You can specify which equipment connections should be displayed on your one-line diagram. This allows you to easily find and insert the large pieces of equipment without having the Insert Distribution Equipment dialog box cluttered with every equipment connection on your project.
To change this setting, use the Query command on the piece of equipment.
Ribbon: DM Electrical->Devices-> 
Query Device
Pulldown Menu: DM Electrical->Modify Devices->Query Device
In the Edit Equipment dialog box, press the One-Line Diagram Settings button. There is a toggle labeled Show on One-Line Diagram. If it is checked, you can insert this equipment on your one-line diagram. If it is not checked, you cannot insert it.
Use the Insert Distribution Equipment command to insert the equipment connection on your one-line.
Ribbon: DM Electrical->One-Line Diagram-> 
Insert Distribution Equipment
Pulldown Menu: DM Electrical->One-Line Diagram->Insert Distribution Equipment