Relays and contactors use a variety of technologies to switch signals and power connections. Many devices called relays use similar techniques and topologies, but the terminology can be confusing.

Here’s an interesting introduction to Reed Relays, Mercury Displacement Relays, Contactors, Polar Relays, Latching Relays, T-Bar Relays, Time Delay Relays, and Stepping Relays. Here’s an interesting ...