How To Select A Suitable Fuse To Cope With The Three-phase Short-circuit Capacity Of The System

In power system design, when selecting a drop out fuse fuse, its rated breaking capacity must be set to cover the possible three-phase short-circuit capacity of the system. The "rated breaking capacity" (also called "interruption rating" or "short-circuit rating") of a fuse represents the maximum fault current it can safely interrupt at rated voltage.

The system's three-phase short-circuit capacity is usually determined by the system power supply, transformer capacity, and line impedance; it represents the highest short-circuit current that may occur when a three-phase short-circuit fault occurs. If the rated breaking capacity of the selected fuse is lower than this short-circuit capacity, the fuse may not be able to reliably interrupt the fault current, thus causing circuit protection failure.