It turns out Leviton makes a switched BS1363 outlet with a NEMA yoke that's designed for NEMA sized boxes. I'm guessing these were intended on USA built equipment intended for export to countries using the BS1363 outlet.

Interesting, though to fully comply with BS1363, the socket should have shutters. 

I think it might have shutters as it claims to be tamper resistant. Now I wonder if the shutters open with the ground prong like on a proper BS1363 outlet or from equal pressure on the live and neutral prongs like on a North American outlet.

The better sockets like these MK ones require a pin into all three. That way you can't just stick a screwdriver or something in the earth to open the shutters.

This outlet does have shutters, as do most newer North American outlets (made after 2014). @Mandolin Girl

Yeah, I think code had required most outlets be protected with shutters so most of the new outlets now have them. You can still buy the traditional outlets in some places.

Interesting that the MK ones require all three pins, the ones I have only require the earth pin. I wonder how the mechanism looks.

I think the mechanism would be similar to the one used for two pin sockets: You need to push the segment at all 3 places to keep it leveled so it canslide aside. Otherwise it will tilt and jam, preventing the insertion.

But what I do not understand, why would the sockets need to prevent realy deliberate insertion? I may understand the shutter to prevent random things insertion by toddlers or some mess falling into the contact area mainly with extension cords, but for that the 2 pin shutter is by far enough.

Plus to me it does not make any sense to require a dummy "PE" pin when the appliance is designed as class II, so has only the working conductors connected anyway. To me that is not safety, but just an a$$ covering BS.

@ Medved - The sockets need to at least try to prevent deliberate insertion. If you have any experience of toddlers, you'll know they can be very determined..!

As for the dummy PE pin, we do not have 2-pin outlets here, except for the specially designed ones for shavers and toothbrushes, which look similar to the europlug, but aren't, and are invariably fed from small isolation transformers. Therefore you need a dummy pin to allow the plug to go into the socket.

I know I'm biased, being British, but I really do believe our plugs and sockets are the safest in the world, and that's not BS.

Interesting that the MK ones require all three pins, the ones I have only require the earth pin. I wonder how the mechanism looks.

JW has a video on it somewhere, I think.

Edit: Found it, see here.