To erase the 3D graphics for a conduit or cable tray, go to
Ribbon: DM Electrical->3D-BIM-> 
Erase 3D Conduit or Cable Tray
Pulldown Menu: DM Electrical->3D-BIM->Erase 3D Conduit or Cable Tray
You will be prompted to identify from which conduit or cable tray the 3D graphics are to be erased.
Select conduit or cable tray in system to erase 3D from:
The 3D graphics for the entire run of the selected conduit or cable tray will be erased.