What Are Common Types of Circuit Protection Devices?

Posted on January 11, 2021 James Hinds Aerospace

Due to the volatile nature of electricity and the sensitivity of electronics that rely on it, it is important that there are a number of protective devices in aircraft and fail-safes present within a circuit for protection. From short circuits to ground faults, surges of electricity can easily travel through wiring and cabling unhindered due to the low resistance of such components. As such, circuit protection devices may be used to ensure that appliances and electronics are well protected, as well as those who are near them or operate them. In this blog, we will provide an overview of fuses, circuit breakers, thermal protectors, and arc fault circuit breakers, all of which are commonly used as circuit protection devices.


Fuses are a useful circuit protection device that guard circuits from current levels that exceed safe values. As a small device featuring a metal strip, the fuse is placed in the path of current so that it passes through it. For its operation, the wire of the fuse is specifically designed to melt when current levels reach a specific threshold which causes the current to be interrupted. Because of this method of operation, fuses are referred to as sacrificial devices and require replacement after their use. When procuring fuses for a specific electrical system or circuit, it is important to ensure that they are the correct type and exhibit the desired capacity for the application in question.

Circuit Breakers

Circuit breakers are another commonly used circuit protection device, and their operation is similar to fuses in the fact that they interrupt currents when values surpass a threshold. Their difference, however, is that they are capable of being reset after they are tripped, thus can be used multiple times with ease. Despite this, most circuit breakers will require manual resetting before they allow for current to pass through as normal.

Depending on the application in question and the amount of current that is running through an electrical system, varying circuit breakers may be implemented. In aircraft, as an example, magnetic circuit breakers are used as electrical faults will cause the activation of a magnetic field, resulting in an armature tripping the breaker. In more recent years, the arc fault circuit breaker has risen as a new circuit breaker type which has capabilities that surpass the thermal protection abilities of traditional breakers. When a typical wiring fault occurs, arcing can result which presents a risk of fires and electrical failures. With an arc fault circuit breaker, signatures of arcing can be detected for breaking the circuit.

Current Limiters

Current limiters are also similar in their functionality as compared to a fuse, though they can withstand a larger amount current when a fault occurs. Within aircraft, current limiters are typically implemented in order to sectionalize the circuit or bus components of the electrical system. Like a fuse, current limiters require replacement when they are activated, though they tend to be able to withstand values of up to 30 amps.

Thermal Protectors

While electricity can cause harm through shock and short-circuiting, there are also high amounts of heat contained within electricity. With a thermal protector, motors can be safe from excessive temperatures that would typically damage the system. To protect devices with a thermal protector, circuits are forced open when heat exceeds set levels due to the expansion of a metallic strip. When the strip begins to cool and returns to its original form, contacts will be established once again to open the circuit.

Control Devices

Control devices are a category of circuit protection devices that contain various components that assist in the management of electrical circuits and systems. As all power routes, circuits, and wires do not often need to be powered all at once for operations, control devices may be used to limit the path of electricity. Coming in the form of switches and relays, such components serve to distribute and control current through a system.

With components such as the push button switch, toggle switch, or microswitch, the paths that current can travel through within a system can be controlled through various means. While switches are fairly simplistic in their design and functionality, they are paramount to the overall operation of a complex electrical system. Relays, on the other hand, are a type of electromechanical switch in which large currents can be controlled with smaller ones. To achieve this, relays utilize electromagnets and the properties of electromagnetism to switch positioning.

With a combination of various circuit protection devices, electronics, appliances, and individuals can all be safeguarded against the dangers of electricity. At ASAP AM Spares, we can offer you competitive pricing on switches, relays, thermal protective devices, and other electronic components that you may need for your operations. Explore our robust part catalogues today, and our team of industry experts are readily available 24/7x365 to assist you through the purchasing process as needed.

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