What Are NO and NC for Push-button Switches?

Logic control systems are essential in every control circuit and automation system. Metal push buttons have an important role as part of the logic control system in circuits and automation systems.

Industrial production machinery can not operate smoothly and permanently without a logic control system. In every control circuit and automation system, logic is developed based on the open or closed state of a switch, sensor, or relay. Therefore, it is essential to understand some terminology. Push button switches, as part of a logic control system, have specialized logic terminology, which is often abbreviated to NO and NC. To better understand the switch control components, it is important to understand the concepts behind NO and NC.

NO and NC are the terms used to define the state of a switch, sensor, or relay contact when the coil is not excited. It means that the mental switch remains open until a specific condition is met. When you press the NO switch, the circuit is turned on, until an abort signal such as a close button or emergency stop arrives. In general, limit switches contain at least one normally open contact. When the actuator is pressed, the contact closes and begins to conduct. This switch control keeps the mechanical path open until it senses that some object is being closed.

NC is the short name for normally closed contact. It means that the industrial mental button remains closed until a specific condition is met. Functionally, the normally closed contact of a professional push button is the exact opposite of normally open contact. The NC contact of a limit switch, when used in a circuit, breaks the circuit or current until a certain condition is met. To avoid operating errors, normally open and normally closed push buttons are colored differently. The common international practice is to use red for normally open buttons and green for normally closed buttons.

Industrial production environments can be very dangerous. In some large industrial production facilities, in order to protect the machine from being consumed in rapid operation and to protect workers from being injured. Industrial designers have added protection measures to the machines. The emergency stop button is a low-voltage switching appliance, which has become an essential industrial protection device with its high sensitivity. You can see an eye-catching red mushroom head on large machinery, which is the safety stop button. Professional emergency stop buttons are usually designed with normally closed contacts. This is because, in terms of action time, the time from closing to the breaking of a normally closed contact is much shorter than the time from the natural state to the closing of normally open contact. As a button supplier, we recommended choosing a high-quality emergency stop button.

The most basic function of the emergency stop button is to stop in case of an emergency to avoid mechanical accidents or personal accidents. However, due to the long-term operation of the machine, the line, especially the emergency stop line part, may cause malfunction and breakage. At this point, if normally closed contacts are used, when the emergency stop part of the line fails, the machine will stop at most, with relatively little loss. It is for these reasons, in the design of the electrical control system, the emergency stop button is best to use normally closed contacts.