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Craftsman Electricity practice questions

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Question 1Electrical Safety and Codes

Which conductor color is the standard equipment grounding conductor in a typical North American branch circuit?

  1. Bare or green Correct answer.
  2. Orange or blue
  3. Black or red
  4. White or gray

Explanation

The equipment grounding conductor is identified by a bare conductor or by green insulation, or green with yellow stripes. This identification is required so that anyone opening a box can recognize the grounding path without tracing the circuit.

Question 2Electrical Safety and Codes

A worker is about to work on a de-energized 480 V panel. Which step must be completed before touching any conductor?

  1. Verify the absence of voltage with a tested meter on the isolated parts Correct answer.
  2. Put on leather work gloves and proceed
  3. Ask a coworker to watch the panel during the work
  4. Apply a lock and tag, then begin work immediately

Explanation

Lockout/tagout isolates and secures the source, but the equipment must still be tested with an adequately rated meter to confirm zero energy before contact. The meter itself should be verified on a known live source both before and after the test.

Question 3Electrical Safety and Codes

The primary purpose of bonding metal raceways and enclosures to the grounding system is to:

  1. Provide a low-impedance fault-current path that lets the overcurrent device open Correct answer.
  2. Balance the voltage between the two ungrounded legs
  3. Reduce radio-frequency interference on the circuit
  4. Carry normal load current back to the source

Explanation

Bonding creates a low-impedance path so that a ground fault draws enough current to trip the overcurrent protective device quickly. It is not intended to carry normal operating current.

Question 4Electrical Safety and Codes

Which of these is the correct way to handle an extension cord that has a damaged outer jacket exposing the inner conductors?

  1. Remove it from service and tag it for repair or disposal Correct answer.
  2. Shorten the cord by cutting off the damaged section at home
  3. Wrap the damaged section with electrical tape and continue
  4. Use it only for low-current tools

Explanation

Damaged flexible cords must be removed from service because the exposed conductors create shock and fire hazards. Field repairs with tape do not restore the insulation integrity required for continued use.

Question 5Electrical Safety and Codes

What is the minimum working clearance requirement most directly related to when selecting a shock-approach boundary for unqualified persons?

  1. The voltage involved and the person's qualifications Correct answer.
  2. The number of circuits in the enclosure
  3. The color of the panel cover
  4. The age of the wiring method

Explanation

Approach boundaries are set by the voltage present and by whether the person is qualified or unqualified. Unqualified persons must stay outside the limited approach boundary unless escorted and protected.

Question 6Electrical Safety and Codes

A GFCI receptacle is installed to protect a kitchen counter circuit. What condition will cause it to trip?

  1. An overloaded circuit drawing too much current
  2. A short circuit between hot and neutral
  3. A loose connection causing voltage drop
  4. A small current leaking from the hot conductor to ground Correct answer.

Explanation

A GFCI compares current on the hot and neutral conductors and trips when the difference, which represents leakage to ground, exceeds its threshold (typically 4–6 mA). It senses ground-fault current, not overload or line-to-neutral short circuit.

Question 7Electrical Safety and Codes

Which practice best minimizes the risk of arc flash when operating a large fused disconnect switch?

  1. Operate the switch with one hand while holding the door open
  2. Stand to the side of the enclosure and wear the required arc-rated PPE Correct answer.
  3. Open the enclosure door to watch the blades separate
  4. Face the enclosure squarely and operate the handle quickly

Explanation

Standing to the side keeps the body out of the arc-flash blast path, and arc-rated PPE protects against thermal energy if an arc occurs. The enclosure door should remain closed and latched during operation.

Question 8Electrical Safety and Codes

In a standard 120/240 V single-phase residential service, the neutral conductor is connected to earth ground at which location?

  1. At every receptacle outlet
  2. At the service equipment only Correct answer.
  3. At the farthest outlet from the panel
  4. At each junction box in the branch circuit

Explanation

The grounded conductor is bonded to the grounding electrode system at the service equipment, and the grounding and grounded conductors are kept separate downstream. Regrounding the neutral at outlets would create parallel return paths and objectionable current.

Question 9Electrical Safety and Codes

A 20 A branch circuit supplies a dedicated motor. Which overcurrent device rating generally provides running overload protection for the motor branch-circuit conductors?

  1. A device sized at twice the conductor ampacity
  2. A device sized at the motor's full-load current only
  3. A device sized to the conductor ampacity, not the motor's starting current Correct answer.
  4. A device sized at the motor's locked-rotor current

Explanation

Branch-circuit conductors are protected against overload at their ampacity, while short-circuit and ground-fault protection is sized separately for motor starting. The motor's own overload relay protects the motor from overload.

Question 10Electrical Safety and Codes

When installing a 15 A receptacle on a 20 A small-appliance branch circuit, which configuration is required?

  1. A 15 A or 20 A receptacle with a 20 A-rated circuit, both acceptable on the 20 A circuit Correct answer.
  2. Only a 20 A receptacle, because the circuit is 20 A
  3. A receptacle rated 30 A to allow future expansion
  4. Only a 15 A receptacle, because the load is small

Explanation

A 20 A small-appliance branch circuit may supply 15 A or 20 A receptacles, provided the receptacle rating is not less than the branch-circuit rating where a single receptacle is used. Multiple 15 A receptacles are permitted on a 20 A circuit.

Question 11Electrical Safety and Codes

A box contains four 12 AWG current-carrying conductors, two 12 AWG equipment grounding conductors, and one device. Using the standard box-fill method, which count correctly represents the required volume?

  1. Grounding conductors are not counted at all
  2. The device yoke is not counted in box fill
  3. Each conductor counts as 1.0 in³ regardless of size
  4. Each 12 AWG conductor counts as 2.25 in³, grounds count as one of that size, and the device counts as two conductors Correct answer.

Explanation

Box fill is calculated by assigning volume to each conductor based on AWG size; all equipment grounding conductors of the same size count as one conductor, and each device yoke counts as two conductors of the largest size present. For 12 AWG the value is 2.25 in³ per conductor.

Question 12Electrical Safety and Codes

Which condition requires a separate equipment grounding conductor to be run with the circuit conductors rather than relying on the metal raceway?

  1. When the circuit is 120 V rather than 240 V
  2. When the raceway is not listed as an equipment grounding conductor or continuity is questionable Correct answer.
  3. When the circuit is protected by a GFCI breaker
  4. When the raceway is made of rigid metal

Explanation

Metal raceways can serve as the equipment grounding conductor only where they are recognized for that purpose and provide a continuous, low-impedance path. Where that cannot be assured, a separate grounding conductor is required.

Question 13Electrical Safety and Codes

A 240 V, 40 A fixed appliance is fed with a 40 A circuit. Which conductor sizing consideration applies to the equipment grounding conductor?

  1. It may be omitted if the appliance is double-insulated
  2. It must be the same size as the ungrounded conductors
  3. It is sized per the overcurrent device rating using the equipment grounding conductor table Correct answer.
  4. It must be larger than the ungrounded conductors

Explanation

The equipment grounding conductor is sized from the overcurrent protective device rating using the applicable equipment grounding conductor table, not simply matched to the ungrounded conductors. For a 40 A device, 10 AWG copper is typically permitted.

Question 14Electrical Safety and Codes

Which statement correctly describes the role of a listed AFCI device on a bedroom branch circuit?

  1. It limits current to prevent electric shock to personnel
  2. It detects arcing signatures and opens the circuit to reduce fire ignition risk Correct answer.
  3. It opens on ground-fault leakage of 5 mA
  4. It protects the circuit from surges on the utility lines

Explanation

An arc-fault circuit interrupter detects the characteristic current and voltage signatures of parallel and series arcing and de-energizes the circuit to reduce fire risk. It is not a shock-protection device like a GFCI.

Question 15Electrical Safety and Codes

A conductor is installed in an ambient temperature of 50°C. Why must the ampacity be adjusted?

  1. Higher ambient temperature reduces the conductor's ability to dissipate heat, lowering its ampacity Correct answer.
  2. Ampacity adjustment is required only for aluminum conductors
  3. Ambient temperature only matters for underground installations
  4. Higher ambient temperature increases conductor resistance so ampacity rises

Explanation

Ampacity depends on how quickly a conductor can shed heat. In a hotter ambient, the temperature difference between the conductor and surroundings is smaller, so the allowable current must be reduced using the correction factors.

Question 16Electrical Safety and Codes

When more than three current-carrying conductors are installed in a raceway, what effect does this have on conductor ampacity?

  1. Ampacity is increased because the conductors share the load
  2. Ampacity is reduced by bundling adjustment factors because heat is trapped Correct answer.
  3. Ampacity is unchanged as long as the conduit is metal
  4. Ampacity is reduced only for conductors larger than 4/0 AWG

Explanation

Conductors bunched together cannot dissipate heat as effectively, so adjustment factors reduce ampacity as the number of current-carrying conductors increases. The adjustment applies regardless of raceway material.

Question 17Electrical Safety and Codes

Which installation method is acceptable for running nonmetallic-sheathed cable through a bored hole in a floor joist?

  1. Laid across the top of the joist in an attic
  2. Through a hole drilled at least 1-1/4 inches from the joist edge, or protected by a steel plate where closer Correct answer.
  3. Notched into the top edge of the joist without protection
  4. Stapled to the bottom edge of the joist

Explanation

Cable must be set back from the framing edge or protected by a steel plate to prevent nails and screws from damaging it. Holes at least 1-1/4 inches from the nearest edge generally satisfy this requirement.

Question 18Electrical Safety and Codes

An electrician must select a disconnect for a motor. Which requirement generally applies to the disconnecting means?

  1. It must open all ungrounded conductors simultaneously
  2. It must be rated for at least twice the motor full-load current
  3. It may be located on a different floor if a sign is posted
  4. It must be capable of being locked in the open position and within sight of the motor Correct answer.

Explanation

Motor disconnecting means must be within sight of the controller location and capable of being locked open for lockout. The disconnecting means must also open all ungrounded conductors, but the lockable and within-sight requirement is the key safety element.

Question 19Electrical Safety and Codes

A 200 A service panel is fed by 3/0 copper conductors. Which conductor may serve as the grounding electrode conductor to a ground rod?

  1. A conductor sized per the grounding electrode conductor table, often 6 AWG copper for a rod electrode Correct answer.
  2. No grounding electrode conductor is required if a water pipe is present
  3. A conductor equal to the service conductors, 3/0 copper
  4. A 14 AWG copper conductor

Explanation

The grounding electrode conductor is sized from the service conductor ampacity using the applicable table, and for a rod electrode it is not required to be larger than 6 AWG copper. The connection to the electrode must be accessible and made with listed fittings.

Question 20Electrical Safety and Codes

In a 3-phase, 4-wire delta system with a high-leg, which conductor color must be used to identify the high-leg?

  1. Orange Correct answer.
  2. Green
  3. Black
  4. White

Explanation

The high-leg conductor in a 3-phase, 4-wire delta system must be identified with orange coloring. This warns that the phase-to-neutral voltage on that leg is higher than on the other two legs.

Question 21Electrical Safety and Codes

A worker is using a multimeter to verify a de-energized 277 V lighting circuit. Which practice is most appropriate?

  1. Test only from line to neutral, not line to ground
  2. Use a meter rated for the voltage and category, verify it on a known source before and after the test Correct answer.
  3. Use any meter set to the highest resistance range
  4. Rely on the panel breaker label as proof the circuit is off

Explanation

The meter must be rated for the voltage and transient category of the circuit, and it should be proven on a known live source before and after testing the isolated conductors. This confirms the meter is functioning when the zero reading is observed.

Question 22Electrical Safety and Codes

Which condition would most likely require the use of a Class A GFCI rather than a standard receptacle GFCI?

  1. Protection of a service entrance from surges
  2. Protection of a motor branch circuit from overload
  3. Protection of a feeder from short circuits
  4. Protection of personnel on a construction site temporary power circuit Correct answer.

Explanation

Class A GFCIs are required for personnel protection in many temporary and construction applications, tripping at 4–6 mA. They are distinct from overcurrent and surge devices, which serve different protective functions.

Question 23Electrical Safety and Codes

A 3-phase motor circuit has a nameplate full-load current of 22 A. Which conductor size is the minimum permitted for the branch-circuit conductors, assuming 75°C terminations and copper conductors?

  1. 14 AWG copper, rated 20 A at 75°C
  2. 12 AWG copper, rated 25 A at 75°C
  3. 10 AWG copper, rated 35 A at 75°C Correct answer.
  4. 8 AWG copper, rated 50 A at 75°C

Explanation

Motor branch-circuit conductors are sized at 125% of the motor full-load current, so 22 A × 1.25 = 27.5 A. A 10 AWG copper conductor rated 35 A at 75°C is the smallest standard size that satisfies this.

Question 24Electrical Safety and Codes

A feeder supplies a 120/208 V panelboard with a calculated load of 180 A. The feeder is installed in a raceway with four current-carrying conductors at an ambient temperature of 40°C. Which factor set must be applied to the conductor ampacity?

  1. Only the conductor bundling adjustment
  2. Only the ambient temperature correction
  3. Both ambient temperature correction and conductor bundling adjustment Correct answer.
  4. Neither factor, because the load is below 200 A

Explanation

Ampacity must be adjusted for the higher ambient temperature and for the number of current-carrying conductors in the raceway. Both correction and adjustment factors apply cumulatively before comparing to the load.

Question 25Electrical Safety and Codes

An electrician is bonding a metal water piping system to the grounding electrode system. Which connection point is generally required?

  1. At the farthest fixture from the water heater
  2. Anywhere on the piping, as long as the clamp is tight
  3. At the water meter only, regardless of insulating sections
  4. Within 5 feet of the point where the piping enters the building, and on the building side of any insulating fitting Correct answer.

Explanation

Bonding of a metal water piping system must be made within 5 feet of the point of entry and on the building side of any insulating fitting or dielectric union. This ensures the bond remains effective even if the meter or a section is removed.

Question 26Electrical Safety and Codes

A journeyman is selecting a plug fuse to protect a 15 A general-purpose lighting branch circuit in an older panelboard. Which fuse type is designed so that it cannot be installed in a higher-amperage fuseholder?

  1. A 20 A plug fuse with a shunted base
  2. A 15 A cartridge fuse in an adapter
  3. A time-delay dual-element fuse rated 15 A
  4. A non-time-delay plug fuse rated 15 A with a rejection base Correct answer.

Explanation

Edison-base plug fuses rated 15 A and below are made with a rejection feature so they cannot be screwed into a fuseholder of larger rating, which prevents overfusing a small circuit. The rejection base is the key safety characteristic, not the time-delay element.

Question 27Electrical Safety and Codes

During a service change, an electrician must connect the grounding electrode conductor to a driven ground rod. Which statement describes an acceptable method of connecting the conductor to the rod?

  1. The conductor may be clamped with a listed acorn-type connector or exothermic welded to the rod Correct answer.
  2. The conductor may be secured with a sheet-metal screw into the rod
  3. The conductor may be wrapped tightly around the rod and taped
  4. The conductor may be laid alongside the rod and buried with it

Explanation

The grounding electrode conductor must be connected to the electrode by a listed clamp, connector, or exothermic welding, and the connection must be accessible. Wrapping, taping, or laying the conductor against the rod does not provide a reliable, listed connection.

Question 28Electrical Safety and Codes

A 120 V receptacle outlet is being installed outdoors on the wall of a detached garage to supply a pressure washer. Which requirement applies to this receptacle?

  1. It must be supplied from a circuit protected by a standard circuit breaker only
  2. It requires only a weatherproof cover because the circuit is 120 V
  3. It may be installed without GFCI protection if a ground rod is driven at the garage
  4. It must be GFCI protected and have an enclosure or cover that maintains weatherproof integrity when in use Correct answer.

Explanation

Outdoor receptacle outlets require ground-fault circuit-interrupter protection, and the enclosure must keep the device weatherproof whether or not a cord is plugged in. A bubble or in-use cover is the usual way to meet that requirement.

Question 29Electrical Safety and Codes

A metal raceway system containing feeder conductors is being installed between a service equipment enclosure and a separate building. Which bonding practice is required for the metal raceway itself?

  1. The raceway may be left unbonded if the conductors inside are insulated
  2. The raceway must be bonded at both ends and made electrically continuous Correct answer.
  3. The raceway must be bonded only at the load end
  4. The raceway must be isolated from the enclosures with insulating bushings at both ends

Explanation

Metal raceways that enclose circuit conductors must be electrically continuous and bonded to enclosures and equipment so that fault current has a low-impedance path back to the source. Bonding at only one point or isolating the raceway leaves a hazardous potential on the metal.

Question 30Electrical Safety and Codes

An electrician is evaluating a 120/240 V, single-phase panel where the neutral bar is bonded to the enclosure. A subpanel is fed from this panel with a 4-wire feeder to a detached structure that also has a grounding electrode. Which arrangement is correct at the detached structure?

  1. Bond the neutral bar to the enclosure and omit the equipment grounding conductor in the feeder
  2. Keep the neutral bar isolated and connect the grounding electrode conductor to the neutral bar
  3. Bond the neutral bar to the enclosure and rely on the detached structure's ground rod as the only ground
  4. Keep the neutral bar isolated from the enclosure, land the equipment grounding conductor on a separate ground bar, and connect the grounding electrode to that bar Correct answer.

Explanation

At a separate structure, the feeder's equipment grounding conductor must terminate on a grounding terminal bar, the neutral must remain isolated from the enclosure, and the local grounding electrode connects to the equipment grounding conductor system. This keeps objectionable neutral current off the grounding path.

Question 31Electrical Theory and Principles

In a DC series circuit, which quantity is the same through every component?

  1. Voltage
  2. Resistance
  3. Current Correct answer.
  4. Power

Explanation

A series circuit has only one path, so the same current flows through each component. Voltage divides across the components in proportion to their resistances, resistance is a property of each component, and power differs because it depends on each component's voltage drop.

Question 32Electrical Theory and Principles

Which instrument is connected in parallel with the load to measure potential difference?

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

Explanation

A voltmeter measures the difference in potential between two points, so it is connected in parallel across the load and must have a very high internal resistance to avoid disturbing the circuit. An ammeter is inserted in series, and an ohmmeter is used on a de-energized component.

Question 33Electrical Theory and Principles

A resistor of 12 ohms carries 2.5 A. What is the voltage across it?

  1. 30 V Correct answer.
  2. 36 V
  3. 9.5 V
  4. 4.8 V

Explanation

Ohm's law states that voltage equals current multiplied by resistance. Multiplying 2.5 A by 12 ohms gives 30 V. Dividing rather than multiplying, or adding the two values, produces the other listed results.

Question 34Electrical Theory and Principles

What is the total resistance of 6 ohms, 4 ohms, and 10 ohms connected in series?

  1. 10 ohms
  2. 2.4 ohms
  3. 1.9 ohms
  4. 20 ohms Correct answer.

Explanation

In a series circuit the total resistance is the sum of the individual resistances. Adding 6, 4, and 10 ohms gives 20 ohms. The smaller values arise from reciprocal or product-over-sum methods that apply to parallel networks.

Question 35Electrical Theory and Principles

A 1 kW load runs continuously for 4 hours. How much energy does it consume?

  1. 0.25 kWh
  2. 400 kWh
  3. 40 kWh
  4. 4 kWh Correct answer.

Explanation

Electrical energy in kilowatt-hours equals power in kilowatts multiplied by time in hours. One kilowatt for four hours gives 4 kWh. Dividing instead of multiplying, or misplacing the decimal, produces the other options.

Question 36Electrical Theory and Principles

Which material is the best conductor of electricity among the following?

  1. Dry wood
  2. Glass
  3. Copper Correct answer.
  4. Rubber

Explanation

Copper has a large number of free electrons and very low resistivity, making it a preferred conductor for wiring. Glass, rubber, and dry wood have few free charge carriers and are used as insulators.

Question 37Electrical Theory and Principles

In a purely resistive AC circuit, how do current and voltage relate?

  1. Current and voltage are in phase Correct answer.
  2. Current lags voltage by 90 degrees
  3. Current leads voltage by 90 degrees
  4. Current is exactly 180 degrees out of phase with voltage

Explanation

With no inductance or capacitance, the only opposition is resistance, so current rises and falls with voltage and the phase angle is zero. Reactive elements, not resistance, cause the 90 degree leading or lagging relationships.

Question 38Electrical Theory and Principles

Which unit expresses electrical resistance?

  1. Tesla
  2. Henry
  3. Ohm Correct answer.
  4. Farad

Explanation

Resistance is measured in ohms, where one ohm permits one ampere of current under one volt of potential difference. The farad measures capacitance, the henry measures inductance, and the tesla measures magnetic flux density.

Question 39Electrical Theory and Principles

A 12 V source is connected across two 24 ohm resistors in parallel. What current does the source supply?

  1. 2 A
  2. 0.5 A
  3. 0.25 A
  4. 1 A Correct answer.

Explanation

Two equal 24 ohm resistors in parallel give 12 ohms. Dividing the 12 V source by 12 ohms yields 1 A of total current. Each branch carries 0.5 A, and the source current is the sum of the branch currents.

Question 40Electrical Theory and Principles

A 2 kW heater operates at 240 V. What is its resistance?

  1. 14.4 ohms
  2. 28.8 ohms Correct answer.
  3. 120 ohms
  4. 8.3 ohms

Explanation

Power equals voltage squared divided by resistance, so resistance equals voltage squared divided by power. Dividing 240 squared (57,600) by 2,000 W gives 28.8 ohms. Using voltage divided by power instead of the squared relationship gives an incorrect result.

Question 41Electrical Theory and Principles

Which change increases the capacitance of a parallel-plate capacitor?

  1. Reducing the applied voltage
  2. Inserting a dielectric between the plates Correct answer.
  3. Reducing the plate area
  4. Increasing the distance between the plates

Explanation

Capacitance equals the permittivity of the dielectric times plate area divided by plate separation. A dielectric with a relative permittivity greater than one raises capacitance, while increasing separation or reducing area lowers it. Applied voltage affects stored charge, not the capacitance value.

Question 42Electrical Theory and Principles

What does the root-mean-square value of an AC waveform represent?

  1. The peak value of the waveform
  2. The value that produces the same heating effect as an equal DC value Correct answer.
  3. The average value over one complete cycle
  4. The peak-to-peak amplitude

Explanation

The RMS value is the effective value of an alternating quantity: it delivers the same power to a resistive load as an equal direct current. For a sine wave it is the peak divided by the square root of two. Peak and average values are different quantities.

Question 43Electrical Theory and Principles

A coil has 5 ohms of resistance and 12 ohms of inductive reactance in series on an AC supply. What is its impedance?

  1. 60 ohms
  2. 13 ohms Correct answer.
  3. 7 ohms
  4. 17 ohms

Explanation

Impedance magnitude is the square root of resistance squared plus reactance squared. The square root of 25 plus 144 is the square root of 169, which is 13 ohms. Reactance and resistance cannot simply be added arithmetically because they are 90 degrees apart in phase.

Question 44Electrical Theory and Principles

What is the purpose of a fuse in an electrical circuit?

  1. To store energy for later use
  2. To regulate the supply voltage
  3. To interrupt current when it exceeds a set value Correct answer.
  4. To improve the power factor of the load

Explanation

A fuse contains a calibrated element that melts when current exceeds its rating, opening the circuit and protecting conductors and equipment from overheating. It does not regulate voltage, correct power factor, or store energy.

Question 45Electrical Theory and Principles

Which statement correctly describes the magnetic field produced by a current-carrying conductor?

  1. Its direction depends on the direction of current flow Correct answer.
  2. It is strongest far from the conductor
  3. It exists only when the conductor carries alternating current
  4. Its strength is independent of current magnitude

Explanation

A current-carrying conductor produces a magnetic field whose direction is given by the right-hand rule and reverses when the current reverses. Field strength rises with current and falls with distance from the conductor. The field exists for both direct and alternating current.

Question 46Electrical Theory and Principles

Three 60 W lamps are connected in parallel across a 120 V supply. What total current do they draw?

  1. 1.5 A Correct answer.
  2. 2 A
  3. 0.5 A
  4. 5 A

Explanation

Each lamp draws 0.5 A because 60 W divided by 120 V equals 0.5 A. In parallel, the branch currents add, so the total is 1.5 A. The supply voltage is common to all three lamps.

Question 47Electrical Theory and Principles

A resistor has color bands brown, black, red, and gold. What is its nominal value and tolerance?

  1. 100 ohms, 5 percent
  2. 1,000 ohms, 10 percent
  3. 10,000 ohms, 5 percent
  4. 1,000 ohms, 5 percent Correct answer.

Explanation

Brown is 1, black is 0, and red is a multiplier of 100, giving 1,000 ohms. A gold fourth band indicates plus or minus 5 percent tolerance. A silver band would indicate 10 percent, and a different multiplier would change the value.

Question 48Electrical Theory and Principles

Which statement about a transformer is correct?

  1. It increases the power output above the power input
  2. It changes AC voltage by mutual induction between windings Correct answer.
  3. It transfers energy by a direct electrical connection between windings
  4. It operates only on steady direct current

Explanation

A transformer couples two windings through a shared magnetic core, so changing current in the primary induces a voltage in the secondary. The turns ratio sets the voltage ratio, and the secondary power never exceeds the primary power because losses occur. Steady direct current produces no changing flux and therefore no induction.

Question 49Electrical Theory and Principles

What is the purpose of earthing the metal enclosure of an appliance?

  1. To increase the operating voltage of the appliance
  2. To improve the power factor of the appliance
  3. To reduce the appliance's power consumption
  4. To provide a low-impedance path that causes protective devices to operate on a fault Correct answer.

Explanation

Bonding the enclosure to earth ensures that a fault connecting a live conductor to the metalwork produces a large fault current, which trips the overcurrent device or residual current device quickly. This limits the time the enclosure remains at a dangerous potential. Earthing does not affect power consumption or power factor.

Question 50Electrical Theory and Principles

A capacitor and a resistor are connected in series across a DC supply. What happens to the current as the capacitor charges?

  1. It falls exponentially toward zero Correct answer.
  2. It rises steadily to a maximum
  3. It remains constant at its initial value
  4. It reverses direction immediately

Explanation

At the instant of connection the uncharged capacitor acts almost as a short circuit, so current is at its maximum. As charge accumulates, the capacitor voltage opposes the supply and the current decays exponentially with the time constant equal to resistance times capacitance.