Guidance Note 1: Selection & Erection is a fundamental guide for specifiers, installers and those inspecting and testing installations. It contains clear guidance on how to apply the relevant sections of BS 7671 and has been fully updated to BS 7671:2018+A4:2026, including Notices and identification labels required by BS 7671; bidirectional and unidirectional devices; insulation monitoring devices (IMDs); co-ordination between RCD types connected in series; guidance for Protected escape routes; conductor classes; updated guidance for the installation of cables in concealed in a wall or partition; Functional earthing and functional equipotential bonding for information and communication technology (ICT) equipment and systems; Stationary Secondary Batteries; Rating of distribution board with multiple sources with practical examples and Power over Ethernet.