Assessment of General Characteristics

What is the first step in assessing general characteristics according to BS 7671?

• AInstalling protection devices
• BDetermining the purpose of the supply and intended use✓
• CTesting the installation
• DSelecting cables

Answer: The purpose, loads, and intended use must be determined before design decisions can be made.

What does 'external influences' assessment include?

• AThe phase rotation only
• BCable color selection
• CEnvironmental conditions, mechanical hazards, and human factors✓
• DVoltage only

Answer: External influences assessment covers temperature, humidity, corrosive atmosphere, mechanical damage risk, and other environmental factors.

In BS 7671, what is meant by 'compatibility'?

• AMatching cable colors
• BThe ability to use different manufacturers' equipment
• CThe suitability of equipment and protective devices to work safely together✓
• DUsing the same gauge throughout

Answer: Compatibility ensures that all components of an installation work together safely and effectively.

What aspect of maintainability must be considered during design?

• ACost of maintenance only
• BWarranty duration
• CSupplier availability
• DEase of inspection, testing, and repair✓

Answer: An installation must be designed to allow safe and practical maintenance, inspection, and testing.

How should an installation be designed regarding accessibility?

• AAll components must be visible at all times, so no accessory may be concealed in a wall or ceiling void
• BEverything must sit below shoulder height, with BS 7671 fixing a maximum mounting height of 1.2m for accessories
• CEquipment must be on the ground, with distribution boards mounted no higher than 300mm above floor level
• DAccess should allow safe operation, inspection, and maintenance✓

Answer: Design must ensure that components are accessible for safe operation, inspection, maintenance, and testing.

What is a key consideration when assessing the electrical demand of an installation?

• AThe type of flooring
• BThe maximum simultaneous load demand✓
• CThe building age only, since properties built before 1966 are assessed at half the calculated demand
• DThe number of rooms only, allowing 3kW per room to be assumed whatever equipment is actually installed

Answer: Maximum simultaneous demand must be determined to correctly size cables, protective devices, and the supply.

In assessing general characteristics, what is 'diversity'?

• AThe probability that not all loads operate simultaneously at full capacity✓
• BUsing different types of cables
• CHaving multiple suppliers
• DThe number of circuits

Answer: Diversity accounts for the fact that not all loads typically operate at maximum simultaneously.

What must be established regarding the continuity of supply?

• AAll supplies are equal, so nothing in particular need be established
• BWhether backup power is available
• CWhether the installation has a UPS only, since standby generators fall outside the scope of BS 7671
• DWhat level of supply continuity is required for critical functions✓

Answer: The required level of supply continuity must be determined for different parts of the installation.

How should an installation be assessed for safety systems?

• AAssess the main switch only
• BIgnore electrical safety systems
• COnly examine fire alarms
• DReview all safety-critical systems and their electrical requirements✓

Answer: Safety systems such as emergency lighting, fire alarms, and emergency shutdown systems must be assessed.

What is the significance of assessing 'special requirements' in BS 7671?

• AIs optional
• BOnly applies to industrial sites, since domestic bathrooms and pools are covered by the Building Regulations instead
• CIdentifies areas needing enhanced protection (bathrooms, swimming pools, etc.)✓
• DApplies to colour coding only, so the assessment need record no more than which manufacturer's sleeving was used

Answer: Special requirements are assessed to identify areas like bathrooms and hazardous zones needing additional protection.

When assessing general characteristics, why is earthing system type critical?

• AIt affects the choice of protective devices and bonding requirements✓
• BIt has no impact on design
• CIt determines conductor colour, which is the only design choice still open once the supply has been connected
• DIt only matters for three-phase systems, since single-phase installations are all treated as TN-C-S by default

Answer: The earthing system type determines RCD requirements, bonding conductor sizing, and protective device coordination.

What should be documented during the assessment of general characteristics?

• AThe designer's name and date only, with the load and earthing assessments recorded on the Schedule of Test Results
• BOnly the cable sizes
• CAll design decisions, assumptions, and assessment outcomes✓
• DVerbal agreements suffice, provided the installer signs the Electrical Installation Certificate afterwards

Answer: All assessments and design decisions must be documented for traceability and future reference.

How does BS 7671 address installations in corrosive environments?

• AIgnores environmental factors, leaving corrosion protection entirely to the equipment manufacturer's warranty terms
• BOnly applies in coastal areas, defined as anywhere within 5km of the mean high water mark of the open sea
• CProhibits all installations
• DRequires selection of equipment with appropriate corrosion resistance✓

Answer: Equipment must be selected to withstand the external influences of the environment, including corrosion risks.

What is meant by 'assessment of human competence' in design?

• AEnsuring the designer has appropriate training and knowledge✓
• BThe designer must be over 21 years old and hold a current driving licence before signing off any design
• COnly qualified supervisors may assess competence, and they must be employed by the same firm as the designer
• DTesting the electrician's ability to calculate voltage drop, which BS 7671 requires to be re-examined every 12 months

Answer: The person designing the installation must have appropriate knowledge and competence for the work.

In BS 7671 Appendix 5, external influences are classified using a two-letter-plus-number coding format. What does the code 'AD4' denote?

• AConstruction materials that are combustible
• BCapability of persons who are unskilled or unsupervised, which Appendix 5 records using the letters AD
• CPresence of water - splashes, requiring equipment with a minimum protection rating of IPX4✓
• DAmbient temperature exceeding 40 degrees Celsius, which Appendix 5 records under the code AD rather than AA

Answer: BS 7671 Appendix 5 classifies external influences with a two-letter-plus-number code: the first letter denotes the category (A = Environment, B = Utilisation, C = Construction of buildings), the second letter the specific condition, and the number the severity or class. AD4 falls under 'AD' (presence of water) and denotes splashes, requiring equipment rated at least IPX4. There is no single blanket 'EI' code in BS 7671 - every external influence has its own specific two-letter-plus-number designation.

What is the importance of assessing the electrical potential of earthing conductors?

• ATo determine wire color
• BTo ensure safe potential distribution and RCD coordination✓
• CTo measure voltage drop only
• DThe matter is unimportant

Answer: Assessment of earthing potential is vital for protection coordination and prevention of excessive touch voltages.

How should installations in high-temperature environments be assessed?

• AInstall larger cables regardless, taking the next size up from the tabulated value without applying any correction factor
• BTemperature does not affect electrical installations, since the tabulated ratings in Appendix 4 already assume 55°C
• CSelect equipment rated for elevated temperatures and derating cable ampacities✓
• DUse standard equipment only, because BS 7671 applies correction factors solely to cables buried in the ground

Answer: High temperatures reduce cable current-carrying capacity and require equipment rated for those conditions.

What must be assessed regarding load changes over time?

• AFuture expansion possibilities and load growth✓
• BThe load can never change
• CLoad assessment is not necessary
• DOnly the current load

Answer: Installations should be assessed for likely future load growth to accommodate expansion.

How does BS 7671 Part 2 distinguish a 'skilled person' (electrically) from an 'instructed person' (electrically)?

• AAn instructed person has the technical knowledge to avoid electrical dangers unsupervised; a skilled person must always work under an instructed person's supervision, and BS 7671 requires both roles to be re-assessed by the Health and Safety Executive every three years
• BBoth terms mean the same thing: any person over 18 who has received basic electrical safety training
• CA skilled person is defined only by holding a formal electrical qualification; an instructed person is anyone without any qualification, regardless of training
• DA skilled person has the technical knowledge or experience to avoid the dangers electricity may create; an instructed person is adequately advised or supervised by a skilled person but lacks that full technical knowledge✓

Answer: BS 7671 Part 2 defines a 'skilled person (electrically)' as someone with the technical knowledge and/or sufficient experience to enable them to perceive risks and avoid the dangers electricity can create. An 'instructed person (electrically)' is adequately advised or supervised by a skilled person, enabling them to avoid those dangers, but does not hold the same depth of technical knowledge themselves.

What aspect of power quality must be assessed?

• AThe color of wiring
• BVoltage variations, harmonics, and frequency stability✓
• CPower quality is not relevant
• DOnly peak voltage

Answer: Power quality issues like harmonic distortion and voltage variations must be assessed for equipment selection.

How should installations in wet environments be assessed?

• AWet environments cannot have electrical installations, so a bathroom may be supplied only by an extra-low-voltage transformer sited outdoors
• BUse normal equipment
• CAssessment is not required, because IP-rated enclosures are fitted as standard to every accessory sold in the UK
• DSelect equipment with enhanced protection against moisture ingress✓

Answer: Wet environments require assessment of moisture effects and selection of appropriately rated equipment.

What is the purpose of assessing 'control requirements'?

• ASelecting switch colors
• BEnsuring safe and effective control of electrical loads✓
• CDetermining cable routing only
• DControl requirements do not need assessment, as isolation is provided by the main switch in every case

Answer: Control requirements must be assessed to ensure equipment can be safely controlled and isolated.

In the context of assessment, what is 'expansion capability'?

• AThe ability to increase the supply voltage from 230V to 400V by re-connecting the busbar in the consumer unit
• BProvision of space and capacity for future additional circuits✓
• CAn invalid consideration, since BS 7671 forbids spare ways being left in a distribution board
• DOnly applies to temporary installations such as construction sites, which are exempt from Chapter 13

Answer: Installations should allow for future circuit additions without major redesign.

How does BS 7671 address the assessment of emergency systems?

• AOnly fire alarms need assessment
• BA battery-inverter alternative supply in the building removes the need for any special assessment
• CEmergency systems are not electrical, so they are assessed under the fire risk assessment rather than the design
• DEmergency lighting and exit routes must be assessed separately✓

Answer: Emergency systems including lighting, alarms, and shutdown systems must be specifically assessed.

What must be considered when assessing installations subject to vibration?

• ASound level only
• BMechanical stress on components and potential for loosening of connections✓
• CVibration does not affect electrical installations, since all terminals are secured with spring washers as standard
• DOnly applies to machines, so fixed wiring in the same building may be clipped direct without extra support

Answer: Vibration can cause connection loosening and mechanical stress, requiring appropriate installation methods.