Guidance Note 3: Inspection & Testing is a fundamental guidance book for all those involved with the testing and inspection of electrical installations. It also contains essential guidance for those studying for inspection and testing qualifications and has been fully updated to BS 7671:2018+A4:2026, including identification of conductors, Stationary Secondary Batteries, Prosumers Electrical Installations, Recommended initial frequencies of inspection of electrical installations and Maximum permissible measured earth fault loop impedance (EFLI).