Electrical Fuse


What is fuse?

A fuse is piece of metallic wire generally connected in series with the load and protect circuit during faulty condition. It is made of material having low melting point.

What is the function of fuse?

The main purpose of fuse in an electric circuit is to give protection against short circuit and overload. fuses can be used as an alternative to circuit breakers. fuse in a electric circuit mainly perform following two functions:
1. work normally when the circuit current is normal.
2. interrupt the power supply when excessive current flow through the circuit.

In short, the function of fuse is to protect electric circuit from any damage due to fault current.

How does a fuse protect electric circuits?

An electric fuse operates on the principle of heating effect of electric current. During normal condition, the fuse element is at a temperature below its melting point. But when a short circuit or overload occurs, an excessive current will flow through fuse element. This raises the temperatures and fuse element melts very quickly. In this way, electric fuse disconnect the power supply and protect electric circuits or equipment.

In short, when a fault occurs the fuse element blow out and disconnect the power supply

Electric fuse, what are its advantages?

1. It is the cheapest among protective devices.
2. It does not produce any noise when interrupt heavy short circuit.
3. It does not require fault sensing device (Relay).
4. It requires no maintenance.
5. Its operation is very simple.
6. Its operating time is very small as compared to circuit breaker.
7. Its inverse time -current characteristics enables its used for overload protection.

What are the disadvantages of an electric fuse?

1. It requires replacement after every operation.
2. It requires a considerable amount of time to replace or rewire after each operation.
3. Electric fuse cannot be used for very high voltage because it may produce huge arcing.

What is fusing factor?

To understand fusing factor we must have idea about minimum fusing current and current rating of fuse.

Minimum fusing current: It is the minimum value of current due to which fuse wire melts.

Current rating of fuse: It is the maximum value of current which can be handle by fuse without melt. (usually the number in ampere are marked on the fuse body)

   Fusing factor: This is the ratio of minimum fusing current and current rating of fuse.

It is clear that the value of minimum fusing current is greater than current rating of fuse. Therefore the value of fusing factor is always greater than one.

On what factors does the fusing current depends?

As we know that the fusing current is minimum value of current at which the fuse element melts. The fusing factor depends upon
1. diameter of fuse element or wire
2. length of element or wire
3. material of the fuse element or wire
4. cross sections area types (rounds or rectangular)
5. size and location of terminals
6. types of enclosures used etc.

What are the differences between fuse and circuit breaker?

1. It is generally used in low voltage application.
2. It can detect and interrupt the fault.
3. Its work on the principle of electrical and thermal properties.
4. Operating time of fuse is very small.
5. Fuse element needs to replace after every operation.
6. Fuse cannot be used as an ON/OFF switch.

Circuit Breaker
1. Circuit breaker is suitable for high voltage application.
2. Circuit breaker cannot detect fault. It perform only interruptions and detection’s of fault is made by relay.
3. Circuit breaker work on the electromagnetic principle.
4. Operating time of circuit breaker is higher as compared to fuse.
5. Circuit breaker can be used again and again after operation.
6. Circuit breaker can be used as an ON/OFF switch.

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