In a ladder diagram, which symbol represents a contact that is usually opened?

In a ladder diagram, the symbol that represents a contact that is usually open is depicted as --| |--. This symbol is known as a normally open contact. When a normally open contact is not energized, it remains in the open position, meaning that it does not allow electrical current to pass through. This is key in control systems, where the flow of current needs to be controlled based on the status of various inputs or devices.

When the circuit is energized or the associated controlling device is activated (like a switch or relay), the normally open contact closes, permitting current to flow through the circuit, and thus allowing the associated output or action to occur. This behavior is fundamental in various automation and control applications, enabling systems to function based on different conditions.

The other symbols represent different functions in a ladder diagram, such as normally closed contacts or output relays, which are not representative of a normally open condition. Understanding these symbols and their operation is crucial for interpreting and creating effective ladder logic diagrams in control systems.