Why fuse wires are always thin? What happens 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.

fuse wire thin size

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.

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8 Responses

  1. K sharma says:

    Do fuse should have high resistance or low resistance?

  2. Bill regen says:

    High resistance

    • K sharma says:

      why fuse wire should have high resistivity?

      • Jim says:

        Actually, we are using a fuse to protect the circuit from over current, short circuit, etc. That is to prevent any condition that causes excessive current flow.
        While saying fuse wire should have high resistance, it should have a higher resistance than the wires they protect or the wiring circuit. Because then only when the current flow increases it can heat and burn out first. But compared to load its resistance should be low enough, that no voltage drops across it or consumes no power during normal condition. If the fuse resistance is higher compared to load, it will burn out every time when the circuit is closed. Its resistance should be ideal that when current increases than permitted amount, it can generate enough heat to melt itself; needs to have a low melting point.

  3. Fernado Francis says:

    A fuse wire should has high resistance and low melting point.

  4. RJ sami says:

    Nice love it

  5. Nobody says:

    Ok I understand what you want to convey. But there is a doubt.
    According to Ohm’s Law,
    V = IR
    So, I=V/R
    So when resistance is decreased current increases.
    From Joules heating law
    H = I^2 R T
    So heat produced is directly proportional to SQUARE of the current and directly proportional to the resistance. Changing the current will have a higher impact on the magnitude of heat produced than the change in resistance.
    So isn’t it actually better to decrease the resistance than increasing it.

  6. Nobody 2 says:

    👆 this guy has a point.

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