PNP vs NPN Sensor Outputs: Clear Differences, Wiring Guide, and Selection Tips
When selecting industrial sensors—such as photoelectric sensors, proximity switches, or safety devices—one of the most important electrical distinctions to understand is the difference between PNP (sourcing) and NPN (sinking) outputs. Although both output types perform the same essential function—switching a load—they behave very differently in a control system. Choosing the wrong kind can cause wiring errors, false signals, or device incompatibility with your PLC or controller.
This guide explains the working principles of PNP and NPN sensors, how to wire them, and how to determine which output type is best suited for your application.
What Is a PNP (Sourcing) Output?
A PNP output source current to the load. This means that when the sensor is activated, it provides a positive voltage (+V) to the output line. PNP sensors are widely used in Europe, North America, and many modern automation systems because they are well-suited for use with PLC inputs designed to receive a positive switching signal.
How PNP Works:
· Brown wire = +V
· Blue wire = 0V
· Black wire = signal output
· Output provides +V to the load when active
· Load is connected between the output and 0V
What Is an NPN (Sinking) Output?
An NPN output sinks current from the load. When the sensor activates, it pulls the output signal down to ground (0V). NPN sensors were historically more common in Asia and in older control systems.
How NPN Works:
· Brown wire = +V
· Blue wire = 0V
· Black wire = signal output
· Output pulls to 0V when active
· Load is connected between +V and the output
Which Type Should You Use—PNP or NPN?
Choosing between PNP and NPN depends on your control system:
✔ Choose PNP (Sourcing) when:
· Your PLC expects positive logic
· You want easier troubleshooting and more common wiring standards
· You follow EU or US industrial automation norms
Most modern control systems prefer PNP.
✔ Choose NPN (Sinking) when:
· Your machine uses older controllers
· You work with systems originally designed for NPN
· Certain Asian-market automation systems require it
How to Avoid Compatibility Issues
To prevent wiring errors, follow these tips:
1. Check PLC Input Type
Determine whether your PLC input cards are PNP-compatible, NPN-compatible, or universal.
2. Match Sensor Output to PLC Input
PNP output → PNP input
NPN output → NPN input
3. Never Swap PNP and NPN
Mixing types can cause:
· Constant ON signals
· No switching response
· Sensor or PLC damage
4. Follow Wire Colour Codes
Most DC sensors follow the IEC standard:
· Brown = +V
· Blue = 0V
· Black = output
Summary: PNP vs. NPN at a Glance
| Feature | PNP (Sourcing) | NPN (Sinking) |
| Active state | Provides +V | Pulls to 0V |
| Wiring style | Load to 0V | Load to +V |
| Common regions | EU, US | Asia |
Compatibility | Preferred by modern PLCs | Used in legacy systems |
