Fuses, Sockets and Circuit Breakers Overview

What Are Fuses?

Fuses protect circuits from overcurrent conditions. A fuse is a resistor that has a low resistance value. In the event that the circuit to which it is attached receives too high a level of current, the fuse will burn out, breaking the circuit. These are low-cost components that are designed to be destroyed in the event that their protection features are needed.

How Does a Fuse Work?

Most fuses have a thin strip of metal in them that serves as the resistor component. When the fuse receives a current over its rated amperage, the metal within the fuse heats up and, eventually, melts, creating an air gap between the contacts on the fuse. This effectively breaks the circuit, providing protection against dangerous electrical conditions.

What Are the Characteristics of a Fuse?

Fuses have various characteristics that denote what types of applications they’re appropriate for. These characteristics include the current that the fuse can carry safely—without burning out—the speed at which the fuse blows and others.

The rated current is usually listed on the body of the fuse with the abbreviation In or IN. This is the level of current that the fuse is designed to carry without blowing out. A 20A fuse, for instance, would be able to function with up to 20A flowing across it, but if the current were to go higher than that the fuse would blow.

The speed of a fuse describes how quickly it melts when it is exposed to an overcurrent condition. The speed with which a fuse melts down depends upon the metal of which it is made and the amount of current that it is actually receiving.

Fuses can be designed to blow quickly, slowly or on a time delay, each type having its specific purpose and appropriate application. For instance, in devices with very sensitive electronics, fast-blowing fuses are generally used to eliminate an overcurrent condition as quickly as possible, providing a better level of safety for the device.

The I2t value is a measure of how much energy is released when the fuse blows. This is typically obtained from documentation about the fuse provided by the manufacturer of the device. Anytime a fuse does blow, heat damage and magnetic forces are generated, and this value gives a measure of that.

A fuse’s operation depends upon the temperature it’s at when installed and operating within the circuit. The temperature derating number denotes the effects of different temperatures on the operation of the fuse. Cold temperatures generally allow more current to flow through the fuse without bringing it out and warm temperatures less.

The breaking capacity of the fuse indicates the highest current level that the fuse can safely break. Fuses need a higher breaking capacity if they are used in high-voltage applications.

The rated voltage denotes the highest voltage that the fuse can safely handle. If the open circuit has a higher voltage than this figure, there is the potential for arcing and other issues that may compromise safety.

The voltage drop is most important for low voltage applications. A fuse’s resistance characteristics change as it is heated up during operation. The fuse will eventually reach a stable state in this regard, but this has to be taken into account in certain applications and the information is provided by the manufacturer.

What Is a Fuse Used For?

Fuses are among the most common of all electrical components, owing to the amount of safety that they provide. They protect the devices in which they are installed from overcurrent conditions and provide an important safety enhancement for users. They are commonly used in circuits where a circuit breaker might be too expensive or inconvenient, as fuses are very low cost and easily replaced. They are used in circuits ranging from very low-voltage designs to the exceptionally high voltages used in electrical utility systems.

What Types of Fuses Exist?

There is a huge number of fuse designs on the market, owing to the fact that they are used in so many different applications. Fuses are very heavily used in the automotive industry and include glass tube fuses, blade fuses, and other designs. These are usually designed to be easy to remove and replace when they are blown and are commonly grouped together in a convenient spot in the car.

House fuses have been largely replaced by circuit breakers. The designs, however, typically have a screw-in socket similar to what would be found on a light bulb and a see-through window, allowing the user to check the state of the fuse material that provides protection.

High voltage fuses are found in very large industrial settings and in power distribution systems. These fuses sometimes have specialized designs that make it easier for technicians to replace blown parts quickly.

What Type of Materials Are Used Within a Fuse?

The fuse material is usually copper, silver, zinc, or aluminum. Alloyed materials are also used to provide specific fusing characteristics.

What Are Considered the Characteristic Parameters of a Fuse?

The characteristic parameters of a fuse, listed in detail above, are usually indicated on the fuse itself or in literature provided by the manufacturer. They include:

  • Rated current
  • Speed
  • I2t
  • Breaking capacity
  • Rated voltage
  • Voltage drop
  • Temperature derating

What Are Fuse Holders?

Fuse holders provide the installation hardware for the fuse. They are usually designed so that the wrong fuse cannot be placed in the holder, with a tab or similar device preventing accidental misuse.

What Are Fuse Tools?

Fuse tools are simple devices that are designed to make it easy to remove or install a fuse. They are designed to be used with a specific type of fuse: blade, screw-in, etc.

How Do You Test a Fuse?

Most fuses have a glass element that makes it easy to inspect a fuse visually to see if it is blown. Alternately, a voltmeter can be used to test whether or not the fuse is allowing current to pass across it.

What Are Circuit Breakers?

A circuit breaker provides the same type of protection for a circuit as does a fuse, but is a switch device that can be reset if it is tripped. Their function is identical to that of a fuse, however; to protect a circuit from an overcurrent condition.

From Where Do Circuit Breakers Originate?

Circuit breakers were first developed in the 1920s. As the need for increased protection for circuits became more pressing with higher-powered and more sophisticated electrical grids, the development of circuit breakers kept pace.

How Does a Circuit Breaker Function?

There are several different types of circuit breakers and they function somewhat differently from one another. All of them, however, detect an overcurrent condition and trip some sort of mechanism, breaking the circuit. The specific design of the circuit breaker depends upon the amount of voltage it is designed to work with.

The circuit breaker contacts open up in the event of a fault condition. This is usually accomplished by way of compressed springs or compressed air. In very large circuit breakers, a solenoid is usually used to provide the mechanical action, with special devices used to suppress arc that may be generated when the circuit is opened up.

What Are Circuit Breakers Used For?

Circuit breakers are protective devices that are used in a huge range of applications. They are used in everything from very small electronic devices to household outlets to substations and beyond. They may be grouped together in a breaker box, such as would be seen in most households, or may be large enough to take up a substantial amount of floor space in an industrial setting. Their main advantage is that they are reusable and that they can react nearly instantaneously in the event of a fault, making them excellent for applications such as the fault-protection switches seen in many household outlets.

What Types of Circuit Breakers Exist?

There are several different circuit breaker designs on the market, with most of them being specialized toward a specific usage.

Magnetic Circuit Breakers

A magnetic circuit breaker uses a solenoid component. The solenoid pulls apart the contacts in the device in the event of an overcurrent condition. These circuit breakers are complex, sometimes employing fluid and hydraulic mechanisms to offer more control over the solenoid’s action.

Thermal Magnetic Circuit Breakers

Thermal magnetic circuit breakers are fast-acting devices that use an electromagnet and bimetallic strips to react to different types of overcurrent conditions. The electromagnet component can react instantly in the event of a quick surge of current and the strips to longer-term overcurrent conditions.

Common Trip Breakers

These are commonly seen on circuit breaker panels. They combine several different conductors into one circuit breaker, allowing the device to trip in the event that any of those conductors reaches an overcurrent condition. They are usually identifiable by the several switches joined into one on the device.

Low-voltage Circuit Breakers

Anything under 1,000VAC is considered to be a low voltage device. Low-voltage circuit breakers are very common devices, used in everything from cars to household circuitry. There are many different designs for these devices, and many of them are mounted together in a board, providing control over several different circuits from one location.

Medium-voltage Circuit Breakers

Voltages from 1,000VAC to 72KV are considered medium voltage. Circuit breakers used for such applications include vacuum circuit breakers, air-break circuit breakers, and oil-filled circuit breakers. Hexafluoride gas is also used in some of these circuit breakers to extinguish arcs. These can be found in industrial settings and in substations.

High-voltage Circuit Breakers

Beyond 72KV is considered high voltage. The circuit breakers used in such applications are very large, often employing air, oil, gas, or other technologies to extinguish the sparks that are generated when the circuit is broken. These are commonly seen in power distribution networks.

Disconnecting Circuit Breaker

A disconnecting circuit breaker is a relatively new device that eliminates the maintenance requirements that went along with some older designs. The breaking chamber houses the disconnecting hardware in these devices, which eliminates the need to have a separate disconnecting device. These circuit breakers often employ advanced technology, such as fiber optics, in their designs.

How Do Fuses Compare with Circuit Breakers?

Fuses are very simple devices that are sacrificed when they are used. Conversely, a circuit breaker can be reset and used over and over again, within the limitations specified by the manufacturer.

What Are Sockets?

A socket is a type of electrical connector designed to join two electrical circuits. They are typically designed so that they can receive only one type of connector. For example, the screw threads and size of a typical household light socket will only be compatible with a specific type of bulb.

Sockets are sometimes outfitted with protection devices, such as the ground fault protectors on common household electrical sockets, which are very likely to be found in areas where a fault is particularly dangerous, such as a bathroom.

Sockets for the same type of appliance may vary from nation to nation, owing to the fact that the voltage used in household mains is different in different countries. The socket design provides a way to prevent the wrong appliance, or an appliance requiring more or less voltage, from being plugged into an inappropriate socket.

Some sockets are provided with locking mechanisms that prevent the junction of the circuits from being broken accidentally.

What Are Electrical Installation Accessories?

Electrical installation accessories include sockets, mounting plates, junction boxes, and other hardware that is required for the installation of a wide variety of different types of electrical circuits.

These accessories are sometimes bundled in kits, making it easy for engineers and electricians to get necessary parts for the installation of specific types of circuits. The accessories have to be rated to withstand the operating conditions under which they will be used, of course and have to be up to building codes to be acceptable. The electrical installation accessories include testers and other safety equipment, as well.

1 comment

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