<< I <was> noticed at HD the other day that many of the 220v plugs were 4 wire.
The only kind of plugin device I can think of that might need 4 wire would be
a dryer. Any others come to mind? >>
Lets turn this around: few 220V appliances, tools, or whatever these days
operate on solely 220V. The majority of things these days have 110V controls,
lamps, whatever, and therefore require a neutral wire. This trend has been
ongoing for some time, so 3-wire plugs will likely be the uncommon type in a
few years just like 2-prong outlets. $0.05 worth...