Fuses and Circuit Breakers

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The motors, switch gear, transformers, and power distribution conductors must be protected against short-circuit current. The motors and other loads must also be protected against slow overcurrents or sustained overload that will allow them to overheat and become damaged. Short-circuit current is defined as any current that exceeds the normal full-load current of a circuit by ten times. When short-circuit current occurs unprotected, any conductor or switch gear that is involved will be severely damaged by excessive magnetic forces as well as by extremely high heat levels that will melt most metal objects. Fuses, circuit breakers, and magnetic overloads can provide protection for motors and other loads against slow over- currents, and fuses and circuit breakers can provide short-circuit protection.

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Slow Overcurrents