A limit switch is an electromechanical device that is operated by the motion of a machine part or the presence of an object. It is used to detect the presence or absence of an object, control machinery as part of a control system, as a safety interlock, or as a counter enumerating objects passing a point. Limit switches are used in a variety of applications and environments because of their ruggedness, ease of installation, and reliability of operation. They can determine the presence, passing, positioning, and end of travel of an object.

Limit switches are available in several switch configurations, including normally open, normally closed, or one of each. There are four general types of limit switches: whisker, roller, lever, and plunger. Depending on the application, a limit switch may be a combination of two of the general types, such as roller-lever.

A standard limit switch used in industrial applications is an electromechanical device that consists of a mechanical actuator linked to a series of electrical contacts. When an object comes in physical contact with the actuator, the actuator plunger’s movement results in the electrical contacts within the switch to either close (for a normally open circuit) or open (for a normally closed circuit) their electrical connection. In most cases, a limit switch begins operating when a moving machine or a moving component of a machine makes contact with an actuator or operating lever that activates the switch.

Limit switches are used in a wide array of applications across the production floor as well as our daily lives. They are used for object detection and machine safety, among other things. A limit switch is one of the most basic mechanical/electronics components on a production floor.