That is single phase. The "hot" (or "live") wire has a nonzero voltage relative to ground, and the neutral wire is usually around the same voltage as ground (do not count on this).

The one-way plug ensures that the "hot" voltage stays in the wall when the device isn't on, so if you shove your wand into a toaster that's off you won't get electrocuted. Devices are always connected to neutral, and the switch connects them to hot.

The two hot wires are perfectly out of phase, so connecting to both of them gives you 240V outlets (used for large appliances like clothes dryers).

Your standard 120V appliance outlets are only using a single phase and neutral. IIRC the smaller prong is hot and the larger prong is neutral.

Fun fact - the reason outlets in new construction are installed upside down (ground prong on top) is that the groudn prong can stop this from happening if something falls on it:

https://i.redd.it/bm1gqw8hzppz.jpg

Of course that's an ungrounded plug so they're in trouble either way, but you get the idea.

Another option (which I've never seen in the US) is plugs where the first chunk of the line/neutral prongs are insulated:

http://www.liddellappliancetesting.co.uk/ESW/Images/insulate...

UK has 240v for everything which may explain the insulation. Has been the standard about as long as I can remember - so back to the 70s.

Someone put a lot of thought into the design. Ground at top to prevent accidents like you show. Ground pin is longer. Insulation covers enough of the pins that live and neutral disconnect before conductor is exposed from socket. Both will be fully disconnected before earth disconnects.

It's not just new constructions, ground pin on the top has been the "correct" orientation for a long time. They've been installed "upside down" this whole time but that's what stuck. It's not in the NEC and while there was a suggestion to put the ground pin up, that has never been required by code and most people think that having the ground pin down looks correct.

If you actually look at a NEMA 5 outlet with the ground pin compared to old ungrounded polarized NEMA 1 outlets the NEMA 5 outlet is rotated 180 degrees. The larger neutral slot is on the right on old outlets and with the ground pin down on a NEMA 5 outlet the neutral is on the left.

It's not just for people dropping coins or paper clips on it though. Some outlet covers are metal and if the screw is loose or damaged that's basically guaranteed to short out if something is plugged in with the ground pin on the bottom. Another common thing is people using a tape measure along a wall, it's so thin that if there's a small gap it could shock someone using it or if you're lucky just short against the neutral.

Correct, and more conventions in the US that are mostly true so don't bet your life on them:

hot has black insulation, neutral white

hot wire insulation will be smooth, neutral ribbed

hot terminal screws will be brass, neutral silver (chrome)

Screw terminals in a house installation?!

Many electricians don't like to use "back-stab" or push-in connectors in receptacles, and prefer to use the screw terminals -- see, e.g., https://diy.stackexchange.com/questions/7977/when-to-use-hol...

https://www.homedepot.com/p/100055784 for example

The lamp sockets I replaced recently also had screw terminals with the brass=hot / silver=neutral convention.

See my reply here: https://news.ycombinator.com/item?id=16380133

The neutral side is connected to the ground. (Literally - they stick a metal pole in the ground.)

The 3rd wire, is also attached to the ground, and in the electrical box the two wires are attached together.

Anyway, that's why it's neutral - because it's attached to the ground, so it's at the same potential as you.

Neutral is tied to earth ground at some point.