I'm not 100% sure but I believe that you don't need a ground wire to the socket, or even the ballast....

I've got a metal halide thats been running without a ground for months with no problems, though it may be dangerous....dunno
redsunknight Reviewed by redsunknight on . HPS Ballast setup I am trying to set up my 400w HPS Ballast but cannot quite figure it out. The ballast itself comes with 2 wires, one for outlet and one with 3 colored wires going into connectors, and the fixture itself has 3 wires that match these, white green and black, but I can't seem to get it going. Any help is appreciated. http://i3.tinypic.com/85boj15.jpg Rating: 5