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

[Steve Schlink]

Does anyone know whether there is actually a US line voltage standard? I 
have spent a few minutes looking and have not been able to find one.
Or is it just left up to the whim of the local utility?
Frequency, obviously, is well standardized, but I can't find anything on 
voltage standards.
I expected to find something on the order of 115/230 +- 5%.

Steve

At 09:37 PM 11/22/2012 -0500, WA5CAB at cs.com wrote:

>On the 120/220 VAC question, there never has been a system with those 
>nominal voltages, whether single or 3-phase.  The standards over the years 
>have been 110/220, 115/230, 117/234 and 120/240 for single phase.  Because 
>the standard single phase pole pig has a center-tapped secondary and you 
>can't get 220 volts line to line if the line to CT is 120.  The most 
>common (probably) low voltage 3-phase system is currently 120/208 wye.