Many people get confused when they hear the question — “Is NPN normally open or closed?” The easy answer is that NPN sensors can be either normally open (NO) or normally closed (NC). The term NPN doesn’t decide whether it’s open or closed. It only tells us how the sensor output works in the circuit. In simple words, an NPN sensor is known as a sinking type sensor, which means when it detects a target, it connects the output to the negative side (0V or ground). Now, if it is normally open, the sensor output stays OFF until an object is detected. The moment the object comes close, the output turns ON and allows current to flow. This type is very common because it’s simple to wire and easy to understand. For example, imagine a light connected to the sensor — it stays OFF when there’s nothing nearby and lights up when an object appears. That’s how a normally open NPN sensor behaves.
On the other hand, an NPN normally closed sensor works in the opposite way. Here, the output stays ON when no object is detected and turns OFF when an object comes near. Think of it like a fan that keeps running until something interrupts it. This setup is used in systems where you want to detect a fault quickly — if a wire breaks or power fails, the output stops, letting you know immediately something is wrong. So, the main difference is just how the output behaves when there’s no target. To keep it simple — NPN sensors can be normally open or normally closed, depending on the design. NPN only tells you the current flows from the load to ground when it switches. Always check the sensor’s datasheet or wiring diagram before installation to know its exact type.
In short, NPN itself doesn’t mean open or closed. It simply describes how the sensor handles current. The “normally open” or “normally closed” part is about how that sensor reacts when nothing is detected.