Widely in electrical engineering and electronics, a fuse serves as an electrical safety device that protects electrical appliances like refrigerators, televisions, computers, etc. from damage by high voltage. A fuse is often applied to the socket of these appliances so that any overcurrent will be stopped before entering the device.
A fuse can be said to be a sacrificial device because when too much current flows through it, the metal wire or strip in it get melted and open. This wire can be either rewired or the fuse must be replaced. So, in this case, fuses defend any overcurrent condition from entering electrical appliances.
Today you’ll get to know the definition, construction, applications, components, diagram, classification, types, and working of a fuse. You’ll also get to know the advantages and disadvantages of fuses in their various applications.
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What is a fuse?
A fuse is a safety device that is used to protect an electrical circuit from overcurrent. It’s applied to various electrical circuits since overcurrent conditions can occur anytime. Fuses works as a circuit breaker or stabilizer that also protect devices from damages. But in its case, a thin strip or strand of metal is used to block a huge amount of current or an excess current flow from entering an electrical circuit. When this happens, the fuse melts, causing the thin strip to separate when then stop the power supply to the appliance.
Since there various types of fuses with different classification out there, their construction will also be of different material to meet the demand of applications. A fuse element is made of zinc, copper, silver, aluminum, or alloys because they provide stable and predictable characteristics.
With this material, the fuse ideally would carry its rated current indefinitely, making melt quickly on a small excess. These elements are not easily damaged by minor harmless surges of current and they do not oxidize or change in behavior after a long period of service. Fuse elements are shaped to increase heating effects. In a larger fuse, the current may be split between multiple strips of metal.
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Applications of fuses
Below are the applications of various types of fuses:
- Fuses are used in all automobiles such as cars, trucks, trailers, boats, etc.
- Gaming console also finds great use of fuses.
- Accessories like laptops, cell phones, printers, scanners. In fact, all electrical accessories have a fuse.
- A high voltage fuse is used in power transformers.
- Other components like capacitors, power converters, motor starters, and transformers make good use of fuses.
- LCD monitors and battery packs contained fuse in them.
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Components of fuses
Because there are many types of a fuse with different working capacity their components are different. However, the basic components of a fuse are a thin strip or strand of metal. The figure below gives more details about the various parts of fuses depending on the types.
Characteristic of fuses
Below are the characteristics of fuses in an electrical electronic system:
This is the maximum amount of current hold in the fuse without melting. It’s known as current ratings. It’s the current carrying capacity, measured in amperes and it’s the thermal characteristics.
Current (Cin)=75%Current (rating)
This is when the voltage connected in series with fuse does not increase voltage rating i.e. V(fuse) >V (open ckt)
This is the amount of energy carried by the fuse element when any electrical fault or when a short circuit happens. It measures the heat energy due to a current flow of fuse and it’s generated when the fuse has blown.
Interrupting or breaking capacity;
This is the maximum rating of current without harm interrupted by the fuse
Breaking capacity > maximum rated voltage
Breaking capacity <short ckt current
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This is when excessive current flows, causing the fuse element to melts and opens the circuit. Because of this resistance change and the voltage, the voltage drop will become lesser.
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This is when the operating temperature is higher, resulting in a lesser current rating, thus the fuse melts.
The graph below shows the temperature and current carrying capacity of a fuse. The process shows that at the point where three lines meet at 25 degrees Celsius, the current carrying capacity of the fuse will be 100%. After some time, the current capacity decreases at slow blow fuse, which then decreases up to about 65 degrees C. the result shows that an increase in temperature will decrease the current carrying capacity of the fuse.
Selection consideration of fuses
Below are the things to consider while selecting types of fuse:
Fuse rating = (watts/volts) x 1.25
- Know the power (watts) of the appliance – it’s usually seen on the appliance manual
- Know the voltage rating; the voltage must be higher than the circuit voltage so that it can properly protect the device.
- Select fuse like the time-delay type for inductive loads and fast-acting fuses for resistive loads.
- Use the highest fuse rating after calculation. For instance, the calculated fuse rating might be 5.334 amps, you’re expected to use a fuse of 6 amp.
Classification of fuses
Classification of fuses is a category where various types of fuses fall into. All fuses can be classified as either AC and DC fuses. AC fuses are also divided into two parts; high voltage fuses or low voltage fuses depending on their design and element they are made. The figure below arranges the various types of fuses according to their classification.
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Different types of fuses
Below are the various types of fuses and their functions:
DC fuses – DC fuses are larger in size and have contact value above 0V so that the circuit won’t be easily neglected and turn off. There is a possibility of an electric arc between melted wires. To overcome this, electrodes are placed at larger distances and thus the size of DC gets increased.
AC fuses – AC types of fuses are smaller in size as they oscillate at about 50-60 times every second from minimum to maximum. Because of this, the chances of arc between the melted wires is eliminated. Hence, they can be parked in small sizes.
Just as earlier mentioned, AC fuses are further categorized into two parts; low voltage fuses and high voltage fuses.
Types of low voltage fuses (LV)
Cartridge fuse types:
these types of fuse are totally closed in a container and have a metal wire contact appearing in glass. Cartridge types of fuses are of two types; D-type and link types or HRC (High Rupturing Capacity) fuse.
D-type cartridge fuses – this fuse consists of a cartridge, fuse base, cap, and adapter ring. The cap is mounted to the fuse base, which is fitted with the fuse element with cartridge through an adapter ring. The fuse begins its work when the cartridge tip makes contact with the conductor.
Link-type or HRC (High Rupturing Capacity) Fuses – these types of fuse allow the flow of current to be given under normal condition. Arc produced by the blown fuse is controlled as the fuse is made of porcelain, silver, and ceramic. The container of the fuse element is filled with silica sand. These types of cartridge fuses are further divided into two;
- Blade or plug-in type – the body of the fuse is made of plastic and can be easily replaced in the circuit without any load.
- Bolted type – conducting plates are fixed to the fuse base in these types of a fuse.
Rewireable or kit-kat fuse:
Rewireable types of fuses are good in such a way that all its body are insulated, they can be easily removing when current is flowing through the fuse without causing electrical shock or injury. Its base acts as an incoming and outgoing terminal made of porcelain and the fuse carrier is used to hold the fuse element which is made up of copper, aluminum, tin, lead, etc.
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Striker types of fuses are used for closing and tripping circuits. They have enough force and displacement.
A switch fuse is basically a metal encloses a switch and fuse. It’s far used for low and medium voltage level.
In a drop out fuse, its melting causes the fuse element to drop under gravity about its lower support. They are used in outdoor transformers for protection.
Types of High voltage (HV) fuse
All types of high voltage fuses are used on voltage rated up to about 1.5 Kv to 138 K. they are used to protect instrument transformers and small transformers. Arc is producing when the heat is created, which causes boric acid to evolve a high amount of gases. This is why it’s used in outdoor applications. It’s made of silver, tin, and copper. The high voltage fuses are of three types:
Cartridge HRC fuse – is similar to the low voltage version of this fuse, only that there are some added features in this type. The figure below shows its components and features.
Liquid HRC fuse – these types of fuse are used for circuits up to 100A rated current and system of about 132 kV. It has a glass tube filled with carbon tetrachloride and it’s one end is packed and the other is fixed with a phosphorus bronze wire. During its operation, a liquid is used in the fuse to extinguish the arc, resulting in to increase in short circuit capacity.
Expulsion HRC fuse – this is an escapable fuse, that is, the expulsion effect of gases produced by internal arcing. Boric acid is filled in the fuse link chamber for the expulsion of gases.
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The working of fuses is less complex and can be easily understood as it works with the principle of heating effect of current. Just as earlier mentioned, it’s made up of a thin strip or strand of metal wire which is a non-combustible element. This metal wire is connected between ends of the terminals. It’s always connected in series with the electrical circuit.
Whenever excessive current or heat is created due to heavy current flow in the circuit, the fuse melts down. This is because of the low melting point of the element and opens the circuit.
This excessive flow may lead to the breakdown of the wire and therefore stops the flow of current. The fuse can be rewired when open or can be replaced or changed with a new one of the same ratings.
Fuses also act like circuit breakers, used to break circuits when a sudden fault occurs in the circuit. It does not act only as a protector but also used as a safety measure to prevent humans from harm. The figure below shows how a fuse work.
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Watch the below to learn more about how fuses work:
Advantages and disadvantages of fuses
Below are the benefits of an electric fuse in their various applications:
- Overload or high current are terminated.
- The absence of a fuse causes electrical faults that can occur in the wiring or burn the electric appliance.
- An electrical hazard is reduced as burning electronics can lead to an uncontrolled fire.
- Safe cost of repair in appliances.
- The fuse itself is cheap and can be easily replaced.
- Most types of fuse are inexpensive.
- Additional care or maintenance is not required.
- They are portable and can be easily moved around.
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Despite the advantages of fuses some limitations still occur. below are the disadvantages of fuse in their various applications:
- The time-current feature will not be every time-synchronized with that of the safeguarding element.
- Features of reversible time-current permit the device to be employed for overload safeguarding
Fuse are protective components that keep electrical appliances from overload or high voltage current. In this article, we’ve gone in-depth on the device called fuse, its definition, application, components, diagram types, working, etc. were discussed.
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