City & Guilds 2393-10 Part P Building Regulations for Electrical Installations in Dwellings — Questions and Answers

Question 1: What does BS 7671 require regarding surge protection devices (SPDs) in domestic installations?

SPDs are optional and never required
SPDs are required on every circuit
SPDs are only required in commercial installations
A risk assessment must be carried out, and SPDs installed where the consequence of an overvoltage could result in serious injury, damage to valuable equipment, or disruption of critical systems (Correct answer)

Correct answer: A risk assessment must be carried out, and SPDs installed where the consequence of an overvoltage could result in serious injury, damage to valuable equipment, or disruption of critical systems

Regulation 443.4 of BS 7671 (18th Edition) requires a risk assessment for transient overvoltages. SPDs must be installed where the consequence of overvoltage could result in serious injury or loss of human life, interruption of public services, or damage to cultural heritage, commercial or industrial installations. For dwellings, SPDs are strongly recommended and increasingly standard.

Question 2: What risk is associated with using PME earth terminals for caravan or boat hook-up?

If the PEN conductor breaks in the supply, the caravan or boat metalwork could rise to near line voltage — PME earth must not be used for caravans, boats or temporarily connected equipment (Correct answer)
PME earth is preferred for caravan hook-ups
There is no risk associated with PME for caravans
PME earth terminals always provide a better earth than a rod

Correct answer: If the PEN conductor breaks in the supply, the caravan or boat metalwork could rise to near line voltage — PME earth must not be used for caravans, boats or temporarily connected equipment

A broken PEN conductor (common in ageing networks) would cause any PME-earthed metalwork to rise to dangerous voltages. For this reason, BS 7671 prohibits using a PME terminal as the earth for caravans, boats or temporary structures.

Question 3: How often should test instruments used for electrical inspection and testing be recalibrated?

At minimum every 12 months (or as specified by the instrument manufacturer and the engineer's certification scheme) (Correct answer)
Every 5 years
Only when they are dropped or damaged
No recalibration is required for electrical test instruments

Correct answer: At minimum every 12 months (or as specified by the instrument manufacturer and the engineer's certification scheme)

BS 7671 and Competent Person scheme requirements specify that test instruments should be calibrated regularly (typically annually) to ensure measurement accuracy; the calibration certificate provides traceability of measurement.

Question 4: What is the purpose of retaining original EICs and MeIWCs for a property?

They are kept by the engineer only, not the property owner
They are only needed until the next inspection
They provide a historical record of the installation, help future inspectors understand the installation, are required for insurance and conveyancing, and support warranty and liability claims (Correct answer)
They are only needed if problems arise

Correct answer: They provide a historical record of the installation, help future inspectors understand the installation, are required for insurance and conveyancing, and support warranty and liability claims

Electrical installation certificates form part of the property's legal records; they are needed for insurance, property sales (conveyancing), future inspection and testing (as baseline data), and resolving any disputes or liability issues.

Question 5: Which document supplements BS 7671 with guidance on regulations and is commonly used alongside it?

The IET Guidance Notes (GN1–GN8) and the On-Site Guide (Correct answer)
The Electrician's Guide to the Building Regulations
The Building Regulations Approved Documents
HSE Guidance HSG85

Correct answer: The IET Guidance Notes (GN1–GN8) and the On-Site Guide

The IET Guidance Notes (GN1 to GN8) and the IET On-Site Guide provide practical guidance on complying with BS 7671 and are widely used by installers alongside the main regulations.

Question 6: What type of consumer unit is now considered best practice for new domestic installations?

A fully RCBO-equipped consumer unit (one RCBO per circuit) or a consumer unit with at least two RCDs (split-load) protecting all circuits (Correct answer)
A consumer unit with only MCBs and no RCDs
A single-RCD consumer unit with all circuits on one RCD
A rewirable fuse board with no RCDs

Correct answer: A fully RCBO-equipped consumer unit (one RCBO per circuit) or a consumer unit with at least two RCDs (split-load) protecting all circuits

Current best practice (and required by BS 7671 for additional protection) uses either a fully RCBO-fitted consumer unit or a split-load dual-RCD board; all socket outlet circuits and bath/shower circuits must have 30 mA RCD protection.

Question 7: Following the 2004 harmonisation with European cable colour standards, what colour is the line conductor in UK fixed wiring?

Blue
Red
Black
Brown (Correct answer)

Correct answer: Brown

After the 2004 harmonisation, the line conductor in UK fixed wiring changed from red to brown, matching the rest of Europe and the existing colour of the live pin on UK plugs.

Question 8: What is the advantage of a fully RCBO-equipped consumer unit over a split-load RCD unit?

Each circuit has its own RCBO so a fault or nuisance trip on one circuit only affects that circuit — all other circuits remain live (Correct answer)
RCBOs provide better overcurrent protection than MCBs
RCBOs are cheaper than MCBs combined with RCDs
A fully RCBO board requires a smaller enclosure

Correct answer: Each circuit has its own RCBO so a fault or nuisance trip on one circuit only affects that circuit — all other circuits remain live

With a dedicated RCBO per circuit, any trip only affects the single faulted circuit; a split-load RCD board can lose half the installation's circuits when one RCD trips, which can be inconvenient or dangerous (e.g., freezer loss).

Question 9: According to BS 7671, what is the maximum earth fault loop impedance (Zs) for a Type B 32A MCB to disconnect within 0.4 seconds on a 230V circuit?

2.30Ω
0.72Ω
1.15Ω
1.44Ω (Correct answer)

Correct answer: 1.44Ω

For a Type B 32A MCB to trip within 0.4 seconds, the fault current must reach 5 times the rated current (5 × 32A = 160A). Using Zs = Uo/Ia = 230/160 = 1.44Ω. This is the maximum tabulated value in BS 7671 Table 41.3. In practice, the measured value should not exceed 80% of this (1.15Ω) to account for temperature increase during fault conditions.

Question 10: What is the purpose of the neutral bar in a consumer unit with RCDs?

Neutral bars are not used in RCD consumer units
In an RCD-equipped consumer unit, each RCD has its own neutral bar for the circuits it protects — neutral conductors must be connected to the correct bar matching their circuit's RCD to ensure correct operation (Correct answer)
All neutral conductors go to a single common neutral bar regardless of RCD
Neutral conductors are connected to the earth bar

Correct answer: In an RCD-equipped consumer unit, each RCD has its own neutral bar for the circuits it protects — neutral conductors must be connected to the correct bar matching their circuit's RCD to ensure correct operation

Correct neutral grouping is critical in split-load RCD consumer units; each circuit's neutral must be connected to the neutral bar associated with its RCD, otherwise the RCD will not sense the correct residual current.

Question 11: What colour is the standard outer sheath of twin and earth cable used in UK domestic fixed wiring?

Yellow
Grey (Correct answer)
Black
White

Correct answer: Grey

Standard UK twin and earth cable has a grey PVC outer sheath, making it readily identifiable as fixed wiring cable in a domestic installation.

Question 12: What size bonding conductor is required for supplementary bonding between two extraneous-conductive-parts (e.g., two metal pipes)?

2.5mm² if mechanically protected, 4mm² if not (Correct answer)
10mm² minimum
6mm² minimum
1.0mm²

Correct answer: 2.5mm² if mechanically protected, 4mm² if not

Regulation 544.2 of BS 7671 requires supplementary bonding conductors between two extraneous-conductive-parts to be at least 2.5mm² copper if mechanically protected (e.g., enclosed in conduit or run along a pipe) or 4mm² if not mechanically protected. If connecting an exposed-conductive-part to an extraneous-conductive-part, the conductor must be at least half the CPC of the circuit.

Question 13: What is the purpose of adding circuit breaker lock-offs or CU isolators during consumer unit replacement?

To comply with Part P only
To prevent accidental re-energisation of circuits while work is in progress, ensuring safe working conditions throughout the replacement process (Correct answer)
To prevent the supply authority from restoring power
To test each circuit individually

Correct answer: To prevent accidental re-energisation of circuits while work is in progress, ensuring safe working conditions throughout the replacement process

Locking off individual MCBs or applying circuit-specific isolators prevents accidental re-energisation by others while the electrician is working on the installation, a fundamental safe working practice under Electricity at Work Regulations.

Question 14: What does a Periodic Inspection Report (PIR/EICR) code C2 signify?

Potentially dangerous — urgent remedial action required (Correct answer)
Danger present — immediate remedial action required
The installation passes with no issues
Improvement recommended — not a safety concern

Correct answer: Potentially dangerous — urgent remedial action required

Code C2 (Potentially Dangerous) indicates a fault that, while not presenting immediate danger, could become dangerous if not addressed. Urgent remedial action is required. Code C1 indicates immediate danger requiring urgent action. Code C3 indicates an improvement is recommended. Code FI means further investigation is needed.

Question 15: What type of electrical work does NOT require notification under Part P?

Consumer unit replacement
Like-for-like replacement of accessories on existing circuits in rooms other than kitchens, bathrooms or outdoors (Correct answer)
Installation of a new circuit
Any work in a bathroom

Correct answer: Like-for-like replacement of accessories on existing circuits in rooms other than kitchens, bathrooms or outdoors

Like-for-like replacement of accessories (sockets, switches, light fittings) on existing circuits in ordinary locations (not bathrooms, kitchens, outdoors) is not notifiable under Part P.

Question 16: During an earth fault loop impedance test, the measured Zs value at a 32A Type B MCB protected socket is 1.20Ω. Is this satisfactory?

Yes — any value below 2Ω is acceptable
No — the value should be below 0.5Ω for all circuits
No — the measured value must not exceed 80% of the tabulated value (1.15Ω) to allow for temperature increase (Correct answer)
Yes — it is below the tabulated maximum of 1.44Ω

Correct answer: No — the measured value must not exceed 80% of the tabulated value (1.15Ω) to allow for temperature increase

While the tabulated maximum Zs for a 32A Type B MCB is 1.44Ω, BS 7671 Regulation 411.4.5 and the IET Guidance Note 3 require that the measured value at ambient temperature must not exceed 80% of the tabulated value to account for conductor resistance increasing with temperature during a fault. 80% of 1.44Ω = 1.15Ω, so 1.20Ω fails.

Question 17: When installing an outdoor circuit for a garden shed, how should the cable route be marked to warn of its presence?

Yellow/black warning tape placed approximately 150mm above the buried cable, plus cable route marker posts at changes of direction (Correct answer)
A sign on the shed is sufficient
Paint the cable route on the ground surface
No marking is required

Correct answer: Yellow/black warning tape placed approximately 150mm above the buried cable, plus cable route marker posts at changes of direction

BS 7671 requires that buried cables are adequately identified with cable route markers. This includes yellow/black warning tape placed approximately 150mm above the cable (so it is encountered before the cable during any excavation), route marker posts or plates at key points, and documentation of the cable route on the as-built drawings or electrical installation certificate.

Question 18: A Part P registered electrician completes notifiable work. Within what timeframe must the notification be sent to the local authority?

Before work commences
Within 30 days of completion (Correct answer)
Within 7 days of completion
Within 6 months of completion

Correct answer: Within 30 days of completion

A competent person registered with an approved scheme must notify their scheme provider within 30 days of completing notifiable work. The scheme provider then notifies the local authority and arranges for the Building Regulations compliance certificate to be issued to the homeowner. Failure to notify within this timeframe is a breach of scheme rules.

Question 19: Are standard socket outlets permitted in Zone 2 of a bathroom?

Yes, if the socket has an IPX4 rating
No — socket outlets are not permitted in Zone 1 or Zone 2; only SELV shaving sockets (BS EN 61558-2-5) may be installed in Zone 2 (Correct answer)
Yes, if protected by a 30 mA RCD
Yes, for electric shavers only without restriction

Correct answer: No — socket outlets are not permitted in Zone 1 or Zone 2; only SELV shaving sockets (BS EN 61558-2-5) may be installed in Zone 2

Standard socket outlets are not permitted in Zones 0, 1 or 2 of a bathroom. Only specially designed SELV shaving units (conforming to BS EN 61558-2-5) containing an isolating transformer may be installed in Zone 2.

Question 20: What information must be provided on a circuit chart fixed inside a consumer unit?

Only the circuit numbers
Only the fuse ratings
The purpose of each circuit, its protective device rating, cable size, and RCD assignment (Correct answer)
The installer's name and date of installation only

Correct answer: The purpose of each circuit, its protective device rating, cable size, and RCD assignment

BS 7671 Regulation 514.9 requires a circuit chart (schedule of circuits) to be fixed inside or adjacent to the consumer unit, showing each circuit's purpose, cable size, protective device type and rating, and RCD assignment.

Question 21: What is a 'BS 1363' socket outlet?

The standard for outdoor IP44 socket outlets
The British Standard for the standard UK 13 A three-pin socket outlet and plug, used on domestic ring and radial circuits (Correct answer)
The British Standard for industrial CEE sockets
The standard for SELV shaving sockets

Correct answer: The British Standard for the standard UK 13 A three-pin socket outlet and plug, used on domestic ring and radial circuits

BS 1363 specifies the 13 A rectangular-pin plug and socket outlet system universally used in the UK; the design with safety shutters in the socket prevents children from inserting objects into live terminals.

Question 22: What is the purpose of an RCD test using a calibrated RCD tester?

To verify the RCD trips within the required time (40 ms for 30 mA at 5×IΔn) and at no greater than its rated residual current (IΔn) (Correct answer)
To test the mechanical operation of the trip lever only
To test the MCBs in the same group as the RCD
To measure the RCD's rated current

Correct answer: To verify the RCD trips within the required time (40 ms for 30 mA at 5×IΔn) and at no greater than its rated residual current (IΔn)

A calibrated RCD tester verifies the actual trip current and trip time of the RCD, confirming it will operate correctly at its rated sensitivity (IΔn) and within the maximum time specified by BS 7671.

Question 23: What is the purpose of the thermal (overload) element in an MCB?

To detect earth faults
To trip the MCB for sustained overload currents (typically 1.13–1.45 × In) by detecting heat from a bimetallic strip (Correct answer)
To trip the MCB instantaneously for short circuits
To limit the maximum voltage

Correct answer: To trip the MCB for sustained overload currents (typically 1.13–1.45 × In) by detecting heat from a bimetallic strip

The thermal (bimetallic) element in an MCB detects prolonged overload current by heating and bending a bimetallic strip, tripping the breaker after a time inversely proportional to the overcurrent.

Question 24: Part P applies to electrical installations in which type of building?

Only new-build properties
All buildings in England and Wales
Commercial premises only
Dwellings and their associated gardens, outbuildings and shared amenities (Correct answer)

Correct answer: Dwellings and their associated gardens, outbuildings and shared amenities

Part P of the Building Regulations applies specifically to dwellings (houses, flats, maisonettes) and their associated outbuildings, gardens, conservatories, and shared amenities in England and Wales. It does not apply to commercial premises, which are covered by other legislation such as the Electricity at Work Regulations 1989.

Question 25: What does a 'C1' classification on an EICR mean?

Improvement recommended
Further investigation required before classification
Danger present — immediate remedial action required (Correct answer)
Potential danger — urgent investigation required

Correct answer: Danger present — immediate remedial action required

A C1 (Code 1) on an EICR indicates a danger present that requires immediate action — the inspector should advise the client to take immediate action to make the installation safe.

Question 26: What is the purpose of initial verification (inspection and testing) of a new electrical installation?

To register the installation with the electricity supplier
To issue an invoice for the work
To obtain planning permission for the work
To confirm that the installation complies with BS 7671 and is safe for use before it is energised for the first time (Correct answer)

Correct answer: To confirm that the installation complies with BS 7671 and is safe for use before it is energised for the first time

Initial verification ensures a new installation complies with the design and with BS 7671, identifying any errors in construction before the installation is put into use, preventing danger to the occupier.

Question 27: What is the recommended approach if the existing main bonding conductors are found to be undersized during a CU replacement?

Leave them as they are if they are in good condition
Oversized bonding conductors are never required regardless of the supply size
Only upgrade them if the customer specifically requests it
They should be upgraded to comply with the current requirements of BS 7671 Table 54.8 as part of the consumer unit replacement work (Correct answer)

Correct answer: They should be upgraded to comply with the current requirements of BS 7671 Table 54.8 as part of the consumer unit replacement work

Upgrading undersized bonding conductors to current requirements is best practice and should be recommended or carried out as part of CU replacement; deficiencies that affect safety must be addressed.

Question 28: What is the key difference between an EIC and a MEIWC?

There is no practical difference between them
An EIC is for domestic; an MEIWC is for commercial work
An EIC is issued by the Local Authority; an MEIWC is self-issued
An EIC covers new complete or significant alterations to installations (with full schedules); an MEIWC covers minor additions/alterations to existing circuits (a simpler single document) (Correct answer)

Correct answer: An EIC covers new complete or significant alterations to installations (with full schedules); an MEIWC covers minor additions/alterations to existing circuits (a simpler single document)

An EIC with full schedules is required for new installations or significant alterations; an MEIWC is a simpler single document sufficient for minor additions to existing circuits (not new circuits or CU replacements).

Question 29: What is the purpose of a visual check of conductor connections during inspection?

To identify loose, incorrectly terminated, corroded or inadequate connections that could cause overheating, arcing or high-resistance faults (Correct answer)
To test for the correct polarity
To measure the resistance of connections
To verify conductor colour coding only

Correct answer: To identify loose, incorrectly terminated, corroded or inadequate connections that could cause overheating, arcing or high-resistance faults

Visual inspection of connections identifies termination issues (loose screws, strands outside the terminal, incorrect ferrules) that are a common cause of overheating, arcing and fire, which no electrical test alone would detect.

Question 30: What does 'Zs' represent in electrical installation testing?

The impedance of the RCD
The total earth fault loop impedance of the circuit (Correct answer)
The supply impedance only
The resistance of the cable

Correct answer: The total earth fault loop impedance of the circuit

Zs is the total earth fault loop impedance, comprising the supply source impedance (Ze) plus the impedance of the phase and protective conductors of the circuit (Zs = Ze + (R1 + R2)).

Question 31: What is Regulation 110.1 of BS 7671 concerned with?

Testing procedures
The purpose, scope and fundamental principles of the regulations — protecting against shock, fire and burns (Correct answer)
Consumer unit specifications
Cable sizing calculations

Correct answer: The purpose, scope and fundamental principles of the regulations — protecting against shock, fire and burns

Part 1 of BS 7671 (including Regulation 110.1) sets out the scope, object and fundamental principles of the regulations, stating the purpose of providing protection against electric shock, fire, burns and other hazards.

Question 32: Can a luminaire (light fitting) be installed in Zone 1 of a bathroom?

Only battery-powered luminaires are permitted in Zone 1
Only recessed downlights regardless of IP rating
No luminaires may be installed in any bathroom zone
Yes, if it has a minimum IP rating of IPX4 and is suitable for use in Zone 1 (or higher-rated SELV luminaire) (Correct answer)

Correct answer: Yes, if it has a minimum IP rating of IPX4 and is suitable for use in Zone 1 (or higher-rated SELV luminaire)

Luminaires rated at least IPX4 may be installed in Zone 1; they must be appropriate for the zone, with no user-serviceable lamp without a tool, and connections within the fitting must be adequately protected.

Question 33: What is required when a new circuit is added to an existing installation?

Only an RCD test is required
A MEIWC is sufficient for any circuit addition
No notification is needed if the installation is less than 10 years old
A new circuit must be notified under Part P and an EIC issued for the new circuit; the existing installation must be assessed to confirm it is capable of safely accommodating the new load (Correct answer)

Correct answer: A new circuit must be notified under Part P and an EIC issued for the new circuit; the existing installation must be assessed to confirm it is capable of safely accommodating the new load

Adding a new circuit is notifiable work under Part P; an EIC must be issued, covering the new circuit. The existing supply, main fuse, earthing and bonding should be assessed to ensure they can support the added load.

Question 34: How many zones are defined in a bathroom containing a fixed bath under BS 7671?

Four zones
Three: Zone 0, Zone 1 and Zone 2 (plus an area outside the zones) (Correct answer)
One single zone
Two: Zone 0 and Zone 1

Correct answer: Three: Zone 0, Zone 1 and Zone 2 (plus an area outside the zones)

BS 7671 Section 701 defines Zone 0 (inside the bath/shower tray), Zone 1 (above the bath/tray up to 2.25 m), and Zone 2 (outside Zone 1 extending 0.6 m horizontally), plus an area outside all zones.

Question 35: What is the purpose of Appendix 3 of BS 7671?

To list cable types
To provide time/current characteristics of overcurrent protective devices for use in calculations (Correct answer)
To specify earthing system requirements
To provide certification forms

Correct answer: To provide time/current characteristics of overcurrent protective devices for use in calculations

Appendix 3 of BS 7671 provides time/current characteristics graphs for fuses and circuit breakers, which are used to verify that protective devices will disconnect within the required time under fault conditions.

Question 36: Which cable type provides inherent mechanical protection suitable for direct burial or outdoor above-ground runs without requiring additional conduit?

Standard flat twin and earth cable
Fire-resistant cable (FP200)
Steel Wire Armoured (SWA) cable (Correct answer)
Flexible cord (3183Y)

Correct answer: Steel Wire Armoured (SWA) cable

Steel Wire Armoured (SWA) cable incorporates a layer of steel wires between the insulation and outer sheath, providing mechanical protection that allows it to be buried directly or surface-run outdoors.

Question 37: What does 'PELV' stand for and can it be used in bathroom Zone 0?

PELV is preferred over SELV in bathrooms
PELV can be used in all bathroom zones
PELV is the same as SELV for bathroom purposes
Protected Extra Low Voltage — no, it cannot be used in Zone 0 because it is referenced to earth, which means a fault to earth in the water could be hazardous; only SELV is permitted (Correct answer)

Correct answer: Protected Extra Low Voltage — no, it cannot be used in Zone 0 because it is referenced to earth, which means a fault to earth in the water could be hazardous; only SELV is permitted

PELV (Protected ELV) operates at extra-low voltage but has a connection to earth; in Zone 0, where the user is immersed in water, an earthed circuit could present a shock risk, so only SELV (separated from earth) is permitted.

Question 38: What does the term 'electrode resistance testing' involve?

Measuring Ze at the supply terminals
Testing insulation resistance of earth conductors
Testing the continuity of the CPC within the installation
Measuring the resistance between an earth electrode and the general mass of earth using a dedicated earth electrode resistance tester (3-probe fall-of-potential method) (Correct answer)

Correct answer: Measuring the resistance between an earth electrode and the general mass of earth using a dedicated earth electrode resistance tester (3-probe fall-of-potential method)

Earth electrode resistance testing uses the fall-of-potential method, injecting current between the electrode under test and a remote current electrode, measuring voltage between the electrode and a probe electrode, and calculating resistance from V/I.

Question 39: What is the purpose of the main switch in a new consumer unit?

To provide a means of isolating the entire installation from the supply for maintenance and emergency isolation (Correct answer)
To protect the installation from overloads
To control all RCDs simultaneously
To control the electricity supply to the meter

Correct answer: To provide a means of isolating the entire installation from the supply for maintenance and emergency isolation

The main switch (rated as a double-pole isolator) allows the entire installation to be safely de-energised for maintenance or in an emergency, disconnecting both line and neutral conductors simultaneously.

Question 40: What is the purpose of a 100 mA time-delayed RCD sometimes used at the origin of an installation?

To replace the 30 mA RCDs in the consumer unit
To provide additional protection for the whole installation
To provide discrimination against downstream 30 mA RCDs — it trips only if the downstream RCD fails to clear a fault, ensuring the main supply is maintained unless all other protection fails (Correct answer)
To protect the main supply cable from overload

Correct answer: To provide discrimination against downstream 30 mA RCDs — it trips only if the downstream RCD fails to clear a fault, ensuring the main supply is maintained unless all other protection fails

A 100 mA time-delayed RCD at the origin provides a last-resort protection level while discriminating against the 30 mA RCDs on individual circuits — it won't trip on a 30 mA fault (cleared by the circuit RCD) but will trip if the downstream device fails.

City & Guilds 2393-10 Part P Building Regulations for Electrical Installations in Dwellings

The Part P (C&G 2393-10) certifies electricians to carry out domestic electrical installation work in compliance with UK Building Regulations Part P, covering BS 7671 wiring regulations, circuit protection, consumer unit installation, and inspection & testing procedures.

Questions

80 min

Time Limit

60%

To Pass

Checking for saved progress...

Exam Rules

You can skip questions and return to them later
Flag questions for review before submitting
No feedback shown until you submit the entire exam
Unanswered questions count as wrong — answer everything
10 pretest questions are mixed in and don't affect your score
Timer auto-submits when time runs out
Your progress is auto-saved every 30 seconds