I am replacing a mechanical 120v (Landscape light) timer in a metal box with a "GE Digital Time Switch" in a plastic box. I gather from the instructions if I have metal conduit coming into the box I need to use a jump wire to tie the metal conduit together (I have two metal conduit and one pvc). Does this mean basically only using a jump wire from one of the metal conduits to the other? Do I need to tie that jump wire into the "bundle" of grounds I will be wire nutting together in the plastic box as well? I am guessing not but want to make sure. Also, is there a real risk if I don't "jump wire" them across the plastic box? I am going too but was curious how necessary it is. Also, is there a good way short of going and buying grounding bushings to connect my jump wire to the metal conduit? Thanks very much for your help!!