Design Basis For Fuses With A Breaking And Making Capacity Of 1.5 Times Rated Current

In power systems, the operational performance of the drop out fuse system under load is an important indicator for measuring its quality. According to IEC standards and national electrical codes, fuse-operated switchgear with load switching function must meet specific current-breaking and making capacity requirements.

The fuse's ability to safely break and make 1.5 times its rated current stems from the precise design of its internal arc-extinguishing structure. When the operating mechanism actuates, an arc is generated momentarily upon contact separation. The arc-extinguishing grid and quartz sand filler in the fuse rapidly cool and elongate the arc, dispersing its energy into multiple series-connected small arc segments, ultimately achieving reliable arc extinguishing.

This breaking and making capacity is not arbitrarily set. 1.5 times the rated current corresponds to common overload conditions in the power grid—short-term current surges during motor starting and transformer inrush current. The fuse completes its breaking and making operation at this current level, meeting normal load switching requirements without causing contact erosion or arc-extinguishing failure due to excessive current.