70V on the Neutral, how are these Edison's wired anyway?


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Got a call over the weekend.

After lots of tribulation about how convience outlets on a 400A three phase AC distro was wired, it was determined that 190 Amps on phases X & Y were fine when balanced with 175 Amps on Z.

Close enough.

Real question was in detecting 70v between neutral and ground.

Given the load is fairly balanced, what would be the next choice for something that would cause this voltage?

Note this is a question for students. Pro's should hold back until the answer is given by the students or contact me off line to debate or discuss what to check first as the most possible cause.
I don't ever do any work on distros- but her is my guess...

Eighter the neutral or the ground is some how tied into X or Y.

By the way- for those of you out there that use the 20A 125V twistlock connecter and need one fast when your in a pinch- you can just run to your local hardware store and pick up a 20A 250V and file down the I think what is the X pin. It works just great, but I would wonder what a fire marshal would say.... but like I said- only in a pinch.
I would say that the neutral is bonded to ground at more than one point, or that there are multiple grounds in the system.
ricc0luke said:
By the way- for those of you out there that use the 20A 125V twistlock connecter and need one fast when your in a pinch- you can just run to your local hardware store and pick up a 20A 250V and file down the I think what is the X pin. It works just great, but I would wonder what a fire marshal would say.... but like I said- only in a pinch.

Hmm, what would the fire marshal say? What would you in being that tech person say is more important. Re-think your advice in filing down the ground pin. While I cannot say for sure if this will work in filing down the hook out verses hook in will work in never having tried a L6-20 to L5-20 conversion, I can't say I would approve of it either. Is this specific application of what equipment otherwise work, sure or not. I would think that a L5-20 outlet has in addition to this hook designed to prevent the mis-use of the plug, that it also has a neutral pin of a different size to prevent a lock but perhaps it does not and you have found a way of bypassing the safety system intended.
Is modifying equipment so it works ever permissible... nope. Not a question of the electrical inspector but you in ensuring it's compliance. How about having some extra plugs in stock instead? This or if the first store does not have what you need in a other wise prior planning type of thing, go to the next store. Why worry about such adaptors at all, you do the 250v plug in a pinch, why not also do the 125v plug in a pinch where needed this universal plug type.

Point is that there is reasons for not doing things and while the electrical inspector might or might not be a stop gap, you and ever tech person is more charged with ensuring the electrical safety of your system than a visitor that does an overall hopeful inspection of your compliance. Fact is that unlike what stantonsound is no doubt used to with inspectors needing to verify every component of what they have done, there is a certain amount of trust if not or inspectors doing when and if they visit a lot less specific detail orientated inspection than with the real electricians.

in further discussion of the 70v. it was learned that this condition was shown to be confusion by way of me understanding what the crew chief was talking about to me in that the 96way dimmer pack had this 70v problems and the AC Distro had others that were completely seperate and not mentioned. So now, should one detect a variance in the dimmer pack balance which still shows a 70v variance between ground and neutral, what would you check first?
I would have to guess that there might be fixtures wired incorrectly. The first place I would check would be at the power source to see if the building has bad power, then check any terminations between the systems. Then again, wouldn't it be worse to have 70 amps on the nuetral and you don't need to worry about the volts?
Robert said:
I would have to guess that there might be fixtures wired incorrectly. The first place I would check would be at the power source to see if the building has bad power, then check any terminations between the systems. Then again, wouldn't it be worse to have 70 amps on the nuetral and you don't need to worry about the volts?

Fixtures were wired correctly.

Can you go into more detail about how you would check the power source and terminations between systems?

Volts read 120v no doubt, and it's normally very bad to have that kind of voltage in the neutral though it would seem that both the designer and crew chief were not worried about this detail much. Must have a little chat with them about "I see it all the time and was not worried about it."
Oooh... maybe a leg got switched with the ground going between the distro and the dimmer...

Here is a graphical depiction of three phase power:


If we plug in the numbers, Vab is 120, Vob is 120 / √3, or about 69.2v

If a leg got swapped with the ground, some of the dimmers wouldn't work and some would have 70v between ground(leg) and neutral.

This would also mean the service had to be delta,
I think.
Then I would say somehow there is a bond between Z and ground with a resistance of 4 1/3 ohms. The math for this is as follows:

ohms = volts / amps

o = 70 / (190 - 175)

o = 70 / 15

o = 4 1/3

So somehow something did that.
Way too complex, think of a more simple solution though the actual nutral voltage amounts is somewhat heightened above a in-balance in the load generally.
Meter the power at the source or their disconnect panel. You said measurements were done at the dimmer. I have been places where in the evening or at show time other units come on line and cause unbalance loads or noise on the power lines. As for the other connections, just verify all that the right cables are landed to the right lug.
Also see if for some reason they have married the nuetral and ground in the box. Then make sure any cams are secure and tight.

Is there another system in place you can compare to? Does audio have the same issue? Clamp on an ammeter and see what kind of current your getting to your nuetral. Might surprise you as well.

I have seen loads show up on the nuetral as well at venues. I remember several years ago Broadway was having trouble with the power grid due to harmonics causing trash on the nuetrals. I can't remeber what their solution was.
My gut is telling me loose neutral causing a sage in the neutral. In trouble shooting I would meeter the disconect and the rack H to H and H to G and H to N and N to G and any other combo I could think of. I would also be looking for loads on the system that were out of the ordinary. Also is there a neon pilot light on the system? How is it wired? Is it lit?
Yes and yes! Loose neutral especially at it's tie in would be the first thing I checked after I knew there was a fairly balanced load. Floating neutral I believe it's called, but in this case it would have contact - just a lot of resistance. Very dangerous and this will destroy equipment. It might also show 120v between hot legs and neutral when first checked and nothing between neutral and ground due to there not being enough load for resistance. Once the load is on the distro/dimmer power drawing equipment, that resistance would show up.

That tie in to the lug would be where I would check first given plugs are enclosed, as is the rack. Only thing that has really changed between such gear will have been tested at the shop and on site, besides the set up of the gear will have been the tie in.

Always do what's simple to check first also than get into more complex stuff.
Speaking of LED lights, today I learned something new.

Bought from a local Ace Hardware a Eagle Electric internally lighted 15a/125v single pole household switch.



Switches > Standard Grade > AC Quiet - Lighted Toggle > Lighted Toggle Grounding Switch - Side Wire and Push Wire - Single-Pole >

under www.eagle-electric.com

It was going on my new lamp bar/cyc light tester. Basically the cyc lights and lamp bars have six circuits each and are fed by a Socapex style muliti-pin plug. To test them in the past, it was always a question of getting a what we call punt or fan-in that goes from individual plugs to a Soco type female receptacle. Than running an extension cord to a GFCI protected wall outlet and plugging each circuit into the hot/live extension cord. This is what's called "hot patch." Very good way in having a 1,000w load to burn up plugs as you make contact, much less in the arc from the jumping current, it's not something you want in your hands.

Doing a hot patch is bad and also does strange things to lamps. Though I would rather a lamp blow in the shop, snapping a toggle switch will have the same cold lamp jumping to full shock to the lamp only be much more safe for the end user and equipment. In theory, all testing should be done with a dimmer except in this case when it's something you want lamps that will soon blow to blow now rather than on the job site. On the other hand, low voltage lamps, especially those wired in series such as PAR 64 Aircraft Landing Lights should be on a dimmer to run the much smaller filaments up so in heating them up.

So I have a short in length punt now assigned to this duty that has a Kellems grip to support the Soco plug and a 4.1/4" screw in bolting all the stage pin plugs together attached to another linkable loop to make it easy to go from plug to plug and hang the punt from both of it’s ends. To this punt, I have added a in-line/cord mounted fused switch off a Altman 2Kw studio Fresnel fixture. Basically a 20amp two pole switch so it turns off both hot and neutral at the same time that’s mounted on a cord. Many times studio lighting equipment has switches so you can on a hot often non-dimmed circuit turn the fixture off before un-plugging. Very important especially on a 10Kw type of light much less any in not hot-patching and having it explode in your hands. I replaced the switch with the internally lit single phase toggle switch and added a 10 Amp fuse mount to it for more safety. Maximum of 1Kw per circuit thus a 10amp switch is sufficient. We now have a cord mounted switch and fuse assembly that with some rings and quick links is attached to the punt all hanging off a J-Clamp mounted to the rear of the switch so it hangs up near where you are working. Nice and flexible and easy to use and no more hot patching. Normally, it's not permissible to kill the neutral on a switch, nor most often needed, but there is Code exceptions such as this Altman is using in ensuring both circuits hot and neutral go out at the same time and it is permissible.

Problem with this Eagle switch was that in spite of there being an internal light that is lit when power is off - a nice thing to have in taking the NEC's rules about cord mounted multi outlet boxes including power strips to hart for this similar application. This way you know when the multi-outlet switch is live and being kicked around on the floor. This specific switch however that’s different than a normal pilot lit switch would be un-safe to use given it’s different nature.

This new style of internally lit switch only had the hot in, hot out and ground terminals as if a normal non-lit switch. No neutral as would be normal for a internally lit switch of a filament or other type. This also by way of how the switch works means that when there was not something plugged into it, it won't be lit. While such a indicator might be useful while plugged in to detect a bad lamp, it won't fulfill the goal of knowing if such a thing is still plugged in while kicked around on the floor. Much less as a home owner, when your lamp was dead, and in not understanding that this specific switch while normally when the lamp was off the switch was lit, they might assume a major electrical problem when given the lamp was only dead, the switch also was not lighting. Beyond safety, I question such an items concept.

We, the other ME and I theorized initally the lamp was getting it's return off the ground, and while it might or might not be against code given the load, it might possibly pop the GFCI it was plugged into, yet we did not see much of another option given the instructions for use were less than useful in any way as to how the internal light worked or what situations to use the switch in. I don't expect this type of switch to be long on the market given the liability of it's design flaw given the intended use.

Had some other theories on how it worked in addition to questioning the labeling of “common” for the switches line out terminals but none panned out. Basically there was three screw mounts - one for ground and two for the line in and line out hots. There was also three solid core wire quick connect holes, one with s “common” pinted on the switch in marking pointing to two terminals at the line out side of the switch. "Common" in pointing to both the line-out outputs of the switch? Common means neutral in most normal language, what's it doing in labeling the line out part of a switch?

Given we assumed it most likely that there was no neutral mounting for the thing and found it very curious given a internal lamp, it had to be somehow run off the ground given all the line out holes beeped out as per common connection points connected together. Granted given a internal lamp they would anyway in a complete circuit thus my below call to Eagle in figuring it out. Problem with the most reasonable assumption that given the lamp does not draw much current, it might just have it’s return path thru the ground, but such a thing would not make sense given other internally lit switches have a neutral to attach to.

If the lamp were run thru the ground, a GFCI senses differences that can be very small between hot and neutral thus were this switch even if in the case of a small lamp working by way of using the ground for a neutral it might have set off the GFCI. This would be the condition were it a washroom where the overhead lights, to be on the same circuit as and fed after the GFCI outlet would offer the GFCI protection to both switch and lamp fixture. Believe this practice is now against code, but it's certainly been done and is still being done in say a washroom.

I had to wonder about it thus GFCI tripping, as since it came from ACE Hardware, it no doubt at some point might potentially be used in a washroom where the lamp was also protected by the GFCI outlet. That would make it pop also given it sensed the difference in current between hot and neutral. Yet there was no neutral lug. This in addition to the label of “common” at the rear of the switch confused both the other ME where I work and I. What might have been a neutral quick solid core wire connection point, did not have the neutral terminal as a fourth screw attached to it, plus there were arrows linking what was certainily line out holes together meaning that you could feed off these holes two outlets as opposed to one. Yet as opposed to other electrical equipment with holes for quick connection on the same side of the outlet next to each other, the other outlet hole was on the opposing dead side of the plug. = that end of the plug that's used for a three or four way switch, or in the case of a normal pilot light, something that with this extra quick connect hole might be assumed to be hole without screw for the neutral.

Called the tech support line at Eagle Electric and actually got a call back which surprised me - though the support person was rather smug "feeding a lamp off the ground would be against the NEC!" (Well da!) Much less in finding one person that was in the office given you could not other than leave a message be on hold, it took many calls to find someone that was working today finally as opposed to sitting on hold in at least a better chance of getting to talk with someone that day. - Hate automatic phone systems especially when very limited. Still, customer service in most cases takes lots of time for a call back, much less if ever called back on more difficult end user questions - much more than the difference between black and white wires they no doubt often have to answer and are easy. I only have one very much un-qualified person doing what he does where I work to answer ignorant questions to about stuff he should not be messing with. Can’t imagine answering calls for a help line. Still when I have to call a help line, I want immediate answer as I can't just put the thing asside and do something else. At least one out of three on the help line as last resort I finally left message with and a few hours later he called me back.

Anyway he while not really helpful in understanding how it worked or that I was doing something safe with it, confirmed the lamp was not fed off the ground nor directly by the neutral, and told me more about how the switch worked that went to some extent over my head but was understood in principle sufficient to understand that there both was no neutral lug, and that it was not fed off the ground. Still it seemed reasonable to use the switch for this use after the call.

I later asked the other ME where I work - the old man and he explained it more to me once I told him what the tech support said. And the light went on for both of us at least in otherwise both of us looking at the switch and scratching our heads and not assuming it to be anything as described. Note both of us together probably have say 50 years of wiring experience between us yet were confounded by something available and potentially un-safe to home owners. We both in discussing how this tester would work than thinking about how it worked, decided that this switch would be very unsafe to use in testing the lamp bars. Might not kill you, but anyone ever work on a lighting system where the dimmers were at zero, yet the system was still on? Same but in this case possibly also much more un-safe. Certainily not something you wanted on a test or work circuit.

Instead, I used a 15amp household grade toggle switch to save on wire fill capacity space given I had already added a panel mount fuse to the assembly in eating up that space needed to cool the conductors within a box. Household toggle switches are not the choice of commercial situations and I expect it’s going to wear out and need replacement sooner than later, but I needed that extra space in the switch being smaller than a commercial grade one.

Why is my question for all of you on this forum, and this is a very difficult question all are welcomed to chime in on. Why would the switch in working how it does be very unsafe for stuff like changing lamps while plugged in - as one designing gear must have safety against because they will anyway no matter the intent of disconnecting from power. - Thus making it also a little easier as a hint. This specific lighted switch especially for home owners to be using who are not even trained beyond switch off means dead circuit in question for this lamp bar tester! It's not because it won't be lit when not plugged into something else and kicked around the floor also. Much more dangerous reason and one you in understanding should explain in depth. Who can express given the below how and why even for a home owner, it potentially might cause a wee bit of a problem? I gave up on the indicator lamp given there was not room in the cord mounted switch body to add an indicator lamp in addition to the fuse.

Effects of Electrical Current on the Human Body
0.005-2mA = Just noticeable
2-10mA = Slight to strong muscular reaction
5-25mA = Strong shock, inability to let go
25-50mA = Violent muscular contractions
50-100mA = Irregular twitching of the hart muscles no pumping action (ventricular fibrillation)
100- >100mA = Paralysis of breathing
(Source: PGS Power Guard Systems, LLC.)

Of the "the old man of the theater" (who these days more deals with hoists and rigging than electrics now that I'm around but we very much have a communitcation back and forth still on most all projects.) He is no longer the Grumpy part of "old man of the theater" given he now has someone to talk to now that understands the same concepts he is thinking about, much less can help him also as he does me. Wiring stuff when alone is not a good idea, even on the theoretical sense. We also discussed the next generation of lamp bar tester in making this gear I was working on already obsolete but I had considered already such a thing and decided given I had a Punt that was otherwise not useful for shows wanted to use it here in that we would need two testers eventually anyway. Much less since I was out of quality plugs, it otherwise would just go in the trash and the test circuit was still needed. A bird in the hand, and one less I have to build in the future.

The next generation will have the soco outlet mounted to it in a hanging box and a single power cord. No more patching needed. It will have a thermo magnetic circuit breaker as better than fuse often, and a multi-position switch so you can simple turn it from circuit to circuit in testing the lamps. A additional momentary contact switch to turn the power on and off would be nice and make things simple, but when doing things like looking at gels, or testing, you might not always be able to keep your finger on the switch thus it as an idea would not work. Granted since this, the multi-position switch would either have to have current block stops between positions so it does not internally arc, or have to be a 12 position switch in doing so with no-load stops between settings also it can't just be a simple six position 10amp rated switch. The thing will also have an amp meter on it so you can tell what wattage of lamp is in the fixture also because it's otherwise needed to examine each lamp to verify it's wattage be it cyc in normally having either 300, 500 or 1Kw lamps or lamp bar in having 500 or 1Kw, or 375 575w or 750w lamp fixtures mounted to it. Yea, that amp meter when marked for what wattage of lamp will be a useful thing.

Still it's done and we now dedicated have a tester box or better than hot patching means for testing just about every type of cable and fixture in the building in making things both safe and easy to use. Want to test the Edison to IEC, much less 208v to IEC adaptor such as used on a computer monitor and dependant upon what country your show was goint to or what equipment was using the IEC plug, we have a tester for that amongst other testers and types of thing safely tested. Some that are multi-position switch, others that are even mini-computer in both sending a signal thru and testing for shorts. The computer is slow thus it's not used as much as opposed to the say 18 position scrolling multi-pin switch for soco cable. Still our tester box both detects what type of cable you test and test it in a very important all things - resistance and shorting type of way as opposed to just LED's on or off with good or bad or shorter circuit. The computer part of the good tester also tests resistance and a good data signal as similar to expensive microphone cable testers that also at times will send a signal in testing for this. In a data or microphone cable, a tester that sends a signal thru the cable will detect and mark as bad cable that say has it's shield wire connected to the wrong pin that a normal tester won't detect in just saying you have continuity.

However, as opposed to re-wiring the punt with longer cords - or in this case it was a staggered punt in being stupid, the manufacturer had made it in using a normal plug with a bunch of wires shoved into the soco plug. Since a normal plug - or one by made by this manufacturer to the soco standard but with their own ideas of how to do a plug, won’t fit a bunch of 12ga wires shoved into it’s strain relief, they removed the plug’s rubber strain relief part that normally bears down on the cable to grip it.

Learned about this far too late to have hope of returning it as un-safe and stupid in general - but they will get an E-Mail. Probably my mistake in buying the staggered punt in copying a PO for some staggered fan-out type that is useful to be staggered, but the plug used was un-safe in itself. Instead of having a proper plug that either separates the individual fan-in or out cords as per the Veam VSC series plug, or has a large two screw strain relief in binding them together with friction tape used to protect the jacket, or at least a large enough PG series weather tight strain relief to fit all the wires, they removed the rubber part of the weather tight strain relief and were using the far too sharp once clamped down plastic gripping fingers in the strain relief part that grips onto the rubber part, to bear directly down onto the individual thin jacket of the fan-in wires. Something that with use will cut into the thin jackets over time and in short order have exposed conductors at the strain relief.

This in addition to the fact by no doubt my mistake, that if the thing has a bunch of plugs on it, having plugs be staggered from 18" to 6', it won’t be of much use since most stuff punts are plugged into have outlets right next to each other. So it both was not really safe to use in having a bad strain relief and even in one case broken strain relief in having broken off fingers that now exposed a sharp edge to the conductors which they still sold to us, if you plugged it into a rack, it would have no extra slack on circuit one, and about six feet of extra slack on circuit six. In making the punt for shop use, I cut them all to 18", than cable tied them together about 3" from the soco connector so the plastic cord grip fingers would not have much wear on the wires given they no longer could flex and be as much damaged by a lack of rubber strain relief between cable and the plastic fingers.

Of three of these punts bought, one was changed over to a good Veam plug that does it’s job well - and all were made the same length, another is still missing, and this last one is for shop usage where we can watch it and replace it once it shows signs of wear.

Both long and question by purpose, in question of the day supplement, I hope to provide a really good challenge into understanding how something works that you can buy something dangerous off the shelf by mistake and get really injured really fast should you use it in the wrong way they were no doubt thinking and in thinking it is something other than it is. And explain how at times the design process for making gear goes and what considerations go into doing it other than in just a hack way task oriented way that does not consider how stuff both will and could potenially be used. This wire space capacity of a box, much less specifically designed to mount on a cord switch thing, much less in having it as a test circuit, both plugging into a GFCI and having at least a fuse on a 1Kw load but given a 20 amp circuit, the need for the sub-overload control protection. While it's obsolete as opposed to better designs, it still was cost effective to make in needing more than one and both short of this use the expensive punt will have been trashed, much less in other than understanding how something worked before I used it in the case of the switch, than really thinking about how it works and how it thus potentially could be un-safe it was not used. This in addition to mounting the whole it on a hanger clamp so it was easy to use in not needing to hold it, and attaching all to that clamp so it’s not suspended or something you need to hold in your hand, much less also the use of a in-line switch to prevent the necessity of a hot patch otherwise. Only problem is if they in me deciding not to go with momentary contact switch, those testing will still do the hot patch thing in leaving the switch on. Hopefully they will not in both training and supervision, but given they still will, at least the damage to the hot patched pins of the plugs will be much less, and the system will in general given the fuse be safer.

Long but hopefully worth the four page effort.
Good Lord that's a post!

I'm not going to even try to break that whole thing down point by point. Just wanted to get one thing straight in my head. Did you say that you did or did not figure out how the pilot was working?

I had a misguided friend attempt a wiring project once that I think leads me to the answer. He wanted to string lights from his house to his daughter's next door, with a 3-way switch on each end, to light the path. Nomally, power would enter the circuit at one end, jump to the other end via some 3 wire and be terminated with a 3-way switch at either end. Then the fixtures are connected to either end with regular two wire. He did it all with a single run of 3-wire and it worked... untill one of the bulbs blew. By wiring the fixtures in-line on the one of the conductors of the jump wire he effectively put them in series with the circuit (incidentally halfing the voltage present on each of two fillaments).

The point is, it worked.. untill he blew a lamp. But the system functioned, with two lamps coming on with a flip of either switch and neither of them with a direct connection to the neutral. I seem to remember a similar thing happening with a neon test light. Connect one end to hot and it lights up, but that's probably because of the type of lamp, a fillament wouldn't do that.

Anyway, there's my 2¢. Feel free to straighten me out if I'm incorrect here. I'm not above pulling a 180 degree turn if it can be shown that I'm wrong. Have a good one and write back when you've finished icing your fingers from your last post.
Yes I did figure out how it was working.

Interesting wiring you describe, can you re-state it in more detail?

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