Incorrect use of fuse characteristics in IEC 62271-105 restricts H.V. fuse application in ring main units

IEC 62271-105 "Alternating current switch-fuse combinations" goes back to IEC 420:1973, when relatively slow acting switches in air and under oil were used in ring main units. SF₆ insulated switchgear did not exist in M.V. secondary distribution systems by then. This may explain why no one cared about the limitations in the use of fuse time-current characteristics in a time range below 100 ms. The paper highlights the conflicting claims of IEC 62271-105 to IEC 60282-1 "High voltage fuses" and IEC TR 60787 "Application guide for the selection of high voltage current-limiting fuse-links for transformer circuits" and explains the consequences with respect to H.V. fuse application in combinations with SF₆ switches. Indeed, important and well established fuse applications will virtually be ruled out by IEC 62271-105. Alternative proposals are presented to resolve the conflicting situation in the International Standards.