# Why do we need Fuse and How does it Work?

**URL:** <https://forumautomation.com/t/why-do-we-need-fuse-and-how-does-it-work/6547>\
**Category:** Electrical\
**Tags:** protection\
**Created:** [June 13, 2019, 5:41pm UTC](https://forumautomation.com/t/why-do-we-need-fuse-and-how-does-it-work/6547 "2019-06-13T17:41:51Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![ashlin](https://forumautomation.com/user_avatar/forumautomation.com/ashlin/32/3775_2.png) [@ashlin](https://forumautomation.com/u/ashlin)\
**Post date:** [June 13, 2019, 5:41pm UTC](https://forumautomation.com/t/why-do-we-need-fuse-and-how-does-it-work/6547/1 "2019-06-13T17:41:52Z")

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**WHAT IS A FUSE?**

A fuse is an overcurrent [protecting device](https://forumautomation.com/t/overcurrent-relays-basics-function-types-of-overcurrent-relay/5828) it is a small piece of metal which is connected between two terminals and it would be mounted on the insulator base it is connected in series with the circuit or appliance which is to be protected. It does the protection from over current, if there is an excessive current in the circuit the fuse will open the circuit.

 ![image](https://cdn.forumautomation.com/original/2X/2/2cfd97561cf6e463bb04a9b78de8c0366b773686.png)

**HOW DOES IT WORK?**

It uses the heating effect of electrical current, during normal working current there won’t be any change in the fusing element but it melts in case of excessive current and it will break the circuit

**CHARACTERISTICS OF A FUSE**

**CURRENT RATING**

It is the current value in which the fuse wire can carry continuously without deterioration this is the maximum amount of current the fuse can hold

**FUSING CURRENT**

It is the minimum value at which the fuse element will start to melt and it would be more than the current rating of the element

**i2t VALUE**

 

This is the measure of energy which is required to blow the fuse element

 

**VOLTAGE DROP**

 

The voltage drop value is usually given by the manufacturer, due to the energy dissipation in the fuse element the fuse may become hot, so voltage drop must need to be taken care if the fuse is used in low voltage applications

 

**BREAKING CAPACITY**

 

This is the maximum current that the fuse can safely interrupt, some fuses are designed to handle high rupture capacity

 

**VOLTAGE RATING**

 

The voltage rating must be greater than or equal to the circuit voltage, by using a low voltage fuse, it can be used at any voltage, some higher voltage fuses doesn’t work properly at lower voltages

 

**DIFFERENCE BETWEEN FUSE AND RELAY**

 

**FUSE VS RELAY**

 

| Fuse | Relay |
| --- | --- |
| Fuses are replaced when it blows, it only has one specific characteristic for an individual type | Relay can be set according to the protection requirements |
| Fuses cannot be reset | Relay can be reset |

![image](https://cdn.forumautomation.com/original/2X/a/a157adaaab24b912ae5ccd3f3a6a741d339faea9.png)

 

**HOW TO SELECT A FUSE?**

 
- **NATURE OF LOAD**
- Steady load
- Fluctuating load
- Fault current
- Grading or discrimination
- **NATURE OF PROTECTION**
- Overload or short circuit protection
- Operating time of fuse weather fast operation is needed

 

**ADVANTAGES OF FUSE**

 
- No maintenance is needed
- It is the cheapest protecting device
- Operation is automatic
- It can be used for overload protection
- Heavy currents can be interrupted without any noise, smoke or flame