What is Fuse – Symbols, Features, Types, Applications & Advantages

What is Fuse :- A fuse is an electrical safety device (a component) that removes electrical current from an electrical circuit when the current in the electrical circuit is too high. Almost all electrical/ electronic appliances and equipment utilize it some way or the other. This post will discuss what is a Fuse, why it is used, its symbols as per standards, features, various types, applications, advantages and disadvantages.

FUSE

Fuse is an electrical safety device (or component) used from the early days of electrical engineering. It protects the circuit from overload. It is also called as the ‘Sacrificial Device’ in the circuit. Its working principle is based on the heating effect of the current. A fuse is a length of wire that melts (breaks or blows) when the current through it is above a certain level – the fuse rating. The 'fuse rating' is the electrical current that will blow the fuse, for instance 3 amps, 10 amps or 13 amps.

A fuse is a current sensitive piece of wire – when the fuse is working the wire is not broken, when the fuse has ‘blown’ the wire breaks.

Current Rating:- This is the current carrying capacity of a fuse measured at normal conditions and temperature. Before adopting this technique, one must make sure that circuit components are able to withstand the overload of current before the fuse act its role.
With this whenever there is a sudden increase of current only the fuses will blow out. Make sure that the circuit’s current is 75% (generally) of your fuse’s current rating.

               Current _Circuit = 75% of Current Rating of Fuse

I²T Value of Fuse:- This is the amount of energy which is carried by fuse element when there is an electrical fault or some short circuit happens. It measures the heat energy(energy due to current flow) of fuse & it is generated when fuse has blown.

                                   I²T _Circuit = I²T _Device
Interrupting or Breaking Capacity:-  It is the maximum rating of current without harm interrupt by the fuse is known as breaking or interrupting capacity of the fuse.

                           Breaking capacity > maximum rated voltage

                          Breaking capacity <short ckt current

Types of Fuse:- There are wide variety of fuses available for variety of applications. The main types of fuses are categorized into two broad categories based on the type of circuits they are used in. They are:-

                      1. DC Fuses   2. AC Fuses

1.   DC Fuse:- AC and DC fuses can be differentiated by their size. Since DC has a constant value greater than zero volt (0v), there will be a chance of occurrence of an electric arc between the melted wires. As it is difficult to avoid, the electrodes are placed at larger distance compared to AC fuses. DC fuses have  larger in size. 

2. AC Fuse:- AC fuses are smaller in size. They oscillated 50-60 times in every second from minimum to maximum. So there is no chance of Arc between the melted wires. Hence they can be packed in small size.

AC Fuses are further categorized into two broad categories based on the amplitude of applied voltage. They are

        1.Low Voltage Fuses  2. High Voltage Fuses

2.1 Low Voltage Fuse:-

As the name suggests, these are the fuses that are used in low voltages. Some of the Low Voltage Fuses are listed below.

2.1.1 Rewireable Fuse:-

Rewireable fuses (also known as Kit-Kat fuses) are of Low voltage type fuses. They are mainly used in small scale industries and house wiring. It consists of 2 parts namely:

• Fuse Base: Contains in and out terminal. It is made up of porcelain.
• Fuselink Carrier: It holds the  main element and is made up of aluminium, copper or lead.
  

Fig. 5 – Rewireable (Kit-Kat) Fuse

The fuselink carrier can be easily removed from the base without any electric shock. When it blows out, we can easily remove the fuselink carrier and replace the wire.

2.1.2 Cartridge Fuse:-

Cartridge Fuses are also known as Totally Enclosed type Fuses. The fuselinks are enclosed in the glass container. By having this type of design, it helps to keep the electric arc inside the container when it blows out.

Fig. 6 – Cartridge Type Fuses

They are used in many electrical and electronics appliances. They not only protect the device but also prevents fire caused by overheating of the circuits. These type of fuses are used in both Low voltage and high voltage.
Cartridge fuses are further classified into following two types:

• ‘D’ Type Fuses
• Link Type Fuses

2.1.2.1 ‘D’ Type Fuse:-

Diazed type fuses are made of bottle shaped ceramic body with metal end caps. ‘These fuses are highly reliable. It consists of cartridge, base, adapter ring and a cap. The cartridge is fitted with a cap and inserted into the base using the adapter ring.

Fig. 7 – ‘D’ Type Fuses

2.1.2.2 Link Type Fuse:-

Link type fuses are also known as High Rupturing Cartridge (HRC) fuses. The current flows under normal condition through the element. The body is made up of porcelain and the chamber of main element is filled with silica sand.
If short circuit occurs then the high current flows through it for some amount of time. If the fault is cleared then it will not blow out. But if the high current continues to flow for longer duration then it blows out by melting the element.
There are 2 types of HRC fuses namely,

• Blade Type Fuses
• Bolted Type Fuses
  

Fig. 8 – Link Type, ‘D’ Type and Bolted Type Fuses

2.1.3 Switch Type Fuse:-

It encloses a metal switch and the fuse. These types of fuses are used in low and medium voltage levels.

2.2 High Voltage Fuse:-

As the name suggests, these are the fuses that are used in high voltages. Some of the High Voltage Fuses are listed below.

2.2.1 Liquid Type HRC Fuse:-

Liquid type HRC fuses are most commonly used in high voltage circuits. These types of fuses are mainly used for transformer protection and circuits which have more than 400A.

Fig. 10 – Liquid Type HRC Fuses

Liquid type HRC fuses are filled with carbon tetrachloride. When there is a short circuit, the current passes through the element which melts and break. The liquid used in the fuses extinguish the arc created by the short circuit.

2.2.2 Cartridge type HRC Fuse:-

These type of fuses are similar to low voltage fuses. It is in the shape of a ring for removing the corona effect. Two fuse elements are used in it which are placed parallel to each other. The elements are made up of tungsten metal due to high resistance property.

Fig. 11 – Cartridge Type HRC Fuses

2.2.3 Expulsion Type HRC Fuse:-

Expulsion type of fuses are used to protect transformers and feeders. It is designed for 11kv and limit is up to 250 MVA. The fuse element is placed inside the cylinder and the tops are linked to the equipment. These fuses have a cylinder designed with synthetic resin bond paper.

Fig. 12 – Expulsion Type HRC Fuses

Applications of a Fuse:-

The applications of Fuses include nearly all electrical/ electronic devices such as:

• Electrical wiring at home.
• Appliances like AC, Refrigerator, TV, Washing machine etc.
• Laptops.
• Mobile chargers.
• Automobiles (Cars, Trucks, Buses, etc).

Advantages of Fuses:-

The advantages of Fuses includes:

• Fuses are cheapest form of protection available.
• No maintenance is required.
• When compared to circuit breakers, fuses require less time to react when circuit breaks.
• They are used in LCD monitors, battery packs, etc.

Disadvantages of Fuses:-

The disadvantages of Fuses includes:

• Considerable time is lost due to rewiring the fuses after operation.
• The current time characteristics of fuses cannot be related with that of protected apparatus.