The most critical component of his circuit, the relay, is just a standard normally-closed relay that is rated at 20A. [Teodor] wired the relay so that it energizes its own coil whenever it is shut.

Single door control unit with normally closed relay. Small stylish combined proximity ID card reader and door control module. Can operate in either online mode with a Galaxy system or in stand-alone ...

Delta Scientific 3546-1 is a digital vehicle loop detector. The Presence relay is normally open or normally closed. Normally open pulse relay with pulse on arrival. Pulse relay can be set to pulse on ...