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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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Fusing factor is always
1
Greater than 1
Less than 1
0
Greater than 1
Quick Summary: The fusing factor is defined as the ratio of minimum fusing current to the current rating of the fuse element. Since a fuse must blow to protect a circuit from overloads, the minimum current required to melt the element must be higher than its nominal continuous current rating, making the ratio always greater than 1.
The fusing factor is defined as the ratio of minimum fusing current to the current rating of the fuse element. Since a fuse must blow to protect a circuit from overloads, the minimum current required to melt the element must be higher than its nominal continuous current rating, making the ratio always greater than 1.
F=IratedImin fusing — Fusing Factor
The current rating of a fuse is the maximum current it can carry continuously without degradation. The minimum fusing current is the minimum current at which the fuse element melts and breaks the circuit. For any practical fuse, to prevent nuisance blowing during normal minor fluctuations, the minimum fusing current is set higher than the rating, resulting in a fusing factor F>1.
Fusing factor is always greater than 1 for all practical fuses.
A lower fusing factor indicates a more sensitive fuse (closer to 1).
Typical values for HRC fuses range between 1.1 and 1.25.
Rewirable fuses have a higher fusing factor, typically around 2.
Ensures circuit protection by requiring a threshold current to trigger.
Differentiates between normal operating current and overload/fault current.
High fusing factors in rewirable fuses lead to delayed protection.
Sensitivity is inversely related to the fusing factor.
Switchgear selection for industrial motors.
Design of distribution board protection elements.
For most commercial HRC fuses, the fusing factor is kept low to ensure precise operation.
Option A is incorrect as 1 would imply the fuse melts at exactly the rated current, leading to nuisance tripping.
B is correct — The fusing factor is the ratio of minimum fusing current to the current rating, and since the minimum current to melt the wire must exceed the rated current, the ratio is always greater than 1.
Remember that for semi-enclosed (rewirable) fuses, the fusing factor is higher compared to HRC fuses, which makes them less precise for critical equipment protection.