Polarity
This thread is really interesting. I am learning things I never knew; and about things I didn't even know existed.
One thing worth noting, polarity.
In a single phase, independently grounded AC setup, it could be argued that there is no need for the consumer to distinguish between "hot" and "neutral". There are several good reasons for doing so.
Historically, the "All American Five" probably did more to wake people up to the dangerous of household current than anything else. These charming little beasts had one side of the chassis at line potential - and the chassis was frequently mounted directly to a metal case or had protruding conductors such as screws, dials, knobs, etc. If the plug was inserted such that the chassis was connected to "N", the risk was the same as that of any grounded object. If the chassis was connected to "L",well - lot of folks were shocked, many killed.
Making the plug only fit one way into the outlet reduced the risks. A little bit. You could, at least theoretically, thus guarantee that the chassis was always at "N" potential. Since many manufacturers didn't pay attention to the "identified" connector (that one is always "N", never "L") you still had a bad situation.
A clearer argument for polarization is the fact that it obviates the need for double pole switches. A simple switch which only interrupts the "L" line becomes realistically safe. Safer. Relatively.
Finally, as anyone who has ever changed an Edison base light bulb in the US knows, their sockets permit contact between the metal base and your fingers at some point in the screwing process. In the interest of safe screwing, having the metal shell at "N" potential and not at "L" is of clear value. Here in Europe, we do, of course, use many polarized plugs. Three phase plugs, for instance are always polarized; DC equipment in any case. Electrical inspectors may well fail an installation if the left side of a Schuko outlet (when facing it) is not "L". There is a binding recommendation, not a requirement - a concept only possible in Germany.
Interestingly enough, back when Apple first brought the iMAC to Europe, they very nearly were not permitted to sell them at the big introduction date. A few weeks prior to introduction, an idiot bureaucrat decided that the line cord was not up to European EMF standards. It was a fight down to the last days - I did some of the translating of the paperwork. For Apple, lest anyone think I was involved in the attempt to impede them. We won, but only in the nick of time.
Yes, the exposed blades of many North American plugs are a real danger. This problem also existed for the Schuko plugs in the beginning, leading to the damn recesses and impossible cleaning.
We do still have zip cord in Europe, it is sold as speaker wire and, yes, the Chinese have been known to use it for line cord...making clear that their "VDE" or "CE" labels are pure lies.
