Electrical fuse is the simplest and cheapest safety device used to break the circuit. It is used to protect the electrical circuit during extreme overload or short circuit. Electric fuse is used in series in electrical circuits. In this article, you will learn in detail about the working principle, function, types, advantages and disadvantages of fuses.
What is the Electric Fuse Definition?
The function of the fuse in an electric circuit is on the principle of thermal effect. An electrical fuse is made of a small piece of metal called fuse wire. Tin, lead, silver, copper, zinc, aluminium or alloy of lead and tin are used as fuse elements.
When a short circuit or overload occurs in the electrical circuit due to some reason. So this fuse metal gets heated and melts due to excessive current flow and the circuit breaks. the Thomas Alva Edison invents the electrical fuse.
Lead and tin alloy is used in the ratio of 37% and 63% in circuits up to 15 A. Copper is used a fuse element in circuits beyond 15 amperes.
Working Principle of Electric Fuse
Fuses are generally used in high voltage up to 66kv and low voltage up to 400v. The material used for the fuse element has certain special properties such as:-
- Low melting point
- Low ohmic loss
- High Conductivity
- Low Resistivity
- Low cost
- Free from deterioration
Now the thing is that all the qualities are not found together in any material. That is why some compromises have to be made to choose the right electrical fuse. See, silver is very good as a fuse material but it is very expensive.
That is why in ordinary form mostly copper, lead and tin are used. Tin, lead and zinc have low melting points but also high specific resistance. Copper has a high melting point but low specific resistance.
Under normal operating condition, the temperature of the fuse wire meterial is below the melting point. Therefore, the fuse wire carries the normal current without overheating.
When some fault occurs, like a short circuit or overloads, the current exceeds the limiting value, this raises the temperature and the fuse wire melts and breaks the circuit.
In this way, the fuse prevents damage to the machine and equipment from excessive current. The time for blowing out of the fuse depends on the magnitude of the current.
The fuse has an inverse time-current characteristic. In other words, the larger the current, the more rapidly the fuse will blow. Electrical fuse is used in the series circuit.
Different Types of Electric Fuse
According to the supply voltage, there are two types of fuse, low voltage fuse and a high voltage fuse. Whereas, according to the current rating also, there are two types, AC fuse and DC fuse.
The categories of fuse diagram flow chart are shown below so that you can understand the types of fuses well.
AC Fuse
AC fuses are used to protect AC circuits and appliances. It protects against both short circuit and overcurrent. Its size is smaller than that of a DC fuse.
AC fuse properties:-
- AC fuses are designed with voltage and current ratings to allow use over a specific range
- The breaking capacity of ac fuse is better without any damage
- Time-current characteristic of AC fuse is available in both fast blow and slow blow modes
- Its arc suppression is better
- It is safe from over heating
DC Fuse
DC fuse is used for dc circuits which is suitable for both short circuit and over current. DC current flows in one direction, which is why it is difficult to extinguish the arc with a DC fuse. DC fuse is also bigger than AC fuse.
- DC current does not have a zero crossing point so it is difficult to extinguish the arc
- To extinguish the arc generated in the DC fuse element, arc-extinguishing materials such as quartz sand or ceramic are used.
- DC fuses also operate on fast-blow or slow-blow Time-Current characteristics
- The breaking current of the DC fuse is high
- The heat dissipation properties of DC fuse are good
Applications of DC Fuse
- Used in Automobiles sector like Car, Truck, Electric Vehicles - EVs etc.
- DC fuse is used in the protection circuits of the battery
- DC fuse is used in Photovoltaic of Solar Power Systems
- This fuse is also used in telecommunication equipment.
- This fuse is used in DC motors, DC machines etc.
There are many types of low voltage fuses.
Rewirable Fuse
It is used in small current circuits, mainly in household wiring. It is also called by various other names such as semi enclosed or kit kat fuse. This fuse is made in two parts, one is the fuse case and the other is the fuse carrier.
The live or phase wires of incoming and outgoing contacts are connected in the fuse case. The fuse carrier holds the fuse conductor, which is also called fuse wire.
Cartridge Type Fuse
In this type of fuse, the fuse element is in a closed container with both the sides connected by metal caps. It is of two types.
- D-type fuse
- Link type fuse
HRC Fuse
HRC fuse full form high rupturing capacity cartridge fuse. This fuse is cylindrical in appearance, and its outer part is made of ceramic. The inner part is filled with quartz sand. Both ends of the fuse unit are connected to a brass cap, and the fuse element is attached inside this cap.
HRC working principle:- When a fault occurs, the fault current flows through the fuse. Due to the flow of current more than the rating, the fuse element gets heated and melts. The fuse element chemically reacts with the ceramic sand to form high resistance glass beads, and the circuit is broken.
High voltage fuses are of the following types:
High Voltage HRC Fuse
They also similar to the low voltage fuse. The only difference is that the fuse element inside it is coiled in a helix form. This is done to reduce the corona loss of the fuse. Inside the high voltage fuse, two fuse wires are connected in parallel. One fuse wire is of high resistance, and the other is of low resistance.
Expulsion type Fuse.
This fuse is used for the safety of the feeder and transformer. This fuse is fitted inside the hollow tube in such a way that when the fuse is blown, the hollow tube falls down.
Advantages and Disadvantages of Fuse
Advantages
- it does not require any maintenance.
- The cheapest way to get protection
- Its operation is completely automatic
- It operate in both short circuit and overload condition
- it is a simple and reliable
- Its replacement process is very easy
Disadvantages
- Fuse replacement is done manually which takes more time
- The protection of the whole circuit depends on this one fuse. If it fails for any reason, the whole circuit gets damaged.
Fuse Wire Properties
fuse are essential components in electrical circuits, designed to protect equipment and prevent hazards by interrupting excessive current flow.
Understanding the characteristics of electrical fuse is crucial for ensuring their proper selection, installation, and operation within electrical systems. Let us know about some special properties of fuse.
1. Current Rating
The current rating of the fuse is one of the most important characteristics. It specifies the maximum current that the fuse can safely carry without opening or failing.
Setting the current rating of the fuse to the normal operating current of the circuit ensures effective protection against overloads and short circuits.
2. Voltage Rating
Electrical fuse have a voltage rating, which indicates the maximum voltage at which they can operate safely without arcing or failing. A fuse of the correct voltage rating must be used in the circuit so that the circuit can be protected properly.
3. Speed of Operation.
Speed of operation refers to how quickly the fuse responds to a fault. Fuses are classified as either fast-blow or time-delay (slow-blow) based on their response time.
Fast-acting fuses react quickly to overload, while time-delay fuses tolerate a temporary surge before opening. Choosing the appropriate speed of operation depends on the characteristics of the load and the specific requirements of the circuit.
4. Interrupting Capacity:
The interrupting capacity of an electrical fuse defines its ability to safely interrupt fault currents without causing damage or creating a safety hazard.
Fuses with higher interrupting capacities can handle larger fault currents, making them suitable for applications with higher fault levels.
5. Temperature Tolerance
Fuse operates in a wide range of temperatures, from extreme cold to high heat. Therefore, they must possess adequate temperature tolerance to maintain their performance and reliability under varying environmental conditions.
Fuse with superior temperature tolerance exhibit consistent behavior and durability across different temperature extremes.
6. Physical Size and Form Factor
Electrical fuse is available in a variety of physical sizes and forms to meet different applications and installation requirements. The size and shape of a fuse determine its compatibility with fuse holders, electrical enclosures, and mounting configurations.
7. Indicator Features:
Many modern electrical fuse have indicator features during operation that provide a visual or audible indication when the fuse is operating.
These indicator characteristics facilitate quick identification of a blown fuse, simplifying troubleshooting and reducing downtime in electrical systems.
8. Material Composition
The materials used in the construction of the fuse influence their performance and reliability. Common fuse materials include ceramic, glass, and various metal alloys, each offering specific advantages in terms of electrical conductivity, thermal stability, and mechanical strength.
Understanding these characteristics enables engineers, electricians, and maintenance personnel to select the most suitable electrical fuse for their applications, ensuring reliable protection and optimal performance in electrical systems.
Characteristic of Fuse Wire
- low cost
- high conductivity
- low melting point
- free from deterioration due to oxidation
To understand the operation of the Fuse, consider some important points.
Current Rating of Fuse Element:-
Now we see that in a fuse element, so many properties are not available at the same time. Alloy materials commonly used for small current rating fuse up to 15A.
For current exceeding 15A, this alloy is not used. Beyond 15A rating circuits, copper wire fuses are employed. Zinc strip is good and does not melt very quickly with a small overload.
Fusing Current :-
this is the minimum value of current which the fuse wire burnt. Obviously, its value is more than the current rating of the fuse element. For round wire, the relationship between fusing current I and diameter d of the wire.
I=Kd^{3/2}
where K is a constant is called fuse constant. The smaller the length. this relationship shows
The Fusing Current Depends On The Following Factor
- diameter of wire
- size and location of terminals
- type of surface
- type of material used
- type of enclosure use
Fusing Factor :– It is the ratio of minimum fusing current and the current rating of fuse element is known as fusing factor. It is always greater than unity. If the fusing factor is small, it is more difficult to avoid degradation due to overheating and oxidation at the rated carrying current. Fusing factor is equal to 1.9 to 2.0.
Prospecting Current :- The RMS value of the first loop of the fault current is called the prospective current. The fault current would normally have a very large first loop, at this point it generates sufficient energy to melt the fuse element.
Cut-Off Current:- The value of current at which the cut-off occurs is called cut-off value. When the fault occurs, the fault current has a very large first loop due to a fair degree of asymmetry. The heat generated is enough to melt the fuse element even before the first loop reaches the peak.
Cut Off Value Depends Upon
- current rating of fuse
- the value of prospective current
- asymmetry of short-circuit current
Pre- Arcing Time :-
It is the time between the commencement of the fault and the instant when cur off occurs. Other words, the time from the start of the fault to the instant the arc is initiated is known as pre-arcing time. The pre-arcing time being 0.001 second.
Arcing Time :-
It is the time between the end of pre-arcing and the instant when arc is extinguished.
Total Operating Time :-
It is the sum of pre-arcing and arcing times. The operating time of an electrical fuse is usually quite low, say 0.02 second as compared to a circuit breaker, say 0.05 second.
Breaking Capacity :-
The breaking capacity of a fuse is the rating corresponding to the RMS value of the ac component of the maximum prospective current and the system voltage. Now a days, several types of electrical fuse are available that find extensive use in low and moderate voltage applications.
Electrical fuses for the distribution system can be classified into ground-mounted and pole mounted. Ground-mounted fuse is normally contained within metal-clad switch gear and designed to protect a local ground-mounted transformer. They are rated up to 160 amps.
Pole mounted electrical fuse for overhead networks can protect a local transformer but may also be installed at the start of a spur line to prevent faults on the spur line affecting customers upstream of the fuses. Pole mounted fuses are rated up to 40 amps.
Electrical fuse is small and relatively cheap, but they suffer from the disadvantage that they need to be replaced after every operation and before load current can be again. By suitable design and the use of metallic elements and filler materials. Different time/current characteristics can be achieved.
Conclusion
electric fuse operated automatically crucial safety device when excessive current flows. With the advancement in technology, modern fuses are currently being developed with greater efficiency and reliability. However, proper selection, installation, and maintenance are necessary for optimal performance. Finally, electrical fuse plays a vital role in various applications with electrical safety smoothly.
A fuse is a device to protect appliances and wires in household electrical circuits from excessive electric current. It is a thin metal wire that is enclosed in a protective material. When the electric current exceeds the safe level, the fuse fitted in the circuit melts and breaks the circuit.
A fuse is provided in an electric circuit to protect electrical appliances.
A fuse works on the principle of heating effect of electric current.
The resistance of a fuse is low but not zero.
- 1A to 5A → For small appliances ( lights, fans, chargers)
- 6A to 15A → For medium appliances ( TVs, refrigerators)
- 16A to 30A → For heavy appliances ( air conditioners, heaters)
- Above 30A → For industrial and high-power circuits
I am an engineer in a government department and also a blogger. I write posts on topics related to electrical and electronics engineering.
