Looking ahead to new Wiring Regulations
A draft of the proposed BS 7671:2018 (IET Wiring Regulations 18th Edition) is now available to view through the BSI’s Standards Development Portal. To help navigate it, we highlight some of the most significant changes being proposed
Note: All of the following comments are on the proposed amendments.
Readers should be aware that these are subject to change as a result of the consultation exercise.
Part 1 - Scope, Object and Fundamental principles
The scope is proposed to be extended to include particular requirements for ‘onshore units of electrical shore connections for inland navigation vessels’. The requirements are in a new section 730 in Part 7 – Special Installations or locations.
Chapter 12 (Object and Effects)
This now requires the technical requirements contained in Part 8 – Energy Efficiency, which is an entirely new concept in the Wiring Regulations, to be considered.
Part 2 – Definitions
Several existing definitions are likely to be amended and a number of new definitions may be included, as follows:
Departure: a deliberate decision to not fully comply with the requirements of the standard for which the designer must declare that the resultant degree of safety is not less than that achievable by full compliance.
The designer would need to record this on the Electrical Installation Certificate.
Electrical Installation Efficiency Class (EIEC): a combination of efficiency measures (EM) and energy efficiency performance levels.
This provides a method for the designer to rate the energy efficiency of the installation into one of five categories from EIEC 0 (very low) to EIEC 4 (the optimized level) in addition to a number of other associated definitions, these will be of relevance to the designer of an installation to meet the requirements and recommendations for Part 8 –Energy Efficiency.
Part 3 - Assessment of General characteristics
There are no significant changes proposed in Part 3.
Part 4 - Protection for Safety
Chapter 41: Protection against electric shock
The maximum disconnection times given in Table 41.1 for fault protection are proposed to be altered and now apply to final circuits with a rated current not exceeding 63A with one or more socket-outlet and 32A supplying only fixed connected current-using equipment.
The previous permitted exception which allowed the omission of additional protection to socket-outlets with rated current not exceeding 20A by an RCD has been removed from Regulation 411.3.3. The regulation will now require RCD protection for all socket-outlets with a rated current not exceeding 32A.
A new regulation 411.3.4 is included for additional protection by RCD not exceeding 30mA for final circuits supplying luminaires in domestic premises.
A note to Regulation 411.4.2 advises that where the means of earthing of the installation is provided by the distributor, a new regulation 542.1.201 requires a supplementary earth electrode to be provided in TN earthing systems.
Chapter 42: Protection against thermal effects
Section 421: Protection against fire caused by electrical equipment Proposed new Regulation 421.1.7. This recognises the use of Arc Fault Detection Devices (AFDDs) which can provide protection from arcing faults becoming the cause of a fire in a building. They operate when variations in the AC waveform is detected, which is typical during the occurrence of a series or parallel arcing fault caused by crushing or compression of conductors or loose connections in equipment.
A designer might consider their installation appropriate if it is assessed that there may be difficulty in evacuating a building due to issues with the mobility of people, such as a children’s nursery or a care home for the elderly.
They may also be useful additional protection where combustible materials are stored or processed, such as agricultural premises or manufacturing plants or where there may be assets and goods of significant value.
The device will typically be installed at the origin of the final circuit either separate from or incorporated with overcurrent and earth leakage protective devices protecting the circuits.
Section 422: Precautions where particular risks of fire exist
Regulation 422.2.1 recognises cables having relevant classification according to the system of Euroclasses for Reaction to Fire as an option to satisfy requirements for wiring systems in escape routes.
This new classification system for cables is a consequence of the implementation of the Construction Products Regulation (CPR) for cable products and their reaction to fire. For most practical purposes, only four of the seven classifications are likely to be applicable to electrical installations (Classes B2, C, D and E) with those classified as B and C having the highest performance levels and providing maximum protection while cables in Classes D and E providing a more basic level of safety.
From 1 July 2017, manufacturers, importers and distributors of cables are no longer able to market cables unless they are classified and comply with the CPR. This means that they are identified with a CE mark on the identification label and the manufacturer provides a declaration of performance.
Note: The classification system is only applicable to a cable’s reaction to fire and does not currently cover a cable’s resistance to fire in respect of functionality (the ability to continue to operate during fire conditions). However, this is scheduled to be covered in the near future.
Chapter 44: Protection against Voltage Disturbance and Electromagnetic Disturbances
Section 443: Protection against Transient Overvoltages of Atmospheric Origin or due to Switching
The criteria for deciding whether or not to install Surge Protective Devices (SPDs) is likely to be changed and will likely remove the previously included design options which allowed them to be omitted. Overvoltage control is required where the consequence of this can affect life, public services and cultural heritage, commercial or industrial activity or a large number of individuals. For other situations a risk assessment will be required. If a risk assessment is not undertaken the default position is that protection must be provided other than in single dwellings where the total value of the installation does not justify this.
Chapter 46: Isolation and Switching
This is a proposed new chapter but it contains some of the requirements previously contained in Chapter 53 (Protection, Isolation, Switching, Control and Monitoring). Requirements are provided for isolation, functional switching (control), switching off for mechanical maintenance and emergency switch-off.
Chapter 52: Selection andErection of cables
Regulation 521.10.202 sees another proposed significant change which will undoubtedly enhance fire safety in buildings. The new regulation will require all wiring systems to be supported in such a way that they will not be liable to collapse in the event of a fire. This was previously only applicable where cables and cabling systems were installed in escape routes.
Wiring should not hang down during fire conditions and hinder people evacuating the building or firefighting activities and surface-mounted wiring systems and cables should therefore not rely solely on non-metallic clips as the method of support.
In relation to selection and erection of wiring systems to minimise the spread of fire, Regulation 527.1.3 (similar to Chapter 42) recognises Euroclasses of cables and requires that a minimum of Euroclass Eca cables be installed without special precautions within a fire segregated compartment in a building. This class of cable although combustible will have been tested with regard to its flame propagation. Typically Euroclass Eca is a PVC type cable while Euroclass D would be a low smoke and fume type.
Chapter 53: Protection, Isolation, Switching, Control and Monitoring
This chapter has been completely revised and Section 531 now includes specific requirements to prevent unwanted tripping of RCDs, for example by sub-division of circuits or where there is protective conductor current by limiting this to less than 30 per cent downstream of the rated RCD.
It also contains requirements for the correct selection and use of RCDs such as Type AC which are recommended for general use.
Section 534: Devices for protection against Overvoltage (where required by Section 443)
This section has also been completely revised. It is now structured more logically in relation to selection and erection, SPD location and type and co-ordination. New requirements are also included in relation to selection with regard to voltage protection level. The presence of SPDs downstream of a distribution board is now to be permanently indicated, eg by a label.
Section 536: Co-ordination of electrical equipment for protection, isolation, switching and control Selectivity (previously known as ‘discrimination’) is necessary to ensure continuity of service and to avoid dangers due to the loss of supply. It is normally achieved by ensuring that a downstream protective device has a lower current setting than the upstream protective device. However other parameters for co-ordination also may require consideration, eg design current, prospective short circuit or fault current, operating time, system voltage, energy let through and for fuses pre-arcing.
Selectivity of protective devices provided for short-circuit, overload and residual currents is required by Regulation 536.3 and has to be verified by either i) a desk study ii) software tools iii) tests in accordance with an applicable product standard, or iv) manufacturers declaration. Regulation 536.5 requires documentation concerning the selection of devices for co-ordination to be added to O&M manuals as per Regulation 514.9. Annex A53.4 Devices and associated functions provides guidance on co-ordination between various protective devices.
Chapter 54: Earthing arrangements and protective conductors
As mentioned earlier in this article, Regulation 542.1.201 now requires an earth electrode supplementing any earth facility provided by the distributor (TN-S or TN-C-S systems) to prevent dangerous touch voltages in the event of the loss of the main connection to earth.
Regulation 542.2.2, which provides requirements for earth electrodes, is planned to be amended with a note advising that for new buildings, the provision of a foundation earth electrode is strongly recommended.
This proposal appears to be a simple solution to the problems that can occur during faults where loss of neutral in PME supplies has occurred.
However, very low earth electrode resistance values will need to be achieved to keep the touch voltage at a safe value and this may not be so easy to achieve.
Part 6 - Inspectionand Testing
Part 6 has been restructured to align with the harmonised document numbering system. Chapters 61, 62 and 63 are deleted, with Initial Verification in a new Chapter 64 and the requirements for Periodic Inspection and Testing in a new Chapter 65. Requirements for certification and reporting, which were previously in Chapter 63, are now contained in the relevant new chapters, ie certification requirements are in Chapter 64 and reporting requirements in Chapter 65.
Part 7 - Special Installations or Locations
There are a number of small changes to Sections in Part 7 including:
Section 722: EV charging installations The opt-out requirement for connection to a PME earthing facility is removed. This allowed connection to a PME system where one of three options was not reasonably practicable for the charging point at a dwelling.
Section 753: Heating cables and embedded heating systems This section has been renamed and the scope now includes electric heating systems for surface heating such as trace heating systems and buried heating systems for de-icing or frost prevention such as in football pitches and sports arenas
Section 730: Onshore Units of Electrical Shore Connections for inland Navigation Vessels This contains requirements which are very similar to those in Section 709: Marinas and Similar Locations. However, there is a difference in the size of supply that will be required which may be up to 125A rather than the 16A which is typical in a marina. The regulations here also recognise the additional risk of electrolytic corrosion from circulating galvanic currents in the protective conductor and therefore require the vessel to be supplied through an isolating transformer which can be either shore mounted or ship mounted.
Part 8 -Energy Efficiency
Energy efficiency is a new concept for the wiring regulations, having previously been focused on safety and proper functioning of the installation. BS 7671 now however requires installers and designers to consider energy efficiency.
Part 8 is unlikely to be applicable to domestic or similar types of installation as the scope advises that, although any design should consider potential areas of saving energy, it may not be suitable for installations with very small loads and short cable lengths such as domestic installations.
These requirements and recommendations are more likely to be relevant to larger commercial and industrial buildings and it will be the responsibility of the designer to decide on what energy efficiency measures are to be taken, if any. This should be done in consultation with the user and the measures applied recorded on the Electrical Installation Certificate.
In larger installations, much of what Part 8 proposes is already being considered by consultant engineers, who may be familiar with the concepts of the Building Research Establishment (BRE) Environmental Assessment Method (BREEAM). This requires a survey of energy requirements and is normally carried out by a trained energy assessor.
The requirements of Part 8 may include obtaining a load energy profile, checking availability of local generation, looking to reduce energy losses in the electrical installation, with consideration to the arrangement of circuits.
A method of determining the most suitable transformer and switchboard location using the barycentre method is provided in Annex A801, which enables this equipment to be located with the largest loads closest to the transformer and LV switchboard.
An example of a method to assess the energy efficiency of an electrical installation using various tables is given in Annex B801.
Bob Cairney I Eng MIET
Technical Standards Adviser, SELECT
