ELEC 255 Lecture Notes - Lecture 3: Electromagnet
Document Summary
A relay is an electrical switch that uses an electromagnet to move the switch from the off to on position instead of moving the switch manually. It takes a relatively small amount of power to turn on a relay but the relay can control something that draws much more power. The contacts at the top are normally open (i. e. not connected). When current is passed through the coil it creates a magnetic field that pulls the switch closed (i. e. connects the top contacts). Usually a spring will pull the switch open again once the power is removed from the coil. T most common are shown to the right. Pole single throw (spst) is the simplest with only two contacts. The contacts are usually labeled common (com), normally open (no), and normally. The normally closed contact will be connected to the common contact when no power is applied to the coil.
