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

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wrote:

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)
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| (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.
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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.
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| wrote:|> |> | (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?
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wrote:

It mighht work but it will not meet Code.
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|> | 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.
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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.
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wrote:
| 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.
Are you referring to "40 ampere receptacle" and "20 ampere receptacle" in terms of the NEMA configuration of the device, or the ampere rating of the device? The NEC says "rating". If the device is _rated_ for 40 amperes, even though it only has a pair of NEMA 6-20Rs on it, how do we know that the writers of the NEC didn't actually intend that? I'll argue that maybe they really did intend that. Such a device could be considered as safe when both loads plugged in do not exceed the rating of their own plugs. That kind of logic and assumption is already made for NEMA 5-15R and 6-15R devices in duplex on a 20 ampere circuit. If the NEC writers _meant_ for the device _configuration_ to apply, instead of the current rating, don't you think they would have said that?
A lot of interpretations of the NEC do often hinge on the exact word used and in some cases even whether a singular or plural form is used.
I personally have no problem with 210.21(B)(3) as written. If they were to change it and refer instead to the device configuration, I'd still have no problem with it. Those who do one way are the other are the ones who should deal with it. If you don't like the fact that it refers to the device _rating_ maybe _you_ should be the one to submit a proposal to change it. I won't oppose it.
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experience performing over 3,000 electrical inspections and finding over 3,000 violations. I already got the egg on my face and served my apprenticeship. I suggest you get some time under your belt before you make an ass out of yourself anymore.
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wrote:
|> Are you referring to "40 ampere receptacle" and "20 ampere receptacle" in |> terms of the NEMA configuration of the device, or the ampere rating of the |> device? The NEC says "rating". If the device is _rated_ for 40 amperes, |> even though it only has a pair of NEMA 6-20Rs on it, how do we know that |> the writers of the NEC didn't actually intend that? I'll argue that maybe |> they really did intend that. Such a device could be considered as safe |> when both loads plugged in do not exceed the rating of their own plugs. |> That kind of logic and assumption is already made for NEMA 5-15R and 6-15R |> devices in duplex on a 20 ampere circuit. If the NEC writers _meant_ for |> the device _configuration_ to apply, instead of the current rating, don't |> you think they would have said that?|> |> A lot of interpretations of the NEC do often hinge on the exact word used |> and in some cases even whether a singular or plural form is used.|> |> I personally have no problem with 210.21(B)(3) as written. If they were |> to change it and refer instead to the device configuration, I'd still have |> no problem with it. Those who do one way are the other are the ones who |> should deal with it. If you don't like the fact that it refers to the |> device _rating_ maybe _you_ should be the one to submit a proposal to |> change it. I won't oppose it.|> |> -- | I am a certified electrical inspector by the IAEI and the ICBO with 8 years | experience performing over 3,000 electrical inspections and finding over | 3,000 violations. I already got the egg on my face and served my | apprenticeship. I suggest you get some time under your belt before you make | an ass out of yourself anymore.
Doing something wrong more than once doesn't make it right. Just because you have done all those inspections and found what you claim to be all those violations does NOT mean you have done them right. Inspectors can, AND DO, make incorrection inspections often. I have no idea how many of the 3,000 violations you found were true violations were wrong, but now I suspect at least some of them might well be.
Do you know that a receptacle device can have a configuration for one amperage and a rating for another? Apparently not. But they do. For example receptacle devices for NEMA 5-15R and 6-15R can be had with a 20 amp rating and even a 30 amp rating.
You'd probably fail an inspection just because it has #10 wire protected by 15 amp or 20 amp circuit breakers.
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The "receptacle" is the single socket and it doesn't matter how many you string out on a yoke when you are applying 210.21(B)(2) If we used your intrepretation you could put one of those 6 socket plug strips on a 90a breaker.
IAEI, SBCCI, ICBO certified and Florida licensed inspector longer than Jack.
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BTW I have a crisp $100 bill for anyone who can show me a 5-20 or 6-20 duplex receptacle device that is actuallty listed and labelled for 40a.
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This topic has generated a major number of orphan posts. Is it because people are switching away from M$ Internet Explorer? Unusual...
Joe
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How to keep the rules secret when they're written into a contract and also summarized in booklet form, available and typically mailed to all of the participants of the agreement?
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Typically, subcontractors hire their workforce and the wiremen on residential jobs are indeed employees of those subcontractors, not self-employed.
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Odd, as millions of homeowners don't seem to have any issues with them.
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<< Re: Can I plug my 230V compressor (NEMA 6-20P) into a dryer (NEMA 10-30R) receptacle >>
<plonk>
Joe
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In other words, you want a one-stop book that will permit a reasonably intelligent handyman or homeowner to accomplish an electrical job flawlessly, which takes most professional electricians at least 5 or more years to master while working side by side with seasoned craftsmen.
It ain't gonna happen.

Is there a book I can get that will teach and show me how to, point by point, design and engineer and build my own trusses?

It's not an excuse, it's all about the opinion as to what is acceptable and what is not according to the Authority having jurisdiction.
In some jurisdictions, running the NM homeruns into a panel using 1 single 2" knockout and a PVC pipe connector is perfectly acceptable, while in others each and every NM cable must be secured with an individual romex clamp.
How does one define "mechanically secure?"
It's just like a court case - the same case in front of 2 different judges might yield 2 different judgements.
If you think it's possible to learn an entire aspect of a trade from a book, then Sally Struthers has a course to sell you.

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Wait, this is legal, right? Suppose I installed #10 wire with 40+ amp.-rated switches and receptacles but only put a 20-amp breaker in the panel. It seems to me this would be a good way to go. The circuit breaker definitely protects the wiring, so it meets its goal. The only downside is that it may be more expensive than really required.
Thanks, Pete
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| |> You'd probably fail an inspection just because it has #10 wire protected |> by 15 amp or 20 amp circuit breakers.| | Wait, this is legal, right? Suppose I installed #10 wire with 40+ amp.-rated | switches and receptacles but only put a 20-amp breaker in the panel. It | seems to me this would be a good way to go. The circuit breaker definitely | protects the wiring, so it meets its goal. The only downside is that it may | be more expensive than really required.
AFAIC, it's safe ... and legal. But someone (and I've heard that inspectors actually have) could argue that mismatching the ratings could lead to some confusion, possibly resulting in future changes being doing wrong or the inspection being done wrong, where something gets underrated because the breaker was replaced with a higher rating. In your example I don't see much chance of that. But an example where it could be a problem is when there is #10 wire and 20 amp rated 5-20R receptacles. Someone working in the panel might assume the circuit is safe at 30 amps because of the #10 cable coming to the breaker. Of course, anyone doing that would be stupid and any licensed electrician doing that should be investigated and maybe have his license yanked.
The biggest problem, I think, is that there being a shift towards more DIY home wiring, perhaps due to the discounted electrical stuff at the big box stores, there is a fear that many people will be installing things in an usafe way. It's a legitimate fear. And I can understand electricians making the suggestions to use their services instead. However, I have seen some terribly unsafe wiring in my time, and most of it was in fact wired by licensed electricians.
People who are going to be doing the wiring themselves do need to learn the safe way to do it, and how to do it meeting the code. But the attitude I seem to be getting from a number of electricians (and also from an inspector in this thread) is that the NEC is something they are reserving to themselves. Well, if they think that, then I say they should inspect on the basis of whatever it is that they suggest DIY-ers read, instead of the NEC. And I have read some of those books. They have nice pretty pictures for learning techniques and information for avoiding the common mistakes. But they just don't over all the possibilities people might run into. That's where the NEC is really necessary. Mostly it's a good resource. But in some areas it's confusing, in some it's open to wide interpretation, and in a few it's even outright misleading. I have not kept a diary of the problems I have found with it since there is still no documented way for the average guy to work with the NFPA to get things reworded (people have said to submit changes, but until I see the NFPA specify exactly where and how, I have to assume they don't want them and I'll spend my time on other things, instead).
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