BOOK_CONTENT
From Electrical Equipment Handbook: Troubleshooting and Maintenance

OVERVIEW

A fuse is an overcurrent protective device with a circuit-opening fusible part that is heated and severed by the passage of current through it. Fuses can meet most of the protection requirements for good system operation.

The fuse is a thermal device. Heat will melt the fuse element regardless of its source.

The fundamental features of fuses are as follows:

  1. The fuse combines the sensing and interrupting elements in one unit.

  2. It is a single-phase device. Only the fuse in the affected phase will melt to isolate the fault.

    Three-phase motors will continue to run on single-phase power for extended periods. This may result in overheating and damage to the motors.

  3. The fuse response is a function of I 2 T, where I is the current and T is the time the current exists. It has an inverse-time characteristic the higher the current, the faster the fuse blows.

  4. Most fuses require considerably more current than their amperage rating to operate. For example, NEMA standards require that E-rated fuses of 100E and below melt in 300 s at 200 to 240 percent of their rating. Fuses above 100E must melt in 600 s at 220 to 264 percent of their rating. These durations are considered extremely long for short-circuit protection.

  5. Fuses should be coordinated with downstream devices to ensure faults are cleared within reasonable times (1 to 5 s or faster). A fault magnitude of 5 or more times the current rating of the fuse is required...

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Products & Services
Disconnect Switches
Disconnect switches rapidly disconnect from power supplies in the event of an emergency.
Power Distribution Units (PDU)
Power distribution units (PDUs) have an electrical input and several outputs, often as electrical outlets, for powering multiple devices. 
Power Strips
Power strips are used in applications where multiple AC outlets are needed, often without surge or line noise protection.
Power Entry Modules
Power entry modules are composed of a connector and a mounting case with features to produce the highly conditioned output necessary for medical or sensitive instrumentation.

Topics of Interest

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