Also washers, dryers.... 3 wire would give you 2 120 volt legs for 240 volts
on motors and heaters. A neutral for 120 volt timers(controls). Nothing was
left to protect you from a short to the cabinet. Thus 4 wire included a
ground(seperate from the neutral) to protect YOU!
"Ken Hall" wrote in message
...
Last time I got involved with it the neutral/ground/return bus in home
breaker boxes were all one bus. It was just brought to my attention
that today the neutral bus is separated from the ground, and 4 wires
are now used for 220v. In the old days 220v only used 3 wires.

When did this change and why?

Ken