Applies to a.c. circuit-breakers designed for indoor and outdoor service for operation on systems with frequencies up to 60 Hz and voltages higher than 1000 V. Sections are included covering service conditions, definitions, ratings, design and construction, type and routine tests, the selection of circuit-breakers for service, information to be given with enquiries, tenders and orders, transport and storage, erection, maintenance, guide for commissioning tests and quality control during manufacture. Nine appendices giving supplementary information are included.