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), or the load is connected to Positive and the Negative is switched (NPN). These diagrams illustrate the differences between the two connections.

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4 Replies to “An Easy Way to Remember PNP and NPN Sensor Wiring”

  1. Can you also add “sinking” and “sourcing” to this diagram? It’s also a common question that comes up.

    1. Henry Menke says:

      Thanks for that helpful suggestion, Ben. We’ve updated the diagram accordingly.

  2. Very well done. I can show this to my craft class who never saw a transistor but need to know how to connect different sensors. Thank you very very much!

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