Do not copy a model from another discipline (background file) into the project as a model file.
Exception to this rule would be for a model that requires the components be exported to 3D solids in order to work with Plant 3D ortho views. Export out a version of this file into the 3d solids necessary to work with the Plant 3d ortho views. Copy this file into the project. Note: when ever this file is updated, it will need to be opened in Plant 3D in order for the changes to be recognized in Plant 3D ortho views.
Create a Plant 3D model file specifically for referencing models from other disciplines. Reference the outside discipline model into the Plant 3D model file as an attachment.
Use the Plant 3D model file to create the ortho view.
Never reference a plant 3D model file into an ortho drawing. This will lock the ortho file and keep the file from binding into other AutoCAD files.
Starting in 2017, Ortho drawing files may be referenced by other disciplines into other AutoCAD files. Ortho drawings can be bound into other AutoCAD files when necessary. I do not endorse this method, but I know it is used quite often. Construction drawing (Ortho’s) change numbers and as such file names often. Changing the file name will lose the correct pathing to any other drawing that has it attached as a reference background.
Preferred Method: Since Ortho drawings can change drawing numbers and with it file names, the preferred practice would be to maintain a separate file as a background reference for other disciplines to use. This can be done by the Save-As method from the Plant 3D ortho drawing to another Xref folder location.
If another discipline requires a Plant 3D model for use as a background file, the model file needs to be exported as 3D solids to a separate Xref folder location.