Relays are electrically operated switches that control high-power devices using low-power signals. Relays control one circuit by switching contacts in a control circuit, usually not directly switching the load. Control signals are typically in the range of 3 – 32 volts DC. Relays also provide protection by detecting electrical abnormalities such as overcurrent, undercurrent, overloads and reverse currents to prevent equipment damage.There are different types of relays, such as machine control relays, reed relays, electromechanical relays (EMRs) and solid-state relays (SSRs). In this article, we examine the differences between these types of relays, and understand seven solid reasons to use solid-state relays.
Types of Relays
Machine control relays are operated by a magnetic coil. These heavy-duty relays are usually used to control starters and other industrial components. They are more durable, but also more expensive, than general purpose relays such as electromechanical and solid-state relays.Reed relays have a switching design with one contact that is normally open, which provides a fast operating switch. Reed relays are hermetically sealed in a glass envelope, so their contacts are protected against contaminants, fumes and humidity. This design ensures reliable switching and longer contact life.Electromechanical relay contacts are operated by a magnetic force. This relay type is robust, but bigger and slower than solid-state relays. EMR operation time is in the range of 5 – 15 ms, which is insufficient for some applications. EMRs also contain moving parts, which are the main reason for their shorter life span. However, EMRs are available in a wide range of switch configurations and they are affordable and easy to replace.

Read more: 7 Solid Reasons to Use Solid State Relays