On Sun, 25 Jul 2010 03:51:43 -0400, mm wrote:
Also get a meter that goes up to 250 VAC and measure the voltage at
all three slots of the receptacle, relative to ground.

I did use the Fluke DMM to measure the connections; I was just double
checking which was the ground/neutral because I didn't wire the house in
the first place.

The ground in the two-phase 220v compressor NEMA 6-20P plug should be the
center pin and the ground/neutral in the NEMA10-30R dryer receptacle should
be the L-shaped center prong.

The two questions I would like to ask here a
a) How do I know if the NEMA10-30R is on a sub panel (it's inches from the
main panel on the other side of the wall outside the garage)?
b) Are my tests correct that the ground on the 20-amp NEMA 6-20P plug is
"equivalent" to the ground/neutral on the 30-amp NEMA10-30R receptacle?