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

[Martin Mickston]

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:

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?

[Speedy Jim]

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

[toller]

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.

[Wayne Whitney]

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

[zxcvbob]

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

[Terry]

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!

[_______]

You are missing your mind !!!

[danny burstein]

some electrical dryers use one hotneutral pair, at 120V, to operate secondary functions such as a light or a clock, etc.

[Phil Scott]

grounding"

the dryer

equivalent to

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?

cold-water pipe;

the

make them

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.

while the

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 fire.

safely.

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

[Girish Jhangiani]

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 adaptor.

So what makes you so upset about that?

[Martin Mickston]

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

[Gerald Newton]

The proposed installation by the original poster is illegal and unsafe. What more needs to be said. The original proposal asked if doing it wrong is safe. No it isn't.

[Pete C.]

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.

[Wayne Whitney]

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?

[Gerald Newton]

Wrong! Your using a 15 ampere general purpose circuit to justify an answer about an individual branch circuit. "210.21(B) Receptacles. (1) Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit." A 20 ampere receptacle cannot be installed on a 30 ampere individual branch circuit when it is the only receptacle. Every dryer circuit that I have seen in many years is on an individual branch circuit. Exceptions do not apply. And I am only getting into the lightweight stuff here. There's the listing requirements (110.3(B), permissible loads (210.23) and on and on.

The ground verses the neutral is not a question of semantics, and is precisely a question of safety. First off, residential 240/120 volt circuits do not have a neutral but a grounded conductor. Secondly, the grounded conductor is for carrying current under normal operating conditions. The equipment grounding conductor is for carrying current under abnormal conditions. They serve two entirely different functions and have two entirely separate sets of safety rules in the NEC..

What is illegal about it? (Your turn)

[Martin Mickston]

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!

[zxcvbob]

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 you posted)

-Bob

[modervador]

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:

%mod%

[phil-news-nospam]

| (1) Single Receptacle on an Individual Branch Circuit. A single receptacle | installed on an individual branch circuit shall have an ampere rating not | less than that of the branch circuit." | A 20 ampere receptacle cannot be installed on a 30 ampere individual branch | circuit when it is the only receptacle. Every dryer circuit that I have | seen in many years is on an individual branch circuit. | Exceptions do not apply.

But if it is NOT the ONLY receptacle, then it isn't an exception, as the rule you quote specifically does not apply.

If a receptacle is constructed with the ability to handle a total of 40 amps between the 2 NEMA 5/6-20R outlets, it seems it would be connectable with up to 40 amp OCP, assuming the wiring handles it, too. You could plug in 2 separate appliances using 16 amps each (under the 80% rule) and pull 32 amps, if the OCP is 40 amps.

We already allow 15 amp devices on a 20 amp circuit because the devices really are rated 20 amps anyway. The 15 is just the plug configuration. So as long as the receptacle device and the wiring to it can handle it, what is the TOTAL branch circuit amperage limit involved?

So back to the OP's idea. He wants to make that 30 amp branch circuit have TWO outlets, a 10-30R and a 6-20R. How is the rule violated.

Suppose his circuit was already 4-wire (e.g. separate ground properly wired in) with a 14-30R for the dryer. Could he now connect a 6-20R on the same branch circuit? How is the rule violated if not?

|> 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. | | The ground verses the neutral is not a question of semantics, and is | precisely a question of safety. First off, residential 240/120 volt | circuits do not have a neutral but a grounded conductor.

It's certainly not neutral if there is voltage present due to an unbalanced load.

| Secondly, the grounded conductor is for carrying current under normal | operating conditions. The equipment grounding conductor is for carrying | current under abnormal conditions. They serve two entirely different | functions and have two entirely separate sets of safety rules in the NEC.. | | |> 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. | | What is illegal about it? (Your turn)

I don't know what he is referring to. There seems to be a perception that the dryer must have a dedicated branch circuit. I don't know that this is the case at all. I don't know what rule would apply. Doing load calculations could consider that the dryer and compressor will intentionally never be used at the same time ... is that a valid way to do the load calculation? If so, then piggybacking them together might be fine, if the 30 amp OCP on 6-20R and the grounded conductor issues were resolve.

This would have been an entirely different thread had the OP had a 4-wire branch circuit and 14-30R on the dryer and wanted a 2nd 14-30R or 6-30R for the compressor that was designed to be connected to a 30 amp circuit.

[Gerald Newton]

Table 210.24 and Table 210.21(B)(3) require a 30 ampere receptacle on a 30 ampere circuit! Boy, you guys just will not give up, will you? You cannot install a 20 ampere receptacle on a 30 ampere circuit.

You can install a 40 or 50 ampere receptalce on a 40 ampere circuit.