NEMA twist lock plug configuration compatibility

[mosseater]

We have quite a few cord and plug attached pieces of small equipment in the building that are using the NEMA L19-20, 4 pole, 4 wire, non-grounding plugs, but are NOT utilizing the single phase 277v component of the plug in their operation. They are strictly 480, 3 phase in operation, even though the 277v single phase is available in our facility system. My contention is that this is a mis-use of this configuration and not code compliant. I think we should be using the L16-20 configuration, which is for 480 v, three phase, w/ground.

Am I correct that this is an illegal use of this configuration and they should all be changed out where applicable? I just replaced one yesterday which said not to use the locking lug as ground, neutral only. Brought it to the super's attention, but he didn't seem willing to comment.

 

[templdl]

Being that you haven't received any comments yet putting the NEMA designation as side is it an electrically safe assembly? It may not be wired and applied by NEMA but the only trouble that I can see that could occur is if you attempt to plug into a female receptacal that is rated and wired for the NEMA rating which is the reason for the configuration. The intent is to prevent a mismatch of system voltages. It may not be the correct way of doing things but if your facility is unique and there is no danger of mismatching voltage configurations that may be the reason why you supervisor doesn't think it is an issue.
In my personal home woodshop with 240v, 1ph, 2w w/grd machines my Twistlock plugs are not designated as such. Being that I had existing twistlocks available and the correct ones are extremely expensive I used what I had. I didn't have to worry about a voltage mismatch in my own shop anyway.

 

[kwired]

Being that you haven't received any comments yet putting the NEMA designation as side is it an electrically safe assembly? It may not be wired and applied by NEMA but the only trouble that I can see that could occur is if you attempt to plug into a female receptacal that is rated and wired for the NEMA rating which is the reason for the configuration. The intent is to prevent a mismatch of system voltages. It may not be the correct way of doing things but if your facility is unique and there is no danger of mismatching voltage configurations that may be the reason why you supervisor doesn't think it is an issue.
In my personal home woodshop with 240v, 1ph, 2w w/grd machines my Twistlock plugs are not designated as such. Being that I had existing twistlocks available and the correct ones are extremely expensive I used what I had. I didn't have to worry about a voltage mismatch in my own shop anyway.

What configuration did you need that was extremely expensive? My guess for the kind of equipment in question is L 6-20 would be most likely needed which is not that expensive.

Getting back to OP question, your existing equipment with a neutral that is not used is not a violation IMO. We have similar thing with household ranges and clothes dryers sometimes where the appliance doesn't utilize a neutral but we still install a 4 wire cord on it. The violation would be to use the EGC as a neutral other then the limited exceptions where it is allowed (like existing ranges and dryers)

 

[mosseater]

What configuration did you need that was extremely expensive? My guess for the kind of equipment in question is L 6-20 would be most likely needed which is not that expensive.

Getting back to OP question, your existing equipment with a neutral that is not used is not a violation IMO. We have similar thing with household ranges and clothes dryers sometimes where the appliance doesn't utilize a neutral but we still install a 4 wire cord on it. The violation would be to use the EGC as a neutral other then the limited exceptions where it is allowed (like existing ranges and dryers)

Re: EGC, yes I see your point, and that was sort of my question. The plug designation has a purpose, and while not used for that purpose may be electrically safe (ie, the plug construction is suitable for the purpose of carrying a ground current on the designated neutral terminal), my concern is if somewhere along the line that someone would plug into it thinking it was good-to-go for 277v single phase (which woud work electrically, given the difference in potential is the same from phase to ground and neutral to ground), just doesn't seem like a very good idea if the right plug is so readily available. Always hearing speeches about doing the right thing from a safety perspective, until it's something we bring up. Then it isn't so important. So from a safety perspective, rather than a purely statutory perspective, the question then becomes, " is it okay to use the EGC and designated neutral plug terminal as a circuit conductor?" Right up there with re-indentifying CCC's which are insulated white out of circumstance of wiring method. We all know the white one is a phase conductor because the SJ cord comes with that color insulation and it's a attached to a three phase plug, but no one tapes them black or blue because they're part of a wiring assembly. Or is this somehow different?

 

[templdl]

What configuration did you need that was extremely expensive? My guess for the kind of equipment in question is L 6-20 would be most likely needed which is not that expensive.

Getting back to OP question, your existing equipment with a neutral that is not used is not a violation IMO. We have similar thing with household ranges and clothes dryers sometimes where the appliance doesn't utilize a neutral but we still install a 4 wire cord on it. The violation would be to use the EGC as a neutral other then the limited exceptions where it is allowed (like existing ranges and dryers)

If you already have a set of twist locks that have been aquired at lottle or no cost then purchasing more is extremely expensive. It doesn't t take a rocket scientist to realize that to purchase the correct ones from the get go would cost about the same asurchasing the incorrect ones.

 

[kwired]

If you already have a set of twist locks that have been aquired at lottle or no cost then purchasing more is extremely expensive. It doesn't t take a rocket scientist to realize that to purchase the correct ones from the get go would cost about the same asurchasing the incorrect ones.

Now you sound like a homeowner:happyyes:



"I got a good deal on this panel and I would like you to use it"

But it is a three phase panel and you only have single phase power available...

Been in that kind of conversation a few times before, but not entirely an apples to apples comparison either.

 

[Jon456]

If you already have a set of twist locks that have been aquired at lottle or no cost then purchasing more is extremely expensive. It doesn't t take a rocket scientist to realize that to purchase the correct ones from the get go would cost about the same asurchasing the incorrect ones.

In other words, you're saying that the correct plugs, even if priced only at a few dollars, are "extremely expensive" compared to the zero-cost plugs you already had. Correct?

So what were the plugs you had and that you installed? You talk about the possibility of a voltage mismatch. So were they NEMA L5 plugs & receptacles for 125V?

 

[kwired]

In other words, you're saying that the correct plugs, even if priced only at a few dollars, are "extremely expensive" compared to the zero-cost plugs you already had. Correct?

So what were the plugs you had and that you installed? You talk about the possibility of a voltage mismatch. So were they NEMA L5 plugs & receptacles for 125V?

Sort of like saying I have a bunch of 1920's wiring materials on hand and wish to wire my new home in 2014 with it:happyyes:

 

[mosseater]

I think what I'm taking from my question is the same as the supposition that, if everybody followed the law, there'd be no need of lawyers. Not that NEMA or the NFPA are "law", but they are surely enforced as such in many areas. If there was never any point in all the various configurations, then why have them??? We could have just as easily used the same configuration for multiple systems and depended upon folks putting labels on or signage to "check voltage and namplate information" when installing or troubleshooting equipment. I thought the whole purpose was to prevent mis-match for electrical safety reasons. Then when it doesn't happen, and the same people in my facility who are tasked with assuring safe, trouble-free, code-compliant work, simply disregard the use of the wrong plug, it makes one wonder what else is "up for grabs" when it comes to code. Maybe I've just been doing this too long and the new breed running the show are simply not to my liking. I get tired of the double standard, cherry picking what is important and what isn't. Thanks for the input, guys. I simply have to remember what I gave up for Lent: expectations! LOL!

 

[Jon456]

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?

 

[mosseater]

The equipment in this case is an old Rockwell drill press. Requirements are 480v, 3 phase. No 277v is utilized, there is no neutral in the service for this machine. That makes up the bulk of our power requirements in the building. In fact, the only place I can think of where 277 is used is in a few flourescent lights in certain rooms. Please don't ask why, I have many times myself and no one knows. I cannot think of an example of any machinery in the building that utilizes 277V. I can tell you there is a lug in all the buss tap boxes for a neutral connection, but none are used (to my knowledge). Someone a long time ago started this trend and no one has changed it. Maybe they're scared of the number of twist lock plugs and recepts. they'll have to change out if they concede on this one and they're hoping I'll let it drop.

Edit to my previous post: Meant to say...no difference in potential from "phase to neutral and phase to ground" not "phase to ground and neutral to ground".

 

[Jon456]

We have quite a few cord and plug attached pieces of small equipment in the building that are using the NEMA L19-20, 4 pole, 4 wire, non-grounding plugs, but are NOT utilizing the single phase 277v component of the plug in their operation. They are strictly 480, 3 phase in operation, even though the 277v single phase is available in our facility system. My contention is that this is a mis-use of this configuration and not code compliant. I think we should be using the L16-20 configuration, which is for 480 v, three phase, w/ground.

The plug designation has a purpose, and while not used for that purpose may be electrically safe (ie, the plug construction is suitable for the purpose of carrying a ground current on the designated neutral terminal), my concern is if somewhere along the line that someone would plug into it thinking it was good-to-go for 277v single phase

So is your concern about the lack of EGC bonding of the drill presses (as suggested by your first post), or the lack of a neutral connection at the receptacle -- and the possibility that someone might plug something into into it thinking that the neutral exists (as suggested by your second post)?

 

[kwired]

I think what I'm taking from my question is the same as the supposition that, if everybody followed the law, there'd be no need of lawyers. Not that NEMA or the NFPA are "law", but they are surely enforced as such in many areas.

NFPA documents themselves are not law. It is when a jurisdiction decides to adopt them that they become law, and not all jurisdictions adopt them, or some adopt them with amendments.

I think you are trying to use a non grounding type plug that has a terminal intended for use as the grounded conductor, but you have no need for a grounded conductor and wish to use that terminal for the equipment grounding conductor. I do see this a lot, in particular with the old crowfoot style range receptacle NEMA 10-50 I believe. When it comes to equipment grounding it is kind of OK, but must be connected to the EGC and not the grounded conductor if it is used for equipment grounding purposes, but if I were to cite a code violation it would be 110.3(B), and I would have to look at listing before deciding to cite that.

 

[templdl]

In other words, you're saying that the correct plugs, even if priced only at a few dollars, are "extremely expensive" compared to the zero-cost plugs you already had. Correct?

So what were the plugs you had and that you installed? You talk about the possibility of a voltage mismatch. So were they NEMA L5 plugs & receptacles for 125V?

If I was the owner of the facility and there was no possibility of a plug voltage mismatch I would see no issue with applying a twistlock at a voltage other than that of the twistlock rating.
As a professional if I were doing the work for someone else there is no way that I would condone doing as such.
However, If a twistlock were to be applied at a rating other that the label I would be concerned with applying a twistlock labeled for 208 or 240v or less at 480v. I would also never use a prong intended as an EGC is a L or N. Since neutrals are normally silver in color using it for a L or EGC would also be of a concern.
One would like to think that if a piece of equipment was delivered with a properly applied twistlock that the twistlock could only be plugged into a matching receptacle. The danger becomes if that equipment is used and that the previous owner installed a twistlock for use in his facility where they did not use properly rated receptacles. Or that the owner of the facility purchasing the equipment for that facility. equipment had chosen to install recepticals configured unequally for that facility.
Of course we are all aware that the EGC prong is longer than the others such that the equipment is grounded first before the others.

 

[kwired]

So do you just walk away from a job if they have existing misuse or tell them they are changing all of them if you are to proceed?

Right or wrong, if there is already a system in place I generally keep things the same. If it is just a single piece of equipment that is misapplied then I am likely to change it to what is correct. I am not too concerned with applying 480 volts to a receptacle only marked as 240 volts. They are basically made out of the same things and both will likely withstand up to 600 volts with no problems. But that is for concerns of the device being able to handle the voltage - it is still misleading to users to see 240 when they actually have 480.

 

[templdl]

TE=kwired;1559277]So do you just walk away from a job if they have existing misuse or tell them they are changing all of them if you are to proceed?

Right or wrong, if there is already a system in place I generally keep things the same. If it is just a single piece of equipment that is misapplied then I am likely to change it to what is correct. I am not too concerned with applying 480 volts to a receptacle only marked as 240 volts. They are basically made out of the same things and both will likely withstand up to 600 volts with no problems. But that is for concerns of the device being able to handle the voltage - it is still misleading to users to see 240 when they actually have 480.[/QUOTE]
NO!! If you read my reply carefully you would have picked up of the fact that as a professional I would never do work for others as such. If the owner of the facility elects to do so that's a separate issue. I could never perpetuate the incorrect application of twistlocks and I would advise them as to why.
As long is the applied voltage is less than the rating of the twistlock and that the prongs were not misapplied it would be the personal decision of the owner of the facility to do so.
Of course there must be assurance that there will be no mismatch of the plug and receptacle ratings.

 

[zbang]

I may have missed it, but is this situation well documented (receptacles marked "480v delta, no neutral" or something like that, etc)? I mean enough that another electrician would know about this setup before they have to start troubleshooting? If yes, and while IMHO it's a misuse of that particular plug, it starts to sound like using Black/Red/Blue for 277/480 and Brown/Orange/Violet for 120/208; that is, unexpected but working.

 

[kwired]

TE=kwired;1559277]So do you just walk away from a job if they have existing misuse or tell them they are changing all of them if you are to proceed?

Right or wrong, if there is already a system in place I generally keep things the same. If it is just a single piece of equipment that is misapplied then I am likely to change it to what is correct. I am not too concerned with applying 480 volts to a receptacle only marked as 240 volts. They are basically made out of the same things and both will likely withstand up to 600 volts with no problems. But that is for concerns of the device being able to handle the voltage - it is still misleading to users to see 240 when they actually have 480.

NO!! If you read my reply carefully you would have picked up of the fact that as a professional I would never do work for others as such. If the owner of the facility elects to do so that's a separate issue. I could never perpetuate the incorrect application of twistlocks and I would advise them as to why.
As long is the applied voltage is less than the rating of the twistlock and that the prongs were not misapplied it would be the personal decision of the owner of the facility to do so.
Of course there must be assurance that there will be no mismatch of the plug and receptacle ratings.[/QUOTE]I don't understand what you are trying to say, I thought the discussion was all about mismatch between marked ratings and the actual application.

 

[petersonra]

There is no requirement that the N wire be connected to anything in a wye system if it is not used, other than at the front end.

What NEMA plug configuration suitable for 480/277V systems has 3 hots and no EGC?

 

[kwired]

There is no requirement that the N wire be connected to anything in a wye system if it is not used, other than at the front end.

What NEMA plug configuration suitable for 480/277V systems has 3 hots and no EGC?

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.