The Difference Between Electrical Relays
Electromechanical Relays vs Solid-State Relays
By: Megan TungA relay is a power switching solution used to allocate power without manually opening and closing a switch. A relay is utilized when it is necessary to switch a small amount of power to a larger amount of power. There is a very high, almost infinite resistance when nonconducting (open) and a very low resistance when conducting (closed). They can be used in various applications, such as heating, lighting, and motion control.
Electromechanical Relays (EMR)

In the image above the plastic outer case of the relay is removed. On the left are the two spring contacts. On the right is the electromagnet coil. When the current flows through the coil it turns into an electromagnet, which pushes a switch to the left, forcing the spring contacts together, and completing the circuit they are attached to.
Solid-State Relays (SSR)

To learn how to wire a solid state relay with ease, check out Tech Tip: Wiring a Solid-State Relay.
Differences
Unlike EMRs, SSRs have no moving parts that will wear out, and therefore no contact bounce issues. Due to an optoisolator rather than moving parts, the life span of the SSR is often longer than the EMRs. The SSR is able to switch “ON” and “OFF” much faster than a mechanical relay’s armature can move. When SSRs are in the on-state, substantial resistance is present, which can lead to significant heat generation when current is flowing. Therefore, SSRs should be mounted on heatsinks. Solid-state relays normally have only one output contact, while electromechanical relays can multiple output contacts.Relay Applications
Solid-state relays can be used for:
- Applications requiring high speed and frequent switching operations
- Applications in high vibration environments
- Applications where the relay has to be located near sensitive automation components, such as PLC’s, HMIs, and temperature controllers
Electromechanical relays can be used for:
- Applications requiring a wide output range from the relay
- Applications using motors and transformers requiring high starting amps
- Applications where the initial installation budget is very limited
Megan Tung is an intern at Jameco Electronics. Megan is a rising junior at the University of California, Santa Barbara. She is interested in photography, music, business, and engineering.