Scope & Definitions

What is the primary scope of BS 7671:2018+A4:2026?

• ADesign of electrical systems only, with installation and inspection covered separately by Building Regulations Part L
• BRequirements for safety of persons and property from electrical hazards✓
• CTesting of electrical equipment only, since design and installation rules are set out solely in the Electricity at Work Regulations 1989
• DInstallation of renewable energy systems only, with all other mains wiring governed by BS 5839, the fire detection standard

Answer: BS 7671 establishes the requirements for the design, installation, inspection and testing of electrical installations to protect against electrical hazards.

Which of the following is NOT a voltage band defined in BS 7671?

• AExtra low voltage (< 50V AC)
• BUltra-high voltage (> 100kV)✓
• CLow voltage (50V - 1000V AC)
• DMedium voltage (1kV - 35kV)

Answer: BS 7671 defines Extra Low Voltage, Low Voltage, and High Voltage bands. Ultra-high voltage is not a classification in this standard.

In a TN-S earthing system, what does the 'S' represent?

• ASeries resistance
• BSingle phase
• CSeparate protective conductor✓
• DSupply neutral

Answer: TN-S means the neutral and protective earth are provided by separate conductors throughout the installation.

Which earthing system uses a separate earth electrode at the installation?

• ATT✓
• BIT
• CTN-S
• DTN-C-S

Answer: TT (Terre-Terre) systems use a separate earth electrode at the installation, independent of the supply earth.

What is the purpose of a protective conductor in an electrical installation?

• ATo measure voltage drops
• BTo carry the neutral current
• CTo supply power to equipment
• DTo provide a return path for fault current✓

Answer: Protective conductors provide a return path for fault current to protect against electric shock.

In BS 7671, what is defined as an accessible conductive part?

• AAny metal part of an appliance
• BA part buried underground
• CAn insulated conductor
• DA conductive part that can be touched and is not a live part✓

Answer: An accessible conductive part is a conductive part that can be easily touched and is not normally a live part.

Which term describes the protective conductor connecting extraneous conductive parts?

• AMain protective conductor
• BSupplementary bonding conductor
• CEarth rod
• DEquipotential bonding conductor✓

Answer: Supplementary bonding conductors connect extraneous conductive parts to enhance protection against electric shock.

What does the abbreviation EICR stand for?

• AElectrical Installation Condition Report✓
• BElectrical Installation Compliance Review
• CElectrical Inspection Certification Record
• DElectrical Installation Certificate Report

Answer: EICR is the Electrical Installation Condition Report used for periodic inspection of existing installations.

In the context of BS 7671, what is an 'extraneous conductive part'?

• AAn external metal enclosure that forms part of the electrical equipment and is connected to the circuit protective conductor
• BA high-voltage conductor operating above 1000V AC that is insulated from earth along its whole length
• CA conductive part introduced from outside the installation✓
• DAn earthing electrode

Answer: An extraneous conductive part is a conductive part, not part of the electrical installation, that introduces the possibility of electric shock.

What is the voltage threshold between Extra Low Voltage (ELV) and Low Voltage (LV)?

• A30V AC
• B50V AC✓
• C40V AC
• D60V AC

Answer: The boundary between ELV and LV is 50V AC (or 120V DC for ELV/LV separation).

Which earthing system requires an RCD for all circuits?

• ATT✓
• BTN-S
• CTN-C-S
• DNone of the above

Answer: TT systems require RCD protection on all circuits because there is no metallic return path to the supply earth.

In BS 7671, what does 'basic protection' refer to?

• ASurge protection
• BProtection against electric shock during normal operation✓
• CProtection of cables from mechanical damage
• DOvercurrent protection

Answer: Basic protection (formerly called 'basic insulation') protects against contact with live parts during normal operation.

What is a 'fault protection' measure?

• AInsulation of conductors
• BProtection during normal operation, provided by basic insulation and by barriers placed around live parts
• CProtection of equipment only
• DProtection in the event of a fault condition✓

Answer: Fault protection protects against electric shock in the event of a fault, such as contact with a live part.

Which of the following is an example of an IT earthing system?

• AComputer network
• BIndustrial three-phase system with floating neutral✓
• CDomestic single-phase supply
• DTN-S residential installation

Answer: IT systems (Isolated or Impedance earthed) have no direct connection to earth, or through a high impedance.

What is the function of a TN-C-S system's protective multiple earthing (PME)?

• ATo reduce current flow
• BTo eliminate neutral current by returning it through the earth electrode at each consumer's installation
• CTo increase voltage
• DTo provide multiple earth points along the supply cable sheath✓

Answer: PME in TN-C-S systems uses multiple earth points (at pole tops, substations) to establish the reference potential.

In BS 7671, what is an 'erecting person'?

• AA person who installs equipment but takes no technical decisions, working strictly to another trade's written instructions
• BA person responsible for design and technical decisions during installation✓
• CA qualified electrician holding an NVQ Level 3, which BS 7671 requires of every person present on site
• DA supervisor only, appointed under the Electricity at Work Regulations to sign the completion certificate

Answer: An erecting person is someone competent to make technical decisions and direct the installation work.

What defines the 'working voltage' of an electrical installation?

• AThe actual voltage present during normal operation✓
• BThe maximum voltage the cables can withstand, taken as 1000V between conductors for 6491X single-core cable
• CThe voltage used for insulation resistance testing, which BS 7671 sets at 250V DC for a 230V circuit
• DThe supply voltage only, taken as 240V nominal for every single-phase installation in the United Kingdom

Answer: Working voltage is the actual voltage present in the installation during normal operation.

Which standard defines 'competent person' in relation to electrical work?

• ABS 7671 alone
• BBS 7671 and IET guidance✓
• CThe Building Regulations only
• DBS 7909 and related standards

Answer: BS 7671 works in conjunction with IET guidance and other standards to define competence requirements.

What is the main difference between TN-C and TN-C-S systems?

• AThe two are identical
• BTN-C combines neutral and protective functions throughout; TN-C-S combines only up to the building✓
• CTN-C requires RCDs, TN-C-S does not
• DTN-C is used only for three-phase supplies and TN-C-S only for single-phase, so the choice follows the number of phases

Answer: TN-C combines N and PE throughout the network; TN-C-S (PME) combines them only to the installation boundary.

In BS 7671, what is meant by 'nominal voltage'?

• AThe average voltage measured
• BThe voltage during a fault
• CThe maximum safe voltage
• DThe voltage for which the installation is designed✓

Answer: Nominal voltage is the voltage to which an installation is designed to operate.

What is the definition of a 'circuit' in BS 7671?

• AA cable run only
• BA single conductor
• CAn installation phase, meaning one of the three line conductors of a 400V supply considered on its own
• DAn assembly of electrical equipment supplied from a single point of protection✓

Answer: A circuit comprises conductors and equipment assembled to supply one or more outlets from a single protective device.

Which of the following best describes 'reinforced insulation'?

• ADouble-layer insulation with an air gap of at least 8mm maintained between the two insulating layers
• BMetallic shielding
• CSingle insulation layer of enhanced thickness and quality✓
• DEarthed conducting layer

Answer: Reinforced insulation is a single insulation system that provides the same level of protection as double insulation.

What is the purpose of defining 'influencing factors' in BS 7671?

• ATo measure voltage drop only, which BS 7671 limits to 6% on every final circuit whatever the load
• BTo assess environmental and operational conditions affecting the installation✓
• CTo determine cost, by fixing the price per point the designer must charge for each accessory installed
• DTo select circuit colours, so that a borrowed neutral can be identified by brown sleeving at each accessory

Answer: Influencing factors (external influences) must be assessed to select appropriate equipment and installation methods.

In BS 7671 terminology, what is a 'final circuit'?

• AThe supply cable
• BThe main circuit breaker at the origin, which BS 7671 requires to be rated at 100A in all domestic premises
• CThe earthing conductor running from the main earthing terminal to the consumer unit enclosure
• DA circuit with outlets for connection of equipment✓

Answer: A final circuit is the last circuit in a distribution system, serving outlets for equipment connection.

What does 'type of earthing system' classification depend on?

• AThe number of circuits in the installation, with more than six final circuits requiring a TT arrangement
• BThe voltage only
• CThe distribution network configuration and the method of earthing✓
• DThe cable size only

Answer: Earthing system type depends on how the supply is earthed and how the installation is earthed relative to the supply.