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The fuse rating is expressed in terms of:
Voltage
Current
kVA
Var
Current
A fuse is a protective device whose primary function is to break the circuit when the current exceeds a predetermined limit. Therefore, its rating is specified based on the maximum current (measured in Amperes) it can safely carry continuously without melting.
A fuse is a protective device whose primary function is to break the circuit when the current exceeds a predetermined limit. Therefore, its rating is specified based on the maximum current (measured in Amperes) it can safely carry continuously without melting.
I=kтЛЕd23тАЛ тАФ Relation between current and fuse wire diameter
Q=I2Rt тАФ Joule heating effect causing the fuse to melt
The fuse element is made of a material with a low melting point and a specific cross-section. According to Preece's Law, the current-carrying capacity follows I=kтЛЕd23тАЛ, where 'd' is the diameter of the wire. When current flowing through the fuse exceeds its rated value, the heat generated (I2Rt) causes the element to reach its melting point, thereby opening the circuit.
The fuse is a series protective device.
Fuses are rated in Amperes (A) for current, and sometimes voltage (V) to define the breaking capacity.
The fuse rating is the maximum current that the fuse can carry without deterioration of the element.
Fusing factor is defined as the ratio of minimum fusing current to the current rating of the fuse.
Cheapest form of protection
Requires no maintenance
Extremely fast operation under short-circuit conditions
Cannot be used as a switch (non-reusable)
Possibility of discrimination difficulty between fuses in series
Domestic wiring circuits
Transformer primary side protection
Low voltage distribution boards
The fusing factor is always greater than 1 (typically 1.4 to 1.9).
Options A, C, and D are incorrect as they refer to potential difference, apparent power, and reactive power, which are system parameters rather than the fundamental rating parameter of a fuse.
B is correct тАФ The fuse rating is expressed in terms of the maximum current (Amperes) it can carry continuously.
In competitive exams, remember that a fuse is rated by current (A), while a transformer or generator is rated in kVA, and a capacitor bank is rated in kVAR.