I have a GE 230V compressor motor with a "2-pole 3-wire grounding"
And an available 250V "3-pole 3-wire" dryer receptacle:
Based on NEMA charts given at:
If I create an adaptor (6-20R <===> 10-20P), my question is:
Q: Will bad things happen when I plug the compressor into the dryer
I guess I'm really asking whether the "ground" wire is equivalent to
the "neutral" wire (for the purpose of turning a motor)?
I realize the household ground wire connects to my cold-water pipe;
and I think the neutral wire essentially goes to ground at the
telephone pole a few houses away ... so ... doesn't that make them
essentially the same for my purpose?
I think the ground wire normally does not carry current while the
neutral wire _might_ carry current if the load is not balanced (but in
a motor it should be balanced, right?).
It seems to me that this 6-20R <===> 10-20P setup would work safely.
But, I ask first: Am I missing something very important?
If so: What?
<SNIP excessive cross-posts>
Bad on 2 counts:
1) Your compressor motor doesn't require a Neutral to run.
The 3rd wire in the plug is to ground the compressor frame against
shocks to users.
Unfortunately, the dryer recept doesn't offer a "grounding"
terminal, only a "grounded" (Neutral) terminal. In days of yore,
the Code allowed this form of cheating for grounding either a dryer
or a stove. No more. And never for compressors.
2) The dryer recept is protected by a 30 Amp breaker.
That's way too big to protect the compressor wiring.
A: Would it work? Yes.
B: Would it be right? No.
I think you have it backwards. Code no longer allows using a common wire
for ground and neutral. His compressor has no neutral, only a ground. Yes,
the third wire is called a neutral, but it goes to the grounding bar exactly
the same as a ground would; it is purely a matter of semantics.
Yes, his compressor frame is attached to the "neutral", but since it is not
being used as a neutral there is no possible hazzard; well, at least no more
hazzard than if it were a "ground" rather than a "neutral".
The breaker is not intended to protect the compressor wiring; it is intended
to protect the house wiring. The classic case is the #18 lamp cord plugged
into a 20a circuit. Is this any more dangerous than that?
If it were me, and this was a permanent and well used project, I would
replace the outlet with a 6-20R, and replace the breaker with a 20a. That
is the correct fix, and won't be all that much more expensive than his
solution. But I can't get too worked up over his solution if that is what
he wants to do.
All older US built 240V electric Clothes Dryers have always had a
parasitic 120V load on the ground, and unless they've been forced to
change their designs recently it is still true... Even if they use a
240V timer motor and controls, they've never required you to find a
240V lamp for the inside-the-drum light, they use a standard 120V
bulb. So in that case, yes, the air compressor is actually a little
bit safer to use than the dryer.
If the safety ground on the dryer gets disconnected and the door
left open, you can have 120V potential on the outside enclosure of the
dryer (current limited by the lamp filament, but still potentially
lethal) because it uses the safety ground as a neutral return for the
(They could add a control transformer to drop the 240V for the lamp
load, but that would cost money - the competition would save $10.)
The old three-wire NEMA 6-30R dryer connection is grandfathered in
older houses - all new locations should be wired with a separate
neutral in the walls back to the power panel, and a 4-wire NEMA 14-30R
receptacle. (Mobile homes have always required the 4-wire 14-30R as
part of their building codes.)
But as long as new electric dryers keep coming with 3-wire cords
already attached to them from the factory, people will still keep
pulling the 4-wire receptacles out of the wall and install 3-wire
receptacles, rather than swap the cords on the dryer like they are
The air compressor as a unit is a straight 240V load 99.99% of the
time - I'm sure there are some companies who would try to rig a
parasitic 120V load to the ground of the compressor, but they should
be vanishingly rare, as they would get nailed the first time they
submitted a sample to UL, CSA, or any safety testing lab.
If the compressor has a contactor or other controls they usually
come with split coils, and can be wired for 120V or 240V. (Or 240/480
on larger units.)
The proper solution for the Original Poster is to make up a
sub-panel box to protect his compressor. Parts List:
1 6' dryer cord with 3-wire or 4-wire cap to match receptacle.
1 cord grip for dryer cord into sub-panel box
1 2/4 indoor breaker sub-panel
1 2-pole 20A breaker (brand and type to match panel)
1 1/2" chase nipple and conduit locknut
(Place nipple in KO's between sub and Handy Box)
1 Handy Box, steel single receptacle box
2 fasteners to secure handy box to sub-panel box, either
1/4-20x1/2" RHMS with nuts or #10x1/2" Hex SMS
1 2-pole 20A single receptacle NEMA 6-20R
3' 10-gauge THHN wire - piece-out scraps in black red and green
1 box cover plate to fit receptacle.
Assemble to taste. ^_^
Important Note: If you want to rig up temporary receptacles for
120V loads off this dryer receptacle and sub-panel assembly (like
breaking out four 120V circuits for plugging in the caterer's coffee
urns and other equipment into for a party) you MUST be using a 4-wire
dryer cord and receptacle, and the house needs a separate neutral wire
going back to the main panel neutral buss - no cheating on this one.
For feeding 240V connected loads, you need to reduce the breaker
rating to protect the 15A or 20A compressor cord and the motor, so the
connected unit doesn't melt or burn before the 30A breaker finally
--<< Bruce >>--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
I wouldn't have commented on this except you said "MUST". :-)
The grounded wire (notice how I carefully avoided calling it a "neutral"
or a "ground") of a 3-wire clothes dryer circuit does go back to the
neutral bus of the main panel. You can use it for the neutral wire of
your temporary patch cable for the coffee urn (etc.) You have to use
GFCI receptacles anyway, so leave the equipment ground disconnected and
mark the GFCI's with the little sticker that comes in the box, saying
"No Equipment Ground". That's how I would do it if all I had was a
6-30R or 6-50R receptacle to supply several temporary 120V loads.
To add and support Pete C who, in my humble opinion gave the best advice.
A ground wire should not be used as a neutral. Conversely a neutral should
not be used as a groundwire. Lots of things 'will work' but may not be safe,
until that fatal day!
Having said that;
I'm slightly surprised that the OPs dryer outlet has a neutral wire! Maybe
the neutral is there but is not required or used?
Or, I guess that tells me that some dryers do use a (say white?) neutral in
addition to the two hot wires (say red and black?). And of course the
Until now I thought that all 230 volt dryers used two wires plus a ground.
All three dryers owned by members of our family do not use the neutral wire
even if it is present to the four pin dryer sockets wired back to its own
dedicated circuit breaker.
So if you don't use the neutral and if there is presently no proper ground
to the metal? outlet box in which the existing dryer outlet is mounted, do
what Pete suggests. Tag wire at both ends connect to an actual ground and
use that unneeded (for a two wire 230 volt machine) neutral as the ground
wire for safety reasons.
An ungrounded situation of an existing 230 volt appliance outlet might
suggest that the wiring is old or was wired non standard and might not meet
insurance requirements if something did happen!
Circuit breaker should be suitable to size/gauge of wiring?
PS does that mean that the dryer that was using that outlet previously was
NOT grounded. Ungrounded equipment around wet/damp clothes could be scary!
Both washer and dryer IMO should'a been grounded!
Wow. The advice here is phenominal.
I'm again sorry I didn't provide more detail.
Hopfully the information provided below helps to answer some of
the questions kindly posed by fellow usenetters.
The house was built in 1961.
The 3-wire dryer circuit appears to be original (but I'm guessing at that).
As noted, it sure is difficult to pull out the plug of the dryer.
The dryer is a Sears Kenmore Model 110.86872800 Stock #68728.
A placard says "3 wire 120/240 volt, 60 hertz motor 4.0 amps" and on
another line of the placard it says "Heater & accessories 23 amps".
I may have been *wrong* about that dryer being alone on one circuit.
There *is* an outdoor permanent air conditioner unit hooked to the same
fuse in the main circut breaker panel. When I shut down that main fuse
(which looks like four fuses wired together with a copper wire), both
the outdoor A/C compressor and the dryer shut off.
The wierd thing (to me) is that the A/C has it's own circuit breaker push/pull
switch (which looks like a toy handle) mounted on the house next to the
external air conditioner (which was obviously put in long after the house
So, I'm no longer sure of the question:
- Is there a subpanel for the dryer.
The dryer doesn't seem to be on the A/C pull-switch (what would you
call it)? but the A/C is on the dryer main circuit breaker.
From what I think people said, the dryer has two hots and a ground
(masquerading as a neutral) while the compressor has two hots and a
ground, so, both the dryer and the compressor use essentially the
same hookup save for the 30 amp breaker for the dryer and the 20 amp
load for the 230 volt compressor motor.
My main concern is, I think, that of safety.
If I were to unplug the dryer and then plug the 20a compressor two
hots and a ground into the 30a fused dryer two hots and a ground
and the A/C were to be turned on ...
Would that cause a voltage to appear in the compressor casing?
Or, if the compressor motor were to short to the compressor casing,
would the ground wire now carry a current or would it simply blow
the fuse in the main panel to protect the house from a fire.
Of course, a GCFI might be a good idea (since fuses can't blow
in time to save a human from electrocution in any case).
Do you recommend an additional in-line GCFI?
Do I have the correct questions?
I do very much appreciate your help.
The caliber of professionalism is astounding.
When you say fuse, I assume you mean circuit breaker. Since you say
it looks like four breakers wired together, could it be two double
pole breakers with a common trip? That would be one double pole for
the A/C and one double pole for the dryer circuit. What are the
markings on the ends of each of these four breakers? You could
definitely answer this question by removing the panel cover and taking
a look at the wiring, but that is not advisable if you are not
comfortable with it.
P.S. If it is two double poles breakers in the space of a single
normal double pull, why would all four be wired to trip together?
Perhaps because the inside pair and the outside pair need to trip
together, but it is not easy to do this separately?
Boy, I've learned a LOT from you guys!
It's exciting to find out so much about things I just took for granted.
You are correct.
What I *thought* was four breakers wired together, *appears* to actually
be two sets of two breakers (one I can read is labelled "TYPE BRD,
2 pole unit J1076, BR3030").
It appears that one set of two breakers handles the dryer circuit.
The other set of two breakers appears to handle the outdoor A/C unit.
All four are wired together with a copper wire through the handles.
Why would they be wired together?
All I know is I seriously doubt the house is not to code as it was
just recently purchased and the inspector & lawyers gave the previous
owners about 5 pages of stuff to do. The electricians had to remove
all the wiring in the garage for example, (bummer, the previous owner
had lights all over, now the garage is dark) and they had to install
that copper wire (making it currently impossible to remove the main
circuit breaker panel covering plate without either cutting the
plate metal between the two middle breakers or snipping the copper
wire looped through all the four breakers).
Why would they have a common trip wire?
Does that play a role in hooking up a 230V x,y plus safety ground
compressor temporarily to the dryer x,y plus neutral-tied-to-ground
P.S. Thanks for all the wonderful help. You guys are great!
Because some idiot put it there. The house inspector is paid to find
stuff that's wrong but can be easily fixed (so as not to break the
deal). Some of the stuff they find is totally imaginary.
The 2 poles of the dryer circuit should be tied together. The 2 poles
of the air conditioner circuit should be tied together. The dryer and
AC should not be tied together (unless for some silly reason the
electrician used a 4-pole breaker and they were tied from the factory)
Some thin 2-pole breakers are installed in pairs, with 4 breakers in one
unit and the middle ones form a pair with internal common trip, and the
outside 2 form a pair with a metal clip that provides the common trip.
Maybe that's what you have (I'm too lazy right now to look up the number
firstname.lastname@example.org (Martin Mickston) wrote in message
Here's my best guess at what you got. Originally, there was a single
"2-pole" "common-trip" 30A breaker to run the dryer. This occupied 2
"slots" in the panel and carried the 2 hot legs to the dryer. Comes
time to add the A/C, there are no more slot pairs to add another
2-pole breaker. So the installer (probably the A/C guy) replaced the
2-pole with a pair of BR3030 "twin-pole" breakers. A twin-pole breaker
is like two half width breakers in the same package which can supply
two 120V branch circuits from a single hot bus in the panel. So, the
side-by-side pair of twins can supply two 240V circuits by considering
them as 4 poles with "inner" and "outer" pairs (poles 1-4 and 2-3) or
"over-under" (poles 1-3 and 2-4). The problem is, when one branch of a
240 circuit overloads and trips the breaker, it's supposed to trip the
other branch so that no part of the circuit is left live. That is why
common-trip breakers exist. The side-by-side twins were not originally
installed to do that, hence the home inspector flagged it. I've seen
Your situation is STILL potentially dangerous. A copper wire threaded
through the breaker handles is not the way to make a group of single
breakers into common-trip. Furthermore, one half of a twin-pole
breaker may not have sufficient strength to trip all 4 breakers hooked
together. The breaker manufacture sells appropriate hardware for
converting independent trip breakers to common-trip, and it is not a
piece of copper wire. If the hardware does not exist to fit that
particular combination, that combination is not meant to be hooked
together. Plus I don't think the BR3030 are listed for HACR service.
Your situation is almost certainly an "off label prescription" that is
not UL approved. Consider yourself so informed.
If you haven't had experience with working in a panel, you might not
want to start now. So the following merely tells some options. It's up
to you to make sure that it's up to code in your area and that it's
being done by qualified personnel.
Free up some slots in your panel by replacing some single breakers
with twin-poles for some 120V circuits. Depending on your needs for 15
or 20 amp branches, these would be Cutler-Hammer BR1515, BR1520,
BR2015 or BR2020 "replacement" breakers or BD1515, BD1520, BD2015 or
BD2020 CTL-tabbed breakers for notched bus stabs. This will leave you
enough space to install the PROPER separate 2-pole breakers for your
dryer and A/C, which would be breaker # BR230 in each case.
Another option is to replace the "homemade quad" with a real quad
breaker that's made specifically for this purpose. Cutler-Hammer makes
a model BRDC230230 which has inner and outer pairs hooked together to
make the equivalent of two 2-pole 230V breakers, but they also have a
less expensive BQC230230 for the notched bus panel if that's what you
have. No, you can't modify the cheaper one to fit the un-notched
See this for pictures:
A triple despard switchplate. Until Decora came out with a triple rocker switch
which fit into a single faceplate, a triple despard switch and faceplace.
factory labeled Heat / Vent / Light was included with every new HVL sold.
and you are clueless on the load too, The size of the motor
is a key issue,,, what is it?
how many amps, phase?
wire size and load are the issues.. you havent stated
either... the plug data is like specifying a car by size of
balanced (but in
If you are this green on electricity you should have help
wiring you gizmo,, and you shouldnt dream of adapting a cord
cap (wall plug) while guessing at this level... you have no
idea what you are doing and are putting your house at risk of
workablilty and safety are separate issues... you are asking
if its OK to shoot the apple off of your sons head from 200
years if you rifle is probably sighted reasonably well....
You can do the job probably...just get a wiring for dummys
book and read up.
Its not what works...it what works and will not burn the house
down when a motor fails or whatever.
I think he provided that succinctly by stating the plug.
The plug designed for his compressor motor is obviously
a 20 amp plug containing two hot wires & a ground.
What more information would you need?
Huh? Obviously (again, from the plug), the maximum compressor
load is 20 amps. What data do you think is missing?
Ugh. That's exactly why he asked us!
Why do you insist on insulting someone for asking his question?
What is this newsgroup for otherwise?
Seems to me most replies indicate he can safely do
exactly as he proposed (with key modifications for
code compliance), so he seems to understand the situation
better than you seem to provide details.
What are you trying to say?
1) He's asking if he can safely put a 20 amp load on a
30 amp breaker (and the answer seems to be yes).
2) He's asking if he can plug his compressor into his
dryer using an adaptor (and the answer seems to be yes).
3) He's asking if the dryer neutral is equivalent to
the compressor ground (and, since there is no subpanel,
the answer seems to be yes).
Basically, he seems to be asking something that you know
nothing about, so you ridiculed him due to your own ignorance?
What value do YOU have to add to the conversation?
I'm not saying I know how to hook up a 220 volt compressor
to a 250 volt dryer receptacle but people have spoken and
they basically seem to have suggested he can wire up the
connection, (x to x, y to y, w to g) and the results would
(apparently) be the same had his home come with the desired
So what makes you so upset about that?
Plugging in a device that uses less than the rated circuit capacity is
in no way unsafe or illegal. If it was you would not be able to plug
your 100w table lamp into your 15A (1,800W) wall outlet.
The question of the ground vs. neutral is a question of semantics, not
safety. In the case of the dryer outlet reguardless of what you call it,
this is a single wire that connects back to the ground/neural bus in the
service entrance panel and nothing else.
In this particular case the last post from the person asking the
question indicates that there may be an air conditioning compressor
piggybacked onto the dryer circuit. If this is the case *that* is
illegal and needs to be resolved.
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