Elmo wrote:
On Sun, 25 Jul 2010 05:41:59 -0700 (PDT), jamesgangnc wrote:
What you really need to do is install a dedicated 220 outlet

I agree that's the by-the-book method. However, the cost of having an
electrician replace the 30-amp NEMA 10-30R with a 20-amp NEMA 6-20R is more
than the cost of a compressor that runs off of 110.

Have you looked at the compressor to see if it can be run on 110?
I didn't realize the 30-year old Sears Craftsman compressor COULD run on
110. How would I know? (I'll try to dig up a model number and google it
after this reply.)

The motor will marked as dual-voltage if it can...wouldn't be too
surprising but I'd stick w/ 240V as you'll need double the amps for 110V
and you may well be in worse conundrum of not having a circuit w/ the
ampacity to run it on 120V...

The safety issue is that you will be using your nuetral line
for a ground and using a 30 amp circuit where a 20 amp
one is called for.

But wouldn't the neutral line ALREADY be used as a ground in the NEMA
10-30R dryer circuit were I to plug in a dryer to that circuit?

There's that turning around of the actual situation on a dryer outlet
wiring again for one and the misconception regarding the point of 30A
circuit protection having anything to do w/ the load plugged into the
outlet. Both are simply wrong.

The third conductor is _NOT_ the neutral serving as ground, it is
THE_GROUND_CONDUCTOR_ sharing service as the neutral for the 120V
components in the dryer (motor/lights/timer/etc.).

For the other, the 30A breaker is there to protect the circuit wiring;
it is the responsibility of the load to have the correct protection for
itself internally.

Isn't the compressor the same as the dryer from an electrical standpoint
with respect to the ground/neutral wire?

For the 240V components (the heater elements) of the dryer, yes;
identically. There is no 120V load on the compressor so the need for
the sharing of ground/neutral disappears and is, therefore, fully
compliant with current NEC for 240V loads whereas the dryer would
require a four-wire connection to be compliant to current NEC. From
that standpoint, the compressor is "more correct" than the intended use
of the dryer on the circuit (that _was_ compliant w/ NEC of the time, of
course).

Again, if the adapter you're using is compliant and well made, ignore
the do-gooders' advice here--they mean well but are simply misinformed
or overly cautious or just don't understand (or maybe even all of the
above ).

--