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How regulation changes affect protection and detection devices


Amendment 2 to BS7671 IET 18th Edition Wiring Regulations includes changes to existing regulations and additions of new regulations and requirements related to protection and detection devices.

Here’s what you need to know:

Overvoltage Protection

Overvoltage protection (SPD) is now a requirement for all installations. There are no exceptions permitted where overvoltage can cause; serious injury to, or loss of, human life, or cause the failure of a safety service (as defined in Part 2) or lead to significant financial or data loss.

For all other cases overvoltage protection must be provided unless the owner of the installation specifically opts out and accepts all the risks of excluding such protection.

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

AFDDs mandated 

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

Higher Risk Residential Buildings (HRRB’s)

Purpose Built Student Accommodation

Care Homes

Homes in Multiple Occupation

Circuits that supply sockets includes radial circuits, ring 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.

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

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 AFDD / RCBOs would be required.

Wider use of RCBOs

Many installers already use RCBOs within installations in residential dwellings, and there is a clear 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 of such protective devices.

Also 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. For example, on simple electric heating appliances or filament lighting. However, these days such applications are 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 been redrafted.

The new content takes account of types of users. There is no option to omit RCD protection where sockets & mobile equipment is liable to be used by ordinary persons, disabled people or children (BA1, BA2, BA3).

RCDs and outdoor lighting installations

Outdoor lighting which is accessible to the public shall have additional protection by an earth leakage protection device with the characteristics specified in Regulation 415.1.1. which requires protection by 30mA device (RCBO or RCD).

Examples where this requirement applies include gardens and spaces open to the public, telephone kiosks, bus shelters, advertising panels and town plans, but there will be many more actual applications.

Testing RCDs and RCBOs

The requirements for RCD testing have been revised.

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


TechTalking podcast

This week Darren and Dave talk to Dave Clark from Electrium about fault detection and protection devices.

Tune in on:

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Discover more about Amendment 2 and what it means from Electrium