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.
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.
#97537 - 03/02/0612:52 AMRe: NEMA configurations for receptacles/plugs
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.
#97539 - 03/02/0611:58 AMRe: NEMA configurations for receptacles/plugs
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...
#97540 - 03/02/0606:33 PMRe: NEMA configurations for receptacles/plugs
"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.
#97541 - 03/11/0605:56 PMRe: NEMA configurations for receptacles/plugs
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.
#97542 - 03/11/0606:03 PMRe: NEMA configurations for receptacles/plugs
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.
#97543 - 03/14/0607:55 PMRe: NEMA configurations for receptacles/plugs