Different Types of Fuses – Constriction, Working & Characteristics
What is a Fuse?
A fuse is an electric / electronic or mechanical device, which is used to protect circuits from over current, overload and ensure the protection of the circuit. Electric fuse was invented by Thomas Alva Edison in 1890. There are many types of fuses, but the function of all these fuses is the same. In this article, we will discuss the different types of fuses, its construction, working and operation and their application in various electronics and electrical systems.
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Construction & Working of a Fuse
A general Fuse consists of a low resistance metallic wire enclosed in a non combustible material. It is used to connect and install in series with a circuit and device which needs to be protected from short circuit and over current, otherwise, electrical appliance may be damaged in case of absence of the fuse and circuit breaker as they are unable to handle the excessive current according to their rating limits
The working principle of a fuse is based on the “Heating effect of Current” i.e. Whenever a short circuit, over current or mismatched load connection occurs, then the thin wire inside the fuse melts because of the heat generated by the heavy current flowing through it. Therefore, it disconnects the power supply from the connected system. In normal operation of the circuit, fuse wire is just a very low resistance component and does not affect the normal operation of the system connected to the power supply.
How to Select Proper Rating Size of Fuse?
While selecting the proper fuse and its rated size for electrical appliances is based on different factors and environments. But the following basic formula shows how to choose the right size of fuse?
Fuse Rating = ( Power / Voltage ) x 1.25
For example, you have to find the right size of fuse for 10A two pin socket.
(1000W / 230V ) x 1.25 = 5.4A
In the above example, 1kW is the power rating which can be controlled through the 2 pin socket and the main supply voltage is single phase 230V AC (120V AC in US).
But you should go for the max i.e. 6A fuse rating instead of 5.4A for safe and reliable operation of the circuit.
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Characteristics of a Fuse
Different types of fuses can be categories on the following characteristics.
- Current Rating & Current Carrying Capacity of Fuse
- Voltage Rating of Fuse
- Breaking Capacity of a Fuse
- I2t Value of Fuse
- Response Characteristic
- Rated voltage of Fuse
- Packaging Size
Below is the brief explanation of the above categories.
Fuse Current Carrying Capacity
Current carrying capacity is the amount of current which a fuse can easily conduct without interrupting the circuit.
The value of maximum current that can safely be interrupted by the Fuse is called Breaking Capacity and should be higher than the prospective short circuit current.
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Rated Voltage of Fuse
Expect the current capacity of current, there is the maximum voltage rating a fuse can handle safely. Each fuse has maximum allowed voltage rating, for example, if a fuse is designed for 32 volts it cannot be used with 220 volts, different amounts of isolation is required in different fuses working on different voltage levels. Bases of voltage rating, a fuse can be HV (High Voltage) LV (Low Voltage), and Miniature Fuses.
I2t Value of Fuse
The I2t terms related to fuse normally used in short circuit condition. It is the amount of energy which carries the fuse element when the electrical fault is cleared by the fuse element.
Response Characteristic of a Fuse
The speed at which the fuse blows, depends on the amount of current flowing through its wire. The higher the current flowing through the wire, faster will be the response time.
Response characteristic shows the response time for an overcurrent event. Fuses which respond rapidly to the over current situation is called ultra fast fuses or Fast fuses. They are used in Many semiconductor devices because semiconductor devices are damaged by over current very rapidly.
There is another fuse which Is called a slow burn fuse, switch fuses do not respond rapidly to the over current event, but blow after several seconds of over current occurrence. Such fuses found their application in motor control electronics systems because motors take a lot more current at starting than running.
As we have mentioned above, AC and DC fuses have a little bit different packaging type, in the same way different applications require different packages to be used accurately in the circuit.
other factors and parameters are marking, temperature derating, voltage drop and speed etc.
Classification of Fuses
Fuses can be classified as “One Time Only Fuse”, “Resettable Fuse”, “Current limiting and non – current limiting fuses” based on the usage for different applications.
One time use fuses contain a metallic wire, which burns out, when an over current, over load or mismatched load connect event occurs, the user has to manually replace these fuses, switch fuses are cheap and widely used in almost all the electronics and electrical systems.
On the other hand, the Resettable fuse automatically reset after the operation when fault occurs at the system.
In the Current limiting fuse, they produce high resistance for a very short period while the non – current limiting fuse produces an arc in case of high current flow to interrupts and limit the current in related and connected circuits.
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Types of Fuses
There are different types of fuses available in the market and they can be categories on the basis of Different aspects.
Good to know: Fuses are used in AC as well as DC circuits.
Click image to enlarge
Fuses can be divided into two main categories according to the type of input supply voltage.
- AC fuses
- DC fuses
There is a little difference between AC and DC fuses used in the AC and DC Systems which has been discussed below.
In a DC system, when the metallic wire melts because of the heat generated by the over current, then Arc is produced and it is very difficult to extinguish this arc because of DC constant value. So in order to minimize the fuse arcing, DC fuse are little bigger than an AC fuse which increases the distance between the electrodes to reduce the arc in the Fuse.
On the other hand, i.e. in the AC system, voltage with 60Hz or 50Hz frequency changes its amplitude from zero to 60 times every second, so arc can be extinct easily as compared to DC. Therefore, AC fuses are a little bit small in sizes as compared to DC fuses.
Fuses can also be categorized based on one time or multiple Operations.
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Cartridge fuses are used to protect electrical appliances such as motors, air-conditions, refrigerator, pumps etc, where high voltage rating and currents are required. They are available up to 600A and 600V AC and widely used in industries, commercial as well as home distribution panels.
There are two types of Cartridge fuses. 1. General purpose fuse with no time delay and 2. Heavy-duty cartridge fuses with time delay. Both are available in 250V AC to 600V AC and its rating can be found on the end cap or knife blade.
Cartridge Fuses are enclosed in a base and can be divided further in Link type cartridge fuses and D Type Cartridge Fuses.
D – Type Cartridge Fuse
D-Types fuse contains an adapter ring, base, cap and cartridge. Fuse base is connected to the fuse cap where the cartridge is inside the fuse cap. The circuit is completed when the tip of the cartridge makes contacts through the fuse link conductor.
HRC (High Rupturing Capacity) Fuse or Link Type Cartridge Fuse
We have already discussed in very details about HRC fuse (High Rupturing Capacity) construction, operation and their applications. It also covers different types of HRC fuses like DIN type, NH Type, Blade Type, Liquid Type HRC Fuse, Expulsion Type HV Fuse, advantages & disadvantage etc.
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High Voltage Fuses
High Voltage (HV) fuses are used in power systems to protect the power transformer, distribution transformers and instrument transformer etc. where circuit breakers may not be able to protect the system. High Voltage fuses are rated for more than 1500V and up to 13kV.
The element of High Voltage fuse is generally made of copper, silver or tin. The fuse link chamber may filled with boric acid in case of expulsion type HV (High Voltage) Fuses
Automotive, Blade Type & Bolted Type Fuses
These types of fuses (also known as spade or plug-in fuses) come in plastic body and two metal caps to fit in the socket. Mostly, they are used in automobiles for wiring and short circuit protection. Fuse Limiters, Glass Tube (also known as Bosch Fuse) are widely used in automotive industries. The rating of automobile fuses are low as 12V to 42V.
In bolted types of fuses, the base of the fuse contacted directly to the base of the fuse, same like HRC Fuses, to read more about Blade Type and Bolted types of fuses related to HRC fuses, check the post. Types of HRC Fuses.
SMD Fuses (Surface Mount Fuse), Chip , Radial, and Lead Fuses
SMD Fuses (Surface Mount Device and the name derived from SMT = Surface Mount Technology) are chip types of fuses (also known as electronic fuse) are used in DC power applications like Hard Drive, DVD players, Camera, cell phones etc where space playing an important role because SMD fuses are very tinny in size and hard to replace as well.
Below are some additional types of SMD Fuses and Leaded fuses.
- Slow – Blow Chip Fuses
- Fast Acting Chip Fuses
- Very Fast Acting Chip Fuses
- Pulse Tolerant Chip Fuses
- High Current Rated Chip Fuses
- Telecom Fuses
- Through-hole styles fuses
- Radial Fuse
- Lead Fuse
- Axial Fuse
The most famous kit-kat fuse (also known as rewireable fuse) mostly used in industries and home electrical wiring for small current applications in Low Voltage (LV) systems.
Rewireable fuse contains 2 basic parts. The inner fuse element as fuse carrier made of tinned copper, Aluminum, Lead etc and the base made of porcelain having the IN and OUT terminals which is used to be in series with the circuit to protect.
The main advantage of a rewireable fuse is that It can be rewired easily in case it is blown due to short circuit or over current which melts the fuse elements. Simple, put another wire of fuse elements with the same rating as before.
As mentioned above, thermal fuse is a one time used only fuse. They are temperature sensitive fuse and the fuse element is made of temperature sensitive alloy. They are known as Thermal Cutouts (TCO) or Thermal Links.
In a thermal fuse, the fuse element holds a mechanical spring contact which is normally closed. When high currents due to over current and short circuit flow through the elements of the fuse, the fuse elements melts down which lead to release the spring mechanism and prevent the arc and fire and protect the connected circuit.
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Resettable fuse is a device, which can be used multiple times without replacing it. They open the circuit, when an over current event occurs and after some specific time they connect the circuit again. Polymeric positive temperature coefficient device (PPTC, commonly known as a resettable fuse, poly-switch or poly-fuse) is a passive electronic component used to protect against short current faults in electronic circuits.
Application of resettable fuses is overcome where manually replacing fuses is difficult or almost impossible, e.g. fuse in the nuclear system or in an aerospace system.
Uses and Applications of Fuses
Different types of Electrical and Electronic Fuses can be used in all types of electrical and electronic systems and applications including:
- Motors & Transformers
- Home distribution boards
- General electrical appliances and devices
- Cell phones
- Game systems
- Digital cameras
- DVD players
- Portable Electronics
- LCD monitors
- Battery packs
- Hard disk drives
- Power convertors
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