An obstruction detection device for use with a truss fabrication system including a table having spaced accessways. The obstruction detection device includes a support structure configured for movable attachment to a table having spaced accessways. An obstruction sensor is connected to the support structure and configured to detect obstructions in the spaced accessways of the table. The obstruction sensor has an activated state and a deactivated state. A control system is operatively connected to the obstruction sensor to activate and deactivate the obstruction sensor in response to a position of the obstruction sensor relative to the spaced accessways. The control system activates the obstruction sensor when the obstruction sensor is aligned with one of the spaced accessways of the table and deactivates the obstruction sensor when the obstruction sensor is out of alignment with the spaced accessways of the table.