Ground-up or ground-down?

The NEC isn't specific. The NEC enables ground plug holes to face up, down, or sideways. 

No standard outlet orientation exists. No upside-down outlets exist, then.

If the outlet is connected properly, neither is safer. Install them as you choose for aesthetics.

The United States instals the ground plug upside down, whereas Canada does the reverse.

NEC code-making committees may reject the proposal for lack of evidence.

In horizontal receptacles, grounding should be on the left and neutral on top. This move is safety-driven.

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