NEMA twist lock plug configuration compatibility

[petersonra]

These are labeled W-X-Y-Z.

I don't think you can use a terminal labeled in some way as "ground" as anything but an EGC, but I don't think there is any requirement that says you can't use a terminal not labeled ground for the EGC.

 

[kwired]

These are labeled W-X-Y-Z.

I don't think you can use a terminal labeled in some way as "ground" as anything but an EGC, but I don't think there is any requirement that says you can't use a terminal not labeled ground for the EGC.

Again if there is any NEC violation it is likely going to be 110.3(B)

 

[templdl]

It does seem inappropriate to not have the grounded conductor connected. But the idea of bonding the frame to the neutral on 480V equipment doesn't appeal to me either; I'd much prefer a dedicated EGC. What are the manufacturer's installation requirements for this equipment?

The reminds me of the way the wired the opld 120\240 1ph 3w appliances where they used 3 conductor sharing the neutral and ground. On the surface it seems OK since the neutral is grounded. But at the appliance the neutral is bonded to the enclosure. The danger of that is should the neutral/ground conductor be disconnected or removed from the distribution panel by defect or in error the neutral current will no longer have a return path back to the source and will be turned loose is the appliance enclosure. Simply touching the enclosure and touching a ground at the same time will make you a return path creating an electric shock.
As such by sharing a neutral/ground on a 3ph4w system would create the same issue.

 

[kwired]

The reminds me of the way the wired the opld 120\240 1ph 3w appliances where they used 3 conductor sharing the neutral and ground. On the surface it seems OK since the neutral is grounded. But at the appliance the neutral is bonded to the enclosure. The danger of that is should the neutral/ground conductor be disconnected or removed from the distribution panel by defect or in error the neutral current will no longer have a return path back to the source and will be turned loose is the appliance enclosure. Simply touching the enclosure and touching a ground at the same time will make you a return path creating an electric shock.
As such by sharing a neutral/ground on a 3ph4w system would create the same issue.

Similar circumstances are introduced way too often by someone installing that bonding screw that came with the panel when it is not service equipment. Grounding and bonding is one of those things that sadly just is not understood well enough by many installers. And unfortunately when they make mistakes there - it generally doesn't have direct impact on operation of things so they have no direct indication of the problem either.

 

[mosseater]

Took me a little while to catch on but I think he has a 277/480 rated plug 4 wire non grounding. It is likely NEMA L19-20 or L19-30 I really don't know what one would ever want to use this at it's actual rating for as they do not include an equipment grounding conductor but they do exist and I have seen them a few times myself. Maybe it would work for internal component use of some equipment, but otherwise for NEC applications you generally need to include the EGC.

When I have seen them was for loads with no neutral and the "neutral" terminal was used with an equipment grounding conductor for the purpose of equipment grounding. I also see this same type of thing a lot with welders that use straight blade 10-50 receptacles. The 10-50 being commonly known as the old 3 wire range receptacle. A 6-50 configuration is really the correct application and what you will typically find on a welder that comes with a cord cap already installed, but many older welders had the 10-50 installed on them, don't know if that is what they came with or just what was put on them years ago, but it is common. I have seen many people change the cord cap on a new welder to this configuration or else make a cheater to adapt to it because they have multiple locations where they use this equipment and do not want to change all the receptacles, or still have older machines they would also need to change caps on if they changed receptacles. I can recall some 120/208 non grounding rated plugs/receptacles being used in similar fashion before, should be NEMA L18-series.

We have a winner! L19-20 plugs all over the shop, and every one of them are using the dedicated neutral prong as the EGC. They do in fact make a 5 prong connector which includes both an EGC and a dedicated neutral, but we don't need the one since we don't have anything that utillizes 277 v. I forget if it was on the box or the plug itself, but somewhere it said, "do not use as ground", or words to that effect. The tip off is the screw is not green like in the proper L16-20 plug. This is not the exeption here, it's the rule. That's why I find it so strange that no one ever picked up on it before. I have every confidence the situation will be ignored this time, too.

 

[kwired]

We have a winner! L19-20 plugs all over the shop, and every one of them are using the dedicated neutral prong as the EGC. They do in fact make a 5 prong connector which includes both an EGC and a dedicated neutral, but we don't need the one since we don't have anything that utillizes 277 v. I forget if it was on the box or the plug itself, but somewhere it said, "do not use as ground", or words to that effect. The tip off is the screw is not green like in the proper L16-20 plug. This is not the exeption here, it's the rule. That's why I find it so strange that no one ever picked up on it before. I have every confidence the situation will be ignored this time, too.

Unless you have some chance of wrong equipment being plugged into the wrong place, or an AHJ whether it be the EI, insurance, OSHA, or whatever that is pretty insistent that the practice is unsafe, wrong, etc. ... I am not too concerned about it. I possibly would even use a L16-20 and a L19-20 right next to one another for a situation where the 16-20 is technically correct for both, but maybe I don't want them to be able to be interchanged for some reason.

 

[Strathead]

Dis anyone clarify this... My read of the original question says that the neutral was available in the facility, it didn't say it was available in the receptacle. If available in the receptacle then I don't see any difference than say a 5-20R with a 2 prong polarized cord to a double insulated piece of equipment. If the neutral is not brought to the receptacle then I would consider it completely illegal.

 

[kwired]

Dis anyone clarify this... My read of the original question says that the neutral was available in the facility, it didn't say it was available in the receptacle. If available in the receptacle then I don't see any difference than say a 5-20R with a 2 prong polarized cord to a double insulated piece of equipment. If the neutral is not brought to the receptacle then I would consider it completely illegal.

His equipment is using the neutral terminal of a device as the equipment grounding terminal. The device has no separate terminal designated for use as an equipment grounding terminal. The connected load does not utilize a neutral conductor. The equipment is still being supplied with the needed three phase conductors and an equipment grounding conductor, it just is not using a plug/receptacle combination that is marked accordingly. If there is any violation it about has to be 110.3(B). I did not look it up but possibly the terminal on the device used for EGC needs proper identification as an EGC would be about the only other potential violation.

 

[GoldDigger]

General comment, not specifically addressing the OP's situation:
On a three phase connector where there are line to neutral loads, it is important that the neutral make before the lines and break after the lines. Otherwise you would have a lost neutral voltage imbalance which could be damaging.
On a system without a neutral but with an EGC you would like the EGC to make first and break last.
What is the mechanical sequence for the NEMA types under discussion? (I do not have any in my junk box.)

Tapatalk!

 

[mosseater]

That's a good point, never considered that. I never bothered to look inside one too closely, but I'm guessing they aren't precise enough to guarantee sequencial connection as you describe. Then again, the prong with the bend on it does seem to be longer. Hmmm, I'll have to look.

 

[mosseater]

Both the neutral of the L19-20 and the ground of the L16-20 are longer and appear to make contact first.

 

[kwired]

I kind of suspect they are longer from what I can recall.

Seems though that the neutral of 10-30, or 10-50 straight blade plugs is same length as the ungrounded conductor blades:huh:

 

[GoldDigger]

I kind of suspect they are longer from what I can recall.

Seems though that the neutral of 10-30, or 10-50 straight blade plugs is same length as the ungrounded conductor blades:huh:

But the wiping contacts in the receptacle might be recessed to different depths?

 

[kwired]

But the wiping contacts in the receptacle might be recessed to different depths?

could be, but those are usually sloppy enough of a fit that if you don't insert it straight you may still be able to make some other connection first. There is still a lot of 10-50 plugs in use on farms around here virtually none with a neutral load just using that blade for the EGC- maybe not the right connector for the task but how do you tell the guy his equipment that he takes from one site to another has to have a different plug on it - and all the other sites of course have this configuration and have had it for years, they are not going to change their other sites, if anything they will make a short cheater to adapt, which in some ways is more dangerous - more parts for them to have to maintain - which they often will not do a very good job of.

 

[ActionDave]

. There is still a lot of 10-50 plugs in use on farms around here virtually none with a neutral load just using that blade for the EGC- maybe not the right connector for the task but how do you tell the guy his equipment that he takes from one site to another has to have a different plug on it .....

Same here. Once in a while someone will build a whole new shop and we will put proper recpts in and change the cords, but otherwise I don't worry about it.

 

[kwired]

Same here. Once in a while someone will build a whole new shop and we will put proper recpts in and change the cords, but otherwise I don't worry about it.

Farmer puts up a grain storage bin. The portable auger(s) he has that he uses for unloading into trucks is moved from bin to bin as needed as well from site to site, and he has 20+ sites or even has a few sites he either rents, or is contracted to operate. If they all have a 10-50 receptacle for connecting these augers it does little good to install a 6-50 even though it technically would be more proper thing to use, He will either change the receptacle to a 10-50 later or make up a cheater cord - that will likely see a lot of abuse in handling and he will keep using it even though there are broken parts - exposed live parts, etc. making it an overall higher hazard then just using the 10-50 receptacle in the first place.