Update on overvoltage protection

With Amendment 2 including several changes to overvoltage protection requirements, Associate Member Electrium outlines what you need to know



As you would expect with a new amendment, there have been a number of changes to existing regulations, with several new requirements also added.


One significant change has seen Section 443 simplified, with overvoltage protection or surge protection devices (SPDs) now a requirement for ALL installations. There are now no exceptions permitted where 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.

For all other cases, overvoltage must be provided unless the owner of the installation specifically opts out – i.e. tells the installer not to fit it – and accepts all the risks of excluding such protection.


“Designers and installers should note that the use of AFDDs is in addition to other existing requirements”

There is also a new requirement for installers to provide an information notice – i.e. a label, at or near to the distribution board or consumer unit, indicating that the installation contains overvoltage protective devices.

Note: Information on the types of SPD installed and confirmation of their operational status should also now be recorded on the model Schedule of Circuit Details and Schedule of Test results

AFDDs mandated Regulation 421.1.7


Arc fault detection devices (AFDDs) are now mandated on final circuits for socket-outlets rated 32A or less in four building types:

  • Higher risk residential buildings (HRRBs)

  • Purpose-built student accommodation

  • Care homes

  • Homes in multiple occupation (HMOs).

Circuits that supply socket-outlets include radial circuits, ring final circuits and cooker control circuits where there is an integrated socket within the cooker control. It also includes sockets in common areas, indoor and outside. AFDDs shall be placed at the origin of the circuit being protected, i.e. in the consumer unit or distributions board.

The changes should help in eliminating causes of short circuits

AFDDs are also recommended on final circuits for socket-outlets rated 32A or less in all other buildings too.


The term “recommendation” is clarified on page 18 in the notes on Amendment 2 as meaning “should”.


Designers and installers should note that the use of AFDDs is in addition to other existing requirements – e.g. in almost all cases final circuits supplying socket-outlets also require additional protection by use of a 30mA device. Therefore combined AFDDs/RCBOs would be required.


RCBOs avoid unwanted tripping


Wider use of RCBOs in residential premises is encouraged and fortunately many installers already use RCBOs within installations in residential premises.


There is a clear and accelerating move away from dual RCD-style consumer units because this type of unit does not always make adequate provision for Chapters 31 or 53 – i.e. division of the installation or for DC influences.


Chapter 31 requires the installation to be divided into as many circuits as necessary to avoid unwanted tripping of RCDs. In other words, maintaining power to healthy circuits and disconnecting the faulty circuit only.


Grouping circuits on one or two 30mA RCDs cannot maintain power to healthy circuits when one circuit in the group becomes faulty. Regulation 531.3.2, Unwanted Tripping, now points out the use of RCBOs for individual final circuits in residential premises as a method to prevent unwanted tripping.


In addition, Regulation 531.3.3, Types of RCD, 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, e.g. on simple electric heating appliances or filament lighting. Such applications are now rare.


Regulation 411.3.3, which requires additional protection by means of a 30mA RCD for sockets-outlets and mobile equipment rated 32A or less, has also been redrafted.

Details can be found in the new Requirements for Electrical Installations

It now takes account of types of users as the primary decisive factor for inclusion of 30mA protection. There is no option to omit RCD protection where socket-outlets and mobile equipment may be used by ordinary persons, disabled persons or children.


RCDs and outdoor lighting installations


Section 714, which deals with outdoor lighting installations, now includes regulation 714.411.3.4.


This states that outdoor lighting which is accessible to the public shall have additional protection by an earth leakage protection device. The characteristics are specified in Regulation 415.1.1. which requires protection by 30mA device, either RCBO or RCD.


Examples where this requirement applies includes gardens and public spaces.


Testing of RCDs and RCBOs


The requirements for RCD testing have been revised. Table 3A in Appendix 3 – which had trip times for a variety of RCDs and RCBOs – has been deleted and replaced with simplified requirements, i.e. regardless of RCD Type, an alternating current test at rated residual operating current (In) is used to verify the effectiveness of the device to disconnect within the required times.

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