IET On-Site Guide 18th Edition (BS 7671:2018+A4:2026)

IET On-Site Guide 18th Edition (BS 7671:2018+A4:2026)

The IET On-Site Guide 18th Edition (BS 7671:2018+A4:2026) is the practical, day to day companion to BS 767, designed to help installers apply the IET Wiring Regulations accurately on site. Updated to reflect the extensive changes introduced across the 18th Edition amendments, it is a reliable reference for staying current with installation requirements and verification good practice.

Written for the competent installer, the guide supports electrical installation up to 100A, three-phase, presenting essential information in a convenient, easy-to-use format. This Edition has been updated to include all four amendments to the 18th Edition and aligns with BS 7671:2018+A4:2026, helping ensure consistent decisions when selecting protective devices, confirming disconnection requirement, and completing compliant test documentation.

It also adds coverage of key updates introduced through the amendments, including guidance on bidirectional and unidirectional protective device, stationary secondary batteries, revised rationale behind maximum Zs values, improved guidance for RCD selection, and clarification around prospective fault current for protective devices.

Key Features

• 9th Edition On-Site Guide aligned with BS 7671:2018+A4:2026 (18th Edition Wiring Regulations)
• Practical companion to BS 7671 for design, installation, inspection and testing decisions on site
• Suitable for installations up to 100 A, three-phase
• Updated to include all four amendments to BS 7671:2018 in one current reference
• New guidance on bidirectional and unidirectional protective devices
• New content covering stationary secondary batteries used for electrical storage and supply
• Updated rationale for maximum Zs values for protective devices
• Guidance on selecting RCD types and applying RCD protection correctly
• Guidance on prospective fault current considerations for protective device selection