Why fuse wires are always thin? if it is thick?
Fuse is a sacrificial electrical safety device used for overcurrent protection. It will isolate the circuit from the source when the current flow exceeds its limit.
As the Fuse is not just an electrical contact, it should connect the circuit; at the same time, it can melt when the current exceeds the limit. That is why conductors with a low melting point are used as a fuse.
To burn out itself a fuse wire should generate a sufficient amount of heat to raise the temperature of the material to its melting point. The heat produced in an electrical conductor is proportional to the product of its resistance and the square of the current. That is, for a rated current a particular value of resistance is required to produce a temperature value equal to the melting point of the fuse.
What happens if the fuse wire is thick?
The resistance of a conductor is proportional to its length and inverse proportional to its cross-sectional area. So, If the fuse wires are thick, the larger cross section decreases the resistance across the fuse wire. So, even a high current flows through the fuse, it doesn’t blow out. Because it just acts as a normal electric contact in the circuit or wiring.
Resistance, R = ρ L / A
ρ – Resistivity per unit length
L – length
A – Area
In order to reduce the area and to maintain a minimum resistance to generate heat, fuses are made as thin.
A fuse wire should not have high resistance or low resistance. It should have enough resistance to carry its rated current without unwanted disconnection and melt instantly for a small excess of current. That is the fuse thickness increases with the current rating.