|> | (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.
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.
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.
|> | 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.
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.
| 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.
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.
|> 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.
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.
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).
I just talked to my dad, a licenced electrician in Ontario. The Ontario Electrical code is loosely based on the NEC, but has some differences. Some things that are forbidden by the NEC are OK according to the Ontario code, and some things accepted by the NEC are not approved in Ontario.
Anyway, according to him, there is one simple legal way to connect that 20 amp compressor to the 30 amp drier connector.
Take a 30 amp drier cord, and using an approved strain relief chassis connector connect that cord to either a breaker or a fuse block in an approved disconnect box fastened to a 2 foot square 3/4" plywood panel.
Mount a 20 amp receptacle to the panel and wire it to the protected side of the disconnect.
Plug the disconnect into the 30 amp drier receptacle, and plug the 20 amp compressor into the 20 amp receptacle.
That way you are connecting a 30 amp device to the 30 amp circuit (you effectively have a 20 amp sub panel) and plugging a 20 amp device into a 20 amp circuit. In the disconnect the neutral must go straight through, and the ground must go straight through - only hitch is the drie plug must be a 4 connector plug.
The Ontario Electrical Code is based on CSA standard C22.1. "Based loosely on the NEC" is not really true; the CSA code was largely developed independently. Though, since the physics is the same on both sides of the border, the results are not fundamentally different. And in order to not unduly burden the far-off manufacturers of wiring devices that fill our lumberyards and home improvement stores, harmonization efforts on both sides of the border have resulted in substantial agreement.
I'd like to find a really authoritative examination of the differences between NEC and CEC.
|> | Canadian regulations would never allow 15 ampere devices on a 20 ampere |> | circuit. |>
|> But what is it that makes it a "15 ampere device"? Is it the maximum |> current rating, or the blade configuration according to NEMA?
And how many words does it take for these guys to make that definition?
The answer to my question could be given in 1 or 2 answers. I'm not looking for who has authority or not to say. I'm looking for a clear well written and concise answer. Given that NEC has numerous poorly written parts, and the wordings of other standards and such can get lengthy, they are of no interest to the issue of resolving exactly what is the formal answer.
I do know the answer, but I want to see it from other people to see if they really know, and to use that for a point of debate (I'll argue the wrong answer is right to see if they are even confindent of their answer if they do get the right one).
Exactly! There is always some info troll that will debate the stated rules for a loophole somewhere. That is why the code is stated with so many words. people that cannot read shouldn't be wiring homes or businesses where people can die in fire because of bad techniques or ignorance.
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