What is the primary difference between an AC and DC relay?

The primary difference between an AC and DC relay lies in the signal type used to operate them. AC relays are designed to operate with alternating current, while DC relays are intended for direct current. This difference in signal type affects the design and functionality of the relay, particularly in how the coil reacts to the voltage supplied.

AC relays typically include features that enable them to handle the characteristics of alternating current, such as the varying voltage and frequency, whereas DC relays are optimized for the steady voltage of direct current. This leads to differences in the coil's construction and the materials used that can withstand the type of current being used.

Understanding the differences in signal types is critical for ensuring the proper relay is selected for a specific application, as using the wrong type could lead to inefficient operation or even damage to the relay. In contrast, coil resistance, physical size, and current capacity may vary among different relays but do not fundamentally differentiate between AC and DC types in the same way that signal type does.