The Insert Leader command is used to add a leader to a label or group of labels.
To insert a leader, go to
Ribbon: DM Electrical->One-Line Diagram-> 
Insert Leader
Pulldown Menu: DM Electrical->One-Line Diagram->Insert Leader
You will be prompted to specify a label to which to add the leader.
Select label to add a leader to:
You will then be prompted to specify an end point for the leader.
Specify end point of leader:
Specify a point on the drawing. The leader will be drawn from the selected label to that point.