What is Fuse? Its Diagram, Application, And Types

Widely in electrical engineering and electronics, a fuse serves as an electrical safety device that protects electrical appliances like refrigerators, televisions, computers, etc., from damage by high voltage. We often apply a fuse to the socket of these appliances to prevent any overcurrent from entering the device.

A fuse can be said to be a sacrificial device because when too much current flows through it, the metal wire or strip in it gets melted and opens. You can either rewire this wire or replace the fuse.

So, in this case, fuses defend any overcurrent condition from entering electrical appliances.

Well, in this reading, we’ll explore what a fuse is, its construction, applications, components, diagram, classification, types, and workings. we’ll also explore the advantages and disadvantages of fuses in their various applications.

Let’s begin!

What is a Fuse?

A fuse is a safety device that is used to protect an electrical circuit from overcurrent. We apply it to various electrical circuits because overcurrent conditions can occur at any time. Fuses function as a circuit breaker or stabiliser, thereby safeguarding devices from potential damage.

But in its case, a thin strip or strand of metal is used to block a huge amount of current or an excess current flow from entering an electrical circuit. When this happens, the fuse melts, causing the thin strip to separate, which then stops the power supply to the appliance.

Construction

Fuses come in many types and classifications, so their construction will vary to meet application needs. Zinc, copper, silver, aluminium, or other alloys make up a fuse element because they offer stable and predictable characteristics.

With this material, the fuse ideally would carry its rated current indefinitely, making it melt quickly on a small excess.

These elements are not easily damaged by minor, harmless surges of current, and they do not oxidise or change behaviour after a long period of service. The shape of fuse elements enhances their heating effects. Multiple strips of metal may split the current in a larger fuse.

Applications of Fuses

Below are the applications of various types of fuses:

Fuses are used in all automobiles, such as cars, trucks, trailers, boats, etc.
Gaming consoles also find great use of fuses.
Accessories such as laptops, cell phones, printers, and scanners are essential. All electrical accessories have a fuse.
Power transformers use a high-voltage fuse.
Other components like capacitors, power converters, motor starters, and transformers make effective use of fuses.
LCD monitors and battery packs contained fuses in them.

Components of Fuses

Because there are many types of fuses with different working capacities their components are different. However, the basic components of a fuse are a thin strip or strand of metal. The figure below gives more details about the various parts of fuses depending on the types.

Characteristic of fuses

Below are the characteristics of fuses in an electrical electronic system:

Current rating: This value is the maximum amount of current held in the fuse without melting. This is known as the current rating. It’s the current carrying capacity, measured in amperes, and it has thermal characteristics.
Current (Cin) = 75% Current (rating)
Voltage rating: This is when the voltage connected in series with the fuse does not increase voltage rating, i.e., V(fuse) > V(open ckt)
I2t Rating: This type of rating is the amount of energy carried by the fuse element when any electrical fault or when a short circuit happens. It gauges the heat energy resulting from the fuse’s current flow, which occurs when the fuse blows.
Interrupting or breaking capacity: This is the maximum rating of current without harm interrupted by the fuse
Breaking capacity > maximum rated voltage, Breaking capacity < short ckt current
Voltage drop: This is when excessive current flows, causing the fuse element to melt and open the circuit. Due to the change in resistance and voltage, the voltage drop will decrease.
Temperature: This is when the operating temperature is higher, resulting in a lesser current rating; thus, the fuse melts.
The graph below shows the temperature and current-carrying capacity of a fuse. The process shows that at the point where three lines meet at 25 degrees Celsius, the current-carrying capacity of the fuse will be 100%.
After some time, the current capacity decreases at the slow blow fuse, which then decreases up to about 65 degrees C. The result shows that an increase in temperature will decrease the current-carrying capacity of the fuse.

Selection consideration of fuses

Below are the things to consider while selecting types of fuse:

Fuse rating = (watts/volts) x 1.25

Know the power (watts) of the appliance – it’s usually seen on the appliance manual
Know the voltage rating; the voltage must be higher than the circuit voltage so that it can properly protect the device.
Select fuse like the time-delay type for inductive loads and fast-acting fuses for resistive loads.
Use the highest fuse rating after calculation. For instance, the calculated fuse rating might be 5.334 amps, you’re expected to use a fuse of 6 amps.

Classification of fuses

Classification of fuses is a category where various types of fuses fall into. All fuses can be classified as either AC or DC fuses. AC fuses are also divided into two parts; high voltage fuses or low voltage fuses depending on their design and the element they are made. The figure below arranges the various types of fuses according to their classification.

Different types of fuses

Below are the various types of fuses and their functions:

• DC fuses – DC fuses are larger and have a contact value above 0V so that the circuit won’t be easily neglected and turned off. There is a possibility of an electric arc between melted wires. To overcome this, electrodes are placed at larger distances and thus the size of DC gets increased.

• AC fuses – AC types of fuses are smaller in size as they oscillate at about 50-60 times every second from minimum to maximum. Because of this, the chances of an arc between the melted wires are eliminated. Hence, they can be parked in small sizes.

Just as earlier mentioned, AC fuses are further categorized into two parts; low voltage fuses and high voltage fuses.

Diagram

Types of low voltage fuses (LV)

Cartridge fuse types:

these types of fuses are closed in a container and have a metal wire contact appearing in glass. Cartridge types of fuses are of two types; D-type and link types or HRC (High Rupturing Capacity) fuse.

D-type cartridge fuses – this fuse consists of a cartridge, fuse base, cap, and adapter ring. An adapter ring mounts the cap to the fuse base, which houses the fuse element and cartridge. The fuse begins its work when the cartridge tip makes contact with the conductor.

Link-type or HRC (High Rupturing Capacity) Fuses: Under normal conditions, these types of fuses enable the flow of current. The porcelain, silver, and ceramic components of the blown fuse control the arc it produces. The container of the fuse element is filled with silica sand. These types of cartridge fuses are further divided into two;

Plastic makes up the blade or plug-in type fuse’s body, which is easily replaceable in the circuit without any load.
Bolted-type – conducting plates are fixed to the fuse base in these types of fuses.

Rewireable or kit-kat fuse:

Rewireable types of fuses are constructed in such a way that all their bodies are insulated; they can be easily removed when current is flowing through the fuse without causing electrical shock or injury. Its base acts as an incoming and outgoing terminal made of porcelain and the fuse carrier is used to hold the fuse element, which is made up of copper, aluminum, tin, lead, etc.

Striker fuse:

Striker types of fuses are used for closing and tripping circuits. They have enough force and displacement.

Switch fuse:

A switch fuse is a metal that encloses a switch and fuse. Low and medium voltage levels commonly use it.

Drop-out fuse:

In a drop-out fuse, its melting causes the fuse element to drop under gravity about its lower support. They are used in outdoor transformers for protection.
Types of High voltage (HV) fuse

All types of high voltage fuses are used on voltage rated up to about 1.5 Kv to 138 K. They are used to protect instrument transformers and small transformers.

Arc is produced when heat is created, which causes boric acid to evolve a high amount of gases. This is why it’s used in outdoor applications. It’s made of silver, tin, and copper. The high voltage fuses are of three types:

Cartridge HRC fuse – is similar to the low voltage version of this fuse, only that there are some added features in this type. The figure below shows its components and features.

Liquid HRC fuse – these types of fuse are used for circuits up to 100A rated current and systems of about 132 kV. It has a glass tube filled with carbon tetrachloride and it’s one end is packed and the other is fixed with a phosphorus bronze wire. During its operation, a liquid is used in the fuse to extinguish the arc, resulting in to increase in short circuit capacity.

Expulsion HRC fuse: this is an escapable fuse— that is, the expulsion effect of gases produced by internal arcing. The fuse link chamber fills with boric acid to expel gases.

Working principle

The working of fuses is less complex and can be easily understood as it works with the principle of the heating effect of current. Just as earlier mentioned, it’s made up of a thin strip or strand of metal wire which is a non-combustible element. The ends of the terminals connect to this metal wire. It’s always connected in series with the electrical circuit.

The fuse melts down whenever heavy current flow in the circuit creates excessive current or heat. This is because of the low melting point of the element which opens the circuit.

This excessive flow may lead to the breakdown of the wire and therefore stops the flow of current. The fuse can be rewired when open or can be replaced or changed with a new one of the same ratings.

Fuses also act like circuit breakers, used to break circuits when a sudden fault occurs in the circuit. It does not act only as a protector but is also used as a safety measure to prevent humans from harm. The figure below shows how a fuse work.

Advantages and disadvantages of fuses

Advantages:

Below are the benefits of an electric fuse in its various applications:

Overload or high current are terminated.
The absence of a fuse causes electrical faults that can occur in the wiring or burn the electric appliance.
An electrical hazard is reduced as burning electronics can lead to an uncontrolled fire.
Safe cost of repair in appliances.
The fuse itself is cheap and can be easily replaced.
Most types of fuses are inexpensive.
Additional care or maintenance is not required.
They are portable and can be easily moved around.

Disadvantages:

Despite the advantages of fuses some limitations still occur. below are the disadvantages of fuse in their various applications:

The time-current feature will not be time-synchronized with that of the safeguarding element.
Features of reversible time-current permit the device to be employed for overload safeguarding

Conclusion

Fuses are protective components that keep electrical appliances from overload or high voltage currents.

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