National Apartment Leasing Professional (NALP)

Correct: According to BS 7671 and standard inspection procedures, polarity verification ensures that all single-pole control and protective devices (such as fuses, circuit breakers, and switches) are connected in the line conductor only. This is critical for safety because it ensures that when the device is opened or the fuse is blown, the equipment or circuit downstream is disconnected from the live supply, preventing it from remaining at a potential relative to Earth.

Incorrect: Connecting single-pole devices in the neutral conductor is a major safety violation because the circuit remains live even when the switch is off, posing a severe shock risk. Interrupting the protective earth conductor is strictly prohibited as it would break the path for fault current, rendering protective measures like RCDs or circuit breakers ineffective. There is no regulation that allows single-pole devices in the neutral based on whether the line is fused; they must always be in the line conductor.

Takeaway: Polarity verification ensures that all single-pole protective and control devices are installed in the line conductor to prevent electric shock risks when the circuit is isolated.

Correct: BS 7671 requires that all electrical equipment be selected and erected to provide safety under the conditions of external influences likely to be encountered. If an inspector identifies equipment that does not meet the required IP rating for a specific environment (such as a laundry with steam), they must assess the severity of the risk based on the external influence codes (e.g., AD for water) and record the observation as a non-compliance in the Electrical Installation Condition Report (EICR).

Incorrect: Temporary shielding is not a recognized method of achieving compliance for permanent installations and does not address the regulatory failure. Adding an RCD provides additional protection against electric shock but does not rectify the underlying issue of equipment being unsuitable for its environment, which could lead to premature failure or fire. Manufacturer IP ratings are determined under standardized laboratory conditions and cannot be modified in the field to change the fundamental rating of the enclosure.

Takeaway: Electrical equipment must be appropriately rated for the external influences of its environment to ensure long-term safety and operational integrity.

Correct: According to BS 7671 Regulation 433.3.1, a device for protection against overload may be omitted for a conductor which is situated on the load side of a point where a change occurs in the cross-sectional area, provided that the conductor is effectively protected against overload by a protective device placed on the supply side. This ensures that the upstream device will disconnect the supply before the smaller conductor reaches a temperature that would damage its insulation.

Incorrect: The 3-meter rule mentioned in other options typically refers to the maximum distance a protective device can be moved from the point of reduction, not the criteria for total omission. Residual current devices (RCDs) are intended for fault protection or additional protection against electric shock, not for overload protection of conductors. While constant loads may reduce the likelihood of overload, the regulations specifically require either upstream protection or that the conductor is of a type not likely to carry overload current, rather than just being in a non-combustible enclosure. Transformer impedance is a factor in fault current calculations but does not satisfy the specific requirements for omitting overload protection.

Takeaway: Overload protection can be omitted at a point of conductor size reduction if the upstream protective device is already rated to protect the smaller downstream conductor.

Correct: According to BS 7671, the verification of polarity (correct connection of conductors) is essential to ensure that all single-pole protective and control devices, such as fuses and circuit breakers, are installed in the line conductor. This ensures that when a device operates or is switched off, the live parts of the circuit are disconnected from the supply, preventing the risk of electric shock during maintenance.

Incorrect: Connecting the neutral and protective conductors at a socket-outlet is a wiring fault that bypasses safety protocols. Transposing phase and neutral conductors at the intake is a dangerous error that would result in the entire installation being live even when switched off. Disconnecting the earth conductor is a procedural step for specific tests like insulation resistance but does not constitute the requirement for verifying the correct connection of conductors.

Takeaway: Polarity verification ensures that all single-pole switching and protective devices are correctly placed in the line conductor to maintain electrical safety and isolation integrity.

Correct: According to Section 536 of BS 7671, selectivity (formerly known as discrimination) is achieved when the protective device closest to the fault operates to clear the fault without affecting the upstream devices. This requires the time-current characteristics of the devices to be coordinated such that the downstream device’s total operating time is less than the upstream device’s pre-arcing or minimum tripping time for any given value of fault current.

Incorrect: Option B is incorrect because breaking capacity refers to the maximum fault current a device can safely interrupt, not how it coordinates with other devices. Option C is incorrect because mixing device types like semi-enclosed fuses and circuit breakers does not inherently guarantee selectivity; coordination must be verified using manufacturer data. Option D is incorrect because selectivity applies to all types of protective devices in series, including overcurrent devices (fuses/MCBs), not just RCD/MCB combinations.

Takeaway: Selectivity requires the downstream device to clear a fault entirely before the upstream device begins its disconnection process to prevent unnecessary power outages.

Correct: According to BS 7671 Part 2, an exposed-conductive-part is defined as a conductive part of equipment which can be touched and which is not normally live, but which can become live under fault conditions. A metal enclosure of electrical equipment fits this definition perfectly as it is part of the electrical system.

Incorrect: Classifying structural steel as an exposed-conductive-part is incorrect because it is not part of the electrical equipment; it is an extraneous-conductive-part. Defining metallic trunking as an extraneous-conductive-part is incorrect because trunking is part of the electrical installation and thus falls under the definition of an exposed-conductive-part. Treating a part that cannot introduce a potential as an extraneous-conductive-part is incorrect because the definition specifically requires the part to be liable to introduce a potential, typically Earth potential; bonding parts that do not meet this criteria is unnecessary and not required by the regulations.

Takeaway: Accurate identification of conductive parts based on Part 2 definitions is essential for determining whether a part requires earthing or protective bonding to ensure electrical safety.

Correct: Regulation 421.1.201 of BS 7671 states that within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with the relevant product standard and have their enclosure made from non-combustible material, or be enclosed in a cabinet or enclosure made from non-combustible material. This requirement was introduced to ensure that any fire resulting from a loose connection or component failure within the unit is contained and does not spread to the surrounding structure.

Incorrect: The requirement for IP4X and IP2X ratings relates to protection against the ingress of solid objects and is not the primary fire protection requirement for domestic consumer unit enclosures. While Arc Fault Detection Devices (AFDDs) are required for certain high-risk locations and recommended for others under Section 421, they are a method of circuit protection and do not negate the physical construction requirement for non-combustible enclosures. Intumescent paint is not a recognized substitute for the non-combustible material requirement specified in the regulations for these assemblies.

Takeaway: Consumer units in domestic premises must be constructed from or housed within non-combustible materials to prevent the spread of fire originating within the assembly.

Correct: Protective equipotential bonding is a fundamental safety principle under BS 7671 Section 411. Its purpose is to connect extraneous-conductive-parts (metallic parts that are not part of the electrical installation but can introduce a potential, such as gas pipes or metal trays) to the main earthing terminal. This ensures that during a fault, the potential difference between any simultaneously accessible conductive parts is minimized, thereby preventing a dangerous touch voltage from occurring across a person’s body.

Incorrect: Providing a low-resistance path to ensure the operation of overcurrent devices describes the function of the circuit protective conductor (CPC) for exposed-conductive-parts, rather than the bonding of extraneous-conductive-parts. Increasing the resistance of the fault loop path is incorrect as safety relies on low impedance to facilitate disconnection or minimize potential differences. Diverting leakage current to a lightning protection system is not the objective of equipotential bonding and does not address the risk of touch voltage between conductive parts.

Takeaway: Protective equipotential bonding is used to minimize the potential difference between simultaneously accessible conductive parts to prevent electric shock during a fault.

Correct: According to Regulation 543.2.4 of BS 7671, when the metal enclosure or frame of a wiring system is used as a protective conductor, its electrical continuity must be assured and it must be protected against deterioration. This ensures that the fault path remains reliable over the life of the installation without relying on supplementary conductors if the enclosure itself meets the required cross-sectional area.

Incorrect: Supplementing with a 4.0mm squared conductor is not a regulatory requirement if the trunking itself provides the necessary cross-sectional area. While the adiabatic equation is one method for sizing, Regulation 543.1.1 also allows for the use of Table 54.7, so it is not the exclusive method. External flexible links are a common site practice to ensure continuity, but they are not a mandatory requirement under Section 543 if the mechanical joints themselves are verified as electrically and mechanically sound.

Takeaway: Metallic enclosures used as protective conductors must maintain permanent and reliable electrical continuity through robust mechanical joints and protection against corrosion.

Correct: According to Regulation 544.1.1 and Table 54.8 of BS 7671, for a TN-C-S (PME) supply, the main protective bonding conductor must be sized based on the neutral conductor of the supply. For a copper equivalent neutral conductor greater than 95mm2 but not exceeding 150mm2, the minimum cross-sectional area for the bonding conductor is 35mm2.