There are two ways to turn off feeder IDs in the one-line diagram.
To turn off the feeder ID on a specific feeder, use the Change Graphics command.
Ribbon: DM->One-Line Diagram-> Change Graphics
Pulldown Menu: DM->One-Line Diagram->Change Graphics
Change the Feeder ID setting from Yes to No.
To turn off the feeder ID on all feeders, go to Options.
Ribbon: DM: Customization->Project Customization-> Options
Pulldown Menu: DM->Customization->Options->Edit Project List
In the One-Line Diagram section, change the Insert feeder IDs inside feeder lines option from Yes to No.