When choosing a push button switch, the contact type is an important specification. Different contact configurations determine how the switch works in a circuit.
The two most common contact types are NO (Normally Open) and NC (Normally Closed).
What Is NO Contact?
NO means Normally Open.
In the normal state, the contact is open and the circuit is disconnected.
When the button is pressed, the contact closes and the circuit is connected, allowing current to pass.
Working principle:
Before pressing:
Contact: Open
Circuit: Disconnected
After pressing:
Contact: Closed
Circuit: Connected
NO contacts are commonly used for:
Start buttons
Control signals
Trigger functions
Machine operation controls
For example, when an operator presses a machine start button, the NO contact closes and sends a start signal to the control system.
What Is NC Contact?
NC means Normally Closed.
In the normal state, the contact remains closed and the circuit stays connected.
When the button is pressed, the contact opens and interrupts the circuit.
Working principle:
Before pressing:
Contact: Closed
Circuit: Connected
After pressing:
Contact: Open
Circuit: Disconnected
NC contacts are commonly used for:
Stop buttons
Emergency stop switches
Safety circuits
Alarm systems
For example, emergency stop buttons usually use NC contacts because the circuit can be interrupted immediately when the button is pressed.
NO vs NC Contact Comparison
| Item | NO Contact | NC Contact |
|---|---|---|
| Full Name | Normally Open | Normally Closed |
| Normal Condition | Open | Closed |
| After Pressing | Closed | Open |
| Main Function | Start / Control | Stop / Safety |
| Common Applications | Start buttons, signal buttons | Stop buttons, emergency stop switches |
What Do 1NO, 1NC, and 1NO+1NC Mean?
Push button switches are often marked according to their contact configuration.
1NO
Means:
One Normally Open contact
Commonly used for:
Start functions
Signal control
1NC
Means:
One Normally Closed contact
Commonly used for:
Stop functions
Safety applications
1NO+1NC
Means:
One Normally Open contact
One Normally Closed contact
This is a common configuration for industrial push button switches because it can provide both control and feedback signals.
How to Choose NO or NC Contact?
Choose NO contact when the switch is used for:
✓ Starting equipment
✓ Sending a control signal
✓ Activating a function after pressing
Choose NC contact when the switch is used for:
✓ Stopping equipment
✓ Safety protection
✓ Monitoring circuit conditions
For emergency stop applications, NC contacts are generally preferred because the safety circuit can detect problems such as broken wires or loss of contact.
Conclusion
NO and NC are the basic contact types used in push button switches.
NO contact: The circuit closes when the button is pressed, mainly used for start and control functions.
NC contact: The circuit opens when the button is pressed, mainly used for stop and safety functions.
Understanding the difference between NO and NC contacts helps customers select the right push button switch for their equipment.
ONPOW provides push button switches with different contact options, including NO, NC, and NO+NC configurations, for various industrial control applications.
ONPOW - Professional Push Button Switch Manufacturer
