Previously, there was the term ‘installations designed after a certain date are to comply to the new edition’. Where there is any doubt about how to use a particular RCD test instrument to verify an RCD designed to operate at 0.25 A the instrument manufacturer should be consulted. A new Appendix 11 is included in the Draft for Public Comment, containing guidance on the requirements for labelling, aimed at those carrying out erection, initial verification and periodic verification.

Equipment with frequency controlled speed drives RCD can detect & respond as for Type A, PLUS high-frequency residual current Where necessary, Regulations in BS 7671 specifying signs and notices have had their terminology modified to align with their classification as either warning notices or instruction notices. Note 1: Completion of an electrical installation designed to the withdrawn standard can be subject to the contractual agreement between all parties involved. Existing installations that have been installed in accordance with earlier editions of the Regulations may not fully comply with Amendment 2 requirements. This does not necessarily mean that they are unsafe for continued use or require upgrading. However, work carried out on an existing installation will need to meet the requirements of Amendment 2 after 27th September 2022. The note to Regulation 643.8 of BS 7671 which gives the requirements for the verification of an RCD to provide additional protection states that: Many of the issues encountered when testing RCDs are down to user error as opposed to faulty RCDs. It may come as a surprise to some, but RCD testing should be carried out at the RCD with the outgoing wiring disconnected. However, this is not usually done. The usual live working procedures must be considered, and suitable precautions taken when carrying out work near live parts.

What is the maximum disconnection time for TT earthing systems using an RCD for fault protection?

NOTE: Effectiveness is deemed to have been verified where an RCD meeting the requirements of Regulation 415.1.1 disconnects within 40 ms when tested at a current equal to or higher than five times its rated residual operating current. David Garrett, Product Management Manager at Deta, says “This is a reminder that the regulations affecting consumer units become mandatory on 28th September, and that all designers, developers and installers should be mindful that they need to be compliant from this date. Deta can assist in providing related information and product solutions to match your needs.” Before we look at testing RCDs, it is worth pointing out that the requirements for selection and erection of RCDs have been amended. Regulation 531.3.3 of BS 7671:2018+A2:2022 states that the appropriate RCD shall be selected according to the presence of DC components and AC frequencies. Further, Type AC RCDs shall only be used to serve fixed equipment, where it is known that the load current contains no DC components.

Each manufacturer’s instrument is different but changing the RCD Type is usually selected by pressing the relevant ‘function’ button on the instrument and the RCD Type symbol will change accordingly: see Figure 2. Most instruments will include a function to test general non-delayed and S Type time-delayed Type AC and Type A RCDs, some test instruments may also include a facility for testing other Types such as Type B RCDs. Where an RCD is installed to provide additional protection, Regulation 643.8 requires that it should be: Connected with this subject is Section 551 Low Voltage Generator Sets. As a PV system is a generating set usually operating in parallel with the normal electrical supply, Regulation 551.7 refers. Given that an RCD may take up to 0.3 seconds (300 ms) to disconnect it would appear at first glance that some disconnection times in Table 41.1 may not be achievable, for example, the maximum disconnection time for some final circuits on a TT earthing system is 0.2 seconds (200 ms), as shown in Table 3. However, a note under the table indicates that earth faults are of negligible impedance and it follows that disconnection times would be commensurately higher since a value of, for example, a residual current of 60 mA would be expected to provide a disconnection time of 150 ms and 40 ms (0.04 seconds) for a residual current of 150 mA, as shown in Table 2. Therefore, an operating time of 300 ms would be considered acceptable for a TT earthing system.

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Solar photovoltaic (PV) installations are covered by Section 712 which has been extensively revised and expanded. If you think you may have a faulty RCD, firstly ensure there are no factors within the installation that are influencing the results. Always carry out RCD testing in accordance with industry guidance and manufacturer’s instructions. 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.” BS EN 62423:2012+A11:2021 Type F and type B residual current operated circuit-breakers with and without integral overcurrent protection for household and similar uses.