What do NO (Normally Open) and NC (Normally Closed) mean in push button switches?
NO (Normally Open) and NC (Normally Closed) describe the default contact state of a push button switch when it is not being pressed.
1. Normally Open (NO)
Meaning: The circuit is open in the normal (unpressed) state.
- When not pressed: the circuit is open, no current flows
- When pressed: the circuit closes and current flows
👉 Simple understanding:
Not pressed = OFF (no connection)
Pressed = ON (circuit connected)
Typical applications:
- Start buttons
- Power ON switches
- Signal triggering devices
2. Normally Closed (NC)
Meaning: The circuit is closed in the normal (unpressed) state.
- When not pressed: the circuit is closed, current flows
- When pressed: the circuit opens and current stops
👉 Simple understanding:
Not pressed = ON (connected circuit)
Pressed = OFF (circuit disconnected)
Typical applications:
- Emergency stop switches
- Safety protection circuits
- Interlock systems
Summary
- NO (Normally Open): open when idle, closes when pressed
- NC (Normally Closed): closed when idle, opens when pressed