Fuses and Its Types

Fuses are the simplest circuit-interrupting elements used as overloading protection devices. Whenever an overload occurs, the fuse element melts, thereby interrupting the current flowing to the load. It is important to note that fuses can only be used as interrupting devices. They can never function as controlling devices like switches, isolators, or MCBs. This is because once the fuse element melts and the circuit is interrupted, the fuse element must be replaced.

Fuses are typically used in applications ranging from small residential loads at 230V to high-tension voltages up to 33 kV. This article explains fuses and their types in detail.

Fuses are classified as follows:

1. Semi-Enclosed Rewirable Fuses
2. Cartridge-Type Fuses (Totally Enclosed)
3. Drop-Out Fuses
4. Expulsion Fuses
5. HRC Fuses (High Rupturing Capacity)
6. Striker Fuses
7. Switch Fuses

These types of fuses are generally made from porcelain material. There are two main components: the base and the carrier. The base is usually mounted on a panel or board, where the incoming terminal is connected at one end and the outgoing wiring at the other. The base holds the carrier, which contains the fuse element of the appropriate current rating.

It is important to note that fuses are always connected in series with the circuit.

These types of fuses are commonly used in residential applications to protect wiring and small-capacity loads from minor overloading or short-circuit currents. When a fault occurs and the circuit becomes overloaded, a high current flows through the fuse. As a result, the temperature of the fuse element rises. Upon reaching a certain temperature, the fuse element melts, cutting off the current in the circuit.

The fuse wire is typically made of lead, a tin-lead alloy, or tinned copper. It is essential to ensure that the replacement fuse element matches the correct size and specifications. Using the wrong fuse can result in failure to interrupt the circuit, potentially damaging the wiring and connected electrical equipment.

Although simple in construction, this type of fuse has several disadvantages:

• Since the fuse wire is exposed to atmospheric conditions, it may become oxidized and deteriorate over time. Rusting can also increase the resistance of the fuse element, reducing its cross-sectional area and causing it to melt at a lower current than its rated value.
• If not properly fixed, loose connections can increase the junction temperature at the terminal where the fuse element is connected.
• During transient currents, such as when starting motors or fluorescent lamps, the fuse element may melt unintentionally.
• As the fuse is partially exposed to the atmosphere, there is a risk of external fire.

These fuses are enclosed in a sealed cylindrical body (usually made of ceramic or glass), with metal caps at both ends. The fuse element is inside the sealed body, making it safer and more reliable.

Advantages

1. It provides betters safety as it is fully enclosed.
2. It can be used from low voltage such 230 V to 1 KV

Disadvantages

1. It is one time use only. Once fuse blown out it should be completely replaced.

Applications

1. Used in electronics, household appliances, and industrial equipment.

Drop-out fuses are mounted on overhead power distribution poles and are designed to physically drop open when the fuse blows, providing a visible indication of a fault.

Advantages

1. Used in medium to high-voltage outdoor applications.
2. When the fuse element melts, gravity causes the fuse holder to drop down.

Disadvantages

1. Helps isolate faulty sections in power lines.

Applications:

1. Commonly used in distribution transformers and overhead lines.

These are high-voltage fuses that use gas expulsion to extinguish the arc after the fuse element melts. When the fuse blows, the arc causes gas generation, which helps extinguish it.

Advantages

1. It is suitable for high voltage outdoor application
2. While fuse blown out, Arc is expelled with noise and good audible indication

Disadvantages

1. Must be replaced after operation.

Applications

1. Used in substations and distribution networks.

HRC fuses are designed to handle high fault currents. They are enclosed in a ceramic body filled with silica sand, which absorbs energy and helps extinguish the arc quickly.

Advantages

1. Very reliable and precise operation.
2. Capable of interrupting very high short-circuit currents.

Applications:

1. Used in industrial systems, motor protection, and control circuits.

Striker fuses are a type of HRC fuse with an additional mechanical striker pin that gets released when the fuse blows. This striker can operate a mechanical switch or provide a visual indication.

Advantages

1. Provides mechanical movement upon blowing.
2. Can be used to trigger auxiliary contacts or circuit breakers.

Application

Often used in control panels and automation systems.

Switch fuses combine the functionality of a switch and a fuse. They allow manual disconnection of the circuit and also provide fuse protection.

Advantages

1. Enclosed in a metal or plastic box with a handle.
2. Can safely isolate the circuit for maintenance.

Applications

Typically used in industrial and commercial distribution boards.