Been working on a very large one line diagram (SLD in europe) for a day or so
when linking a SLD Symbol to the parent symbol you can end up with a large selction of items to choose from (see Picture)
now if you add the same filter controls that you have when selecting source /destination wires see red box below
you will have the ability to only display parents symbols that donot have a One line Symbol ascociated with it
this will make working with large One line Diagrams a lot easier as the selection list will shrink as one line symbols get linked