A key switch is a mechanical switch that can only be activated using a key. Keys are generally assigned to users, allowing the restriction of access to the controls. The most commonly recognizable example of a key switch may be an automobile ignition. Such switches, however, are frequently used in manufacturing and industrial environments as well.
The principle behind an industrial key switch is virtually the same as the principle behind an automotive one. In order to turn a machine on or off, a key that fits the switch must be inserted and the switch turned. In a manufacturing environment, these switches frequently provide access to other actions as well, such as the ability to adjust settings and speeds.
One main purpose behind a key switch is to restrict access to the machine. Switches are often used in the cases of very expensive or potentially dangerous equipment. Machines critical to operations may also be turned on and off via a key switch.
Another primary benefit of key switches is that they are virtually impossible to engage accidentally. Unlike a flip switch or push switch that can be bumped, unintentionally turning a machine on or off, the operator of a key switch must actively insert the correct key and then turn the chamber. This makes such switches a natural choice for machines that take a long time to shut down or restart and for critical operations equipment, such as that controlling the air or power inside a plant.
Often, the keys that fit such switches are traditional metal keys with a series of notches carved into one or both edges. These notches engage with wards inside the switch, much like the wards of a lock. Only keys with the right pattern, or master keys made to work with a number of different switches, can be used to engage the switch.
Many modern key switches, however, now use electronic keys. These switches are significantly more expensive, but have the advantage of being able to assign a specific key to a specific individual. This allows a company to track who activated switches at a given time.
To add a second layer of security, a machine may be installed with a second distinct key switch. In these cases, the keys needed to activate each switch are different and are assigned to different individuals. Usually, each switch must be activated in sequence. In some cases, the switches must be activated simultaneously.