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UNTIL the advent of the dual-element fuse, co-ordinated fuse protection for low-voltage distribution systems was virtually impossible because the time-current characteristic of the nonrenewable and renewable fuse did not match the safe time-current characteristic of the circuit. Even short-circuit protection on a-c distribution systems was doubtful because of the lack of data on the interrupting capacity of nonrenewable and renewable fuses. The greatly enhanced time-lag characteristic of the dual-element fuse makes it possible to protect the low-voltage system against dangerous overloads and its interrupting capacity assures satisfactory performance under fault conditions. Since dual-element fuses only are made in National Electrical Code sizes, the Hi-Cap fuse was designed in ratings up to 5,000 amperes to fill co-ordinated fuse protection needs.