Material used in fuse wire
Fuse wire is a thin wire made of different types of alloys of chromium, aluminum, iron, nickel etc. The fuse wire alloys are:
- Aluchrom alloy
- Cronifer alloy
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: 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 it doesn't blow
quickly. Rather it 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 blow and open the circuits. Semiconductor fuses are of these types which are used to protect semiconductor devices.
- 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 fuse are specially made for military application.
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 that is required by the appliance. If the amount of current exceeds that level then the fuse wire gets heated and melt and thus breaks the circuit which in turn blocks the flow of current through the circuit as well as through the device.
Why the resistance of fuse wire is selected higher than the 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 exceed it melt other wise it will take some time to melt and for that much time the extra amount of current will enter the device and may damage it.
How does the length of fuse wire affects its resistance?
The resistance of a wire is directly proportional to its length. According to the resistivity formula:
where, R=Resistance of wire ρ=Resistivity of wire l=Length of wire a=Cross-sectional area of wire. From this formula we can see 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 to consider.
Electrical schematic drawing symbol for the 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. It is done so that when the fuse blows it open 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.
Important specifications of fuse wires
- 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.
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 in that case 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.
