by Simon Hobbs
Amendment 2 of the IET Wiring Regulations, BS7671:2018 was released on 28th March 2022. A replacement for amendment number 1 (issued on 1st February 2020) and is arguably the first major update of this national standard since its release in 2018.
The Regulations apply to the design, erection and verification of electrical installations, also additions and alterations to existing installations. Existing installations that have been installed in accordance with earlier editions of the Regulations may not comply with amendment 2 in every respect. This does not necessarily mean that they are unsafe for continued use or require upgrading.
Below is a summary of the major changes introduced by amendment 2. It is not exhaustive and is focused on changes that will either directly affect the majority of our highway electrical clients or will be of general interest to them. For that reason, we will start with Section 714 and then deal with each Part in sequential order thereafter:
Section 714 Outdoor lighting installations
714.411.203 Where street furniture is connected directly to a distributor’s PME network, the earthing conductor and any main protective bonding conductors to any extraneous-conductive parts shall have a minimum copper equivalent cross-sectional area of 6 mm2 cross-sectional areas up to 10 mm2 . For larger sized neutral conductors, the main bonding shall comply with Table 54.8.
Comment: The earthing and bonding conductor sizes remain unchanged however the wording has changed and suggests that street furniture will be an extraneous-conductive part.
714.411.3.4 Additional protection
Lighting that is accessible to the public shall have additional protection by an RCD having the characteristics specified in Regulation 415.1.1. Examples include:
(i) gardens, spaces open to the public
(ii) telephone kiosks
(iii) bus shelters
(iv) advertising panels and town plans.
This list is not exhaustive.
The following are excluded:
(v) Street lighting & traffic signage
(vi) Illumination of monuments
(vii) Platform lighting at rail / bus stations.
Comment: This is a new regulation requiring additional protection by use of a 30mA RCD.
Chapter 41 Protection against electric shock
Regulation 411.3.1.2 has been redrafted. The regulation now requires that in each consumer’s installation within a building extraneous-conductive-parts that are liable to introduce a dangerous potential difference be connected to the main earthing terminal.
Comment: This wording clarifies that bonding is only required if there is a dangerous potential difference. Therefore, a metal pipe in the middle of a field would not necessarily require protective bonding.
411.3.3 In AC systems, additional protection by means of an RCD with a rated residual operating current not exceeding 30 mA shall be provided for:
- socket-outlets with a rated current not exceeding 32 A in locations where they are liable to be used by persons of capability BA1, BA3 or children (BA2, BA3),
- socket-outlets with a rated current not exceeding 32 A in other locations, and
- mobile equipment with a rated current not exceeding 32 A for use outdoors.
Comment: This regulation means that where the user’s capability is BA1 (ordinary), BA2 (children) or BA3 (disabled) socket outlets not exceeding 32A shall have 30mA RCD protection.
411.4.2 It is recommended that an additional connection to Earth, by means of an earth electrode in accordance with Chapter 54, is made to the main earthing terminal. This recommendation does not apply to outbuildings of dwellings served by the installation.
Comment: In amendment 1 there was a note that referenced that an additional earthing connection could be made to the protective earth or PEN conductor. This has now been expanded upon and introduced as a recommendation. Essentially, with metal pipework and lead covered cables being replaced by plastic equivalents, the risks associated with PME supplies are increasing and customers are having to provide additional reinforcement to the DNO network by installing an additional electrode to the MET.
Chapter 44 Protection against voltage disturbances and electromagnetic disturbances
Regulation 443.4 for determining if protection against transient overvoltages is needed has been redrafted. Regulation 443.4.1 now requires protection against transient overvoltages to be provided where the consequence caused by the overvoltage could result in:
- serious injury to, or loss of, human life
- failure of a safety service, as defined in Part 2
- significant financial or data loss.
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For all other cases, protection against transient overvoltages shall be provided unless the owner of the installation declares it is not required due to any loss or damage being tolerable and they accept the risk of damage to equipment and any consequential loss.
Comment: A regulation that has seen major changes with each amendment since its first introduction. In previous editions the AQ criteria was replaced by a complex risk assessment had to be completed however this has now all been removed (443.5). The installation of an appropriate SPD is still a requirement for certain scenarios listed (serious injury, safety services, data loss), but in all other situations the owner of the installation can now choose to omit these safety devices.
Section 514 Identification and notices
514.4.2 It is no longer permissible to oversleeve the green/yellow protective conductor in a multicore cable to use it as a live conductor.
Comment: There have been several minor changes to notices, mainly stating exceptions for domestic properties and a new appendix 11 providing additional details. It should also be noted that regulation 514.14 has been deleted and so the ‘mixed wiring colours’ label is no longer required (and its omission will not constitute a defect).
Chapter 53 Protection, isolation, switching, control and monitoring
Comment: Regulation 531.3.3 now states that RCD Type AC shall only be used to serve fixed equipment, where it is known that the load current contains no DC components.
Chapter 64 Initial verification
642.3 lists those inspection items which should be checked during initial verification, where applicable. Inspection of any earth electrodes, if present, has been added to the listing.
643.3.2 has been modified to clarify that, for initial verification, all conductors should be tested at least once at the DC test voltage given in Table 64 of BS 7671 appropriate to the circuit’s nominal voltage. This is to confirm that the integrity of the insulation has survived the installation process.
Regulation group 643.3 has been redrafted and 643.3.3 in particular.
643.3.3 Where connected equipment is likely to influence the measurement or result of the test, or be damaged, the test shall be applied prior to the connection of such equipment, in accordance with Table 64.
Following connection of the equipment, a test at 250 V DC shall be applied between live conductors and the protective conductor connected to the earthing arrangement. The insulation resistance shall have a value of at least 1 MΩ.
NOTE: Manufacturer’s instructions may recommend some equipment to be disconnected during 250 V DC insulation resistance tests as it may influence the results of the test.
Comment: The change to this regulation is primarily aimed at when the installation of equipment takes place during a ‘1st and 2nd fix’. A likely scenario would be to pull in cables and carry out an insulation resistance test on them at 500V DC during a 1stfix, and then carry out a 250V DC insulation resistance test between live conductors and ‘earth’ with all equipment (luminaires etc) connected on the whole system.
The requirements for RCD testing have been changed and Table 3A (Time/current performance criteria for RCDs) in Appendix 3 has been deleted.
643.7.1 Regardless of RCD Type, effectiveness is deemed to have been verified where an RCD disconnects within the time stated below with an alternating current test at rated residual operating current (IΔn).
Comment: The x1 test at IΔn should still be carried out at 0o and 180o and the result should be less that 300ms for a general RCD. The requirement for x ½ and x5 tests have been removed.
Section 722 Electric Vehicle Charging Point Installations
722.411.4.1 Note 1 of this regulation has been modified substantially to clarify how to determine suitability for purpose when items of equipment such open-PEN protective devices are installed, given that no British of Harmonized standard exists currently for such products.
722.531.3.101 has been modified to clarify that each charging point shall be protected individually by an RCD of the appropriate type for the installation.
Chapter 82 Prosumer’s low-voltage electrical installations (PEI)
This is an entirely new chapter. Historically, utility companies have managed the public transmission and distribution network from the point of view of having central production adapted to demand variation.
The objective of this chapter is to provide requirements, such that, low-voltage electrical installations are compatible with the current and future ways to deliver safely the electrical energy to current-using equipment either from the public network or from other local sources.
Chapter 82 provides additional requirements, measures and recommendations for design, erection and verification of all types of low voltage electrical installations. This includes local production and/or storage of energy in order to achieve compatibility with existing and future ways to deliver electrical energy to current-using equipment or to the public network by means of local sources.
Appendix 6 Model forms for certification and reporting1
Minor changes have been made to the model forms and guidance for recipients. These include the addition of fields for recording the details of SPDs and AFDDs.
The schedule of inspections has been simplified for initial verification. A new example checklist of items requiring inspection during initial verification has been added to Appendix 6 but is not required to be provided with the certificate.
The single page generic schedule of test results used for EIC and EICR has been redrafted. There is now a separate page for the schedule of circuit details and a separate page for the schedule of test results.
Final thoughts on PME networks and Amendment 2
Something that appears to have been recognised during the various institution and awarding organisation BS7671 A2 release webinars, is the issue of DIVERTED NEUTRAL CURRENTS on PME networks.
The consequences of these dangerous voltages and currents are best shown in videos provided by the IET2 where the PEN conductor of a PME system is broken (or high resistance) and the return path to the star point of the transformer is through the pipework/metalwork of the installations on the system.
This can raise bonding and metalwork to a dangerous potential, with potentially high currents flowing.
What was suggested in an awarding organisation amendment 2 webinar, is that to complete safe isolation fully, if there is a risk of a diverted neutral current then you may need to check if there is any current flowing in the main protective bonding, using a clamp meter before removing the bond or working on the installation.
HSE3 guidance states ‘There are no voltage limits in the Regulations; the criteria are whether danger (as defined) may arise. It is appropriate for the Regulations to apply even at the very lowest end of the voltage or power spectrum…’
So, with the replacement of metal utilities with plastic, PME networks and their inherent risks are slowly starting to materialise, and consequences being felt. One such consequence would be that carrying out isolation without verifying if there is current flowing in the main protective bonding may constitute a breach of the law3, not just BS7671:2018.
This briefing note is provided with the information available at the time of writing and is supplied ‘without prejudice’.