Basic Knowledge: Normally Open / Closed

Normally Open/Closed

When a momentary switch is not actuated, it’s in a “normal” state. Depending on how the button is constructed, its normal state can be either an open circuit or a short circuit. When a button is open until actuated, it’s said to be normally open (abbreviated NO). When you actuate an NO switch, you’re closing the circuit, which is why these are also called “push-to-make” switches.

Conversely, if a button usually acts like a short circuit unless actuated, it’s called a normally closed (NC) switch. NC switches are “push-to-break”; actuating the switch creates an open circuit.

Among the two types, you’re probably much more likely to encounter a normally open momentary switch.