When a circuit overloads, it can be dangerous and damaging to electrical devices that are connected to it. Fortunately, there is an electrical device designed specifically to prevent this. That device is known as a fuse. There are many types of fuses available, each with different characteristics.
Here in this article, we will explain fuses in-depth. First, we start with the definition: what is a fuse. Next, we explain its construction and how it works. Then we continue to characteristics, classification, types, uses, and applications. Finally, how to select a fuse. With no further ado, let’s start.
What is a Fuse?
First thing first, what is it? What exactly is a fuse? To put it simply, a fuse or electric fuse is an electrical device designed specifically to protect a circuit’s components from overload and overcurrent. It is a safety device and is meant to be a circuit’s weak link, sacrificed when overload or overcurrent occurs.
There are many types of fuses. However, regardless of the type, all fuses work on the same principle. All are meant to protect the circuit. The fuse was patented in 1890 by Thomas Edison. It was patented as part of Edison’s electric distribution system. The idea of a fuse, however, has been around as early as 1864.
Construction & Working of a Fuse
The main purpose of a fuse is the same: to break the circuit in the case of overload or overcurrent. The types of fuses don’t matter as all have this same purpose. The simplest type of fuse consists of a resistive element. This resistive element is selected for its melting point.
When a current flows through this resistive element, a small amount of voltage is created across it. The voltage drop does not affect the circuit downstream as the amount is small enough. At the same time, some power transforms into heat. This, in turn, increases the element’s temperature.
For normal currents, the heat is not enough to melt the resistive element. In the case of overload or overcurrent, where the current exceeds the fuse’s rated current, the melting point of the element is reached fast. When this happens, the element melts, thus interrupting the circuit.
The rated current of a fuse depends on how long and thick the resistive element is. As for the material, fuse elements are made of different alloys. For example, aluminum, zinc, copper, silver as well as other alloys that have predictable trip currents. Also, the material the element is made of must not corrode or oxidize over time.
Characteristics of a Fuse
Before we delve into types of fuses, we will explain the characteristics of a fuse first. What makes an ideal fuse element? An ideal fuse element has the following characteristics:
- High conductivity
- Low melting point
- Does not deteriorate over time due to oxidation
- Low cost
Unfortunately, there is no material that possesses all the above. There are only materials that fit some characteristics but not the others. Let’s take copper as an example. Copper has low cost and high conductivity. However, it oxidizes quickly. Thus, a compromise must be made when selecting a fuse.
Classification of Fuses
Fuses work in a simple way. While that is true, there are many different types of fuses. The question is, how are these types classified? The basic classification of fuses is its usability. That is, whether they are for one-time use only or resettable.
When an overload or overcurrent occurs in a circuit, the fuse is blown out. As the fuse is blown out, it has to be replaced manually. These types of uses are commonly used in electronics systems and electrical devices in industries, houses, consumer products, and others.
Unlike one-time-only fuses, resettable fuses don’t need to be replaced manually. Instead, resettable fuses will reset automatically after the overload or overcurrent occurs by changing their resistance.
That is not the only classification of fuses, of course. Fuses are also classified based on whether they are current limiting or not. When overload or overcurrent occurs, current-limiting fuses work by briefly creating high resistance in the circuit while non-current-limiting ones disrupt the current by producing gases.
Types of Fuses: DC and AC
There are actually two main categories of fuses type: AC and DC fuses. That said, the categories can be divided into three, as AC fuses are further categorized based on their voltage. What are the 3 types of fuses? They are DC, High Voltage (HV), and Low Voltage (LV) fuses. HV and LV fuses belong to the AC fuse category.
What makes these types of fuses different from AC fuses? The main difference between the two types is in their size. In the case of the DC circuit, when the current exceeds the rated current, the fuse’s metallic wire melts, separating the connection between the rest of the circuit and the power supply.
DC is always above 0V as well as a constant value. As a result, there is a risk of an electric arc being made between the melted wires. This will be hard not only to avoid but also to turn off. This is the reason why compared to AC fuses, DC fuses’ electrodes are situated at a greater distance.
As the electrodes’ distance is greater, the risk of an electric arc created is minimized. With the increased distance, the size of the fuse is also increased. This is why these types of fuses are relatively larger than AC fuses.
There are five types of DC fuses, they are
All automobile has fuses. There are three common types of automotive fuses: blade type, glass tube, and fuse limiters.
This is the most common type of all. The fuse element is inside a glass envelope, which makes it easy to determine if it has been blown from overload or overcurrent. There are many cartridge fuse variants. Two of the most commons are slow-blow fuses and fast-blow fuses.
These are self-resetting fuses. Due to their construction, the conductivity of these types of fuses is restored as their temperature decreases. This is why there is no need to physically replace them.
Semiconductor switching devices are quite sensitive to current spikes, including even small ones. Semiconductor fuses are used to protect them.
Fuse is also used with an overvoltage protection device in order to protect circuits from current and voltage spikes.
The current and voltage of AC circuits oscillate 50 to 60 times per second, with the frequency changing from minimum to maximum. Due to this, there is no risk of an electric arc being created between the melted wires. As a result, AC fuses are much smaller in size than their DC counterparts.
As we explained earlier, these types of fuses are further categorized into HV and LV fuses. There are two types of HV fuses, HRC and expulsion fuses and there are five types of LV fuses: drop out, cartridge, striker, switch, and rewireable fuses.
- HV Fuses
- HRC fuses
These fuses are usually used for very high fault currents.
- Expulsion fuses
These fuses contain chemicals that produce gases when heated, which extinguish the electric arc.
- LV Fuses
- Drop out fuses
Drop out fuses are equipped with a spring-loaded lever arm. When an overload or overcurrent occurs, this lever arm retracts, preventing damage to other parts of the circuit.
- Cartridge fuses
These fuses consist of a transparent envelope that surrounds the fuse element. There are two types of cartridge fuses: blade type and bolt type.
- Striker fuses
Fuses that are equipped with a spring-loaded striker. This striker can be used to activate other switchgear besides being a visual indicator that shows if the fuse has blown.
- Switch fuses
They are manually operated using a handle, which can both connect and disconnect the fuses.
- Rewireable fuses
As the name suggests, these types of fuses can be rewired and put back in their socket when the fuse is blown.
Uses and Applications of Fuses
Fuses are among the main components in almost every electronic circuits and systems. Below are some of the uses and applications of fuses:
- All electrical appliances
- Home electrical wiring
- Power transformers
- Power adapters
- Motor starters
- All automobile
- All electronic devices
- Mobile phones
- Gaming consoles
How to Select Proper Rating Size of Fuse?
How do you choose a fuse? You choose it by considering the fuse rating. The fuse rating equals to power divided by voltage multiplied by 1.25. As a formula, it looks like this:
Fuse rating = (Power/Voltage) x 1.25
And here are the steps:
- First, select a fuse. For example, if you want resistive load, select fast-acting fuses. Or if you want inductive load, select time-delay fuses.
- Write down the power of the appliance. You should find it in the appliance manual.
- Next, write down the voltage rating. The voltage rating has to be larger than the circuit voltage. This is so the appliance can be protected properly.
- Use the formula and calculate the fuse rating. After the calculation, use the next highest rating after the result. For example, if the result of the calculation is 8.6 amps, select a 9 amp fuse.
In short, a fuse is a safety device that works based on a simple principle. If a short circuit or overload occurs, the fuse will shut off the power to the rest of the circuit. Thus, protecting the rest of the circuit from damage. There are many types of fuses, each with their own characteristics.