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Fuse Wires

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Fuse wires are used in special current protection devices(OCPD) called fuse. It is used in connecting the fuses and thus completing the circuit of flow of electricity. It is one of the very important house wire cables from the protection point of view of our electrical devices and for home wiring.

Initially fuse was known as fusible link. Electrical fuse and fuse wire is an important section of a power distribution system to prevent any damage due to fire or any overload or short-circuits. A fuse wire should be chosen with a rating just above the normal operating current of the wiring or equipment which it is to protect.

Material used in fuse wires
Fuse wire is a thin electrical wire made of different types of alloys of chromium, aluminum, iron, nickel etc. The electrical fuse wires alloys are:

Aluchrom alloy
Cronifer alloy

Types of Fuses
There are many types of fuses that are used as circuit breakers. They can be categorized on the basis of different factors like opening time or specific applications for which they are used.

Types of fuses based on opening time
Some fuses are intended to blow very fast while some are designed for increased opening times. It totally depends on the application of fuse wire. Depending on the time factor fuses are mainly of two types- slow blow fuses and fast blowing fuses.

Slow Blow Fuses: They are also called 'Time Delay Fuses' and are used where the starting inrush current is high but decay slowly. These fuses are designed in such a manner that even if the amount of current exceeds the appropriate level, they do not blow quickly. They take some time before blowing. The perfect use of these type of fuses is in electric motor protection, where the inrush currents of up to ten times of normal operating current is experienced every time the motor is started. If fast blowing fuses are used in these applications then the motor will never get started.
Fast Blowing Fuses: They are also called 'Quick Acting Fuses' and are used in circuits with small inrush currents. These fuses are designed in such a way that as soon as the amount of current exceeds the limit, the fuse blows and breaks the circuit.

Types of fuses based on application
Fuse wires used in home wiring fuses are different from those used in industrial applications or for other specific purposes. Based on their applications, the types of fuses include the following.

Automotive Fuses: They are used in automobiles for the safety of lights and other electrical components.
Electronic Fuses: These fuse are used in different electronic devices to provide the protection from overcurrent.
Industrial Fuses: Industrial fuses are used in different industries. Their current ratings are very high as the devices and appliances in the industries require much more current and voltage.
Semiconductor Fuses: Semiconductor fuses are used in semiconductor devices to protect the sophisticated chips and circuits. These fuses are quick acting because even small increment in input current for small time may be dangerous for the devices.
Military Fuses: These electrical fuse wires are specially made for military application.

How Does a Fuse Wire Work?
To run most electric appliances, alternating current (AC) is needed. This current reaches the appliances after passing through the fuse wire fixed in the fuse. The fuse wire is chosen in such a way that it only allows that much amount of current to pass through it which is required by the appliance. If the amount of current exceeds that level then the fuse wire gets heated and melts and thus breaks the circuit which in turn blocks the flow of current through the circuit as well as through the device.

Why Resistance of Fuse Wire is Higher than Appliances?
The resistances of fuse wires are slightly higher than the resistance of the appliances. It is due to the fact that when the amount of current in the circuit exceeds the appropriate level, the fuse wire starts melting. If the resistance of fuse wire is more then as soon as the amount of current exceeds, it melts otherwise it will take some time to melt which may lead the current to enter the device and damage it.

How the Length of Fuse Wire Affects its Resistance?
The resistance of a fuse wire is directly proportional to its length. According to the resistivity formula:

R=pl/a

Resistivity Formula

where, R = Resistance of wire; p = Resistivity of wire; l = Length of wire; and a = Cross-sectional area of wire.

From this formula, it can be seen that as the length of a given fuse wire increases, its resistance power also increases, and as the resistance increases the wire gets more heated and melts soon. So, while choosing the wire for fuse purpose, its length is important factor to consider upon.

Electrical Schematic Drawing Symbol for Circuit and Fuse Wire

Fuse wires or fuses are usually joined in series with the electric components which are to be protected from over current on cables. It is done so that when the fuse blows it opens the circuit and further no current is passed through the components. However, a fuse or fuse wire connected in one branch of a parallel circuit will not affect the flow of electricity in other branches.

Fuse Wire Specifications- Important Considerations
There are certain factors that may be called important specifications of fuse wires. These are as follows.

Voltage rating: It is the maximum current up to which there are chances of safe fault current interruption for particular fuses.

Current rating: It is the maximum continuous operating current of the circuit at which the circuit works properly.

Rated braking capacity: It is the short circuit current at which the fuse can melt without destruction or arcing.

Fuse Ratings
The ratings of fuse wire is usually done in amperes and it is important to choose the wire of proper ratings. If the fuse wire isn't compatible to the load of circuit then it will be dangerous for the appliances as well as for the building and lives of people. We are providing here a brief description of fuse wire current rating to help you to select correct fuse wire.

Current Rating	Where to Use and Apply
3 AMP	For appliances up to 700 watts, such as table lamps and alarm clocks.
5 AMP	For lighting circuits. The maximum permissible load of a lighting circuit is 1200w or 12* 100 watt lamps.
13 AMP	For appliances between 700 and 3000w (3kw).
15 AMP	For single appliance circuits up to 3kw (3000 w).
20 AMP	For storage and water heater circuits.
30 AMP	For socket ring mains, some cooker and shower circuits up to 7kw (7000 w).
45 AMP	For circuits of more than 13kw (13000 w).

Apart from fuse wire, fuse holder- used for containing, mounting and protecting fuses- is also an important component of an electrical fuse.

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