PBX Loop Start Trunk Port

In this configuration, the unit supplies a 24V talk battery and loop current detection.When the unit detects a loop resistance between Tip and Ring, it activates.When the loop opens, the page ends.The unit follows the status of the trunk port.

Before configuring the UTI312 for a loop start trunk port, make sure that the power is disconnected and all other connections are completed. Move the slide switches on the UTI312 to the positions shown below. Use a modular telephone cord to connect the unit to the phone system.

The center two conductors are Tip and Ring (24V DC) and have a specific polarity as shown in the figure below. If the polarity that the trunk requires is opposite, you can use a reversing modular cord to make the connection or reverse the connection through a modular block.The Trunk Disconnect feature is available in this mode (description on page 9).

PBX Ground Start Trunk Port

In this configuration, the unit supplies 24V talk battery, a contact in the Tip circuit, and loop current detector in the ring circuit. When the ground start trunk grounds Ring, the unit responds by closing the connection to Tip, which completes the access procedure.When the loop is opened, the page ends.The unit follows the status of the trunk.

Before proceeding, make sure that the power is disconnected and all other connections are completed. Move the slide switches on the UTI312 to the positions shown below. Use a modular telephone cord to connect the unit to the phone system. Connect the GND STRT terminal on the UTI312 to the PBX ground. This is typically the AC ground for the PBX system. If the PBX is using the same Earth Ground as the UTI312, the Earth Ground terminal can be shorted to the GND STRT terminal instead of running a ground wire from the PBX.

IMPORTANT - When the GND STRT terminal is connected to Earth Ground, it is important that none of the UTI312 system ground terminals are connected to Earth Ground. These terminals may accidentally be connected to Earth Ground when external equipment, such as a CD player, tuner, announcement device, etc., is connected to the UTI312. The UTI312 ground points are: the closure return terminal for the Trunk/Page Port jack, the contact closure (GND) and the left-most Dry Audio input terminal of the Override jack, the C terminal for the Night Ring, and the Tone Trigger input.The background music input and page outputs are transformer-isolated and are unaffected by Earth Ground. If the UTI312 system ground is tied to Earth Ground, then the UTI312 talk battery voltage will be shorted to ground and the unit will not function properly. For location of UTI312 system ground terminals, refer to the UTI312 Block Diagram.