Working Principle of an Electric Fuse

What is Electric Fuse?

An electric fuse is an electric device which interrupts the flow of current in an electric circuit. It is installed in a circuit to stop the flow of excessive current. A fuse is usually a short piece of wire. The fuse is made up of a material which has high resistivity and low melting point, so that it melts down due to overheating of the wire during high current flow.

The thickness of the fuse wire is determined based on the amount of current flow in the circuit. Normally an alloy of tin and lead is used as the fuse wire, as it has high resistivity and low melting point.

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The resistance of fuse wire is greater than that of live wire.

The diagram represents a basic electric circuit.

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Function of Fuse

Here is a list of some major functions of an electric fuse.

  • An electric fuse acts as a barrier between an electric circuit and the human body.

  • It prevents any damage to the electric device by restricting excess current flow.

  • It prevents overload of current. When too many appliances are connected in a single circuit, it leads to overload which requires a fuse to terminate the circuit connection.

  • It prevents damage that occurs due to mismatched loads.

  • Prevents blackouts: if any dis-function occurs in the components of the circuit, the nearest circuit breaks.

Information about the ampere rating, voltage rating, approval standards of the fuse and interrupt rating are generally marked on the fuse. This information must be checked and verified before buying a fuse.

Working of Fuse

An electric fuse is based on the principle of heating effect of electric current. It is made up of thin metallic wire of non-combustible material. A fuse is always connected between the ends of the terminal in a series connection with the circuit.

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When an excessive current flows in the circuit, it generates heat in the circuit which leads to melt the fuse due to its low melting point, and it also opens the circuit. The excessive flow of current may lead to breakdown of the circuit and stop the current flow. Once a fuse melts, it can be changed or replaced with a new fuse.

A fuse is normally made up of elements like zinc, copper, aluminum and silver.

A fuse acts as a circuit breaker and breaks the circuit in case any fault occurs in the circuit. It acts as a protector of electric appliances and also as a safety measure for humans. The figure below represents a fuse operation, fuse barrel and fuse link.

Characteristics of Fuse Wire

Here are some important characteristics of a fuse wire.

  • Current Rating: It is defined as the continuous conduction of maximum current holded by the fuse without melting. It is the capacity of current, and is measured in Amperes. Current (Cin)=75% current (rating)

  • Voltage Rating: If voltage is connected in series with the fuse, it does not increase voltage rating.


V (fuse) >V (open circuit)

  • I2t Rating: It is the total energy which is carried by the fuse element in case of a short circuit. It measures the heat energy of the fuse, and is generated when the fuse breaks out.

  • Interrupting or Breaking Capacity: The maximum rating of current without harming the interruption by the fuse is known as interrupting capacity of the fuse.

Breaking capacity > maximum rated voltage

Breaking capacity < short circuit current

  • Voltage Drop: The fuse element melts whenever there is an excessive current in the circuit, and opens the circuit. Due to this, voltage drop and resistance change reduces.

  • Temperature: The fuse melts when the operating temperature is higher and the current rating is lower.

The graph represents temperature vs current carrying capacity of a fuse. The current carrying capacity of a fuse is 100% when the temperature is 25°C (three lines meet at this point). After that the current carrying capacity decreases upto 82% at 65°C. This shows that increase in temperature decreases the current carrying capacity of a fuse.

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FAQ (Frequently Asked Questions)

1. What are the Different Types of Fuses?

Ans- Fuses were invented by Sir “Thomas Alva Edison”. Many fuse types are available in the market. Mainly the two types of fuses are :

  • DC Fuses: DC fuses are large in size. DC supply has a constant value, slightly above 0V. So, it becomes hard to turn off the circuit, thereby creating a chance for an electric arc between melted wires. To overcome this, electrodes are placed at a larger distance in the fuse. For this reason the DC fuse is bigger in size.

  • AC Fuses: AC fuses are generally smaller in size. They oscillate around 50-60 times per second from minimum to maximum. No chance of Arc between the melted wires arises. For this reason the AC fuse is small in size.

AC fuses are further categorized into two types, i.e., High voltage fuse and Low voltage fuse.

2. What is the Principle of Fuse?

Ans- Electric fuse is based on the principle of heating effect of electric current. Heat is produced when current flows in the wire. When heat production is more due to excessive flow of current, it melts the fuse which normally has a low melting point, thereby preventing any damage to the electric circuit and appliances.

3. What are the Uses of Fuse?

Ans- The fuses are one of the most important parts of an electric circuit and an electronic system. Here are some uses of a fuse:

  1. They are used in home distribution boards, electric devices and electric appliances to prevent any damage due to excess current flow.

  2. They are used in gaming consoles and all automobiles like cars, bikes, scooters, trucks and all other vehicles.

  3. They are used in laptops, printers, cell phones, hard disk drives, scanners, and portable electronics.

  4. Fuses are used in capacitors, power converters, transformers, power transformers, motor starters if an electrical distribution system.

  5. They are also used in LCD monitors and battery packs to stop excessive current flow to the device and preventing it from damage that may occur to electronics.