[GreenKeys] History - Why voltages and frequencies are chosen(5v & 3.3v l...

[Keith Mc]

There have been a number of fascinating stories on this thread.
(eg some of the 25Hz stories).

But PLEASE remember: My ORIGINAL question was not asking WHAT
people did, but *WHY* they chose a particular voltage or frequency 
in the first place.

For Example:  I understand that the slow upwards "creep" in mains 
voltage over the years (from 110->115->117->120) is PROBABLY 
driven by financial reasons - Any wire has a max CURRENT, so 
simply tweaking the voltage up in tiny steps often allowed a BIT more 
POWER to be sent over the SAME line, (up to a different, saturation limit).  
This saved the utilities money by reducing/slowing the need to upgrade 
many of the expensive long line wires, as they slowly grew customers.

... Now how many things blew out, wore out faster (eg light bulbs), 
or had to be replaced as a result of each voltage increase would 
be an interesting thing to analyze {grin}, but is not my "current 
question" (pun intended ;-).

**BUT**   That doesn't explain WHY they chose "110V" in the first place!
(vs 100, 130, or ANY other number)  Does anyone know?
(It is not necessarily safety - you can easily be electrocuted with 110.)

... and why did many places choose (roughly) TWICE the voltage, 
for mains?  You don't see "1.5x" the voltage, so could there be 
some physical or design property involved in the number selection?

- Keith Mc.