Since 1996, the NEMA 10 column (10-20, 10-30) is no longer allowed in new installations. That was, for decades, the standard dryer outlet. No ground. The frame of the dryer is grounded to the neutral! Not to protective ground. This is idiotic by modern standards, but is still found in older houses.

(Haven't had to look at the NEMA outlet chart in years. I once had to specify a computer room back when DEC was a company. DEC used about five different connectors - some 110V, some 220V, some 3-phase, various current ratings. Needed custom-fabricated raceways with all the correct outlets.

Plus the electrical people at the aerospace company insisted on putting a hulking big copper busbar tied to ground on top of each raceway, and all cabinets were grounded to that. That was to give RF noise a very low resistance path to ground. Much RF R&D took place in that building, and things which blithered all over the RF spectrum were seriously annoying to the RF engineers. Computer grounding used to be a big deal, before everybody started using differential signals for almost everything.)