energy Metering Concepts

A consumer's meter shows a reading of 04521 kWh at the start of the billing cycle and 04987 kWh at the end. What is the energy billed for the cycle?

  1. 446 kWh
  2. 534 kWh
  3. 9466 kWh
  4. 466 kWh Correct answer.

Explanation

Billed energy is the difference between the closing and opening readings. Subtracting 4521 from 4987 gives 466 kWh. Adding the readings or misaligning the digits produces the other options.

Question 36Power Consumer Energy Metering Concepts

What is the primary purpose of the current transformer (CT) in a CT-operated energy meter installation?

  1. To store energy for use during power failure
  2. To step down the line current to a safe, measurable value for the meter Correct answer.
  3. To correct the power factor of the consumer load
  4. To step up the voltage supplied to the meter terminals

Explanation

A CT reduces the high primary line current to a standard low secondary current so the meter can measure it safely. It does not change voltage, improve power factor, or store energy.

Question 37Power Consumer Energy Metering Concepts

A CT-operated meter has a CT ratio of 200/5 A. If the meter records 100 kWh, what is the actual energy consumed?

  1. 4000 kWh Correct answer.
  2. 2000 kWh
  3. 100 kWh
  4. 40 kWh

Explanation

The multiplying factor equals the CT ratio, 200/5 = 40. Multiplying the meter reading 100 kWh by 40 gives 4000 kWh of actual energy. Ignoring the factor or halving it gives the other options.

Question 38Power Consumer Energy Metering Concepts

In a static energy meter, which component performs the multiplication of voltage and current signals and their integration over time?

  1. The potential transformer only
  2. The metering integrated circuit or microcontroller Correct answer.
  3. The meter terminal block
  4. The display LCD

Explanation

In a static meter, a dedicated metering IC or microcontroller multiplies the sampled voltage and current and integrates the product to obtain energy. The terminal block only provides connections, and the LCD only displays results.

Question 39Power Consumer Energy Metering Concepts

An energy meter is described as 'class 1.0'. This classification indicates the meter's:

  1. limit of permissible error as a percentage of the measured value Correct answer.
  2. maximum current rating in amperes
  3. number of tariff registers available
  4. type of communication protocol supported

Explanation

The accuracy class number gives the maximum permissible error as a percentage under reference conditions. A class 1.0 meter may deviate by up to 1.0 percent. It does not indicate current rating, registers, or communication features.

Question 40Power Consumer Energy Metering Concepts

A consumer suspects the meter is fast. Which test most directly checks whether the meter registers energy correctly against a known load?

  1. Insulation resistance test of the service cable
  2. Phantom load test using a known resistive load and stopwatch Correct answer.
  3. Polarity check of the service connections
  4. Earth resistance measurement at the consumer premises

Explanation

A phantom load test applies a known resistive load and times the disc revolutions or pulses to verify registration accuracy. Insulation, earth resistance, and polarity checks verify safety and connection correctness, not energy accuracy.

Question 41Power Consumer Energy Metering Concepts

What does 'tamper detection' in an electronic energy meter refer to?

  1. Automatically disconnecting the supply at a fixed time daily
  2. Recording events such as opening of the meter cover or magnetic influence Correct answer.
  3. Converting a postpaid meter into a prepaid meter
  4. Reducing the billing tariff when load is low

Explanation

Tamper detection logs abnormal events like cover opening, magnetic interference, or reverse current so utilities can investigate theft. It does not schedule disconnection, change billing mode, or reduce tariffs.

Question 42Power Consumer Energy Metering Concepts

A prepaid energy meter differs from a conventional postpaid meter mainly because it:

  1. measures only reactive energy
  2. eliminates the need for a current transformer in all installations
  3. requires the consumer to pay in advance and disconnects supply when balance is exhausted Correct answer.
  4. cannot record energy in kWh

Explanation

A prepaid meter works on advance payment and cuts supply when the credit balance reaches zero. It still measures real energy in kWh and may still use CTs where required.

Question 43Power Consumer Energy Metering Concepts

The term 'connected load' in consumer billing context refers to:

  1. the maximum current the meter can carry
  2. the sum of rated capacities of all appliances connected to the installation Correct answer.
  3. the reactive power drawn by motors
  4. the energy consumed in the highest-demand month

Explanation

Connected load is the arithmetic sum of the rated wattages of all appliances in the premises. It is a fixed declared figure used in tariff and sanction, distinct from actual demand or energy consumed.

Question 44Power Consumer Energy Metering Concepts

A meter records 1 kWh for every 800 pulses. If the pulse LED blinks 2400 times, how much energy has been registered?

  1. 2.4 kWh
  2. 0.33 kWh
  3. 3 kWh Correct answer.
  4. 2400 kWh

Explanation

Dividing 2400 pulses by 800 pulses per kWh gives 3 kWh. Treating the pulse count as energy directly or inverting the constant produces the wrong answers.

Question 45Power Consumer Energy Metering Concepts

Why is the potential transformer (PT) used in high-voltage metering installations?

  1. To compensate for reactive power
  2. To reduce the high line voltage to a low standard value for the meter Correct answer.
  3. To increase the current reaching the meter
  4. To provide backup supply to the meter

Explanation

A PT steps down high line voltage to a standard low value that the meter can safely measure. It does not boost current, correct reactive power, or supply backup power.

Question 46Power Consumer Energy Metering Concepts

A consumer with a load of 2 kW for 3 hours and 1 kW for 5 hours in a day consumes how much energy daily?

  1. 16 kWh
  2. 6 kWh
  3. 8 kWh
  4. 11 kWh Correct answer.

Explanation

Energy is computed separately for each period and then summed: 2 kW × 3 h = 6 kWh and 1 kW × 5 h = 5 kWh, giving 11 kWh. Adding loads and hours incorrectly yields the distractors.

Question 47Power Consumer Energy Metering Concepts

Which of the following best describes 'power factor' as it affects energy metering and billing of an industrial consumer?

  1. The ratio of energy consumed to connected load
  2. The ratio of real power to apparent power, which may attract a penalty if low Correct answer.
  3. The total number of units registered in a month
  4. The voltage at which the meter operates

Explanation

Power factor is real power divided by apparent power; a low value means poor utilisation and often attracts a reactive-power penalty. It is not a ratio of energy to load, a unit count, or a voltage level.

Question 48Power Consumer Energy Metering Concepts

In a three-phase three-wire system, energy measurement is typically done using:

  1. two wattmeter elements or two CT/PT sets Correct answer.
  2. four elements always
  3. one element only
  4. no current transformers under any condition

Explanation

Three-phase three-wire measurement uses the two-wattmeter method, so two elements or two CT/PT sets suffice. Four elements belong to four-wire systems, and one element is insufficient for three-phase.

Question 49Power Consumer Energy Metering Concepts

A meter reading is found to be 0.5 percent lower than the true energy over a test. This indicates the meter is:

  1. faulty and must be replaced immediately
  2. fast beyond permissible limits
  3. recording reactive energy only
  4. slow within its permissible accuracy class Correct answer.

Explanation

A deviation of 0.5 percent is within a class 1.0 meter's permissible error, so the meter is slow but acceptable. It is not fast, not necessarily faulty, and it still records real energy.

Question 50Power Consumer Energy Metering Concepts

An installation has a CT ratio of 100/5 A and a PT ratio of 11000/110 V. What is the overall multiplying factor for the meter reading?

  1. 20
  2. 2000 Correct answer.
  3. 100
  4. 1100

Explanation

The overall factor is the product of the CT ratio and PT ratio: (100/5) × (11000/110) = 20 × 100 = 2000. Using only one ratio or miscomputing the PT ratio gives the distractors.