# 240V neutral to ground on 120V GFCI



## LGLS

See the wiggy thread(s).


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## FishinElectrcian

mburtis said:


> So I wasn't quite sure where to put this question as its not really typical industrial but the power supply isn't typical residential. Doesn't really fit anywhere else either. So i work at a water plant and the operators at the other plant said they needed a couple of GFCI receptacles replaced as they wouldn't reset, chocking it up to cheapo GFCIs didn't think much of it. Had a few minutes this afternoon so we figured we would have a nice easy end of the day.
> 
> Show up, find the breakers and lock them out. Leds on the GFCI go out. Breaker panel is a 120/240 hi leg panel, each receptacle is wired to its own breaker. Test it for voltage, and with the breakers off, I have 0 V from hot to neutral, 120V from hot to ground, and 120V from neutral to ground. So we turn the breaker back on just to see. Now I got 120 V from hot to neutral, but 240 v to ground. I'm a lot more experienced with motors and controls so don't do this sort of thing that often. Showing same behavior of three different GFCIs, one of which seems to be working fine, fourth one seemed to test out normal.
> 
> Getting towards quitting time at this point, so we decide to wait for another day to dig into it. Thinking there is something wrong in terms of the ground/neutral back at the panel. Only other thought was induced voltage but we seem to typically see about 80V.


Hey so yeah the whole wiggy induced voltage deal is valid I suppose. I apparently have a low Z voltage setting on my meter which also works.

Single pole or double pole breaker?

What do you mean by a high leg panel? 

I'm in for bad grounding...


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## paulengr

Forget about the high leg and just think of it as single phase 240/120. So we have two hots 240 V apart and both are 130 to the neutral. The ground is supposed to be jumpered to the neutral. You are only looking at one hot and one neutral.

The system bonding jumper might be missing and you have a ground fault to the opposite hot or it is tied to the other hot. That gives you 120 hot to neutral and 240 hot to ground and 120 from neutral to ground.


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## splatz

If your tester is accurate, something's very wrong there. I can't connect the dots how an open neutral get you those readings. There is nothing 240V to ground in the high leg delta. 

L1-N = L1-G = L2-N = L2=G = 120V
L3-N = L3-G = 208V 
L1-L2 = L2-L3 = L3-L1 = 240V


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## joebanana

120v from neutral to ground with the breaker off? 240 to ground with the breaker on? Isn't that a clue? What's the voltage on the ground? And, what would you reference that voltage to?


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## MechanicalDVR

You have an energized ground.


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## splatz

FishinElectrcian said:


> What do you mean by a high leg panel?



Do you have these up north of the border?


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## FishinElectrcian

splatz said:


> FishinElectrcian said:
> 
> 
> 
> What do you mean by a high leg panel?
> 
> 
> 
> 
> Do you have these up north of the border?
Click to expand...

Yeah I've run into it a few times.. Up here though it's supposed to be A phase that high legs it. I'd expect 120 to ground except on the high leg which should be 208. I was assuming the Delta but you wouldn't think they'd tap something like a subpanel off a high leg. Should be off the other two. 

If a GFI is tapped off the high leg it should let the smoke out. Did it once with one of our panels, I saw the GFI breaker glow red inside for about 10 seconds before it smoked. After that we always tapped control voltage off the black instead of red phases. 

I suppose with a possible induced voltage of 80V give or take phase shift + 120 = 240 maybe. 
Or (80V / 1.73) + 208V (high leg) = 254V

If that's the case try moving the breakers to the other phase like the one GFI that works.

I was kinda wondering if something like the GFI was trying to share a neutral with something else or between the two off a 2 pole breaker. Which doesn't work. One GFI would set and the others won't. You would get some read through from the coil inside the inactive GFI's.

I've also seen ground potential from ground to ground in high rises where I clocked 100V and it was enough to get a buzz off.

Of course if they worked at some point then something has changed...


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## paulengr

You don’t have a high leg delta either intentionally or not. It’s corner grounded delta with a split phase. So one phase will be 0 to ground and the other two are 240. The “neutral” is 120 to ground. On the center tapped side it’s 240/120 as expected. The neutral isn’t neutral as in a grounded conductor though...one of the hots is.

As to how this happened one is the bonding jumper is on the wrong terminal. The other is you’ve lost that connection so it was ungrounded and nobody noticed until now when a fault has grounded one of the hots.



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## splatz

paulengr said:


> As to how this happened one is the bonding jumper is on the wrong terminal. *The other is you’ve lost that connection so it was ungrounded and nobody noticed until now when a fault has grounded one of the hots.*


I could buy this theory and remember if you're ungrounded the first fault is free ... the second is not!


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## mburtis

Our plan is to hopefully take a day next week and open up the panel and start looking into this a little more. I think the four breakers for the four receptacles (two two gang boxes) are all on the same leg but need to check on that. This panel is fed off a 480 transformer and was added a few years ago.


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## mburtis

paulengr said:


> You don’t have a high leg delta either intentionally or not. It’s corner grounded delta with a split phase. So one phase will be 0 to ground and the other two are 240. The “neutral” is 120 to ground. On the center tapped side it’s 240/120 as expected. The neutral isn’t neutral as in a grounded conductor though...one of the hots is.
> 
> As to how this happened one is the bonding jumper is on the wrong terminal. The other is you’ve lost that connection so it was ungrounded and nobody noticed until now when a fault has grounded one of the hots.
> 
> 
> 
> Sent from my iPhone using Tapatalk


So I'm not experienced enough to truly picture all the details in my head, but in essence this is basically the only theory I have came up with.


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## Weasel

Joe if you have that delta panel and I’m sure the orange middle phase is the high leg in the panel. That panel should not have single pole breakers in it unless you put your breaker on A phase or C phase never on the orange phase. You also could check it to see if you have what we call a floating neutral which can cause a lot higher voltage up to 180 vac to ground. 3 phase delta transformer is really good for nothing but 3 phase loads only


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## just the cowboy

mburtis said:


> Our plan is to hopefully take a day next week and open up the panel and start looking into this a little more. I think the four breakers for the four receptacles (two two gang boxes) are all on the same leg but need to check on that. This panel is fed off a 480 transformer and was added a few years ago.


Has anyone change anything lately?

Also IS it 240 volts or 208 volts, I have seen a lot of people troubleshoot high leg problems and just round it up to 240 volts when meter goes into the 200's.


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## mburtis

just the cowboy said:


> Has anyone change anything lately?
> 
> Also IS it 240 volts or 208 volts, I have seen a lot of people troubleshoot high leg problems and just round it up to 240 volts when meter goes into the 200's.


As far as i know nothing has changed lately. One of the GFCIs has been broken for over a year. When i was testing it, with the breakers off i was getting 117-121 volts or so and with the power on I was getting 238-243 volts or so.


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## micromind

About the only thing I can think of that would cause voltage from neutral to ground is that the neutral - ground jumper is....

1) Missing, as in never installed.

2) Was originally installed but has been removed or came loose.

3) Has been blown up. 

The fact that it's a 3Ø high-leg panel doesn't make any difference, it still needs to have a solid neutral - ground jumper. 

This can be installed at the transformer or the panel but not both.


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## paulengr

micromind said:


> About the only thing I can think of that would cause voltage from neutral to ground is that the neutral - ground jumper is....
> 
> 
> 
> 1) Missing, as in never installed.
> 
> 
> 
> 2) Was originally installed but has been removed or came loose.
> 
> 
> 
> 3) Has been blown up.
> 
> 
> 
> The fact that it's a 3Ø high-leg panel doesn't make any difference, it still needs to have a solid neutral - ground jumper.
> 
> 
> 
> This can be installed at the transformer or the panel but not both.




Option 4 is the grounding jumper was installed to A or C phase instead of neutral. I want to say to X0 but I don’t know what it’s called on a high leg delta.


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## sparkiez

I'm just going to toss this out there and say that there could be a field device somewhere on another phase that is connected to ground, but through a resistance in a fault somewhere. The breaker won't trip, stuff will continue to work, but if you open the circuit you will find a voltage on your earth.


When you go checking out breakers, turn them off one at a time and see if any specific circuit removes the problem. I've seen this specific situation twice in my career.


Once when a 480V 400W M-85-E balast was shorted to ground. It didn't trip a breaker, but caused one phase to read 480V to ground. The second time was recently, and it was a keyless fixture where the ground wire was ever-so-slightly touching a hot wire and it was putting 120V on the ground, but not tripping the breaker. Once we opened and cleaned up that particular box the problem disappeared.


I have a feeling that you are facing that situation here, and the best place to start is to see if a specific breaker removes the fault.


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## mburtis

sparkiez said:


> I'm just going to toss this out there and say that there could be a field device somewhere on another phase that is connected to ground, but through a resistance in a fault somewhere. The breaker won't trip, stuff will continue to work, but if you open the circuit you will find a voltage on your earth.
> 
> 
> When you go checking out breakers, turn them off one at a time and see if any specific circuit removes the problem. I've seen this specific situation twice in my career.
> 
> 
> Once when a 480V 400W M-85-E balast was shorted to ground. It didn't trip a breaker, but caused one phase to read 480V to ground. The second time was recently, and it was a keyless fixture where the ground wire was ever-so-slightly touching a hot wire and it was putting 120V on the ground, but not tripping the breaker. Once we opened and cleaned up that particular box the problem disappeared.
> 
> 
> I have a feeling that you are facing that situation here, and the best place to start is to see if a specific breaker removes the fault.


At this point i think my plan is to open up the panel and give it a good visual inspection/meter test a few things and see if there is any obvious problems. Then Ill probably do just like you describe and start shutting 1 circuit off at a time to see if anything changes. Other than that will just have to start working backwards till i find what is going on.


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## sparkiez

Giving the panel a good visual is fine, but you have fault that is raising the potential on your grounding system. I would start with the gfi circuit, but that fault can be on any circuit fed from that transformer. Because of this, working backwards is a crap shoot.


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## mburtis

well thought i would share what we found on this. So we pulled the front off the panel and started checking it. Still had 120V from ground to neutral so we turned one breaker off at a time until we found which breaker it was. Turned out it was a breaker that fed another breaker panel across the room. Pulled it apart and checked, 120V from neutral to ground. Started turning breakers off again until we found which one it was. Turned out that it was the power feed to the UPS system for our scada/computer stuff. There is another breaker panel with four breakers in it that are powered off the UPS. Turned these off one at a time until the voltage between the neutral and ground disappeared. it was a power feed to an outlet that is powering a big control enclosure with the PLC that manages the communications for the entire water distribution scada network (Why this walk in cooler sized enclosure is plugged into an outlet i don't know). So trouble shot it through this cabinet, power came in went though another breaker then got distributed to half a dozen different points powering all kinds of stuff. Went through these until we found what was causing it. Find out its one red wire, no tag or label, goes out the top of the cabinet in a conduit with a wad of other stuff, runs in this conduit clear across the building, out the wall, down the outside wall and into the ground. Have no idea where it runs from there and going to take some serious searching for prints and going through them to figure it out. Unhooked this wire and all is well, GFCIs all reset, all readings are normal, after some computer restarts and internet issues even got scada from the other plant to come back. I'm assuming there is some piece of old outdated obsolete abandoned equipment at the end of the wire that is blown up and shorted out. 

After digging into it, it seems we really lucked out that nobody got lit up seeing as there was a lot of surface mounted double gang boxes, breaker panels, etc that would have been energized. First GFCI went out over a year ago so who knows how long this condition has been going on. Need to do more checking now into how this happened with the only symptom being a GFCI that wouldn't reset, seems something is not bonded properly, it didn't appear that the ground and neutral were bonded in any of the panels we were in. I think power comes from the utility through a transformer, then through a breaker in an MCC to the first panel in question.


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## paulengr

mburtis said:


> well thought i would share what we found on this. So we pulled the front off the panel and started checking it. Still had 120V from ground to neutral so we turned one breaker off at a time until we found which breaker it was. Turned out it was a breaker that fed another breaker panel across the room. Pulled it apart and checked, 120V from neutral to ground. Started turning breakers off again until we found which one it was. Turned out that it was the power feed to the UPS system for our scada/computer stuff. There is another breaker panel with four breakers in it that are powered off the UPS. Turned these off one at a time until the voltage between the neutral and ground disappeared. it was a power feed to an outlet that is powering a big control enclosure with the PLC that manages the communications for the entire water distribution scada network (Why this walk in cooler sized enclosure is plugged into an outlet i don't know). So trouble shot it through this cabinet, power came in went though another breaker then got distributed to half a dozen different points powering all kinds of stuff. Went through these until we found what was causing it. Find out its one red wire, no tag or label, goes out the top of the cabinet in a conduit with a wad of other stuff, runs in this conduit clear across the building, out the wall, down the outside wall and into the ground. Have no idea where it runs from there and going to take some serious searching for prints and going through them to figure it out. Unhooked this wire and all is well, GFCIs all reset, all readings are normal, after some computer restarts and internet issues even got scada from the other plant to come back. I'm assuming there is some piece of old outdated obsolete abandoned equipment at the end of the wire that is blown up and shorted out.
> 
> After digging into it, it seems we really lucked out that nobody got lit up seeing as there was a lot of surface mounted double gang boxes, breaker panels, etc that would have been energized. First GFCI went out over a year ago so who knows how long this condition has been going on. Need to do more checking now into how this happened with the only symptom being a GFCI that wouldn't reset, seems something is not bonded properly, it didn't appear that the ground and neutral were bonded in any of the panels we were in. I think power comes from the utility through a transformer, then through a breaker in an MCC to the first panel in question.



So that cleared the short to ground.


Now back to problem #2. You don't have a ground. Running ungrounded is possible but not recommended on 3 phase loads especially in a water plant. You can get a ground fault and not even know it like you just experienced. But if you get a second ground fault on a different phase, you get a short across your grounding system. It has high impedance so it may not trip anything at all but you can burn up a lot of electrical equipment and create a huge electrocution hazard before the problem "fixes itself" in what is called a burn down. IEEE has a documented case that wiped out hundreds of motors over a 40 minute period from one of these. It is a Code violation to run this way on high leg deltas because you can't have any 120 V loads.



Look for where the ground rod comes in (almost always bare wire or green). In the main breaker panel you will find one of three situations. You will find either 1 or 2 ground bars. If there is just one all the neutrals and all the grounds will be on the same ground bar. If there are two, there is either a jumper in between or the ground bars can be connected to the enclosure by a screw or just about anything else that gives a conductive path between them. In your case it is either missing or corroded away.. Measure the resistance between the grounds and neutrals and this should tell you that the jumper was either never installed (most likely) or corroded away or removed (illegal) because it stopped a breaker from tripping. Either way, need to fix it the way that it is supposed to be.


When you make the measurement be very careful. With power off or if there is almost no voltage difference you can safely make the reading. It should read dead shorted (0 ohms). If you have a milliohm meter that's even better because the reading should be 1 milliohm (0.001 ohms) or less but with a standard meter all you should get is 0.0 ohms.



You are in a water plant though so turning the power off is not always very practical. If the voltage between ground and neutral is very close to zero, that's fine. You can go ahead and get your resistance reading safely. But if there is voltage present, even a few volts, one of three things can happen. In a good quality industrial meter it might get confused since it is expecting a battery voltage and instead reads an AC voltage. You will get wild blinking, twitching readings instead of the resistance. In some meters depending on the voltage and resistance, it can blow the very expensive (and rare) high voltage meter fuse. In a Megger DLRO and some other very high end industrial meters it will give you a voltage present error. In a cheap Chinese $10 meter without a "CAT III" or "CAT IV" rating it can explode on you. Just take the whole meter and toss it in the nearest trash can. Those have no place in water plants in the first place.


If you have to add/repair a jumper, don't do it while energized. If you find one that is corroded badly, turn off the power before messing with it. I once had to deal with two side by side 2300/480 transformers one of which fed a water plant. The only difference between your situation and mine was that in my case, everything read "480/480/0" instead of "240/240/0". Everything at the transformers looked like nice straight lines (disconnects and transformers in line with each other) but the room that they were in had a huge mess of conduits running every which way from the better part of 100 years of operations and modifications. It was in a foundry that had been there since the turn of last century. We shut off, locked out, and tested the correctly marked 2300 V disconnect and the 480 V disconnect (possible backup generator) to the water plant. They were dry outdoor style transformers. Both disconnects read 0 V everywhere except the top of the 2300 V disconnect where we expected to see voltage.


I had a helper and this was training for him. Wet behind the ears is an understatement. Plant management at that time was in shambles. They had a production superintendent that washed out so of course they assigned him to a job with less responsibility, you know...maintenance superintendent! The kid was buddies with this guy. The master electrician wanted the kid gone so he said that we were "sink or swim" and put the kid basically by himself on second shift. I sort of had this little thing called a conscience so I was either going to have to do the job myself and maybe use this as a training exercise for the kid or bring in a contractor since there was no way the master electrician was going to help by assigning anyone from first shift to work overtime. But wait it gets better and better...



The wiring between the enclosures was criss-crossed. The transformer we opened was the other one which was live. We did not test for voltage first before going in. At this point I noticed two things right off. First off the jumper to X0 was never installed. The same master electrician ran this job, too. Second one of the voltage taps was severely corroded. I grabbed the tap that was almost corroded in two to give it a shake and see how bad the corrosion was. And lived to tell about it. It lit up immediately and I froze in place before it came completely apart. My helper was too busy freaking out about the fact that it was 2300 V to do anything when it lit up. I mustered up one of those deep Darth Vader/cop voices and ordered him to open the other disconnect. He managed to finish crapping himself enough to do that before he fled the room. Apparently my voice literally put the fear of God in him and I found him hiding afraid that I was going to kill him. I was definitely pissed off but not at him.


Next day is when the chief electrician told me, "Oh yeah we swapped those years ago. Guess we forgot to swap them back. Why did you even open the wrong one?" "Oh yeah guess it isn't so obvious, and maybe we forgot to swap the labels" At this point I was sort of having mixed emotions about a bunch of things involving a live 2300 V wire and a grounded metal chair. We had a couple meetings at the plant manager's office to say the least. Keep in mind that the master electrician ran around as a kid calling himself "Zoltan from Zoltar", rode the short bus, and got to master electrician because he had more years than anyone else and didn't quit. Anyone reading this who knew Tommy knows exactly what I mean. Space case is putting it politely. As I said...we had management problems.


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## mburtis

luckily we don't have anything over 480V, not that it really matters whether its 90V or 90000V, fried is fried. The journeyman that is my mentor seen a contract electrician let a fire ball out of 480 breaker in an MCC tightening lugs hot, said he thought he died but walked away without a scratch. I'm to much of a chicken for any of that, I mean I triple checked a 120 outlet for voltage before touching it, which is how we found this problem. Other than voltage/currents checks with a meter we don't do hot work, I don't get paid enough to do that even on 24VDC. We have millions of gallon of storage capacity so if need be i can just shut the plant down for a couple of hours to do something given some planning. 

I did find what i think is an up to date one line drawing for the power coming in so at least i can trace it back reasonably easy. If i remember right the main transformer for this was replaced less than 2 years ago because the old one was failing, work was done by a contractor and i wasn't involved so I don't know the specifics. Also this whole system was redone 5-6 years ago when they added onto the plant and moved the utility coming in and installed a new generator and everything. Was before my time so I don't know much about it so it is highly likely that something could have never got installed. I do know the initial breaker panel i started in was installed at that time, that replaced the original from the 60s in the same location, but a lot of stuff upstream from there changed during that project as well.

I have been trying to go through and collect all the random electrical tools that have been purchased over the years. I have my personal Fluke T5-1000 as my primary meter but until recently it was sorta a free for all as far as who did electrical work, which is why we have an almost brand new fluke process meter that appears to be blown up.


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## mburtis

So learned a bit more about this system today. 

Utility service is 480V three phase delta (used to be 240V which was upgraded several years ago, which is why half the plant is still on 240V)

So the 480 comes into the plant at a breaker panel, in this panel there is a breaker that is feeding a large 480 delta to 240 delta (with 120 lighting tap) transformer (what the sticker says). This breaker has a tape label that says caution ungrounded system. (at this point the other electrician and me look at each other muttering confused but colorful language). The secondary of this transformer feeds the old 240v MCC, which contains the breaker that is supposed to feed the panel that we had the initial problem with. Now according to drawings the breaker in the MCC feeds the panel directly, However that is not the case. The power for the panel comes from another transformer, which unless i looked at it wrong was 240 delta with a lighting tap to 240 delta with a lighting tap. I don't understand what this would be doing or why it would be there and its not on any of the drawings. 

Regardless of that we did check voltage between ground and neutral in the panel and got 24V. Shut the panel off to kill the voltage and ohmed it and it showed open. So at this point half the plant is un-grounded. Going to open the transformer feeding the panel (thats not on the drawings) next week and see if there is any sort of ground/neutral connection. 

We are thinking none of the stuff upstream really matters, we just need to get the neutral on the secondary side of the last transformer grounded. We were not sure if it was supposed to be done at the transformer or if it could be done in the panel. This is assuming that there is some means of actually grounding the transformer. 

Not the type of stuff us maintenance guys typically mess with so its quite the learning experience for me.


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## sparkiez

That system was left undergrounded and labeled as ungrounded for a reason. You don't just arbitrarily ground an entire section of your plant, and no one on this forum can tell you what to do without assessing that situation. Get you a master electrician / electrical engineer there to assess the situation and make that decision.


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## mburtis

That is actually our next step is to get a hold of our master electrician who is also the electrical inspector (city owned plant). I am also going to try to find the engineering documentation from this update. The prints i thought where the most up to date clearly show the transformer labeled as ungrounded as being grounded, and then the other transformer isn't even on them so i don't know what is going on, but surely there had to be documentation if the engineers purposely left it ungrounded. If i cant find anything ill have to try to track down the engineer that signed off on it and figure out what the deal is. From the little research i have done on ungrounded systems, the rest of the system doesn't seem to be kosher for it, since it seems like you are supposed to have ground fault monitors/indicators, and trained maintenance protocols, etc, which we obviously don't have considering we didn't know such a thing existed until today. I don't know enough to know what i don't know but sure seems like an unnecessarily sketchy way to do it for this application.


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## sparkiez

mburtis said:


> That is actually our next step is to get a hold of our master electrician who is also the electrical inspector (city owned plant). I am also going to try to find the engineering documentation from this update. The prints i thought where the most up to date clearly show the transformer labeled as ungrounded as being grounded, and then the other transformer isn't even on them so i don't know what is going on, but surely there had to be documentation if the engineers purposely left it ungrounded. If i cant find anything ill have to try to track down the engineer that signed off on it and figure out what the deal is. From the little research i have done on ungrounded systems, the rest of the system doesn't seem to be kosher for it, since it seems like you are supposed to have ground fault monitors/indicators, and trained maintenance protocols, etc, which we obviously don't have considering we didn't know such a thing existed until today. I don't know enough to know what i don't know but sure seems like an unnecessarily sketchy way to do it for this application.



You know enough to know what your next steps are. You also know enough to not just start changing stuff. That is important and it sounds to me like you are doing exactly what you need to.


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