Guidance Note 3: Inspection & Testing (Electrical Regulations)

Product Information

Carrying out an inspection of electrical installations is a complex task, the person carrying out the inspection and testing is required to have comprehensive knowledge and experience of different types of electrical installations. Rewireable or semi-enclosed fuses to BS 3036 as they are referred to in BS 7671:2018+A1:2020, are indeed still permitted providing the appropriate correction factor (0.725) is used when determining the size of the conductor. In fact, Table 533.1 identifies the sizes of tinned wire for use in semi-enclosed fuses. This is a new appendix that provides guidance for the types of safety signs, warning signs and instructions required to be applied to electrical installations. Appendix 13 Escape routes and fire protection

There seems to be some slight differences with regards to acceptable Zs values when comparing the two documents BS7671 17th Edition A3 and Guidance Note 3 Inspection and Testing 17th Edition A3. The IET Wiring Regulations does not provide requirements for specific qualifications for electricians, and the IET cannot advise the exact qualifications which are required. 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. Put more simply, my tester measures to +/- 0.5% +/- 1d; or +/- 1% +/- 1d depending upon the range selected and gives a reading to two decimal places. Also for the D type some times the thermal part gets there at about the same time as the magnetic, depending on the ambient temperature ,and so maybe we have to assume the breaker is cold and the cable hot.V low voltage rated bathroom fans are permitted in zone 1 of the bathroom. All circuits must be RCD protected I suggest you go and measure Zs on a real system with a real meter early in the morning, then go out for lunch and polish the meter probes and re-test with the same meter at the same point in the afternoon. The two readings will be both as valid, but are unlikely to be the same in all digits. As an aside what meters do you suggest with this accuracy (not precision) ? Note that two half lengths of meter lead is a good few milli-ohms on its own. I have used both Fluke and Meggar machines and neither is this good.

This is where knowledge of relevant product standards is essential, it would be reasonable to expect a 40 ms maximum disconnection time for a test at five times I Δn as would be the case with an AC test. However, this is not the case as the product standard BS EN 61008 requires a half wave pulsating residual current of 0.35 A (350 mA), see Table 4 extracted from BS EN 61008-1:2012+A2:23-1:2012+A11:2015. Similarly, for instruments with a setting for Type B RCDs a multiplier of two times I Δn is applied as required by the product standard, BS EN 62423:2012 Type F and type B residual current operated circuit-breakers with and without integral overcurrent protection for household and similar uses.The equipment at the intake position is owned by the distributor and the meter and tails belong to the supplier. However, as part of the inspection process, BS 7671:2018 requires the inspector to carry out a visual inspection of the external condition of the distributor’s equipment, to ensure it is safe for continued use. 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. A vital guide to an important safety aspect of working with electricity. It is aimed at everyone involved with fire safety in electrical installations, including consulting engineers, electrical installers, inspectors and technicians and has been fully updated to BS 7671:2018:2022. Whoops, you don’t have access to that! Please register with the IET to join the community and access this area.

Regulation 443.5 (Risk assessment method) has been deleted and Annex A443 (examples of calculated risk level CRL for use of SPDs) has also been deleted. Section 514 - Identification and notices A fundamental guidance book for all those involved with the testing and inspection of electrical installations Table 51 has been modified slightly to take into account changes of colour identification for DC and abbreviations have been added. 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.Predicted measured resistance = r y//r g = 0.6511×0.3515 ÷ (0.6511+0.3515) = 0.2283 Ω Results and conclusion This section includes changes to automatic disconnection of supply and additional protection. Section 717 - Mobile or transportable units

so 20* 6A is 120A - so to be safe assume no instant break unless the current is >120A , probably similar magnetic parts as a 32A B type. Includes the latest guidance on third-party certification schemes and covers relevant parts of the Building Regulations, including Fire Safety, Ventilation and Conservation of Energy. This guide has been fully updated to BS 7671:2018+A2:2022. Type AC RCDs are affected by residual DC components and can become desensitized or ‘blinded’ and may not operate within the required time or, in some instances, may not operate at all. Table 1 summarizes the various types of RCD referred in BS 7671:2018+A2:2022 and their resilience to DC components. In some cases, the inspector may not be able to reach a conclusion and further investigation will be required. In which case the observation will be attributed with F/I. The classification of further investigation should not be used to locate the problem, it should only be used where it is reasonably expected to reveal a dangerous or potentially dangerous situation. I beg to differ. The difference is less than nothing in that application,or if you prefer language with rather more mathematical rigour, it is less than the combination of instrumentation error and experimental variation and the results are statistically indistinguishable.

On-Site Guide (BS 7671:2018+A2:2022) 8th Edition

The early style Residual Current Devices (RCDs) were highly effective protective devices but they have proven to be less reliable in modern buildings as a consequence of DC leakage and DC fault currents caused by electronic equipment. Subsequently, new types of RCD have been developed. The inspector is also required to recommend a date for further inspection and testing to be carried out. These dates are often assumed or taken from Table 3.2 of IET Guidance Note 3 Inspection & Testing. For all other cases, protection against transient overvoltages shall be provided unless the owner of the installation declares it is not required due to any loss or damage being tolerable and they accept the risk of damage to equipment and any consequential loss. Whilst deficiencies observed on fire alarm and emergency lighting systems during the inspection may be worthy of a general note, a classification code should not be attributed. Summary