I found a great document from Panasonic that goes over a bunch of relay and contactor terminology.
Shortened Doc
Component’s Purpose
A relay is an electrically activated switch using a low power control to form or break a high-power circuit.
How They Work
Normally open – power flows through the input circuit, activating an electromagnet that attracts/repulses causing a contact to join with the second larger circuit, allowing current to flow. When power is removed, a spring draws the contact away from the second circuit, stopping the flow of electricity.
Normally closed – fundamentally the same as normally open, but with the default states reversed.
Selection
