How the Safety Relay Works

The Safety Relay is powered by a DC power source, and is placed on the secured side of a door. It connects to the Video Intercom, which is installed on the unsecured side of the entrance. This device can be used to control the entrance strike via a digital output or a controller panel. The Safety Relay can also be connected to a request-to-exit (REX) sensor on the secured side of the door.

The Safety Relay receives inputs from:

  • The Video Intercom when:
    • An access grant has been issued by the operator to unlock the door.

    • Someone physically tampers with the Video Intercom, to put the door into the tampered (lock-out) state. (Optionally, the Video Intercom can be configured to put the door into lock-out state when video tampering is detected.)
  • The REX sensor on the secured side when someone swipes their badge or enters their code to exit, to unlock the door.

When these inputs are received, the Safety Relay outputs a signal to generate the appropriate action by the door lock. In the lockout state, the unlock request signal from the Video Intercom is ignored so the Video Intercom can no longer be used to unlock the door while the REX input remains unaffected and can be used to unlock the door from the secured side. After the Safety Relay is in the tampered state, the normal door state can only be restored by manually resetting the Safety Relay.

The Safety Relay has non-volatile memory so the current door state (normal or locked-out) is preserved across power cycles.

Use the following guidelines to plan the connection of the Safety Relay to your existing security access infrastructure:

  • The power source must be a 12V DC or 24V DC AC-to-DC power supply. The Safety Relay requires 1W to operate, excluding all external devices like door latches and REX sensors.
  • Wiring from the Video Intercom device, the AC-to-DC power supply, the REX sensor, and the door lock or door latch device should already be in place.

    See Installing the Safety Relay for the wiring details for fail-secure and fail-safe door locks, and for integrating a Video Intercom with the Safety Relay for tamper detection into a site where an ACM appliance is connected to your ACC System. 

  • The door lock or door latch device must be connected such that current flows IN through the NC or NO input, and OUT through the COM terminal. This current flow direction is needed for the contact protection circuit to be effective.
  • When you are connecting a Safety Relay to a door lock, a freewheel diode, 60V (greater than 1 amp), must be installed at the lock device to prevent high-voltage inductive kick-back voltages when the relay contacts open. Failure to do so can significantly decrease relay contact lifetime and increase electro-magnetic emissions from the system.

Note: Make sure the wires are carefully tucked into the electrical lock-box and are not pinched.