Originally Posted by Alan Wheeler
Just why the 110/115/120/220/230/240 around the world, I don't have a clue.
The choice of 120 or 240 volt AC power is arbitrary, as is the choice of 50 or 60 Hz. But if you are installing one of the first electrical distribution systems, you have to pick something. Higher voltages mean thinner wires for the same amount of power, but then why 240 instead of 500 volts? There are tradeoffs to be made, you pick something, and design around your choice. A hundred years later, somebody wonders why you didn't make the same choice as the guy 5000 miles away.
Typically, conventions like this follow political alignments. For example, many former British colonies use the 240 V 50 Hz power. I expect this is because they sent people to study in the UK and bought UK equipment
. If they bought stuff from the US, they would have 120 volt 60 Hz. Some countries do have both.
In the US, we have 120 volts 60 Hz pretty much everywhere, but that was not always the case. For example, San Francisco
originally had 50 Hz power until sometime in the 1930's (IIRC). A 50 Hz clock would run 20% fast on 60 Hz power. At the transition, the city would either fix your clock or let you trade
it in for a new one if they couldn't fix it easily enough. They dumped tens of thousands of useless 50 Hz clocks in the bay.
You can see that changing is disruptive, but at the time it was considered an advantage to use the same standards as the rest of the country. Now, we have such a large installed base of equipment that it would be prohibitively expensive to change, so we just keep doing what we've been doing...