High earth fault loop impedance values associated with TT earthing systems mean the earth fault current level is unlikely to be sufficient to operate the distributor’s protective device within the permitted time of 1 second, as required in Regulation 411.2.4, or at all in some cases, depending on Earth resistance values.
There is nothing to prevent a metal consumer unit being installed with a TT earthing system, but it’s important to ensure that an earth fault cannot develop between the meter tails and the metallic enclosure before the RCD.
Methods of reducing an earth faults include keeping the meter tails as short as possible, the installation of proprietary clamps and glands to secure the cables and prevent strain on the terminations, minimising the risk of damage to the meter tails and a subsequent earth fault.
Requirements for Electrical Installations, IET Wiring Regulations, Eighteenth Edition, BS 7671:2018 (Electrical Regulations)
The IET Wiring Regulations are of interest to all those concerned with the design, installation and maintenance of electric wiring in buildings. The market includes electricians, electrical contractors, consultants, local authorities, surveyors and architects. This book will also be of interest to professional engineers, as well as students at university and further education colleges. All users of the IET Wiring Regulations need to be aware of the coming changes in the 18th Edition (BS 7671:2018). This is intended to come into effect on 1st January 2019, although industry needs to start preparing for this from its point of publication (2nd July 2018).
The On-Site Guide is an essential guide to BS 7671. It incorporates the extensive changes in BS 7671:2018, making this a vital guide for keeping up to date. It enables the competent electrician to deal with installations (up to 100 A, 3-phase) providing essential information in a convenient, easy-to-use format. The 18th Edition IET Wiring Regulations publishes in July 2018 and comes into effect on 1st January 2019. All new installations from this point must comply with BS 7671:2018.
All above links on this page offer you the ability to order the above publications via Amazon directly.
The following list provides an overview of the main changes within the 18th Edition IET Wiring Regulations (publishing 2nd July 2018). This list is not exhaustive as there are many smaller changes throughout the book not included here.BS 7671:2018 Requirements for Electrical Installations will be issued on 2nd July 2018 and is intended to come into effect on 1st January 2019.
Installations designed after 31st December 2018 will have to comply with BS 7671:2018.
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 this edition in every respect. This does not necessarily mean that they are unsafe for continued use or require upgrading.
A summary of the main changes is given below. (This is not an exhaustive list).
Part 1 Scope, object and fundamental principles
Regulation 133.1.3 (Selection of equipment) has been modified and now requires a statement on the Electrical Installation Certificate.
Part 2 Definitions
Definitions have been expanded and modified.
Chapter 41 Protection against electric shock
Section 411 contains a number of significant changes. Some of the main ones are mentioned below:
Metallic pipes entering the building having an insulating section at their point of entry need not be connected to the protective equipotential bonding (Regulation 418.104.22.168).
The maximum disconnection times stated in Table 41.1 now apply for final circuits up to 63 A with one or more socket-outlets and 32 A for final circuits supplying only fixed connected current-using equipment (Regulation 422.214.171.124).
Regulation 411.3.3 has been revised and now applies to socket-outlets with a rated current not exceeding 32A. There is an exception to omit RCD protection where, other than a dwelling, a documented risk assessment determines that RCD protection is not necessary.
A new Regulation 411.3.4 requires that, within domestic (household) premises, additional protection by an RCD with a rated residual operating current not exceeding 30 mA shall be provided for AC final circuits supplying luminaires.
Regulation 411.4.3 has been modified to include that no switching or isolating device shall be inserted in a PEN conductor.
Regulations 411.4.4 and 411.4.5 have been redrafted.
The regulations concerning IT systems (411.6) have been reorganized. Regulations 4126.96.36.199 and 4188.8.131.52 have been deleted and 411.6.4 redrafted and a new Regulation 411.6.5 inserted.
A new Regulation group (419) has been inserted where automatic disconnection according to Regulation 411.3.2 is not feasible, such as electronic equipment with limited short-circuit current.
Chapter 42 Protection against thermal effects
A new Regulation 421.1.7 has been introduced recommending the installation of arc fault detection devices (AFDDs) to mitigate the risk of fire in AC final circuits of a fixed installation due to the effects of arc fault currents.
Regulation 422.2.1 has been redrafted. Reference to conditions BD2, BD3 and BD4 has been deleted. A note has been added stating that cables need to satisfy the requirements of the CPR in respect of their reaction to fire and making reference to Appendix 2, item 17. Requirements have also been included for cables that are supplying safety circuits.
Chapter 44 Protection against voltage disturbances and electromagnetic disturbances
Section 443, which deals with protection against overvoltages of atmospheric origin or due to switching, has been redrafted.
The AQ criteria (conditions of external influence for lightning) for determining if protection against transient overvoltages is needed are no longer included in BS 7671. Instead, protection against transient overvoltages has to be provided where the consequence caused by overvoltage (see Regulation 443.4)
(a) results in serious injury to, or loss of, human life, or
(b) results in interruption of public services/or damage to and cultural heritage, or
(c) results in interruption of commercial or industrial activity, or
(d) affects a large number of co-located individuals.
For all other cases, a risk assessment has to be performed in order to determine if protection against transient overvoltage is required.
There is an exception not to provide protection for single dwelling units in certain situations.
Chapter 46 Devices for isolation and switching – A new Chapter 46 has been introduced.
This deals with non-automatic local and remote isolation and switching measures for the prevention or removal of dangers associated with electrical installations or electrically powered equipment. Also, switching for the control of circuits or equipment. Where electrically powered equipment is within the scope of BS EN 60204, only the requirements of that standard apply.
Chapter 52 Selection and erection of wiring systems
Regulation 521.11.201 which give requirements for the methods of support of wiring systems in escape routes, has been replaced by a new Regulation 521.10.202. This is a significant change.
Regulation 521.10.202 requires cables to be adequately supported against their premature collapse in the event of a fire. This applies throughout the installation and not just in escape routes.
Regulation 522.8.10 concerning buried cables has been modified to include an exception for SELV cables.
Regulation 527.1.3 has also been modified, and a note added stating that cables also need to satisfy the requirements of the CPR in respect of their reaction to fire.
Chapter 53 Protection, isolation, switching, control and monitoring
This chapter has been completely revised and deals with general requirements for protection, isolation, switching, control and monitoring and with the requirements for selection and erection of the devices provided to fulfil such functions.
Section 534 Devices for protection against overvoltage
This section focuses mainly on the requirements for the selection and erection of SPDs for protection against transient overvoltages where required by Section 443, the BS EN 62305 series, or as otherwise stated.
Section 534 has been completely revised and the most significant technical change refers to the selection requirements for the voltage protection level.
Chapter 54 Earthing arrangements and protective conductors
Two new regulations (542.2.3 and 542.2.8) have been introduced concerning earth electrodes.
Two further new regulations (5184.108.40.206 and 5220.127.116.11) have been introduced. These give requirements for the insertion of a switching device in a protective conductor, the latter regulation relating to situations where an installation is supplied from more than one source of energy.
Chapter 55 Other equipment
Regulation 550.1 introduces a new scope.
New Regulation 559.10 refers to ground-recessed luminaires, the selection and erection of which shall take account of the guidance given in Table A.1 of BS EN 60598-2-13.
Part 6 Inspection and testing
Part 6 has been completely restructured, including the regulation numbering to align with the CENELEC standard.
Chapters 61, 62 and 63 have been deleted and the content of these chapters now form two new Chapters 64 and 65.
Section 704 Construction and demolition site installations
This section contains a number of small changes, including requirements for external influences (Regulation 704.512.2), and a modification to Regulation 704.410.3.6 concerning the protective measure of electrical separation.
Section 708 Electrical installations in caravan/camping parks and similar locations
This section contains a number of changes including requirements for socket-outlets, RCD protection, and operational conditions and external influences.
Section 710 Medical locations
This section contains a number of small changes including the removal of Table 710.
Changes to Regulations 710.415.2.1 and 710.415.2.3 concerning equipotential bonding.
A new Regulation 710.421.1.201 which states for all final circuits supplied by medical IT system in medical locations of group 2, AFDD shall not be used.
Section 715 Extra-low voltage lighting installations
This section contains only minor changes including modifications to Regulation 715.524.201.
Section 721 Electrical installations in caravans and motor caravans
This section contains a number of changes including requirements electrical separation, RCDs, proximity to non-electrical services and protective bonding conductors.
Section 722 Electric vehicle charging installations
This section contains significant changes to Regulation 722.411.4.1 concerning the use of a PME supply.
The exception concerning reasonably practicable has been deleted.
Changes have also been made to requirements for external influences, RCDs, socket-outlets and connectors.
Section 730 Onshore units of electrical shore connections for inland navigation vessels
This is an entirely new section and applies to onshore installations dedicated to the supply of inland navigation vessels for commercial and administrative purposes, berthed in ports and berths.
Most, if not all, of the measures used to reduce the risks in marinas apply equally to electrical shore connections for inland navigation vessels. One of the major differences between supplies to vessels in a typical marina and electrical shore connections for inland navigation vessels is the size of the supply needed.
Section 753 Floor and ceiling heating systems
This section has been completely revised.
The scope of Section 753 has been extended to apply to embedded electric heating systems for surface heating.
The requirements also apply to electric heating systems for de-icing or frost prevention or similar applications, and cover both indoor and outdoor systems.
Heating systems for industrial and commercial applications complying with IEC 60519, IEC 62395 and IEC 60079 are not covered.
The following main changes have been made within the appendices
Appendix 1 British Standards to which reference is made in the Regulations includes minor changes, and additions.
Appendix 3 Time/current characteristics of overcurrent protective devices and RCDs
The previous contents of Appendix 14 concerning earth fault loop impedance have been moved into
Appendix 6 Model forms for certification and reporting
This appendix includes minor changes to the certificates, changes to the inspections (for new installation work only) for domestic and similar premises with up to 100 A supply, and examples of items requiring inspection for an electrical installation condition report.
Appendix 8 Current-carrying capacity and voltage drop
This appendix includes changes regarding rating factors for current-carrying capacity.
Appendix 14 Determination of prospective fault current
The contents of Appendix 14 concerning earth fault loop impedance have been moved into
Appendix 3. Appendix 14 now contains information on determination of prospective fault current.
Appendix 17 Energy efficiency
This is a new appendix that provides recommendations for the design and erection of electrical installations including installations having local production and storage of energy for optimizing the overall efficient use of electricity.
The recommendations within the scope of this appendix apply for new electrical installations and modification of existing electrical installations. Much of this appendix will not apply to domestic and similar installations.
It is intended that this appendix is read in conjunction with BS IEC 60364-8-1, when published in 2018
The worldwide need to reduce the consumption of energy means that we have to consider how electrical installations can provide the required level of service and safety for the lowest electrical consumption. The draft proposals enable a client to specify the level of energy efficiency measures applied to an electrical installation. Installations can also be awarded points for energy efficiency performance levels, for example, transformer efficiency. These points can be added together with points for efficiency measures to give an electrical installation an efficiency class, ranging from EIEC0 to EIEC4, depending on the number of points awarded.
The new section will cover several energy efficient areas, such as electric vehicles, lighting, metering, cable losses, transformer losses, power-factor correction, and harmonics.