There are several types of relays: furnace relays, circuit board relays, time delay relay (sequencer). In most relays, a lower voltage activates a magnet which closes or opens a switch to a higher voltage circuit. For example, if you connect a low voltage to a 24V furnace relay and test it using a voltage meter, you will notice the meter making a beeping sound, which signifies a complete (closed) circuit. If you power up your coil with the meter still connected to your relay, you will notice the beeping sound stops, signifying an open circuit.
- - How Do Relays Work?