Can I plug my 230V compressor (NEMA 6-20P) into a dryer (NEMA 10-30R) receptacle?

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I have a GE 230V compressor motor with a "2-pole 3-wire grounding" plug: NEMA 6-20P And an available 250V "3-pole 3-wire" dryer receptacle: NEMA 10-30R Based on NEMA charts given at: http://www.et-sales.com/Documents/Straight%20Blade%20Nema%20Chart.htm
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 receptacle?
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?
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Martin Mickston wrote:

<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.
Jim
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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?

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.
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Do you mean any dryer circuit should be on the main panel, rather than a subpanel, or just these funky no-longer-code 3-wire 240V/120V dryer circuits?
Thanks, Wayne
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Wayne Whitney wrote:

I just meant 3-wire 120/240V. 4-wire 120/240V or 3-wire pure 240V fed from a subpanel should be fine.
Best regards, Bob
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On 19 Oct 2004 13:21:41 -0700, snipped-for-privacy@yahoo.com (Martin Mickston) wrote:

You are missing your mind !!!
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On Fri, 22 Oct 2004 06:23:19 GMT, Vatsal Thakkar

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 lamp.
(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 supposed to.
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 trips off.
--<< Bruce >>--
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
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Bruce L. Bergman wrote:

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.
Best regards, Bob
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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 ground. 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? Terry 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!
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some electrical dryers use one hot<->neutral pair, at 120V, to operate secondary functions such as a light or a clock, etc.
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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 was built).
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.
MM
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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.
Cheers, Wayne
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?
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Boy, I've learned a LOT from you guys! It's exciting to find out so much about things I just took for granted. Thanks!
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 at-the-breaker circuit?
MM P.S. Thanks for all the wonderful help. You guys are great!
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Martin Mickston wrote:

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.

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 you posted)
-Bob
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snipped-for-privacy@yahoo.com (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 worse combos.
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 busses.
See this for pictures: http://www.eatonelectrical.com/unsecure/cms1/TB00300001E.PDF
%mod%
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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.

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no and you are clueless on the load too, The size of the motor is a key issue,,, what is it? how many amps, phase?

no wire size and load are the issues.. you havent stated either... the plug data is like specifying a car by size of hub caps.

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 fire.

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.
Phil Scott
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On Wed, 20 Oct 2004 03:56:53 GMT, "Phil Scott"

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?

load is 20 amps. What data do you think is missing?

Why do you insist on insulting someone for asking his question? What is this newsgroup for otherwise?

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 adaptor.
So what makes you so upset about that?
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wrote:

What more needs to be said. The original proposal asked if doing it wrong is safe. No it isn't.
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Gerald Newton wrote:

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.
Pete C.
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