400W HPS Plug

okay so i have a 400W HPS lamp that i been tryna hook up for the past week. it has 2 bare naked wires (black and yellow) that i have put into a 15A Plug..the screws on the plug are green (ground), silver, and yellow. i dont know which one the yellow plugs into..the lamp turns on when i plug yellow to yellow but then turns off 3 minutes later but you can still hear the bulb and ballast still running. help me!!! is the plug to small?? do i need a 20A