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A lock is a deliberate and sometimes necessary blockage. For mechanical locking are bars used. In electrical engineering, an interlock designates the intended blocking of one switching device by another. The English technical term interlocking is also used here.


A lock is intended to prevent undesired states, processes or events. This is to prevent certain actions from being accidentally carried out that could cause damage to the environment, technical equipment or danger to life and limb. In order to remove a lock, conscious action is usually necessary. A lock must be designed in such a way that it cannot be accidentally overcome, but at the same time it must not be possible to accidentally switch on the lock itself (too easily). The latter could lead to the failure of machines and systems.


Locks are possible mechanically, electromechanically, electrically, pneumatically , hydraulically or by software . A corresponding mechanical lock or a contact prevents a mechanism or a switching command from being actuated or executed. For example, many electrical devices cannot be turned on when the kill switch is pressed.

Electric lock

According to the International Electrotechnical Dictionary , a locking device is a device that makes the operation of electrical equipment dependent on the state, position or operation of one or more other equipment. For a secure locking z. B. in switchgear there are some basic rules; in addition, these can be expanded by the operator of the system.

Examples of rules:

  • Disconnectors can only be operated when the circuit breaker is switched off (protection against switching under load).
  • In the intermediate position of a disconnector, the circuit breaker cannot be switched on (fault position detection).
  • Disconnectors can only be operated when the earthing switch is switched off.
  • Earthing switches can only be operated when the disconnector is switched off.
  • If the auxiliary voltage fails, the circuit breaker is blocked and all other switch positions remain unchanged.

These functions are also referred to as switching fault protection (see disconnector ). In many modern controls, locking is implemented using logical links .

Further examples

  • As mentioned, a mechanical lock is found in modern emergency stop switches. The safety of a weapon also represents a type of locking. Here, the trigger is locked through and against the safety.
  • Electrical interlocks can be found on various devices and controls. For example, with a motor that can run counterclockwise and clockwise, you must not be able to switch on both directions at the same time - here the clockwise rotation is locked and vice versa.
  • In the case of traffic lights , the red lamp is locked against the green one, and the traffic lights in the individual streets are locked against each other (not all traffic lights must be on "green" at the same time).
  • In the interlocking technology in the railway locks are used to collisions of trains to avoid. In the case of mechanical interlockings, this is actually done using bolts.

Individual evidence

  1. IEV ( Memento of the original from December 17, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.dke.de
  2. ^ Stefan Kämper, Gerald Kopatsch (ed.): Switchgear manual . 12th edition, Cornelsen 2011, ISBN 978-3064507265 , p. 749.

See also