Basics of Fuses

The fuse is an electronic component which contains a piece of wire which joins in series with the circuit. It is a protection device which melts under the excessive current thus leading to an open circuit which protects the other components.

In this post, you'll learn:
  1. Types of fuse (Practical)
  2. Design features of fuse (Theory)
  3. Basic terms associated with fuses (Theory)
  4. Important questions about fuse

Types of fuse

different types graphic

Rewireable fuses

These fuses contain a porcelain body which contains a wire. In the start of 19th century, nichrome wire was used in these fuses. These fuses do exist today. However, the material used in mostly a combination of tin, lead, and copper.

Cartridge Fuses

These fuses are used in laptop chargers, in consumer electronics as well as in electrical motors and protection systems. The word cartridge actually means insertion. Since these fuses are inserted in some casing they are named as cartridges. In the figure above you can see glass and simple cartridge.

Blade Fuses

These fuses are usually employed in the automobiles. Generally (not always) their size indicates their rating. 

Strip Fuses

These are flat fuses which are used in diesel vehicles. High power vehicles involving large batteries utilize them. Their voltage ratings are at 32, 80 volts DC and the amperage rating varies from 25-500A.

SMD Fuses

They are surface mounted electronic fuses which have high inrush current stand capability. Obviously, they are used to protect SMD circuits.

Power Fuses

These high duty fuses are used in our electrical power systems for the protection of power transformers and heavy machinery at power stations. The image below displays a fuse mounted with the transformer rated at 115 kV.

Design features

The fuse manufacturers often want the fuses which have:
  1. High conductivity so as to facilitate the current flow without any loading
  2. Low deterioration from environmental effects so as to extend the usable life of component
  3. Low melting point so as to quickly melt at overcurrent and protect the connected circuit

Basic terms associated with the fuse

Rated current

It is the maximum continuous allowed current which should flow through the fuse.

Blowdown current/Fusing current

It is that specific value at which the fuse element blows down. Usually is 1.20 times of the rated current value.

Potential/Voltage Rating

It is the maximum amount of voltage which is allowed for a fuse.

Arc

After exceeding rated current the material (wire) of fuse begins to melt. Once close to blowdown current the metal get converted into the flash of arc. This flash of arc is termed as the arc.

Important questions

Can we use a fuse at a voltage value lower than its rated voltage?

Yes, a fuse can be employed at a value lower than rated one. For example, a 500 V rated fuse can deal with 10 V or 20 V. Actually, a fuse deals with the current value.

Differentiate rated and fusing current?

The rated current is the normal operating value of current whereas the fusing current is the value at which the wire melts.

What are power fuses, give an example of their application?

The power fuses are the heavy duty fuses which are designed to protect large machines. An example is a transformer.

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