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Difficulty: MediumProtective Devices

When servicing a 120 V120\text{ V} alternating current (AC) power supply, a technician replaces a blown glass cartridge fuse with a replacement that has the correct 2 A2\text{ A} current rating but a lower voltage rating of 32 V32\text{ V}. Why is installing a fuse with this lower voltage rating a serious safety hazard?

  1. A
    The fuse will immediately melt and open under normal continuous load current.
  2. The fuse may sustain an internal electric arc after the element melts, failing to clear the fault current.Answer
  3. C
    The fuse will produce an excessive series voltage drop across its terminals, starving the load of operating voltage.
  4. D
    The fuse will automatically reset and re-energize the circuit before the short circuit is removed.

Answer

The fuse may sustain an internal electric arc after the element melts, failing to clear the fault current.
A fuse's voltage rating specifies its ability to safely suppress and extinguish the electrical arc formed when the internal wire link melts under overcurrent or short-circuit conditions. In a 120 V120\text{ V} circuit, a 32 V32\text{ V} rated fuse lacks sufficient dielectric gap and arc-quenching capability, allowing an arc to persist across the open terminals and continue conducting hazardous fault current.

Step-by-Step Solution

1
Identify the primary electrical function of a fuse's voltage rating.
The voltage rating defines the maximum open-circuit voltage the fuse can safely interrupt without allowing sustained electrical arcing across the blown element gap.
When a fuse blows, the full source voltage appears directly across the open fuse gap.
2
Evaluate the risk of using a 32 V32\text{ V} rated fuse in a 120 V120\text{ V} circuit.
Because 120 V120\text{ V} exceeds the 32 V32\text{ V} breakdown threshold of the fuse housing and gap, the ionized air can maintain a conductive plasma arc.
Exceeding the voltage rating prevents arc extinction, leading to continuous current conduction, explosive case rupture, and fire hazard.

Key Concept

Fuse voltage ratings and arc-extinguishing capability
Estimated Time:1m 0s
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Protective Devices

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