For further information on the different RCD Types and the selection process, see IET Wiring Matters article (Issue 77 September 2019), ‘Which RCD Type?’ The requirements for RCD testing in BS 7671:2018+A2:2022 are given in the notes to Regulation 643.7.1 for fault protection and Regulation 643.8 for additional protection. A note in each section states the requirements and the key points are highlighted below. Some test instruments have a variable trip current setting, if a tripping current of 50 mA at five times I Δn was selected on the Type A setting, a trip current of 350 mA could be simulated (50 x 5 x 1.4 = 350 mA). However, the variable test current feature is not available on all test instruments.

Indent (ii) however requires the use of overvoltage protection devices to protect a Safety Service. This is defined in Part 2 as; “An electrical system for electrical equipment provided to protect or warn persons in the event of a hazard, or essential to their evacuation from a location.” To aid those carrying out testing, a number of manufacturers of devices employing the 0.25 A characteristic are now providing an advisory label explaining this which can be affixed inside the lid of the consumer unit or distribution board in which the RCD is installed. Regardless of RCD type, e.g. AC, A, F or B, an alternating current test shall be used at the rated residual operating current (I Δn), with a maximum operating time not exceeding 300 ms for general non-delay type RCDs. It must be recognised that this guidance was written before the issue with verification of RCDs designed using 0.25 A residual operating current characteristic came to light.A fire or smoke detection system would fall into this definition. If this system is supplied from the electrical installation then an overvoltage could cause it to fail and, as such, requires protection. The simplest way to provide this protection may be to supply it at the distribution board or consumer unit. Protection against transient over voltages shall be provided where the consequence caused by the over voltage could result in: However, clause 4.2 of BS EN 61557-63, the standard for RCD test instruments, specifies that ‘the measuring equipment shall be capable of indicating whether the fault voltage at the rated residual (operating) current of the protective device is less than or equal to the conventional touch voltage limit’. There may be some equipment however that would show false readings at this test. It is therefore important that manufacturer’s instructions be consulted and if necessary the equipment disconnected during this 250 V DC test.

If the Type A RCD setting is selected on the test instrument, the test current is increased by a factor of 1.4. Therefore, if the instrument is set to perform a test on a 30 mA RCD at five times I Δn, a test current of 210 mA (30 x 5 x 1.4 = 210 mA) would be produced which may not be sufficient to operate the RCD within the required time as the product standard requires a test current of 350 mA (0.35 A), as described previously.

This installation, or part of it, is protected by a device which automatically switches off the supply if an earth fault develops. Test six monthly by pressing the button marked ‘T’ or ‘Test’. The device should switch off the supply and should then be switched on to restore the supply. If the device does not switch off the supply when the button is pressed, seek expert advice. These proposed changes are also reflected in proposed updates to Appendix 7. In addition, the informative Appendix 7 Harmonized cable core colours includes a new item 8: Colour codes for diagrams and specifications, which summarizes (in Table 7F) the BS 7645 colour codes, and recommends that they are used, where required, to identify conductors in operation and maintenance information, such as wiring diagrams and termination schedules. Proposed new Regulation 514.9.2

BS EN 61009-1:2012+A12:2016. Residual current operated circuit-breakers with integral overcurrent protection for household and similar uses (RCBOs). The requirements for testing RCDs have been simplified, a single test is all that is required to show compliance with the minimum requirement laid out in BS 7671:2018+A2:2022. Regardless of RCD type, the test is carried out using an alternating test current, applied at the RCD’s rated residual operating current I Δn, the maximum disconnection time is expected to be less than 300ms for a general non-delay type RCD. For S type time-delayed RCDs, the operating time should be 130 - 500 ms. Other kinds of RCD testing may be useful for fault finding purposes.Table 1 summarizes the proposed changes to the Regulations specifying signs and notices in BS 7671. It is also recognized that, for domestic (household) premises, certain instruction notices providing general information can be provided with other documentation, accompanying the Electrical Installation Certificate (EIC), where it is not practicable or desirable to fix the notice in the premise.

a proposed change to the colours used to identify + and – conductors in DC systems. M conductors in DC systems, which are current-carrying conductors earthed at one point in the system, are to remain Blue. This change, also aligning with BS EN 60445:2017, results from the need to be able to distinguish the live conductors of DC systems from those of AC systems, due to the increase in the use of low voltage (LV) and extra-low voltage (ELV) DC in modern installations. Figure 2 Examples of the label required by proposed Regulation 514.13.1, when the label is not part of an earthing/bonding clamp to BS 951BS EN 60445:2017 Basic and safety principles for man-machine interface, marking and identification. Identification of equipment terminals, conductor terminations and conductors Whilst BS 7671:2018+A2:2022 doesn’t require other types of RCD testing, however additional tests are not precluded and may be useful for fault finding purposes, these tests could include: It has been reported that contractors have experienced difficulties when testing 30 mA RCDs having a 0.25 A residual operating current characteristic. These difficulties seem to stem from the devices being tested at a current of 150 mA, rather than the necessary 250 mA (0.25 A), based on the assumption that using a test current of 5 I Δn will always be sufficient to cause the device to operate within the required time (0.04 s). This is not the case.