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What Is the Difference Between an AC and DC Relay?

In the world of electrical engineering and automation, alternating current (AC) and direct current (DC) relays both play a crucial role in controlling and switching electrical circuits. However, it is important to note that there are distinct differences between them. In this article, we will delve into the disparities between these two types of relays, exploring how their unique features define their usage. Knowing these essential differences can be helpful not only for understanding how each can be used, but also for choosing the right device for an assembly.

Understanding AC Relays

AC relays are a type of relay which handles alternating current, a form of electrical current that is defined by the way it periodically changes its direction. To accomplish operations, the relays work on the principle of a magnetic circuit, where an alternating current in the coil of the relay creates a varying magnetic field. This magnetic field then attracts or repels the relay's armature, resulting in the opening or closing of its electrical contacts. As a device made to handle AC, these relays are typically used in applications where an AC power supply is involved, such as residential and commercial electrical systems. They are also engineered to handle high voltage and current levels, making them suitable for controlling heavy-duty electrical equipment.

Understanding DC Relays

On the other hand, DC relays are specifically designed to handle direct current, which flows consistently in a single direction. That said, DC relays are commonly used in applications where a DC power supply is present, such as automotive systems, battery-powered devices, and electronic control circuits. Because DC signals are generally less powerful than AC, these relays are typically smaller in size and have lower voltage and current ratings compared to AC relays. Moreover, they require the addition of a flyback diode, a protective feature which is not needed in AC relays. When a DC relay is used to control an inductive load, such as a relay coil or motor, the sudden interruption of current can produce a voltage spike. The use of a flyback diode provides a path for this energy, protecting the relay and other components from potential damage.

Choosing the Right Relay for the Job

The decision between using an AC or DC relay depends on the specific requirements of the application. With these requirements in mind, some specific factors to consider include the present power source, voltage levels, current ratings, and the type of load being controlled. Additionally, it is always important to use AC relays with equipment that uses an AC power system, while DC must be used for DC power supplies.


AC and DC relays are designed to handle different types of electrical currents and have distinct characteristics that make them suitable for specific applications. Nevertheless, both are helpful elements in a number of electrical applications where they can assist in controlling the way that current flows through a circuit. If you are in need of a dependable relay to support your operations, there is no better source than NSN Gamut. Check out our inventory of available items in the “electrical connectors” section of our website to find a diverse range of high-quality relays, in addition to other key industrial parts. With quality assurance at the forefront of our operations, we promise expert solutions that can match even your harshest operational requirements.


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