ECN Forum Forums Code Related Discussion NEC & other Code issues NEMA configurations for receptacles/plugs

Hi,
I am trying when the current NEMA 250V and 277V receptacle configurations (6-20R, 6-30R, 7-20R, 7-30R) were adopted.
Does anyone know if the adopted configurations for 250V and 277V were different 20 to 30 years ago?
Does anyone know when approved applications for 277V receptacles/plugs changed?
I cannot provide specific details, but the matter I am looking into may involve a misapplication of a 250V plug with a 277V source.
Any information or suggestions about where to find more information would be appreciated.

sounds like a lawyer to me....

And I hate lawyers...

Dnk...

Even today, there is no NEC requirement that NEMA plug patterns be followed....there is only a requirement that differing systems have different patterns.

NEMA designations didn't really get codified until, I think, 1972. There were earlier attempts, as far back as 1965 (again, I think), but there were numerous changes made in the interim.

There were a number of patterns that were "rated"..that is, accepted by trade practice, and marketed for, multiple types of service. UL would list these things, and test them, as for the uses intended by the manufacturer.

Two notable exceptions to the use of NEMA patterns are Recreational Vehicles (which still have their own pattern) and the three-prong clothes dryer and range devices (which are being phased out). Indeed, the computer you posted from probably has a non-NEMA 120 plug on the back of the monitor.

NEMA stands for "National Electrical Manufacturers' Association. They would have the definite answers to your questions. UL also has published "standards" that define their listing criteria.

Tammy, your post is a little thin on details. Exactly how is it hooked up now, and what are trying to do with it?


[This message has been edited by SolarPowered (edited 03-02-2006).]

I am not a lawyer. I have a PhD in electrical engineering. I also have a severe case of multiple chemical sensitivities. (I am allergic to the world.)

For the last couple of years, I have managed to make a living working at home, by working for the person who was my PhD advisor in college. A lot of what I do is just try to provide some background on the problems that he is dealing with.

I don't have the particular details. I know that there might be some type of problem with how a room air conditioning unit was wired. The building is probably 25 to 30 years old.

I have viewed the current NEMA WD6 standard online, but what I would like to know is -- could the configurations have changed over the years. That is could the current configuration, say for example, for 250V,20A at one time have been the approved configuration for 277V, 20A?

I don't know how to locate older versions of the current NEMA WD6 standard.

I would also like to know if NEC 440.62 on Room Air Conditioners has changed over the years. 440.62(2), 2005ed, says that a room ac unit cannot be more than 40A and 250V,single phase. I would like to know if that provision changed, and 277V used to be allowed (and when it changed).

Any information would be appreciated.

Sorry about that Tammy, my apologies...

(still hate lawyers)


Now then, I haven't found anything on the net that would help you, right now, but I'll continue searching. I haven't heard of anything like what your asking, in regards to using the same config for different application voltages. But maybe they did.

Hang in there, some of these guys respond after work hours, and some of them may know for sure...

Good luck.

Dnk...

"240v" air conditioning is usually set up for 240 v "single phase;" that is, two "hot" wires, each having 120 volts to ground, but measuring 240v between them. I suppose that, in theory, you might find a 3-phase, 240 volt air conditioner....but not very likely!

"277v" is the nominal voltage of one "hot" leg in a 3-phase 440v system. I have only seen 277v used for lighting, and never for HVAC equipment.

That things might be "wired wrong" is very possible. HVAC is an art of its' own, and I -even with several courses under my belt- am not qualified to comment on the specifics. I will say that you need a wiring diagram -either 'ladder logic' or a schematic- to do your troubleshooting. If one is not present, you'll have to find a HVAC person to look it over.

When I was growing up in the 1960's I managed to get hold of a big Leviton catalog. I remember it specifically included a duplex grounded 277 volt 15 amp receptacle. They also had both grounded and non-grounded plugs for it. I hadn't actually heard of 277 volt utilization at that point, but after playing with some math on it a bit, I figured out it came from 480 volt three phase systems. So that's why it stuck in my mind.

They also had receptacles for 120 volt up to 30 amp, and for 240 volt up to 50 amp. But for 277 volt, the 15 amp model was all there was and it was only in straight blade; there was no locking 277 volt receptacles at all.

So I wondered what would need to use 277 volts. The only conclusion I could come to was portable fluorescent lighting units.

The point there is that if someone needed to have a way to plug to 277 volts with more than 15 amps, they very well could have had no choice but either using a 240 volt receptacle configuration, or hard wire it. I don't know if any other brands might have had something larger in 277 volt, but Leviton certainly didn't in that catalog (about 500 pages).

Even today, with downloaded PDF catalogs from both Hubbell and Leviton, I don't see 277 volt receptacles or plugs above 15 amp, even though the NEMA PDF shows larger ones.

This also brings up an interesting issue I wondered about a year or so ago. What if you had to choose a receptacle and plug type for a 240 volt circuit that was wired with a hot at 240 volts relative to ground, and a grounded conductor? Using a 6-XX configuration might not be safe. Something could be plugged in that could not handle the way it was wired. I'd say the 7-XX configurations would be safe in the sense that they would be designed for at least that much voltage (and more) and for the single hot and grounded conductor combination. But even that could pose a hazard if you put a 7-15P on something that can only handle 240 volts. If pressed to do so today, I might use a German Schuko configuration instead, or maybe the British or Australian configuration.

pdh:
In my Leviton Catalog, I show NEMA 7-30 products which are 30A 277V.

They also show NEMA 7-50 which are 50A 277V.
go to http://www.levitonhelpdesk.com/catalog/
and search for "9730" or "9750".

I don't see any 277V 20A, however, except in the locking style L7-20.

[This message has been edited by kale (edited 03-14-2006).]

IT dosen't sound like you are asking the right questions. THis forum is chock full of Professionals. In my 45 years in the industry I do not remember any major changes in NEMA Configurations.

If I could remember the name of that plug system... the plugs had 3 pins that looked somewhat rounded like the NEMA locking plugs.

A google search popped up so-called solar receptacles without any mentioned standards, simple flat round pin sockets with two different pin diameters.

440.62 does not limit the size of a room air conditioner to 40 Amps or to 250 Volts.




BTW, even though it doesn't apply, 440-62 has remained basically unchanged since it was added in the 1975 Code.
(Before the addition of Article 440 in the 1971 NEC, the info for Room AC's was in "Appliances", Article 422(F) Provisions for Room Air Conditioners)

NEC 440.62 says that the voltage is limited to 250 V or less, single phase and the current is limited to 40 A or less.

It seems to me that a 277-V, single-phase supply would violate NEC 440.62.

2005 NEC 440.60 states that if the supply voltage is over 250 V, then NEC 440.62 DOES NOT apply.

Larry

All it is saying is that if it is over 250V or over 40A, then the "Single Motor Unit" method of determining the sizing of the branch circuit conductors and overcurrent protection can't be used.

Because motors briefly draw a large current at startup, and then much less current while running, the code in some circumstances will allow a bigger-then-normal circuit breaker on a motor circuit to account for the startup surge. The 250V, 40A test is simply a test to determine which rules you are required to use to determine the wire and OCPD sizing, not a limit on what voltage can be used to power an A/C unit.


[This message has been edited by SolarPowered (edited 09-25-2006).]

Thanks for the replies. It has been so long since I posted that I didn't remember the context of the NEC code 440.62.

What I really would like to know about the NEC code is about 440.60:

The provisions of Part VII cover equipment rated not over 250 volts, single phase, and such equipment shall be permitted to be cord-and-attachment-plug-connected.

A room air conditioner that is rated three phase or rated over 250 volts shall be directly connected to a wiring method recognized in Chapter 3, and provisions of Part VII shall not apply.


Does this say that a room AC with 277-V supply must be hard-wired and not attached with cord and plug?

Tammy, I would not go quite that far. I think you can make a case, though, that things be rated for their use.

Ordinary plugs, and receptacles, are not rated as a disconnecting means for larger loads and higher voltages. There are exceptions; one company ("Meltric" I think) makes such connectors as their primary business. There are others that incorporate a switch in the receptacle, so you actually 'turn it off' as you begin to remove the plug.

Looking at the code, we see that cords and plugs are allowed to be the disconnecting means for only the smalest of motors. This does not mean you cannot use cords on larger stuff; it only means that there must be an additional disconnecting means.

So, using your air conditioner example, I would say that the receptacle would need to have a switch controlling it.

John you remember correctly Meltric makes great disconect rated receptacles.