British Standards Bs 7671 Electrical Installation Exam Practice Test

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British Standards Bs 7671 Electrical Installation Exam Practice Test - Quiz

It’s easy to flip a light switch or turn on your television without thinking of the processes going on behind them. What powers them up? Electricity! How does that electricity work? That’s for you to tell us! In this quiz, we’ll be trying to gauge your knowledge on all things electricity, with specific reference to the United Kingdom. What do you know about it all? Let’s find out!


Questions and Answers
  • 1. 

    Requirements are included in BS 7671 for electrical installations of

    • A.

      Lift installations

    • B.

      Mobile offshore electrical systems

    • C.

      Distributor's networks

    • D.

      Locations containing a bath or shower

    Correct Answer
    D. Locations containing a bath or shower
    Explanation
    BS 7671 includes requirements for electrical installations in locations containing a bath or shower. This is because these areas are considered to be high-risk zones due to the presence of water, which can increase the likelihood of electrical accidents and shocks. The requirements in BS 7671 aim to ensure the safety of individuals using these areas by specifying guidelines for the installation, protection, and use of electrical equipment. These requirements may include the use of appropriate electrical devices, such as residual current devices (RCDs), to provide additional protection against electric shocks.

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  • 2. 

    Which of the following is excluded from the scope of BS 7671?

    • A.

      Cabins containing sauna heaters

    • B.

      Fountains

    • C.

      Highway power supplies

    • D.

      Lightning protection

    Correct Answer
    D. Lightning protection
    Explanation
    Lightning protection is excluded from the scope of BS 7671 because it is covered by a separate standard, BS EN 62305. BS 7671, also known as the Wiring Regulations, provides guidance and regulations for electrical installations in the UK. It covers various aspects of electrical installations, but lightning protection falls under a different standard as it requires specific measures and considerations to protect against the effects of lightning strikes. Therefore, lightning protection is not within the scope of BS 7671.

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  • 3. 

    Which of the following is not included in BS 7671?

    • A.

      Demolition site installations

    • B.

      Electric fences

    • C.

      Medical locations

    • D.

      Motor caravans

    Correct Answer
    B. Electric fences
    Explanation
    BS 7671 is a British Standard for electrical installations. It provides requirements for the design, installation, and maintenance of electrical systems. Electric fences are not included in BS 7671 because they are not considered as typical electrical installations. Electric fences are specialized systems used for animal containment or security purposes, and they have their own specific standards and regulations that need to be followed. Therefore, they are not covered under the scope of BS 7671.

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  • 4. 

    Which of the following documents is non-statutory?

    • A.

      Electricity Safety, Quality and Continuity Regulations

    • B.

      Electricity at Work Regulations

    • C.

      The Building Regulations

    • D.

      Requirements for Electrical Installations

    Correct Answer
    D. Requirements for Electrical Installations
    Explanation
    The correct answer is "Requirements for Electrical Installations" because this document is not a statutory regulation or law. It is a non-statutory guidance document that provides recommendations and best practices for electrical installations. The other options listed are all statutory regulations that have legal force and must be followed.

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  • 5. 

    Protective equipotential bonding is achieved by

    • A.

      Preventing current from passing through the body

    • B.

      Ensuring adequate continuity between extraneous conductive parts

    • C.

      Automatic disconnection of supply in the event of a fault

    • D.

      Separation of equipment from the supply using a safety isolating transformer

    Correct Answer
    B. Ensuring adequate continuity between extraneous conductive parts
    Explanation
    Protective equipotential bonding is achieved by ensuring adequate continuity between extraneous conductive parts. This means that all conductive parts, such as metal pipes or structural steel, that are not part of the electrical installation but could become live in the event of a fault, are connected together to maintain the same electrical potential. This helps to prevent the formation of potential differences that could cause electric shock or other hazards. By ensuring continuity between these extraneous conductive parts, any fault current will be safely and effectively conducted away, reducing the risk of electrical shock or damage.

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  • 6. 

     The type of earthing arrangements requiring a consumer’s earth electrode to be installed is where 

    • A.

      No earth facility is supplied by the distributor

    • B.

      The supply is from a low voltage generator

    • C.

      Earthing is via the distributor’s cable armour

    • D.

      The electrical system is TN-C

    Correct Answer
    A. No earth facility is supplied by the distributor
    Explanation
    In this type of earthing arrangement, the consumer's earth electrode needs to be installed because there is no earth facility provided by the distributor. This means that the consumer needs to create their own earthing system to ensure the safety of their electrical system.

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  • 7. 

    Low-voltage is defined in BS 7671 as having a value exceeding

    • A.

      24V ac

    • B.

      48V ac

    • C.

      50V ac

    • D.

      120V ac

    Correct Answer
    C. 50V ac
    Explanation
    In BS 7671, low-voltage is defined as having a value exceeding 50V ac. This means that any voltage below 50V ac is considered low-voltage according to this standard.

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  • 8. 

    Tables showing the classification of external influences when considering environmental conditions during the design of an installation can be found in BS 7671

    • A.

      Chapter 32

    • B.

      Chapter 53

    • C.

      Appendix 4

    • D.

      Appendix 5

    Correct Answer
    D. Appendix 5
    Explanation
    The correct answer is Appendix 5 because it is mentioned that tables showing the classification of external influences can be found in BS 7671, and Appendix 5 is a part of BS 7671.

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  • 9. 

    An assessment must be made of harmful effects on other electrical systems when installing

    • A.

      Large electric motors

    • B.

      Fire alarm systems

    • C.

      Emergency lighting circuits

    • D.

      Reduced low voltage supplies

    Correct Answer
    A. Large electric motors
    Explanation
    When installing large electric motors, it is necessary to assess the potential harmful effects on other electrical systems. This is because large electric motors can draw a significant amount of power, which may cause voltage fluctuations or electrical disturbances that can affect the operation of other electrical systems in the vicinity. Therefore, it is important to evaluate and mitigate any potential adverse effects on the overall electrical system before installing large electric motors.

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  • 10. 

    For a 32A ring final circuit in similar premises to a dwelling, the minimum size of thermoplastic insulated copper live conductors allowed is

    • A.

      1.0mm2

    • B.

      1.5mm2

    • C.

      2.5mm2

    • D.

      4.0mm2

    Correct Answer
    C. 2.5mm2
    Explanation
    In similar premises to a dwelling, the minimum size of thermoplastic insulated copper live conductors allowed for a 32A ring final circuit is 2.5mm2. This size is necessary to ensure the conductors can safely carry the current without overheating or causing a fire hazard. Using a smaller size conductor could result in excessive heat buildup and potential damage to the wiring system. Therefore, a minimum size of 2.5mm2 is required to meet safety standards and regulations.

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  • 11. 

    In a domestic dwelling a 32A ring final circuit incorporating BS 1363 socket-outlets historically serves a floor area up to

    • A.

      75m2

    • B.

      100m2

    • C.

      50m2

    • D.

      200m2

    Correct Answer
    B. 100m2
    Explanation
    A 32A ring final circuit with BS 1363 socket-outlets historically serves a floor area up to 100m2. This means that the circuit is designed to supply power to electrical devices and appliances in a domestic dwelling with a floor area of up to 100 square meters. The 32A rating indicates the maximum current that the circuit can safely handle, while the BS 1363 socket-outlets are the standard outlets used in the UK. This circuit size is commonly used in residential buildings to ensure that an adequate amount of power is available for typical household needs within the specified floor area.

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  • 12. 

    The following final circuits are to be installed using thermoplastic insulated multicore non-armoured cables 3 x 6A lighting                      1 x 20A UPS supply                             3 x 32A ring                           1 x 40A cooker   If the cables are enclosed in a non-metalic trunking where entering the distribution board, how many live conductors would be enclosed?

    • A.

      9

    • B.

      16

    • C.

      22

    • D.

      32

    Correct Answer
    C. 22
    Explanation
    If the cables are enclosed in a non-metallic trunking, the number of live conductors enclosed can be determined by adding up the number of live conductors for each circuit. In this case, there are 3 lighting circuits (3 x 1 live conductor = 3 live conductors), 1 UPS supply (1 live conductor), 3 ring circuits (3 x 2 live conductors = 6 live conductors), and 1 cooker circuit (1 live conductor). Adding these together gives a total of 3 + 1 + 6 + 1 = 11 live conductors. However, since each circuit has a live and neutral conductor, the total number of conductors enclosed would be double that, which is 11 x 2 = 22 live conductors.

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  • 13. 

    The required current carrying capacity of a three-phase circuit conductor Iz  is 26A.  From the correct table, the minimum size of three single-core thermoplastic covered, heavy duty MICC cables, installed flat on a perforated cable tray and spaced by two cable diameters is

    • A.

      1.0mm2

    • B.

      1.5mm2

    • C.

      2.5mm2

    • D.

      4.0mm2

    Correct Answer
    B. 1.5mm2
    Explanation
    The correct answer is 1.5mm2 because it is the minimum size of three single-core thermoplastic covered, heavy duty MICC cables that can carry a current of 26A. This size is determined by the required current carrying capacity of the circuit conductor, which is 26A.

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  • 14. 

    Which of the following is not a characteristic of the supply?

    • A.

      Nominal voltage

    • B.

      frequency

    • C.

      Earth loop impedance Ze

    • D.

      Power factor

    Correct Answer
    D. Power factor
    Explanation
    The power factor is not a characteristic of the supply. It is a measure of how effectively electrical power is being used in a circuit. It represents the ratio of real power (used to perform useful work) to apparent power (total power supplied to the circuit). A power factor of 1 indicates that all the power supplied is being used effectively, while a power factor less than 1 indicates that some power is being wasted. The other options, nominal voltage, frequency, and earth loop impedance Ze, are all characteristics of the supply.

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  • 15. 

    The requirements for mobile or transportable units are applicable to the following types of unit

    • A.

      Health screening services

    • B.

      Pleasure craft

    • C.

      Mobile machinery to BS EN 60204-1

    • D.

      Traction equipment of electric vehicles

    Correct Answer
    A. Health screening services
    Explanation
    The requirements for mobile or transportable units are applicable to health screening services. This means that any mobile units providing health screening services must adhere to certain requirements and guidelines. These requirements could include regulations related to the safety, cleanliness, and functionality of the mobile unit to ensure that it meets the necessary standards for providing health screening services.

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  • 16. 

    Basic protection by means of obstacles is intended to prevent 

    • A.

      Ordinary persons from operating equipment

    • B.

      Intentional contact with exposed parts

    • C.

      Intentional bodily approach to a live part

    • D.

      Unintentional bodily approach to a live part

    Correct Answer
    D. Unintentional bodily approach to a live part
    Explanation
    Basic protection by means of obstacles is put in place to prevent unintentional bodily approach to a live part. This means that the obstacles are meant to physically block or restrict access to the live parts of equipment, preventing people from accidentally coming into contact with them. This is an important safety measure to reduce the risk of electric shock or other injuries that could occur if someone unintentionally gets too close to a live part.

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  • 17. 

    Which of the following is a method of fault protection?

    • A.

      Electrical separation

    • B.

      Barriers or enclosures

    • C.

      Insulation of live parts

    • D.

      Placing out of reach

    Correct Answer
    A. Electrical separation
    Explanation
    Electrical separation is a method of fault protection that involves physically separating different electrical systems or components to prevent faults from spreading. This can be achieved by using barriers, enclosures, or insulation to isolate live parts and prevent contact with other parts of the system. By implementing electrical separation, the risk of faults causing damage or harm to other components or individuals is minimized.

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  • 18. 

     The value of the external earth loop impedance Ze  can be obtained by measurement at

    • A.

      The supply point and subtracting the value of internal loop impedance (R1 + R2)

    • B.

      The furthest socket-outlet from the supply

    • C.

      The origin of supply

    • D.

      both the supply and at the furthest socket-outlet, and subtracting one result from the other

    Correct Answer
    C. The origin of supply
    Explanation
    The origin of supply refers to the point where the electrical supply enters a building or premises. In this context, obtaining the value of the external earth loop impedance at the origin of supply means measuring the impedance at the point where the electrical supply enters the building. This measurement allows for the calculation of the total impedance of the earth loop, which is the sum of the external impedance and the internal impedance (R1 + R2) of the electrical circuit.

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  • 19. 

    In a TN system, final circuits not exceeding 32A supplying fixed equipment are subject to a maximum disconnection time of

    • A.

      0.4s

    • B.

      0.8s

    • C.

      4.0s

    • D.

      5.0s

    Correct Answer
    A. 0.4s
    Explanation
    In a TN system, final circuits not exceeding 32A supplying fixed equipment are subject to a maximum disconnection time of 0.4s. This means that if there is a fault or overload in the circuit, the disconnection time should not exceed 0.4s in order to quickly isolate the faulty equipment and prevent any potential damage or hazards. This ensures the safety and efficiency of the electrical system.

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  • 20. 

    The temperature limit for metalic equipment which is intended to be touched but not hand-held is

    • A.

      30 degrees Celsius

    • B.

      55 degrees Celsius

    • C.

      65 degrees Celsius

    • D.

      70 degrees Celsius

    Correct Answer
    D. 70 degrees Celsius
    Explanation
    Metallic equipment that is intended to be touched but not hand-held may include items such as metal surfaces, handles, or knobs. These objects are typically found in various settings like kitchens, laboratories, or industrial environments. The temperature limit of 70 degrees Celsius indicates that the equipment can be heated up to this point without causing discomfort or harm to the user. This temperature threshold ensures that the equipment remains safe to touch and minimizes the risk of burns or injuries.

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  • 21. 

    Overload current is defined as an overcurrent

    • A.

      Due to low insulation resistance

    • B.

      In a circuit which is electrically sound

    • C.

      Due to a fault of negligible impedance

    • D.

      In a line conductor in contact with earth

    Correct Answer
    B. In a circuit which is electrically sound
    Explanation
    Overload current is defined as an overcurrent in a circuit which is electrically sound. This means that the current flowing through the circuit exceeds the normal operating current, but there are no faults or issues with the circuit itself. It could be caused by an excessive load being connected to the circuit or by a malfunctioning device drawing more current than it should. In any case, the circuit is still functioning properly and there are no faults or low insulation resistance causing the overcurrent.

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  • 22. 

    The prospective fault current at the origin of a single-phase installation is the greater of the prospective

    • A.

      Maximum demand and diversity value

    • B.

      Short circuit and overload current

    • C.

      Design current and distributor’s main fuse

    • D.

      Short circuit and earth fault currents

    Correct Answer
    D. Short circuit and earth fault currents
    Explanation
    The prospective fault current at the origin of a single-phase installation is determined by the short circuit and earth fault currents. These currents represent the maximum potential flow of electricity in the event of a fault or abnormal condition in the electrical system. By considering both the short circuit and earth fault currents, the installation can be designed to handle the highest possible fault current, ensuring the safety and reliability of the electrical system.

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  • 23. 

    To meet the requirements of BS 7671, all overcurrent devices without upstream backup protection must

    • A.

      Be rated lower than the design current

    • B.

      Meet the requirements of BS 7846

    • C.

      Be able to withstand the prospective fault current

    • D.

      Not operate due to a line to earth fault

    Correct Answer
    C. Be able to withstand the prospective fault current
    Explanation
    In order to comply with the requirements of BS 7671, all overcurrent devices without upstream backup protection must be able to withstand the prospective fault current. This means that these devices should be able to handle the maximum amount of current that could flow through them during a fault condition without being damaged or tripping. This ensures the safety and reliability of the electrical system, as the overcurrent devices can effectively protect against excessive current flow and prevent damage or hazards.

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  • 24. 

    Which of the following devices can not be used for emergency switching?

    • A.

      A push-button controlling an all-pole contactor

    • B.

      A manually operated switch

    • C.

      A circuit-breaker

    • D.

      A luminaire support coupler

    Correct Answer
    D. A luminaire support coupler
    Explanation
    A luminaire support coupler is a device used to connect and support light fixtures. It is not designed or intended for emergency switching purposes. It does not have the capability to control or interrupt electrical circuits in emergency situations. Therefore, it cannot be used for emergency switching.

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  • 25. 

    Which of the following arrangements of a firefighter’s switch controlling a discharge lighting installation would comply with BS 7671?

    • A.

      Switch with off position at the bottom and mounted at 2.75m from the ground

    • B.

      Switch with off position at the top and mounted at 3.75m from the ground

    • C.

      Switch with off position at the bottom and mounted at 3.75m from the ground

    • D.

      Switch with off position at the top and mounted at 2.75m from the ground

    Correct Answer
    D. Switch with off position at the top and mounted at 2.75m from the ground
    Explanation
    The correct answer is "switch with off position at the top and mounted at 2.75m from the ground." This arrangement complies with BS 7671 because it follows the standard practice of having the off position at the top, which is the most common and easily identifiable position for a switch. Additionally, mounting the switch at 2.75m from the ground ensures that it is easily accessible and within reach for operation.

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  • 26. 

    Where overvoltage protection is to be provided in a household appliance, the minimum impulse withstand voltage for Category II equipment would be

    • A.

      1.5kV

    • B.

      2.5kV

    • C.

      4.0kV

    • D.

      6.0kV

    Correct Answer
    B. 2.5kV
    Explanation
    In household appliances, overvoltage protection is necessary to safeguard against electrical surges. Category II equipment refers to appliances that are directly connected to the mains supply. The minimum impulse withstand voltage for Category II equipment would be 2.5kV. This means that the appliance is designed to endure a surge of up to 2.5kV without any damage or malfunction. Hence, 2.5kV is the correct answer for providing overvoltage protection in Category II household appliances.

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  • 27. 

    In locations with risk of fire due to the nature of processed or stored materials (conditions BE2), a wiring system which requires protection by a suitably rated RCD is

    • A.

      Overhead busbar trunking

    • B.

      Powertrack systems

    • C.

      90 degrees Celsius thermosetting cables

    • D.

      MICC cables

    Correct Answer
    C. 90 degrees Celsius thermosetting cables
    Explanation
    In locations with a risk of fire due to the nature of processed or stored materials, a wiring system that requires protection by a suitably rated RCD is 90 degrees Celsius thermosetting cables. This is because thermosetting cables have a higher temperature rating compared to other types of cables, making them more resistant to heat and less likely to cause a fire. Therefore, using 90 degrees Celsius thermosetting cables can help mitigate the risk of fire in such locations.

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  • 28. 

    Which of the following external influences would likely require an increase in the current rating of cables above that normally required?

    • A.

      Exposure to flooding

    • B.

      An ambient temperature below 0 degrees Celsius

    • C.

      Exposure to mechanical damage

    • D.

      An ambient temperature of 40 degrees Celsius

    Correct Answer
    D. An ambient temperature of 40 degrees Celsius
    Explanation
    Exposure to an ambient temperature of 40 degrees Celsius would likely require an increase in the current rating of cables above that normally required. This is because high temperatures can cause cables to overheat and potentially lead to insulation degradation or failure. Increasing the current rating of the cables would allow them to handle the higher temperatures and prevent any damage or safety hazards.

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  • 29. 

    Precautions must be taken against the spread of flammable liquid from electrical equipment such as a transformer, if the liquid is

    • A.

      Less than 25 litres in capacity

    • B.

      Of a type where combustion produces smoke and gas

    • C.

      Of quantity 25 litres and above

    • D.

      In a location under supervision of instructed persons

    Correct Answer
    C. Of quantity 25 litres and above
    Explanation
    The correct answer is "of quantity 25 litres and above." This is because the question is discussing precautions that need to be taken against the spread of flammable liquid from electrical equipment such as a transformer. The question states that if the liquid is less than 25 litres in capacity, precautions must be taken. However, if the liquid is of a quantity 25 litres and above, it implies that additional precautions need to be taken due to the larger quantity of flammable liquid.

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  • 30. 

    The symbol used to denote the rating or setting of a protective device is

    • A.

      I2

    • B.

      In

    • C.

      Ib

    • D.

      Iz

    Correct Answer
    B. In
    Explanation
    The symbol "In" is used to denote the rating or setting of a protective device.

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  • 31. 

    For 5-core flexible cables in three-phase four wire systems, the alphanumeric marking of conductors as L1, L2,  L3 and N would correspond to the following conductor colour identification in accordance with BS 7671 

    • A.

      Brown, black, black, blue

    • B.

      Black, brown, grey, blue

    • C.

      Brown, black, grey, blue

    • D.

      Brown, blue, grey, black

    Correct Answer
    C. Brown, black, grey, blue
    Explanation
    The alphanumeric marking of conductors L1, L2, L3, and N corresponds to the following conductor color identification: brown for L1, black for L2, grey for L3, and blue for N. This is in accordance with BS 7671.

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  • 32. 

    At which of the following protective conductor terminations would a warning notice not need to be fixed

    • A.

      An earth electrode

    • B.

      A connection to exposed structural metalwork

    • C.

      A gas service metal pipe

    • D.

      Main earthing terminal in a distribution board

    Correct Answer
    D. Main earthing terminal in a distribution board
    Explanation
    A warning notice would not need to be fixed at the main earthing terminal in a distribution board because it is a standard and expected component of the electrical system. The main earthing terminal is designed to provide a safe path for electrical faults to be directed to the earth, preventing the risk of electric shock. Therefore, there is no need for a warning notice as it is already understood that this is an essential part of the system.

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  • 33. 

    A device capable of making and breaking load current and automatically breaking fault current is a

    • A.

      BS 88-2 fuse

    • B.

      Residual current device to BS EN 61008

    • C.

      Circuit-breaker

    • D.

      Disconnector

    Correct Answer
    C. Circuit-breaker
    Explanation
    A circuit-breaker is a device that can control the flow of current in an electrical circuit. It can make and break the load current, meaning it can allow or interrupt the flow of electricity to the load. Additionally, it is designed to automatically break fault current, which is an abnormal current that occurs when there is a short circuit or overload in the circuit. Therefore, a circuit-breaker is capable of both making and breaking load current, as well as automatically breaking fault current.

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  • 34. 

    Extraneous-conductive-parts require protective equipotential bonding to ensure that

    • A.

      The exposed parts are isolated from earth

    • B.

      No dangerous potential difference can occur

    • C.

      Utility pipes can be used as earth electrodes

    • D.

      No connection with a cpc is required

    Correct Answer
    B. No dangerous potential difference can occur
    Explanation
    Extraneous-conductive parts refer to any conductive objects or surfaces that are not intended to carry electrical current but can become energized due to faults or other electrical issues. These parts can pose a safety hazard if a dangerous potential difference occurs between them and other objects or the ground. Protective equipotential bonding ensures that all extraneous-conductive parts are at the same potential, preventing any potential difference and reducing the risk of electric shock or other accidents. Therefore, the correct answer is that protective equipotential bonding is necessary to ensure that no dangerous potential difference can occur.

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  • 35. 

    Where the supply to a caravan park is PME, a TT system of earthing must be used in the supply to

    • A.

      Underground cables

    • B.

      Pitch socket-outlets

    • C.

      Lighting circuits

    • D.

      Instantaneous water heaters

    Correct Answer
    B. Pitch socket-outlets
    Explanation
    In a caravan park where the supply is PME (Protective Multiple Earthing), a TT system of earthing must be used in the supply to pitch socket-outlets. This is because a TT system provides a separate earth connection for each socket-outlet, ensuring safety and reducing the risk of electric shock. By using a TT system, any faults or leakage currents can be detected and isolated, protecting both the users of the socket-outlets and the electrical equipment connected to them. Therefore, it is necessary to use a TT system for the supply to pitch socket-outlets in a caravan park with PME supply.

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  • 36. 

    Except where PME conditions apply, main protective bonding conductors shall have a cross-sectional area not less than

    • A.

      Half the c.s.a. of the earthing conductor of the installation subject to a minimum of 6.0mm2

    • B.

      The c.s.a. of the earthing conductor of the installation subject to a minimum of 6.0mm2

    • C.

      Twice the c.s.a. of the earthing conductor

    • D.

      Half the c.s.a. of the earthing conductor of the installation subject to a minimum of 10.0mm2

    Correct Answer
    A. Half the c.s.a. of the earthing conductor of the installation subject to a minimum of 6.0mm2
    Explanation
    Main protective bonding conductors must have a cross-sectional area that is at least half the cross-sectional area of the earthing conductor of the installation. However, there is also a minimum requirement of 6.0mm2, meaning that the cross-sectional area of the main protective bonding conductor cannot be less than 6.0mm2, even if half the c.s.a. of the earthing conductor is smaller than that.

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  • 37. 

    When using a Class II electric drill outdoors, BS 7671 requires that

    • A.

      The earth loop impedance at the drill is not less than that shown in Table 41.1

    • B.

      It is supplied from a BS EN 60898 protected socket-outlet

    • C.

      An earth connection is made to the drill casing

    • D.

      It is supplied from an RCD protected socket-outlet

    Correct Answer
    D. It is supplied from an RCD protected socket-outlet
    Explanation
    The correct answer is "it is supplied from an RCD protected socket-outlet." This is because BS 7671 requires that Class II electric drills used outdoors be supplied from an RCD (Residual Current Device) protected socket-outlet. An RCD is a safety device that quickly switches off the electricity supply if it detects an imbalance in the electric current, which can occur if there is a fault or if someone accidentally touches a live wire. This helps to protect against electric shock and reduce the risk of injury.

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  • 38. 

    A 13A socket outlet in a garage of a domestic dwelling must have the following

    • A.

      Basic protection, fault protection and RCD protection not exceeding 30mA

    • B.

      Protection by a 30mA RCBO

    • C.

      Basic protection and additional protection

    • D.

      Ingress protection to IP56

    Correct Answer
    A. Basic protection, fault protection and RCD protection not exceeding 30mA
    Explanation
    The correct answer is basic protection, fault protection, and RCD protection not exceeding 30mA. This means that the 13A socket outlet in the garage must have measures in place to protect against basic electrical hazards, such as insulation failure or overloading, as well as fault protection to prevent electric shocks in case of a fault. Additionally, it must have RCD (Residual Current Device) protection not exceeding 30mA, which detects and rapidly shuts off the power supply in case of a leakage current, preventing serious electric shocks.

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  • 39. 

    Socket-outlets supplying 230V equipment used in the garden must be protected by a residual current device.  This device is fitted because the equipment is being used 

    • A.

      Within the equipotential zone and requires additional protection

    • B.

      Where the earth loop impedance Zs can not be determined

    • C.

      Where the overload tripping time exceeds 5 seconds

    • D.

      Outside the equipotential zone and requires additional protection

    Correct Answer
    D. Outside the equipotential zone and requires additional protection
    Explanation
    The correct answer is "outside the equipotential zone and requires additional protection." This is because the question states that the equipment is being used in the garden, which is considered to be outside the equipotential zone. The equipotential zone is an area where all exposed conductive parts are at the same potential, reducing the risk of electric shock. Since the equipment is not within this zone, it requires additional protection, which is provided by a residual current device.

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  • 40. 

    Starters incorporating overload protection must be provided for electric motors with a rating exceeding

    • A.

      3.7W

    • B.

      37W

    • C.

      0.37kW

    • D.

      3.7kW

    Correct Answer
    C. 0.37kW
    Explanation
    Electric motors with a rating exceeding 0.37kW require starters incorporating overload protection. This means that motors with a power rating higher than 0.37kW need a starter that can protect them from excessive current and prevent damage to the motor. Starters with overload protection are designed to monitor the current flowing through the motor and trip the circuit if it exceeds a certain limit, thus protecting the motor from overheating and potential burnout. Therefore, the correct answer is 0.37kW.

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  • 41. 

    The circuit of a safety service should be

    • A.

      Coloured red

    • B.

      Independent of any other circuit

    • C.

      Housed in compartmentalised trunking

    • D.

      Unprotected

    Correct Answer
    B. Independent of any other circuit
    Explanation
    A safety service circuit should be independent of any other circuit to ensure its reliability and functionality. This means that it should not be connected or reliant on any other electrical circuit in the system. This independence allows the safety service circuit to operate autonomously and without any interference or dependence on other circuits. By being independent, the safety service circuit can provide uninterrupted power and protection in case of emergencies or faults in other circuits.

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  • 42. 

    Where an installation and generator are not permanently fixed, every circuit must be protected by a residual current device with a maximum I∆n rating of

    • A.

      10mA

    • B.

      30mA

    • C.

      100mA

    • D.

      500mA

    Correct Answer
    B. 30mA
    Explanation
    In installations where the installation and generator are not permanently fixed, it is necessary to protect every circuit with a residual current device (RCD). The RCD is designed to detect any imbalance in the electrical current flowing through the circuit, which could indicate a fault or leakage to earth. The maximum I∆n rating of the RCD refers to the maximum level of leakage current that the device can detect and respond to. In this case, the correct answer is 30mA, meaning that the RCD will trip and disconnect the circuit if the leakage current exceeds 30mA, providing an effective level of protection against electrical hazards.

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  • 43. 

    In Zone 1 of a bathroom, the following fixed equipment may not be installed

    • A.

      Whirlpool units

    • B.

      Towel rails

    • C.

      Shaver supply units

    • D.

      luminaires

    Correct Answer
    C. Shaver supply units
    Explanation
    Shaver supply units may not be installed in Zone 1 of a bathroom because this zone is considered the most hazardous in terms of electrical safety. Zone 1 is the area directly above the bath or shower, up to a height of 2.25 meters. Since shaver supply units are electrical devices, they pose a risk of electric shock if they come into contact with water. Therefore, for safety reasons, it is prohibited to install shaver supply units in this zone to prevent any potential accidents or electrical hazards.

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  • 44. 

    The correct temperature rating of the insulating material for flexible cables installed in a hot air sauna is?

    • A.

      60 degrees Celsius

    • B.

      105 degrees Celsius

    • C.

      90 degrees Celsius

    • D.

      170 degrees Celsius

    Correct Answer
    D. 170 degrees Celsius
    Explanation
    The correct temperature rating of the insulating material for flexible cables installed in a hot air sauna is 170 degrees Celsius. This high temperature rating is necessary because saunas typically have high temperatures and humidity levels. Using an insulating material with a lower temperature rating could result in the insulation melting or deteriorating, leading to potential safety hazards or damage to the cables. Therefore, a temperature rating of 170 degrees Celsius ensures that the insulating material can withstand the extreme heat and humidity conditions inside a sauna.

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  • 45. 

    A reduced low-voltage supply is strongly preferred on a construction site to supply portable equipment with a loading less than

    • A.

      0.375kW

    • B.

      1.0kW

    • C.

      2.0kW

    • D.

      3.75kW

    Correct Answer
    C. 2.0kW
    Explanation
    A reduced low-voltage supply is strongly preferred on a construction site to supply portable equipment with a loading less than 2.0kW because it allows for a more efficient and cost-effective power supply. By reducing the voltage, the electrical current required to power the equipment is also reduced, resulting in lower energy consumption and reduced costs. Additionally, a lower voltage supply is safer for portable equipment as it reduces the risk of electrical hazards and equipment damage.

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  • 46. 

    In agricultural premises, a residual current device is required for protection against fire.  The RCD operating current must not exceed

    • A.

      30mA

    • B.

      150mA

    • C.

      300mA

    • D.

      500mA

    Correct Answer
    C. 300mA
    Explanation
    A residual current device (RCD) is a safety device that protects against electrical fires by detecting imbalances in the electrical current. It works by continuously monitoring the flow of electricity and instantly cutting off the power if it detects any leakage or imbalance. The operating current of the RCD determines the threshold at which it will trip and cut off the power. In this case, the correct answer is 300mA, meaning that the RCD will trip and cut off the power if it detects a current leakage or imbalance of 300mA or higher, providing protection against potential fire hazards in agricultural premises.

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  • 47. 

    The main wiring installed in a frequently used touring caravan should preferably be inspected and tested at intervals not exceeding

    • A.

      1 year

    • B.

      3 years

    • C.

      5 years

    • D.

      Change of owner

    Correct Answer
    A. 1 year
    Explanation
    The main wiring installed in a frequently used touring caravan should preferably be inspected and tested at intervals not exceeding 1 year. This is because frequent use of the caravan can lead to wear and tear on the wiring, increasing the risk of electrical faults and potential hazards. Regular inspections and testing ensure that any issues can be identified and addressed promptly, reducing the risk of accidents or damage to the caravan. By conducting these inspections annually, caravan owners can maintain the safety and functionality of their electrical system.

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  • 48. 

    The maximum disconnection time for circuits supplying fixed equipment used in highway power supplies is

    • A.

      0.1s

    • B.

      0.4s

    • C.

      0.5s

    • D.

      5.0s

    Correct Answer
    D. 5.0s
    Explanation
    The maximum disconnection time for circuits supplying fixed equipment used in highway power supplies is 5.0s. This means that in the event of a fault or overload, the circuit supplying power to the equipment should disconnect within 5.0 seconds to ensure the safety of the equipment and prevent any further damage or hazards.

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  • 49. 

    Where a protective conductor current is likely to be 15mA in a ring final circuit, it must be provided with

    • A.

      Protective conductors of minimum csa 2.5mm2

    • B.

      A high integrity protective conductor connection

    • C.

      Connection to the supply via a PME facility

    • D.

      Connection via socket-outlets to BS EN 60309

    Correct Answer
    B. A high integrity protective conductor connection
    Explanation
    A high integrity protective conductor connection is necessary in a ring final circuit where the protective conductor current is likely to be 15mA. This type of connection ensures that the protective conductor can effectively carry fault currents and provide protection against electric shock. It is important to have a high integrity connection to ensure the safety of the electrical installation and minimize the risk of electrical hazards.

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  • 50. 

    Which of the following requirements is not part of the inspection of fixed equipment, when inspecting and testing an installation in accordance with BS 7671?

    • A.

      Presence of BS mark or certification

    • B.

      Correct selection and erection

    • C.

      No visible damage

    • D.

      Type acceptable to the electrical distributor

    Correct Answer
    D. Type acceptable to the electrical distributor
    Explanation
    The requirement that is not part of the inspection of fixed equipment, when inspecting and testing an installation in accordance with BS 7671, is "type acceptable to the electrical distributor". This means that the type of equipment being used does not need to be approved or accepted by the electrical distributor. The other requirements, such as the presence of BS mark or certification, correct selection and erection, and no visible damage, are all important factors that need to be checked during the inspection.

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  • Current Version
  • Mar 21, 2023
    Quiz Edited by
    ProProfs Editorial Team
  • Jul 29, 2011
    Quiz Created by
    Testers Direct
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