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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Fuse blows off by
Burning
Arcing
Melting
None of above
Melting
Quick Summary: A fuse is a self-sacrificing current-limiting protective device that operates on the heating effect of electric current ($I^2R$). When the current exceeds the rated value, the heat generated causes the fuse element to reach its melting point, thereby breaking the circuit.
A fuse is a self-sacrificing current-limiting protective device that operates on the heating effect of electric current (I2R). When the current exceeds the rated value, the heat generated causes the fuse element to reach its melting point, thereby breaking the circuit.
H=I2Rt — Joule's law of heating representing the energy dissipated as heat in the fuse wire
Im=k⋅d3/2 — Preece's law relating fuse current Im to the wire diameter d (k is a constant)
The operation relies on Joule's law of heating: H=I2Rt. The fuse element is designed with a specific material (like tin, lead, or copper) and a precise geometry to ensure that when fault current flows, the temperature rises rapidly above the material's melting point. Once the solid fuse element transitions to a molten state, the mechanical continuity is interrupted, effectively isolating the circuit.
Fuses operate primarily on the thermal effect of electrical current.
The melting point of the fuse material determines its fusing current.
A fuse is a non-restorable protective device requiring physical replacement after operation.
Simple and inexpensive construction
Provides reliable inverse time-current characteristics
Cannot be reused after operation
Prone to deterioration over time due to oxidation
Domestic wiring protection
Low voltage distribution circuits
Option B (Arcing) is a phenomenon that happens AFTER the fuse melts, leading to the final extinction of the current path.
Option A (Burning) is a chemical combustion process, not the physical principle of fuse operation.
C is correct — A fuse blows by the melting of the fuse element due to excessive heat generated by overcurrent.
In protection exams, remember that a fuse is an I-t characteristic device; it is not instantaneous but inversely proportional to the magnitude of the fault current.