Black and white are hot. Bare copper wire is connected to the grounding post. The grounding post is connected to the sheet metal that in the back of the unit and the metal that wraps around the outlets where a ground wire could connect. The outlets have a rivet on the top and bottom holding them to the same piece of metal the ground is connected to.
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The metal goes all the way to the other side of the unit and wraps the other plugs and also out of the top of the unit to the wire clamp