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

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

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?

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.

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.

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)

The thing you're missing, is a compressor is *not* a dryer.There's a reason, why in receptacles both in US and Europe there's a different prong for neutral and earth.The explanation is what you mentioned, that in *all* single-phase circuits current flows through the neutral wire (in fact the same current that flows through the live conductor in Amperes).I am not an expert in US receptacles, but I don't think that it's worth the risk.

| (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.

| The thing you're missing, is a compressor is *not* a dryer.There's a reason, | why in receptacles both in US and Europe there's a different prong for | neutral and earth.The explanation is what you mentioned, that in *all* | single-phase circuits current flows through the neutral wire (in fact the | same current that flows through the live conductor in Amperes).I am not an | expert in US receptacles, but I don't think that it's worth the risk.
The term "neutral" is a poor choice. It might have been Edison that used the term first. If the currents on both opposite poles (phases) in the split 120/240 volt system common in North America and Japan were the same, no current would be on the "center conductor" (which also happens to be the grounded conductor). But with an unbalanced condition, some current will be flowing, and some voltage drop across that conductor will be present.
The term "neutral" is an worse choice when dealing with harmonic loads on a three phase system. You do have those in the form of 400/230 in Europe (maybe 380/220 or 415/240 where you are). Is the center wire called "neutral" there? Whole new threads are needed for a discussion of this topic, as well.

On 3 phase there is no neutral. You have L1, L2, and L3
On the American 110/220 0r 115/230 system there is NO neutral current on a 220/230 volt load, and a straight 220/230 volt device will run without any problems on only the L1 and L2 (black and red) wires.
Electric heating units run this way, as do 220 volt motors not requiring a magnetic starter.
Some compressors will require 3 wire plus ground because they either use 110 volt heaters on the starter switch, or use 110 volt pressure control switches to activate the magnetic starter (contactor) to start and stop the compressor according to tank pressure.
Most of these compressors will be larger than 20 amp, and ALL of them will be hard wired, so are outside the realm of this discussion.
In the north American system the "neutral" is "bonded" at the panel, and a separate "ground" or "bond" wire is connected to both the metal outlet box, the frame of the receptacle, the "ground" connector, and from there, the case or chassis of the connected device.
This is a "safety ground". The maximum voltage from any live conductor to ground is the nominal syatem voltage of 110, 115, or 120 volts. If either line conductor shorts to ground the breaker/fuse trips. On a 220 volt line code requires the breakers to be "tied" so if one trips, they both trip. On a fused panel, code requires the fuses to be in ganged removeable fuse blocks, so it is impossible (or at least much less likely) to accidentally remove one fuse, leaving one side of the device live. If, as is often the case, only one fuse blows, there is still the danger of having a device that does not function, but is still "live" with 110 volts. The same fuse blocks are generally also used for "split" receptacles for the same reason, with one half of the duplex receptacle connected to L1-N and the other L2-N

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.

|
|> |> |> | (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. | | 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.
But what if it is a 40 amp receptacle that has 2 NEMA 6-20R outlets?
| You can install a 40 or 50 ampere receptalce on a 40 ampere circuit.
OK. So the 40 amp dual 6-20R will work?

| On 3 phase there is no neutral. You have L1, L2, and L3
That's not what I've seen.
| On the American 110/220 0r 115/230 system there is NO neutral current | on a 220/230 volt load, and a straight 220/230 volt device will run | without any problems on only the L1 and L2 (black and red) wires.
And there is no connection to a neutral wire, either. His compressor doesn't need any neutral. It does need a ground for safety.
| Electric heating units run this way, as do 220 volt motors not | requiring a magnetic starter.
Of course.
| Some compressors will require 3 wire plus ground because they either | use 110 volt heaters on the starter switch, or use 110 volt pressure | control switches to activate the magnetic starter (contactor) to start | and stop the compressor according to tank pressure.
Then they need a "neutral".
But, IMHO, it is dumb to design it that way. If the compressor needs 240 volts, then other parts should be made for 240 volts, too. It's not like they can't design such parts for that voltage, else they'd not even have them at all in Europe.
| Most of these compressors will be larger than 20 amp, and ALL of them | will be hard wired, so are outside the realm of this discussion.
Why would the have to be hard wired?
| In the north American system the "neutral" is "bonded" at the panel, | and a separate "ground" or "bond" wire is connected to both the metal | outlet box, the frame of the receptacle, the "ground" connector, and | from there, the case or chassis of the connected device. | This is a "safety ground". The maximum voltage from any live conductor | to ground is the nominal syatem voltage of 110, 115, or 120 volts. If | either line conductor shorts to ground the breaker/fuse trips. | On a 220 volt line code requires the breakers to be "tied" so if one | trips, they both trip. On a fused panel, code requires the fuses to be | in ganged removeable fuse blocks, so it is impossible (or at least | much less likely) to accidentally remove one fuse, leaving one side of | the device live. If, as is often the case, only one fuse blows, there | is still the danger of having a device that does not function, but is | still "live" with 110 volts. | The same fuse blocks are generally also used for "split" receptacles | for the same reason, with one half of the duplex receptacle connected | to L1-N and the other L2-N
So I've seen nothing that supports your statement that 3 phase has no neutral. 208Y/120 sure does. The lights would not work if the neutral is gone. You must be thinking of corner grounded delta.

The 4th wire..the green one is not neutral, but a safety ground.
Gunner
Confronting Liberals with the facts of reality is very much akin to clubbing baby seals. It gets boring after a while, but because Liberals are so stupid it is easy work." Steven M. Barry

I have seen lots of BS flying around on this topic but very little actual code. There are two issues. Is the cord protected and is the motor protected
240.5(B)(1) Supply Cord of Listed Appliance or Portable Lamps. Where flexible cord or tinsel cord is approved for and used with a specific listed appliance or portable lamp, it shall be permitted to be supplied by a branch circuit of Article 210 in accordance with the following: (1) 20-ampere circuits ? tinsel cord or 18 AWG cord and larger (2) 30-ampere circuits ? 16 AWG cord and larger
430.52 says a single phase motor can be protected at 250% of Full Load Amps using an inverse time breaker and you can round up to the next larger breaker size so if the motor is >10.1 FLA, 250% is greater than 25 so a 30a breaker is OK.

Bullshit. A cheap plug is a cheap plug. I have seen plenty of broken NEMA 5-15s too. Buy a good plug

It mighht work but it will not meet Code.

|> | You can install a 40 or 50 ampere receptalce on a 40 ampere circuit. |> |> OK. So the 40 amp dual 6-20R will work? | | It mighht work but it will not meet Code.
But the code says a 40 amp rated receptacle can be installed on a 50 amp branch circuit.
Read my other post about how the NEC writers are probably knowledgeable about electricity and safety, but are wording things poorly in such a way that it focuses only on a subset of the audience they should be addressing.

Table 210.21(B)(3) Receptacle Ratings for Various Size Circuits Circuit Rating (Amperes) Receptacle Rating (Amperes) 15 Not over 15 20 15 or 20 30 30 40 40 or 50 50 50

Sure the NEC says you can install a 40 ampere receptacle on a 50 ampere circuit, but it does not say you can install a 20 ampere receptacle on a 30 ampere circuit. I just bought the 2005 Code and it says the same thing. If you don't like this then why don't you submit a proposal to change the NEC.