Introduction To The 18th Edition Of BS 7671

Introduction To The 18th Edition Of BS 7671

The 18th Edition of BS 7671 was issued on 1st July 2018 and comes into full effect on the 1st January 2019. This article from the experts at NICEIC looks at some of the changes incorporated.

Disconnection for final circuits

Previously, Regulation 411.3.2 applied to all final circuits not exceeding 32 A where the protective measure of automatic disconnection of supply is employed. However, the scope has been expanded so that the disconnection times stated in Table 41.1 now apply to final circuits having a rated current not exceeding:

63A supplying one or more socket outlets,


32A supplying only fixed connected current-using equipment.

Additional protection

The scope of Regulation 411.3.3 has also been extended whereby the requirement for the provision of additional protection for socket-outlets has been increased from a current rating not exceeding 20A up to 32A. Other than for an installation in a dwelling, an exception to this requirement is still permitted, but the decision to omit RCD protection must be based on a documented risk assessment.

The exception that applied to a specific labelled or otherwise suitably identified socket-outlet provided for connection of a particular item of equipment has been deleted.

It should be noted that whilst Regulation 411.3.4 requires additional protection by 30 mA RCD to be provided for AC final circuits supplying luminaires within domestic (household) premises. This provision is normally required anyway, due to the requirements for impact protection of cables concealed in walls and partitions.

As shown, the recommended frequency for operation of an RCD test button has been altered from quarterly to every six months. In addition, Regulation 514.12.2 requires that the RCD advisory label is installed in a prominent position at or near the location of each RCD, not just at the origin.

Isolation and protection

Chapter 46 has been reintroduced and contains requirements for provision of isolation and switching, but requirements concerning the devices used to provide such functions are contained in Section 537. Section 536 contains significantly revised and expanded requirements for ‘selectivity’, previously known as ‘discrimination’, back-up protection, and combined short circuit protection.

Premature collapse in the event of fire

The extent of Regulation 521.10.202, is not only applicable to ‘escape routes’ but applies wherever there is a risk of cables collapsing prematurely in the event of fire and impeding entry or exit. The requirement includes all wiring systems within the scope of BS 7671.

Shock protection for TT installations

In order to minimise the risk of shock where Class I enclosures, such as a metallic consumer units, are installed in installations forming part of a TT system and RCD protection is used on outgoing circuits, Regulation 531. requires that all live conductors on the supply side of the incoming device must have double or reinforced insulation. This includes the incoming conductors and any consumer unit components on the ‘supply’ side of the main switch.

For the purpose of this regulation, insulated and non-metallic sheathed cables are deemed to meet the requirements of double or reinforced insulation. A note to the Regulation clarifies that only internal interconnecting cable links approved by the assembly manufacturer should be used.

Inspection and testing

The model forms contained in Appendix 6 have been revised to incorporate changes to the requirements for Initial verification and Periodic Inspection and Testing, which are now contained in Chapters 64 and 65 respectively. As a result of changes to the model forms contained in Appendix 6 of BS 7671, all NICIEC certificates and report forms have been updated. Changes to the combined ‘Schedule of Circuit Details and Test Results’, which is included as part of an NICEIC certificate and report form include the following:

Insulation resistance

An additional column is included to record the insulation resistance, DC test voltage. Where tests are performed at different voltages the lowest test voltage applied should be recorded in this column.

RCD operating time

Only one column is provided to record the operating time of an RCD. This is because the purpose of this test is to confirm that the RCD will operate within the disconnection time required by BS 7671.

Where an RCD is installed to provide fault protection it should disconnect within the relevant time stated in Chapter 41 of BS 7671 when subjected to a test current greater than or equal to the residual operating current of the device (Regulation 411.3.2.1 refers). Whereas an RCD installed to provide additional protection should disconnect within 40ms when subjected to a test current greater or equal to 5I∆n (Regulation 643.8).

In addition to a confirming the satisfactory operation of an RCD when manually tested, an additional column is included for confirming the operation of an arc fault detection device AFDD (Regulation 643.10). AFDDs conforming to BS EN 62606 are recommended to provide additional protection against fire caused by arc faults, in AC final circuits (Regulation 421.1.7 refers).

For more technical information regarding the 18th Edition click here.

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