In the normal state (not energized), the contact that is in the open state is called a normally open contact. When the coil is energized, the normally open contact will close, and the normally closed contact will open. For the auxiliary switch configured on the electrical appliance linked to the main switch: when the main switch is closed, the auxiliary switch is also closed.

The choice of normally open and normally closed contacts in electrical design?

Application: Normally open and normally closed contacts are connected to the input point of the plc. Normally closed contacts should be selected for safety-related contacts, such as emergency stop buttons, stop buttons, travel switches, safety gratings, safety doors, etc., because these contacts Once there is a problem with the line, the circuit will be disconnected and the PLC will detect it. If you use a normally open contact here, once the line is broken, pressing the button again will not have any effect. The operation button is still disconnected. Although no matter what the contact is in the PLC, it will be executed according to your program, but for safety reasons, you must use normally closed contacts for wiring.