The Break Conduit or Cable Tray command will break a single conduit or cable tray centerline into two pieces.
To break a conduit or cable tray, go to
Ribbon: DM Electrical->3D-BIM-> 
Break Conduit or Cable Tray
Pulldown Menu: DM Electrical->3D-BIM->Break Conduit or Cable Tray
You will be prompted to specify the location of the break on the conduit or cable tray centerline.
Select conduit or cable tray at break point:
The centerline will be broken into two pieces. One piece will go from the original starting point to the break point. The other piece will go from the break point to the original ending point.