"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

From my memory only.
I know for sure that in 1996 the NEC required four wires for dryer and
ranges for example. The change might have been made in 1993 but I am fuzzy
about that.

Manufactures make residential service panels with two busses because some
authorities require the grounds to be separate from the neutrals. The
ground and neutral are connected by some means dependant on the manufacture.
Commercial/industrial services have always been separate.

You can still run 3 wires to a motor and meet the NEC. As long as your load
does not require a neutral for anything.

The concept is...... using the ground as a neutral has always been a
violation of the NEC, it was just ignored in the residential market for a
long time.