An Easy Way to Remember PNP and NPN Sensor Wiring Here’s a simple way remember how to wire up a 3-wire DC PNP or NPN sensor: PNP = Switched Positive NPN = Switched Negative “Switched” refers to which side of the controlled load (relay, small indicator, PLC input) is being switched electrically. Either the load is connected to Negative and the Positive is switched (PNP), Continue reading "An Easy Way to Remember PNP and NPN Sensor Here’s a Quick Way to Wire NPN and PNP devices | Acc The following is a wiring diagram of an open collector PNP sensor. You will notice that the load appears between the 0V (Blue) and Switching wire (Black). When connecting to the PLC, the PLC input acts as the load. The 0V (Blue) will be attached to the common input and the Switching wire (Black) will be attached to the input number. What is the difference between PNP and NPN when describing Two specific types of 3 wire sensors are available; PNP and NPN. The difference is a result of the internal circuit design and type of transistors used. A key point to observe is that PNP and NPN has nothing to do with whether the sensor is normally open (N/O) or normally closed (N/C), i.e. a PNP sensor may be either N/O or N/C as can an NPN be either N/O or N/C.