HENGSTLER safety relays, i.e. relays with forcibly guided contacts to EN 50205, are used wherever people and high-quality products are to be protected against potentially hazardous machine movements. If, for any reason, a relay should fail, e.g. due to a melted relay contact, the second, redundant, relay can still be used to close the installation down safely. A principle of these captive contact is that, after the installation has been closed down, it cannot be simply restarted and a potentially hazardous situation for people and machines is effectively prevented. The special functionality of positive guided contacts is achieved by ensuring the contacts are mechanically linked together so that it is impossible for the NO (normally open) and NC (normally closed) contacts to be closed at the same time. The contacts are linked so that no one contact in a relay can change state without changing all the contacts in that relay. If e.g. one NO contact fails because it has melted or jammed, the corresponding NCC remains open. This ensures that the installation or machine can not simply be restarted because of the open NC contact.