Just to add to Colins point.
Generally the push to operate switch adjacent to each door is used every time that someone goes through the door, if its a busy door that can be hundreds of times a day,after a while they do become erratic and fail.
Having the Green BGU adjacent allows persons an alternative for emergencies.
Bill
Whilst the liklihood of failure of a request to exit (RTE) switch due high use is obviously a potential problem, there is also another more important reason why a green emergency door release unit may be an absolute necessity.
If a push-to-break RTE switch is wired in the electrical feed to the door locking mechanism it only releases whilst the button is pressed, and locks again immediately it is released.
But not all RTE switches are wired as a push-to-break switch in the electrical feed to the fail-safe door locking mechanism, they are quite often wired as a push-to-make switch across special terminals provided for the purpose on the keypad, swipe or proximity reader controller that may be associated with the door.
In this latter scenario, operation of the RTE switch will cause the locking mechanism to release for a pre-set time, even after the RTE switch is released, and therefore allow easy access through a door which may be some way from the RTE switch, or where the door users have their hands full. However, with this version of connection, if the wiring between the RTE switch became disconnected or the controller circuitry failed, then the lock would not fail-safe released.
Therefore a green emergency door release unit wired as a normally-closed switch in the feed to the door locking device is essential, in case the push-to-make RTE switch or controller circuitry failed.
