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OVERVOLTAGE PROTECTION TECHNICAL


By Bob Cairney I Eng MIET Technical Standards Adviser, SELECT


D


uring the erection and completion of a new electrical installation, before putting it into service it is important to verify compliance with BS 7671: 2018 as


amended to ensure that the installation operates correctly and is safe to use. It is therefore essential to carry out relevant inspection and testing as part of the initial verification process and to issue correct certification on completion of work.


The certification should include


details of the extent of the work covered and provide a record of the items inspected, and the tests carried out, with the details of these normally recorded on schedule(s) of inspections and schedule(s) of test results. It would however appear that there is some concern in the industry that not all relevant checks are being properly carried out and recorded, i.e. where overvoltage protection has been provided and surge protective devices (SPDs) have been installed.


The failure to record the outcome of the checks carried out on these devices may be due in part to a lack of industry guidance providing details on what to check and where to record it. For instance, minimal detail is given on what to check in the requirements given for initial verification in Chapter 64 of BS 7671, and there is nothing specific provided for indicating the presence of


Going onthe record


SPDs when recording information in the model forms given in Appendix 6.


Requirements for overvoltage protection Requirements to provide protection against voltage spikes and current surges due to lightning strikes or switching are given in Section 443 of BS 7671:2018. These include new requirements which have, since being introduced, undoubtedly resulted in SPDs becoming more commonly installed in new electrical installations. The assessment methods previously


given for determining if this type of protection was required or not included application of the AQ criteria, therefore protection against overvoltages of atmospheric origin was not usually necessary in Scotland as the environment would have met the AQ1 criteria, i.e. the risk associated with surge currents and overvoltages caused by lightning was negligible with fewer than 25 thunderstorm days per year. SPDs were therefore not commonly installed other than perhaps where a lightning protection system was necessary for a building.


36 CABLEtalk AUGUST/SEPTEMBER 2021


Our expert provides more timely guidance after recent concerns were raised over the recording of overvoltage protection through the installation of surge protection devices


The introduction of the new requirements in BS 7671:2018 however changed this, with overvoltage protection now dependant on whether the consequences could result in: ●Serious injury or loss of human life, or ●The interruption of public services and/or damage to cultural heritage, or ●The interruption to commercial or industrial activity, or ●A large number of co-located individuals being affected. For all other situations, a risk assessment method is necessary and only where the outcome from this indicates the protection is not required may it be omitted.


Note: A risk assessment method and examples of applying this calculated risk level (CRL) are given in Regulation 443.5 and there is also an exception for single dwelling homes. However, to apply this a cost analysis must be carried out to see if any subsequent losses due to damage caused by an overvoltage are tolerable.


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