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SOLAS Electrical Apprenticeship practice questions

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Question 1Electrical Craft Practice (installation, testing and maintenance)

On a 230 V single-phase final circuit protected by a 32 A BS EN 60898 type B MCB, which conductor size is the minimum permitted for a two-core PVC-insulated and sheathed cable clipped direct, assuming no derating factors apply?

  1. 1.5 mm²
  2. 2.5 mm²
  3. 4.0 mm² Correct answer.
  4. 6.0 mm²

Explanation

Clipped-direct reference method C gives a current-carrying capacity of about 27 A for 2.5 mm² and about 37 A for 4.0 mm², so the 32 A device needs at least 4.0 mm². The protective device rating must not exceed the cable's tabulated capacity after all correction factors are applied.

Question 2Electrical Craft Practice (installation, testing and maintenance)

Before working on a distribution board, which sequence correctly applies the safe isolation procedure?

  1. Isolate, prove dead, lock off, prove the tester on a known source
  2. Prove dead at the conductors, isolate, lock off, re-prove the tester
  3. Lock off, prove the tester, isolate, prove dead, re-prove the tester
  4. Isolate, lock off, prove the tester on a known source, prove dead at the conductors, re-prove the tester Correct answer.

Explanation

Safe isolation requires identifying and isolating the supply, securing the isolation with a lock and warning notice, then proving the voltage indicator on a known live source, testing the conductors to confirm dead, and re-proving the indicator afterwards. The prove-test-prove sequence confirms the tester itself was functioning throughout.

Question 3Electrical Craft Practice (installation, testing and maintenance)

A ring final circuit wired in 2.5 mm² thermoplastic twin and earth has a 30 A BS 3036 semi-enclosed fuse as its overcurrent device. Which requirement of the ring circuit design must be checked specifically because of this device type?

  1. That the cable's csa is at least 4.0 mm²
  2. That the ring has no more than ten socket outlets
  3. That the fuse's fusing factor of about 1.9 means the cable's effective capacity must be derated by 0.725 Correct answer.
  4. That the earth fault loop impedance is below 1 ohm

Explanation

BS 3036 rewireable fuses have a fusing factor of roughly 1.9, so the cable capacity must be multiplied by 0.725 before comparing it with the device rating. This derating rule is specific to semi-enclosed fuses and is why 2.5 mm² ring circuits on 30 A BS 3036 fuses need careful checking.

Question 4Electrical Craft Practice (installation, testing and maintenance)

Which instrument is used to confirm the continuity and resistance of a circuit protective conductor during initial verification?

  1. Low-resistance ohmmeter Correct answer.
  2. Earth electrode resistance tester
  3. Clamp meter
  4. Insulation resistance tester at 500 V

Explanation

A low-resistance ohmmeter, often a multifunction tester set to continuity, passes a small test current and measures the resistance of the protective conductor path. The reading confirms the CPC is continuous and its resistance is low enough for the loop impedance to be acceptable.

Question 5Electrical Craft Practice (installation, testing and maintenance)

During an insulation resistance test on a 230 V final circuit, a reading of 0.8 MΩ is obtained with all equipment connected. What is the most appropriate action?

  1. Record the value as satisfactory because it exceeds 0.5 MΩ
  2. Repeat the test at 1000 V to obtain a higher reading
  3. Immediately replace the circuit wiring
  4. Investigate and disconnect equipment likely to be causing the low reading, then retest Correct answer.

Explanation

A 0.8 MΩ result passes the 1 MΩ minimum for a 500 V test only marginally and often indicates connected equipment such as surge protection or electronic dimmers. The correct approach is to disconnect suspect equipment and retest the wiring alone before recording a result.

Question 6Electrical Craft Practice (installation, testing and maintenance)

A prospective fault current of 4.5 kA is measured at the origin of an installation. Which characteristic of the main switch or protective devices must be confirmed?

  1. That their rated current is at least 4.5 kA
  2. That their IP rating is at least IP4X
  3. That their rated short-circuit breaking capacity or conditional rating is at least 4.5 kA Correct answer.
  4. That their breaking capacity is at least 450 A

Explanation

The prospective fault current at the point of installation must not exceed the short-circuit capacity of the protective devices, either their rated breaking capacity or a conditional rating with a backup device. A 4.5 kA PFC therefore requires devices rated at 4.5 kA or higher at that point.

Question 7Electrical Craft Practice (installation, testing and maintenance)

What is the purpose of equipotential bonding of extraneous conductive parts in a bathroom?

  1. To provide a return path for earth leakage current
  2. To increase the earth fault loop impedance
  3. To limit touch voltage between simultaneously accessible metal parts during a fault Correct answer.
  4. To reduce the operating current of the circuit

Explanation

Supplementary equipotential bonding connects extraneous conductive parts so that any potential difference between them during a fault is minimised, limiting touch voltage to a safe level. It does not carry load current or provide a fault return path.

Question 8Electrical Craft Practice (installation, testing and maintenance)

Which test is carried out to verify that the polarity of every outlet is correct before energising an installation?

  1. Earth electrode resistance test
  2. RCD trip time test
  3. Prospective short-circuit current test
  4. Polarity check using a continuity tester or dedicated polarity test Correct answer.

Explanation

Polarity testing confirms that line and neutral are connected to the correct terminals at every accessory and that single-pole devices are in the line conductor. It is normally done with a continuity or dedicated polarity test before the installation is energised.

Question 9Electrical Craft Practice (installation, testing and maintenance)

A 30 mA RCD protecting a socket outlet circuit trips at 25 mA in 28 ms during a test. How should this result be interpreted?

  1. Unacceptable, because the trip time exceeds 40 ms
  2. Acceptable, because it tripped within the 300 ms limit at the rated residual current Correct answer.
  3. Acceptable only if the test was done at five times rated current
  4. Unacceptable, because it tripped below 30 mA

Explanation

For a 30 mA RCD the maximum permitted trip time at rated residual operating current is 300 ms, so tripping at 25 mA in 28 ms is well within requirements. Tripping at or below the rated residual current is expected behaviour, not a fault.

Question 10Electrical Craft Practice (installation, testing and maintenance)

Which of the following is the correct method for terminating a stranded conductor in a screw terminal to reduce the risk of strand damage?

  1. Cut the strands back to the insulation
  2. Twist the strands and fit a suitable ferrule or crimp terminal before insertion Correct answer.
  3. Insert the strands loosely and tighten firmly
  4. Solder the strands together before insertion

Explanation

Fitting a ferrule or crimp terminal contains the strands and spreads the clamping pressure, preventing strand breakage and loose connections. Twisting alone or soldering can cause stress concentrations and is not the preferred method for screw terminals.

Question 11Electrical Craft Practice (installation, testing and maintenance)

What does the 'let-through energy' (I²t) rating of a protective device describe?

  1. The energy consumed by the device under normal load
  2. The energy required to reset the device
  3. The thermal energy the device allows to pass before clearing a fault Correct answer.
  4. The dielectric strength of the device

Explanation

The I²t let-through energy is the quantity of thermal energy permitted to pass into the circuit while the device clears a fault. It must be compared with the cable's withstand capability so the cable is not damaged during a short circuit.

Question 12Electrical Craft Practice (installation, testing and maintenance)

A single-phase motor circuit is protected by a type C MCB. Which statement best explains why type C is chosen over type B?

  1. Type C has a lower magnetic trip threshold
  2. Type C has a higher thermal trip rating
  3. Type C tolerates higher inrush currents before tripping Correct answer.
  4. Type C provides residual current protection

Explanation

Type C devices have a magnetic trip range of 5 to 10 times rated current, compared with 3 to 5 times for type B, so they ride through motor starting inrush without nuisance tripping. The thermal characteristic is essentially the same for both types.

Question 13Electrical Craft Practice (installation, testing and maintenance)

Which document should be completed and issued to the client after initial verification of a new installation?

  1. Minor Electrical Installation Works Certificate
  2. PAT test record
  3. Electrical Installation Certificate with schedules of test results and inspections Correct answer.
  4. Periodic Inspection Report

Explanation

New installations, and alterations involving new circuits, require an Electrical Installation Certificate supported by schedules of inspections and test results. The certificate declares the design, construction and verification comply with the regulations.

Question 14Electrical Craft Practice (installation, testing and maintenance)

During a periodic inspection, a circuit's insulation resistance tests at 0.3 MΩ between live conductors and earth. What does this most likely indicate?

  1. An acceptable reading because the circuit is protected by an RCD
  2. A normal reading for a lighting circuit
  3. A fault in the test instrument leads
  4. Deterioration or damage in the insulation requiring investigation Correct answer.

Explanation

A value of 0.3 MΩ is below the 1 MΩ minimum for a 500 V test and points to moisture, damage or degradation of the insulation. The circuit should be investigated and the cause rectified before it is returned to service.

Question 15Electrical Craft Practice (installation, testing and maintenance)

Which of the following is the primary reason for installing a circuit protective conductor with a low impedance?

  1. To ensure sufficient fault current flows to operate the protective device within the disconnection time Correct answer.
  2. To improve the power factor of the installation
  3. To carry the neutral return current
  4. To reduce the voltage drop on the circuit

Explanation

Earth fault loop impedance must be low enough that a fault current large enough to trip the protective device flows within the required disconnection time. This is the fundamental requirement for automatic disconnection of supply.

Question 16Electrical Craft Practice (installation, testing and maintenance)

What is the main function of a residual current device in a TT system?

  1. To balance the load across phases
  2. To provide additional protection against earth fault currents that the overcurrent device may not clear Correct answer.
  3. To reduce the earth fault loop impedance
  4. To limit the prospective short-circuit current

Explanation

In a TT system the earth fault loop impedance is often too high for an overcurrent device to disconnect within the required time, so an RCD senses the residual current and disconnects. It provides the fault protection that the overcurrent device cannot reliably deliver.

Question 17Electrical Craft Practice (installation, testing and maintenance)

Which of the following conductor colours is used for the protective conductor in a flexible cord to BS EN 50525?

  1. Brown
  2. Green-and-yellow Correct answer.
  3. Blue
  4. Black

Explanation

Green-and-yellow is the standard colour for protective conductors in flexible cords and fixed wiring. Blue is neutral and brown is line in single-phase flexible cords.

Question 18Electrical Craft Practice (installation, testing and maintenance)

A cable is run through thermal insulation in a loft. Which action is required in the design?

  1. Change the cable to a lower csa
  2. Ignore the insulation if the cable is clipped
  3. Increase the protective device rating to compensate
  4. Apply an appropriate derating factor to the cable's current-carrying capacity Correct answer.

Explanation

Thermal insulation traps heat and reduces a cable's ability to dissipate it, so a derating factor must be applied to the tabulated current-carrying capacity. The factor depends on how much of the cable is surrounded by insulation.

Question 19Electrical Craft Practice (installation, testing and maintenance)

What is the correct interpretation of a 'main protective bonding conductor' in an installation with a 25 mm² line conductor?

  1. A conductor equal in csa to the line conductor
  2. A conductor of at least 10 mm² copper connecting extraneous conductive parts to the main earthing terminal Correct answer.
  3. A conductor of at least 1.5 mm² copper
  4. A conductor used only for supplementary bonding in bathrooms

Explanation

For a line conductor of 25 mm², the main protective bonding conductor must be at least 10 mm² copper, in accordance with the table relating bonding conductor size to supply conductor size. It connects extraneous conductive parts to the main earthing terminal.

Question 20Electrical Craft Practice (installation, testing and maintenance)

Which of the following practices best reduces the risk of electric shock when using a portable electric drill on a construction site?

  1. Using a 110 V centre-tapped-to-earth supply with a suitable plug and lead Correct answer.
  2. Removing the earth pin to fit a two-pin socket
  3. Using a 230 V drill with an extension lead
  4. Working with wet hands to improve grip

Explanation

A 110 V centre-tapped-to-earth supply limits the maximum voltage to earth to 55 V, greatly reducing the severity of any shock. Site tools and leads should be rated for this reduced low voltage system and inspected regularly.

Question 21Electrical Craft Practice (installation, testing and maintenance)

A three-phase motor is found to be running in reverse after reconnection. What is the most appropriate correction?

  1. Reverse the neutral and one line conductor
  2. Increase the overload setting
  3. Interchange the earth and neutral conductors
  4. Interchange any two of the three line conductors at the motor terminals Correct answer.

Explanation

Reversing the rotation of a three-phase motor is achieved by swapping any two line conductors, which reverses the phase sequence. Changing the neutral or earth connection does not alter rotation and can be dangerous.

Question 22Electrical Craft Practice (installation, testing and maintenance)

Which test confirms that the resistance of the earth fault loop is low enough for the protective device to operate within the required disconnection time?

  1. Earth fault loop impedance test Correct answer.
  2. Polarity test
  3. Continuity of ring final circuit conductors test
  4. Insulation resistance test

Explanation

The earth fault loop impedance test measures the total loop resistance and is compared with the maximum Zs for the protective device. If the measured value is below the tabulated maximum, disconnection will occur within the required time.

Question 23Electrical Craft Practice (installation, testing and maintenance)

During maintenance, a capacitor in a motor control panel must be worked on. Which precaution is essential before touching the terminals?

  1. Reduce the supply voltage to 110 V
  2. Leave the capacitor connected and work with insulated tools
  3. Isolate the supply and discharge the capacitor through a suitable resistor Correct answer.
  4. Isolate the supply and immediately touch the terminals to discharge

Explanation

Capacitors can retain a dangerous charge after isolation, so they must be discharged through a suitable resistor and proved dead before work begins. Simply isolating the supply does not remove the stored energy.

Question 24Electrical Craft Practice (installation, testing and maintenance)

Which of the following is the correct action when a test instrument's calibration certificate has expired?

  1. Continue using it and note the expiry on the certificate
  2. Use it only for low-voltage tests
  3. Adjust the readings manually to compensate
  4. Withdraw the instrument from use and have it recalibrated before further testing Correct answer.

Explanation

Test instruments must be within calibration to give reliable results, so an out-of-calibration instrument should be withdrawn and recalibrated. Continuing to use it undermines the validity of any test results recorded.

Question 25Electrical Craft Practice (installation, testing and maintenance)

A final circuit is protected by a 16 A type B MCB. The measured earth fault loop impedance is 2.4 Ω. What does this indicate for a 230 V TN system with a 0.4 s disconnection time?

  1. The value is irrelevant because the MCB is type B
  2. The value is acceptable because it is below 5 Ω
  3. The measured value exceeds the maximum permitted Zs and the circuit is not compliant Correct answer.
  4. The value is acceptable only if an RCD is fitted

Explanation

For a 16 A type B MCB the maximum Zs for a 0.4 s disconnection time is about 2.87 Ω at 230 V, but the measured 2.4 Ω must be compared against the tabulated value after applying the 0.8 rule-of-thumb for conductor temperature. On that basis the circuit requires investigation.

Question 26Electrical Craft Practice (installation, testing and maintenance)

An apprentice is preparing to carry out an insulation resistance test on a newly wired lighting circuit. Which instrument setting is appropriate for this test?

  1. A clamp meter set to the 200 A AC range
  2. A multimeter set to the continuity buzzer range
  3. A 500 V DC insulation tester with the circuit isolated and sensitive equipment disconnected Correct answer.
  4. A low-resistance ohmmeter set to measure milliohms

Explanation

Insulation resistance is measured with a dedicated insulation tester applying a DC test voltage, typically 500 V for a 230/400 V installation, with the supply isolated and electronics removed to prevent damage. The result is read in megohms and compared with the minimum acceptable value. Instruments intended for continuity or current measurement cannot apply the required test voltage.

Question 27Electrical Craft Practice (installation, testing and maintenance)

Which of the following is the standard test voltage applied between live conductors and earth when carrying out insulation resistance testing on a 400 V three-phase installation?

  1. 250 V DC
  2. 5000 V DC
  3. 500 V DC Correct answer.
  4. 50 V DC

Explanation

For low-voltage installations operating at 230/400 V, insulation resistance is normally tested at 500 V DC, with a minimum acceptable result of 1 MΩ for the whole installation. The test voltage is chosen to stress the insulation without exceeding its rating. Higher voltages are reserved for equipment rated accordingly, such as some motors and cables.

Question 28Electrical Craft Practice (installation, testing and maintenance)

A ring final circuit is being verified. Which test confirms that the ring is continuous and that the conductors are connected in the correct loop arrangement?

  1. An RCD trip-time test at the origin
  2. An end-to-end resistance test on each conductor with the cross-connections removed Correct answer.
  3. An earth loop impedance test at the furthest point
  4. A polarity test at each socket outlet

Explanation

Measuring end-to-end resistance of line, neutral and protective conductors with the ring open confirms continuity, and comparing the readings identifies a break or a reversed connection. The values should be broadly proportional to conductor cross-sectional area. Polarity and loop impedance tests do not prove ring continuity.

Question 29Electrical Craft Practice (installation, testing and maintenance)

Before making a live measurement inside a distribution board, which action best protects the operative from an arc flash incident?

  1. Working quickly to minimise exposure time
  2. Isolating the board and proving dead wherever practicable before working Correct answer.
  3. Using a multimeter with a low battery warning
  4. Wearing cotton gloves and standing on a rubber mat

Explanation

The primary control for arc flash risk is to de-energise and prove dead before work, using live work only where it is genuinely necessary and justified. Where live testing is unavoidable, a documented risk assessment, suitable PPE and insulated tools are required. Speed and improvised measures do not reduce the hazard.

Question 30Electrical Craft Practice (installation, testing and maintenance)

A 230 V single-phase circuit is protected by a 32 A type B MCB. The measured earth fault loop impedance (Zs) at the furthest point is 1.1 Ω. What is the correct interpretation?

  1. The circuit fails, because the device will not trip within the required disconnection time
  2. The circuit complies, because Zs is below the maximum permitted value for the device Correct answer.
  3. The circuit fails, because Zs must be below 0.4 Ω for all final circuits
  4. The result is invalid and the test must be repeated at the origin

Explanation

For a 32 A type B MCB the maximum Zs for a 0.4 s disconnection time is approximately 1.37 Ω at 230 V, so a measured 1.1 Ω satisfies the requirement, allowing for conductor temperature correction. Compliance is judged against the device's published maximum Zs, not a single universal figure. The measured value must also be adjusted for conductor operating temperature where relevant.

Question 31Electrical Craft Practice (installation, testing and maintenance)

During a periodic inspection, a 30 mA RCD protecting a socket circuit is tested with the test button and trips. What additional verification does this provide?

  1. It confirms the earth electrode resistance is satisfactory
  2. It proves the RCD trips at its rated residual current within the specified time
  3. It confirms the mechanical trip mechanism operates but does not verify the residual current sensitivity Correct answer.
  4. It confirms the circuit's insulation resistance is adequate

Explanation

The integral test button applies an internal imbalance to check that the mechanism operates, but it does not measure the actual residual operating current or trip time. Instrument-based testing at half, full and five times rated residual current is needed to verify sensitivity and speed. The button test is therefore a functional check only.

Question 32Electrical Craft Practice (installation, testing and maintenance)

A motor rated 400 V, 50 Hz, 11 kW is to be connected to a DOL starter. Which conductor size selection factor is most relevant when the cable is grouped with four other loaded circuits in a trunking?

  1. The motor's power factor only
  2. The grouping (derating) factor applied to the tabulated current-carrying capacity Correct answer.
  3. The ambient temperature only
  4. The starter's enclosure IP rating

Explanation

When cables are bunched, mutual heating reduces the current each can carry, so a grouping factor is applied to the tabulated capacity before comparing with the design current. Ambient temperature and installation method are applied as separate correction factors. Power factor affects current magnitude but is already reflected in the design current calculation.

Question 33Electrical Craft Practice (installation, testing and maintenance)

Which of the following best describes the purpose of a protective multiple earthing (PME) arrangement in a distribution network?

  1. It disconnects the supply if the neutral rises above 50 V
  2. It provides a combined neutral and earth conductor that is earthed at multiple points along the network Correct answer.
  3. It isolates the earth from the neutral to prevent diverted neutral currents
  4. It uses a local earth electrode as the sole means of earthing

Explanation

In a PME (TN-C-S) system the neutral conductor also performs the earthing function and is connected to earth at several points, giving a low earth fault loop impedance. The combined conductor is split into separate neutral and protective conductors at the origin of the installation. This arrangement requires particular care with extraneous conductive parts.

Question 34Electrical Craft Practice (installation, testing and maintenance)

A three-phase induction motor is to be reversed by changing two line connections at the starter. Which additional check is essential before energising?

  1. Confirm the motor is mechanically free to rotate and the driven equipment is safe to run in reverse Correct answer.
  2. Confirm the cable gland is of the correct colour
  3. Confirm the motor insulation resistance exceeds 1 MΩ
  4. Confirm the overload relay settings match the new direction of rotation

Explanation

Reversing rotation can damage driven machinery such as pumps or conveyors, so the mechanical system must be checked as safe to run in the opposite direction. The electrical connections should also be verified against the manufacturer's diagram. Overload settings depend on current, not direction.

Question 35Electrical Craft Practice (installation, testing and maintenance)

A portable appliance is being inspected. The label shows the last formal inspection was 14 months ago and the appliance is used daily in a workshop. What is the appropriate action?

  1. Apply a new label showing the current date without testing
  2. Remove it from service and arrange for its inspection and testing to be brought up to date Correct answer.
  3. Continue using the appliance because it is still functioning correctly
  4. Increase the inspection interval to two years to reduce disruption

Explanation

In-service inspection and testing intervals are set according to the appliance type, environment and use; a daily-used workshop appliance will typically require more frequent checks than the interval shown. An overdue appliance should be withdrawn until it has been inspected and tested. Functional operation alone does not demonstrate electrical safety.

Question 36Electrical Craft Practice (installation, testing and maintenance)

A capacitor bank is connected across the terminals of a large three-phase motor for power factor correction. Which procedure must be followed before working on the motor terminals after isolation?

  1. Open the capacitor contactor and begin work immediately
  2. Discharge the capacitors through a suitable resistor and prove the terminals dead Correct answer.
  3. Short the capacitor terminals directly with a screwdriver
  4. Wait five minutes and then touch the terminals to confirm discharge

Explanation

Capacitors can retain a dangerous charge after the supply is removed, so they must be discharged through a suitable resistor and the terminals proved dead with an approved voltage indicator. Direct shorting can cause a violent arc and damage. The isolated supply should also be locked off.

Question 37Electrical Craft Practice (installation, testing and maintenance)

A cable installed in a wall at a depth of less than 50 mm from the surface runs vertically to a socket outlet. Which requirement applies to its protection?

  1. No protection is required because the cable is vertical
  2. It must be protected by a 30 mA RCD only, with no mechanical protection
  3. It must be protected by an earthed metallic covering, conduit or an equivalent mechanical protection, or be installed within a safe zone Correct answer.
  4. It must be armoured regardless of the safe zone

Explanation

Cables buried at less than 50 mm must be protected against penetration by nails and screws, either by earthed metallic covering, conduit or equivalent mechanical protection, or by being run within a recognised safe zone aligned with an accessory. A 30 mA RCD may provide additional protection but does not by itself satisfy the mechanical protection requirement.

Question 38Electrical Craft Practice (installation, testing and maintenance)

An earth electrode resistance for a TT installation measures 180 Ω. Which conclusion is most appropriate?

  1. The value is likely too high to ensure RCD operation and the electrode arrangement should be improved Correct answer.
  2. The value indicates the electrode is correctly installed and no further action is needed
  3. The value is irrelevant because the RCD provides all necessary protection
  4. The value is acceptable because any earth electrode below 200 Ω is permitted

Explanation

In a TT system the electrode resistance must be low enough, in combination with the RCD, to limit touch voltage under fault conditions; a value of 180 Ω will generally give an unacceptably high touch voltage at 30 mA and should be reduced by adding electrodes or improving the soil contact. There is no single universal pass value of 200 Ω. The RCD is essential but does not remove the need for a satisfactory electrode.

Question 39Electrical Craft Practice (installation, testing and maintenance)

A newly installed submain has a measured prospective fault current of 6 kA at its origin. The selected MCB has a rated short-circuit capacity of 10 kA to BS EN 60898. Which statement is correct?

  1. The device is unsuitable because BS EN 60898 devices cannot be used on submains
  2. The device is suitable because its breaking capacity exceeds the prospective fault current Correct answer.
  3. The device is unsuitable because its capacity must be at least twice the fault current
  4. The device is suitable only if backed up by a 30 mA RCD

Explanation

The rated short-circuit capacity of a protective device must be at least equal to the prospective fault current at its point of installation, so 10 kA is adequate for a 6 kA fault level. Where the fault level exceeds the device rating, a suitable upstream device with energy limitation may be used. The RCD has no role in short-circuit breaking capacity.

Question 40Electrical Craft Practice (installation, testing and maintenance)

During commissioning, an insulation resistance test on a three-phase distribution board gives 0.4 MΩ between phases and earth, while the individual circuits each test above 200 MΩ when isolated. What is the most likely explanation?

  1. A connected load or surge protection device is providing a low-resistance path to earth Correct answer.
  2. The tester is faulty because the individual results were high
  3. The test voltage was too low to polarise the insulation
  4. The earthing conductor is disconnected from the board

Explanation

When individual circuits test high but the board as a whole tests low, a connected item such as a surge protection device, filter or electronic equipment is the usual cause, since these present a low impedance to the test voltage. Such equipment should be disconnected before testing. A disconnected earth would tend to give a high or unstable reading rather than a low one.

Question 41Electrical Science and Principles

A 12 V battery is connected across a 4 Ω resistor. What current flows through the resistor?

  1. 0.33 A
  2. 16 A
  3. 3 A Correct answer.
  4. 48 A

Explanation

Ohm's law states that current equals voltage divided by resistance, so I = V/R = 12/4 = 3 A. This relationship holds for a purely resistive circuit at constant temperature.

Question 42Electrical Science and Principles

Two 6 Ω resistors are connected in parallel. What is the total resistance of the combination?

  1. 6 Ω
  2. 0.33 Ω
  3. 3 Ω Correct answer.
  4. 12 Ω

Explanation

For two equal resistors in parallel the equivalent resistance is half of one value, so 6/2 = 3 Ω. The reciprocal formula 1/Rt = 1/6 + 1/6 gives the same result.

Question 43Electrical Science and Principles

Which unit expresses electrical power in a direct current circuit?

  1. The farad
  2. The coulomb
  3. The joule
  4. The watt Correct answer.

Explanation

Power is the rate of energy transfer and is measured in watts, where one watt equals one joule per second. In a DC circuit power equals voltage multiplied by current.

Question 44Electrical Science and Principles

A conductor carries a steady current of 2 A for 30 seconds. How much charge passes a point in the conductor?

  1. 60 C Correct answer.
  2. 15 C
  3. 32 C
  4. 0.067 C

Explanation

Charge equals current multiplied by time, so Q = I × t = 2 × 30 = 60 C. The coulomb is defined as one ampere flowing for one second.

Question 45Electrical Science and Principles

Which material is classed as a good electrical insulator in a ship's wiring installation?

  1. Sea water
  2. Aluminium
  3. Rubber Correct answer.
  4. Copper

Explanation

Insulators have very few free electrons, so they resist the flow of current; rubber is used as cable insulation for that reason. Metals and salt water contain mobile charge carriers and conduct readily.

Question 46Electrical Science and Principles

What is the principal purpose of earthing the metal enclosure of electrical equipment?

  1. To reduce energy consumption
  2. To provide a low-impedance path so protective devices operate on a fault Correct answer.
  3. To increase the insulation resistance of the equipment
  4. To improve the power factor of the load

Explanation

Earthing bonds exposed metalwork to the hull or earth so that a fault current returns through a low-impedance path, quickly tripping the protective device. This limits the touch voltage that a person could experience.

Question 47Electrical Science and Principles

A resistor is marked with brown, black, red and gold bands. What is its nominal value?

  1. 1 MΩ with 5 percent tolerance
  2. 10 Ω with 5 percent tolerance
  3. 1 kΩ with 5 percent tolerance Correct answer.
  4. 100 Ω with 10 percent tolerance

Explanation

Brown is 1 and black is 0, giving 10, and the red multiplier is 100, so the value is 1000 Ω or 1 kΩ. The gold band indicates a tolerance of plus or minus 5 percent.

Question 48Electrical Science and Principles

Which statement correctly describes conventional current flow?

  1. It exists only in alternating current circuits.
  2. It is identical to electron drift direction in a metal.
  3. It flows from positive to negative externally through the load. Correct answer.
  4. It flows from negative to positive inside the source only.

Explanation

Conventional current is defined as flowing from the positive terminal through the external circuit to the negative terminal. Electron drift in a metal is in the opposite direction to this convention.

Question 49Electrical Science and Principles

A 24 V supply feeds two resistors in series, 8 Ω and 4 Ω. What is the voltage across the 8 Ω resistor?

  1. 24 V
  2. 8 V
  3. 16 V Correct answer.
  4. 12 V

Explanation

The total resistance is 12 Ω, so the current is 24/12 = 2 A. The voltage across the 8 Ω resistor is then 2 × 8 = 16 V, following the potential divider principle.

Question 50Electrical Science and Principles

A 2 kW immersion heater runs on a 230 V supply. What current does it draw, to two significant figures?

  1. 4.6 A
  2. 8.7 A Correct answer.
  3. 460 A
  4. 0.12 A

Explanation

Power equals voltage multiplied by current, so I = P/V = 2000/230 = 8.7 A. The heater's resistance would then be about 26 Ω.