I have a new chandelier, all metal, hanging in the office. It only has positive and neutral wires coming from lights up metal chain to connect in the junction box. A small ground wire is attached to the metal crossbar supplied with the fixture.
My junction box is plastic with positive, neutral and ground wires.
I contacted the manufacturer, and was told a short ground wire is all that is needed.
How do I properly wire this up so the fixture is grounded?
If the frame of the light fixture is metal and the chain is metal (which you have already confirmed) and the ring at the top is metal which attaches to the "metal crossbar" (assuming that is the circular plate you show already attached to the junction box) then I don't think you actually need a separate ground wire. You attach your ground wire (from the NM /2 cable) to one of the green screws on the "metal crossbar". Everything else is grounding "metal parts to metal parts".
From a practical standpoint, unless you have people literally swinging from the chandelier, grounding just isn't that much of an issue here. But in general the grounding is in case a hot part or wire touches the case - in which case it should make its way up all the metal to the green screw to your standard ground wire and work as it is supposed to.
