⚡ Protection Against Electric Shock: Basic and Fault Protection (Part 4, Chapter 41)

1. Under Chapter 41 of BS 7671, what are the two complementary protective provisions against electric shock for normal use?

1. Basic protection and fault protection
2. Overcurrent protection and overvoltage protection
3. Insulation resistance and continuity testing
4. Earth electrode resistance and bonding

Chapter 41 provides basic protection (under normal, fault-free conditions) and fault protection (under single-fault conditions) as the two complementary provisions against electric shock. (BS 7671:2018, Part 4, Chapter 41, Regulation 410.3)

2. In the terminology of earlier editions of the Wiring Regulations, what was 'fault protection' formerly known as?

1. Protection against indirect contact
2. Protection against direct contact
3. Protection against overcurrent
4. Protection against thermal effects

Fault protection (protection under single-fault conditions) was formerly termed 'protection against indirect contact'; basic protection was formerly 'protection against direct contact'. (BS 7671:2018, Part 2 Definitions; Regulation 410.3)

3. Which protective measure is set out in Section 411 of BS 7671 and combines basic protection with fault protection by automatic disconnection in the event of a fault?

1. Automatic Disconnection of Supply (ADS)
2. Double or reinforced insulation
3. Electrical separation
4. SELV

Automatic Disconnection of Supply (ADS), in Section 411, is the principal protective measure combining basic protection with fault protection by automatic disconnection. (BS 7671:2018, Part 4, Section 411 (411.1))

4. For the protective measure ADS to be applied correctly, which of the following is a fundamental requirement for exposed-conductive-parts?

1. They must be connected to a protective conductor with protective equipotential bonding provided
2. They must be insulated to twice the nominal voltage
3. They must be supplied from a separated source
4. They must be made of non-conductive material

ADS requires exposed-conductive-parts to be connected to a protective conductor and that protective equipotential bonding (main bonding) is provided in the installation. (BS 7671:2018, Regulations 411.3.1.1 and 411.3.1.2)

5. In a TN system with a nominal line-to-earth voltage U0 of 230 V AC, what is the maximum disconnection time from Table 41.1 for a final circuit not exceeding 63 A with one or more socket-outlets?

1. 0.4 seconds
2. 0.2 seconds
3. 1 second
4. 5 seconds

Table 41.1 specifies a maximum disconnection time of 0.4 s for such TN final circuits where 120 V < U0 ≤ 230 V AC. (BS 7671:2018, Table 41.1 and Regulation 411.3.2.2 (TN system))

6. In a TT system with U0 of 230 V AC, what is the maximum disconnection time from Table 41.1 for a final circuit not exceeding 63 A with socket-outlets?

1. 0.2 seconds
2. 0.4 seconds
3. 1 second
4. 5 seconds

For TT final circuits where 120 V < U0 ≤ 230 V AC, Table 41.1 requires a maximum disconnection time of 0.2 s. (BS 7671:2018, Table 41.1 and Regulation 411.3.2.2 (TT system))

7. What is the maximum permitted disconnection time for a distribution circuit in a TN system?

1. 5 seconds
2. 1 second
3. 0.4 seconds
4. 0.2 seconds

Regulation 411.3.2.3 permits a maximum disconnection time of 5 s for TN distribution circuits and circuits not covered by 411.3.2.2. (BS 7671:2018, Regulation 411.3.2.3)

8. What is the maximum permitted disconnection time for a distribution circuit in a TT system?

1. 1 second
2. 5 seconds
3. 0.4 seconds
4. 0.2 seconds

Regulation 411.3.2.4 permits a maximum disconnection time of 1 s for TT distribution circuits and circuits not covered by 411.3.2.2. (BS 7671:2018, Regulation 411.3.2.4)

9. For AC socket-outlets rated up to 32 A for use by ordinary persons, what additional protection does Regulation 411.3.3 require?

1. An RCD with a rated residual operating current not exceeding 30 mA
2. An RCD with a rated residual operating current of 100 mA
3. A residual current monitor only
4. Double insulation of the wiring

Regulation 411.3.3 requires additional protection by a 30 mA RCD for socket-outlets rated up to 32 A used by ordinary persons. (BS 7671:2018+A2:2022, Regulation 411.3.3)

10. Regulation 411.3.3 requires additional protection by a 30 mA RCD for mobile equipment rated up to 32 A used in which location?

1. Outdoors
2. Only in bathrooms
3. Only in agricultural premises
4. Only in medical locations

Regulation 411.3.3 requires a 30 mA RCD for mobile equipment rated up to 32 A intended for use outdoors. (BS 7671:2018+A2:2022, Regulation 411.3.3)

11. Under Regulation 411.3.3, an exception to providing a 30 mA RCD by means of a documented risk assessment is permitted only in which circumstance?

1. For socket-outlets in installations not under the control of ordinary persons
2. For all socket-outlets in domestic premises
3. For outdoor mobile equipment up to 32 A
4. For socket-outlets used by ordinary persons indoors

The documented risk-assessment exception applies only to socket-outlets in installations not under the control of ordinary persons; it does not apply to those used by ordinary persons or to outdoor mobile equipment. (BS 7671:2018+A2:2022, Regulation 411.3.3)

12. Which statement best describes the role of a 30 mA RCD providing additional protection?

1. It is provided in addition to basic and fault protection and is not a sole means of protection
2. It replaces the need for correct disconnection times
3. It removes the requirement for circuit protective conductors
4. It is recognised as the sole means of shock protection

Additional protection by a 30 mA RCD supplements basic and fault protection; it does not replace correct disconnection times, CPCs or compliant Zs, and is not a sole means of protection. (BS 7671:2018, Section 415 (Regulation 415.1.1))

13. What is the upper limit of extra-low voltage (ELV), being the upper limit of voltage Band I?

1. 50 V AC rms or 120 V ripple-free DC
2. 230 V AC or 400 V DC
3. 12 V AC or 30 V DC
4. 25 V AC or 60 V DC

ELV is a nominal voltage not exceeding 50 V AC rms or 120 V ripple-free DC, whether between conductors or to Earth. (BS 7671:2018, Part 2 Definitions (extra-low voltage); Voltage Bands (Band I))

14. Which protective measures are addressed by Section 414 of BS 7671?

1. SELV and PELV
2. ADS and electrical separation
3. Double insulation and barriers
4. Earth-free local equipotential bonding

Section 414 sets out the protective measures of extra-low voltage provided by SELV and PELV. (BS 7671:2018, Section 414 (Regulation 414.1))

15. SELV and PELV are deemed to provide both basic and fault protection provided which condition on nominal voltage is met?

1. The nominal voltage does not exceed the upper limit of Band I (50 V AC / 120 V DC)
2. The nominal voltage does not exceed 230 V AC
3. The nominal voltage is at least 110 V AC
4. The nominal voltage does not exceed 1000 V AC

Where the nominal voltage does not exceed Band I limits (50 V AC / 120 V DC), the source meets 414.3 and conditions of 414.4 are met, SELV and PELV provide both basic and fault protection. (BS 7671:2018, Section 414 (Regulations 414.1, 414.3, 414.4))

16. Which of the following is the key distinction between SELV and PELV systems?

1. A PELV system may be connected to earth whereas a SELV system must be electrically separated from earth
2. SELV uses a higher voltage limit than PELV
3. PELV must be supplied from a battery only
4. SELV permits exposed-conductive-parts to be earthed but PELV does not

Both use a safety source within Band I, but a PELV circuit may be earthed (or have earthed exposed-conductive-parts), whereas a SELV circuit must be electrically separated from earth and other circuits. (BS 7671:2018, Section 414 (Regulations 414.3, 414.4))

17. The protective measure of double or reinforced insulation (Class II) provides fault protection principally by which means?

1. Preventing the appearance of a dangerous voltage on accessible parts even under a single insulation fault
2. Automatically disconnecting the supply within 0.4 s
3. Bonding all exposed-conductive-parts to earth
4. Limiting the voltage to below 50 V AC

Double or reinforced insulation (Class II) provides fault protection by ensuring no dangerous voltage appears on accessible parts even if the basic insulation fails, without reliance on earthing. (BS 7671:2018, Section 412 (double or reinforced insulation))

18. For the protective measure of electrical separation supplying a single item of equipment, the separated circuit is typically supplied from which source?

1. A source providing at least simple separation, such as an isolating transformer
2. The PEN conductor of a TN-C-S system
3. A direct connection to the distribution board busbar
4. An earthed neutral of the supply

Electrical separation supplies the circuit from a source providing at least simple separation (e.g. an isolating transformer), keeping the separated circuit insulated from earth and other circuits. (BS 7671:2018, Section 413 (electrical separation))

19. In a TN-C or TN-C-S system supplying ADS, what is the rule regarding switching or single-pole isolation devices in a PEN conductor?

1. No switching device or single-pole device for isolation may be inserted in the PEN conductor
2. A single-pole switch is permitted if it is lockable
3. A fuse may be inserted in the PEN conductor
4. An RCD must be inserted in the PEN conductor

Regulation 411.4.3 prohibits inserting any switching device or single-pole isolation device in a PEN conductor, as interruption could leave exposed-conductive-parts live. (BS 7671:2018, Regulation 411.4.3)

20. Which new regulation group, introduced by Amendment 2 (2022), addresses situations where automatic disconnection within the times of Regulation 411.3.2 cannot be achieved?

1. Regulation 419
2. Regulation 433
3. Regulation 314
4. Regulation 543

Regulation group 419 was introduced by Amendment 2 (2022) to cover cases where the required disconnection times cannot be met, requiring measures such as supplementary bonding or a 30 mA RCD. (BS 7671:2018+A2:2022, Regulation 419)

21. Where a 30 mA RCD provides fault protection in a TT system, which condition relating to the conventional touch voltage limit must be satisfied?

1. The product of the rated residual operating current and the earth fault loop impedance must not exceed 50 V (IΔn × Zs ≤ 50 V)
2. The earth fault loop impedance alone must not exceed 50 Ω
3. The rated residual operating current must not exceed 100 mA
4. The disconnection time must not exceed 5 s

In a TT system using an RCD for fault protection, IΔn × Zs must not exceed the conventional touch voltage limit of 50 V. (BS 7671:2018, Regulation 411.5.3)

22. Which of the following are recognised provisions for basic protection used within the ADS measure?

1. Basic insulation of live parts and barriers or enclosures
2. Protective equipotential bonding and earthing
3. Residual current devices and overcurrent devices
4. Class II construction and electrical separation

Within ADS, basic protection is provided by basic insulation of live parts or by barriers or enclosures preventing contact with live parts. (BS 7671:2018, Section 411 (411.2) and Section 416)

23. The maximum rated residual operating current (IΔn) for an RCD providing additional protection is:

1. 30 mA
2. 100 mA
3. 300 mA
4. 500 mA

Additional protection is provided by an RCD with a rated residual operating current not exceeding 30 mA. (BS 7671:2018, Section 415 (Regulation 415.1.1))

24. Within BS 7671, what is the purpose of 'basic protection' against electric shock?

1. Protection against electric shock under fault-free (normal) conditions
2. Protection against electric shock under single-fault conditions only
3. Protection against thermal effects and overcurrent
4. Protection against the effects of lightning and overvoltage

Basic protection (formerly 'protection against direct contact') guards against contact with live parts during normal, fault-free operation. (BS 7671:2018, Part 2 Definitions; Regulation 410.3)

25. Basic protection by insulation of live parts requires that the live parts be completely covered with insulation that can only be removed how?

1. By destruction of the insulation
2. By using a standard screwdriver
3. By hand without tools
4. By removing a single fixing screw

Insulation intended for basic protection must be capable of removal only by destruction, ensuring live parts remain covered during normal use. (BS 7671:2018, Regulation 416.1 (insulation of live parts))

26. A coat of paint has been applied to a busbar that would otherwise be exposed. Is paint an acceptable means of basic protection by insulation?

1. No, because paint, varnish, lacquer and similar products alone are not considered adequate insulation for basic protection
2. Yes, provided two coats are applied
3. Yes, because any covering of live parts is acceptable
4. Yes, provided the paint is rated for outdoor use

BS 7671 specifically states that paints, varnishes, lacquers and similar products are not generally regarded as adequate insulation for basic protection. (BS 7671:2018, Regulation 416.1 (Note on paints/varnishes))

27. For equipment manufactured in the factory, the insulation used for basic protection must comply with which requirement?

1. The relevant product standard for that electrical equipment
2. Only the colour-coding requirements of BS 7671
3. The supplier's verbal assurance of suitability
4. No specific standard, provided it looks intact

Where basic insulation is part of manufactured equipment, it must comply with the relevant product standard for that type of equipment. (BS 7671:2018, Regulation 416.1)

28. In BS 7671, what does the term 'live part' mean?

1. A conductor or conductive part intended to be energised in normal use, including a neutral but excluding a PEN conductor
2. Only the line (phase) conductor of an a.c. circuit
3. Any exposed metalwork connected to earth
4. Only conductors operating above 230 V

A live part is a conductor or conductive part intended to be energised in normal use, which includes the neutral but specifically excludes a PEN conductor. (BS 7671:2018, Part 2 Definitions (live part))

29. When basic protection is provided by an enclosure or barrier, live parts must be inside an enclosure or behind a barrier providing at least which degree of protection against contact with live parts?

1. IPXXB or IP2X
2. IPXXA or IP1X
3. IP00
4. IP67

Barriers and enclosures must provide a minimum of IPXXB or IP2X to prevent finger contact with live parts. (BS 7671:2018, Regulation 416.2.1)

30. For the readily accessible horizontal upper surface of a barrier or enclosure, what minimum degree of protection is required by BS 7671?

1. IPXXD or IP4X
2. IPXXB or IP2X
3. IPXXA or IP1X
4. IP3X only

Readily accessible horizontal top surfaces of enclosures require the higher rating of IPXXD or IP4X to resist ingress of small objects such as wires. (BS 7671:2018, Regulation 416.2.2)

31. A consumer unit lid is removed for maintenance, exposing live terminals behind the barrier. Which condition must be satisfied for opening to be acceptable for basic protection purposes?

1. Opening is only possible by use of a key or tool, or after disconnection of the supply, or where an intermediate barrier of at least IPXXB/IP2X prevents contact
2. The enclosure may be opened by hand at any time without further provision
3. A warning label alone is sufficient regardless of access
4. The barrier may be omitted entirely if the room is locked

Removal of barriers/opening of enclosures is only permitted by key/tool, after isolation, or where an intermediate barrier of at least IPXXB/IP2X is in place. (BS 7671:2018, Regulation 416.2.4)

32. What does the IP rating element 'XXB' specifically signify when used for basic protection?

1. Protection against access to hazardous parts with a finger (jointed test finger)
2. Protection against access with the back of a hand
3. Protection against access with a 1 mm test wire
4. Protection against total dust ingress

IPXXB indicates protection against access to hazardous live parts by a standard jointed test finger. (BS 7671:2018, Regulation 416.2.1; BS EN 60529)

33. Where an opening larger than IPXXB/IP2X is necessary in an enclosure (for example to replace a lamp), which combination of conditions does BS 7671 require?

1. The opening is necessary for the function, suitable precautions prevent unintentional contact, and persons are made aware that live parts can be touched through the opening
2. No additional conditions are required because the opening is functional
3. The enclosure must be fully sealed to IP67 instead
4. A 30 mA RCD must be fitted in place of the barrier

Larger openings are only acceptable where required for proper functioning, where precautions stop unintentional contact and where users are aware that live parts may be touched and should not be touched deliberately. (BS 7671:2018, Regulation 416.2.3)

34. Barriers and enclosures used for basic protection must be:

1. Firmly secured in place and have sufficient stability and durability to maintain protection in normal service
2. Removable by hand to allow quick access
3. Made only of non-metallic material
4. Fitted only in domestic premises

Barriers and enclosures must be firmly secured and robust enough to maintain the required degree of protection under expected service conditions. (BS 7671:2018, Regulation 416.2.2)

35. On site you find that the original factory insulation of a cable has been damaged during installation. To restore basic protection by insulation, what is the correct action?

1. Restore insulation that withstands the mechanical, electrical, thermal and environmental stresses to which it may be subjected in service
2. Wrap the conductor in ordinary adhesive tape as a temporary fix and leave it
3. Apply a coat of paint over the damaged area
4. Rely on the downstream RCD to provide protection instead

Insulation applied during installation must withstand the stresses (mechanical, electrical, thermal, environmental) likely in service, equivalent to factory insulation. (BS 7671:2018, Regulation 416.1)