The direction of an electrical outlet doesn’t matter to the electrons. Electricity will flow regardless of the way you mount the outlet on the wall, whether it looks upside down, right side up, or sideways. So whether the ground prong should be up or down is simply a matter of practicality.
Legally, nothing says which side of an outlet is up. But there is a practical safety argument for the ground going on top on an electrical outlet.
Does the ground go up or down on a receptacle?
Traditionally, we orient outlets with the ground plug down in the United States because it looks familiar to us. With the two prongs at the top and the ground prong underneath, it looks like a face. Aesthetically, it looks better.
Why do electricians install outlets upside down?
Sometime around the turn of the century, someone had a good idea. They noticed that if a plug wasn’t completely plugged into an outlet, and something fell on it, would bridge the hot prong and the neutral prong, causing a dead short. That’s both a shock hazard and a fire hazard. But if the output was oriented with the ground plug on top, something that fell on the ground plug might not come in contact with anything else at all. If it did come in contact with one of the other prongs, it would blow the breaker.
Putting the ground prong on top looked a little less natural. But it’s a safety improvement that doesn’t cost anything.
So that’s why you see the ground prong facing up on buildings that were built in the 21st century, but with the ground prong down on buildings built in the 20th century. Contrary to belief, the National Electric Code doesn’t say what direction to install them in. Professionals install them with the ground facing up for safety. But you can do what you want.
Does the ground have to face up on an outlet?
I once had a co-worker who had some decorative lights that had logos of his favorite sports teams that plug into an outlet. And because the prongs were polarized or grounded or both, he could only plug them in with the logo upside down. I told him he wasn’t breaking any laws if he opened up the outlets and turned them around. Or he could have a contractor do it if he wasn’t comfortable doing the work himself. He would be defeating a safety improvement. But at least the team logos in his man cave would look right.
Anytime I replace a worn or broken receptacle, I always install the new one with the ground prong up. It’s not important enough to be worth taking a full Saturday to spin every outlet in the house around. But if I’m in there anyway, it’s an easy and common sense safety improvement. It doesn’t cost me anything in terms of money or convenience. And it might save someone some pain someday. So why wouldn’t I?