Fake Neutral!!

[Delta5]

Hi there gentlemen,
I like to run this troubleshooting call through your minds, that I have just been involved with. Called out to a water department well pump station( very small building containing one large pump), where they lost power and when power came back on, the VFD drive was not operating( was powered up with display working would not operate motor, in manual or auto). Their concern was the fuses needed to be checked after checking the fuses and seeing they were good I went on to check the voltage. 480v between all phases, 280v to ground phasea A.B.C. Now all these readings were taken at the motor controller compartment where the VFD drive was located off the top of its disconnect.

Then I went to the buildings main disconnect and meter a 200amp service which i shut it down for more readings. Notice it a 4 wire service one with neutral markings also terminated like a neutral through the disconnect an meter socket. Took some more readings found 480 between all phases but then(now remember that the building load is disconnected) phase A 100v to neut/ground phase b 480v to neut/ground phase c 480 neut/ground.

But then when I turn the building back on adding the load to the service, my readings go to my original readings that I had at the VFD compartment,
480 volts phase to phase--280volt each phase to neut/ground in main disconnect. With this discrepancy in mind I told them to call the power company to check the transformer out.
Overview
All these readings at the main service disconnect.
building powered up-480volt phase to phase.... 280 volt phase A,B,C to neut/ground
building power down-480volt phase to phase....phase A 100 to voltsneut/ground phase B 480 to neut/ground phase C 480 to neut/ground

miscellaneous thoughts and information.
This service feeds a motor Control Center, then off one of the compartments feeds a 3 phase transformer for 208 and 120 Volt power panel for lights and plugs.
When the power company did arrive which I was not there for,it was explained to them that they had a "FAKE NEUTRAL" and there was no issue with the power quality.
So my own thoughts tells me that they must have a 480 volt grounded delta corner service.( wish I could have confirmed this with the utility). But why am I getting 100 volts on phase A when I should get zero is this possibility a ghost voltage, did use a fluke meter. And if my memory(been in the trade since 1990) serves me correct when I troubleshooted these types of services in the past even with the building load on or off line, I would get the same readings!
And does the code permit to have a "FAKE NEUTRAL"!!!
Can a utility just provide you with just three hots and no ground reference back to their transformer??
I think the utilities faking it(lol)
If you gentlemen can help me out to understand how a delta readings should take place with building load on or off . Trying to really understand why phase to neut/ground value is changing with the building load being on/off line.

Looking forward to your feedback gentlemen.

 

[winnie]

My very rough guess is an _ungrounded_ service from the utility with balanced coupling to ground, or even an intentional grounding transformer, when the loads are connected.

Jon

 

[ActionDave]

Well you have me intrigued. I don't know any way you can convert a 480V corner ground service to a 480/277 wye service just by turning the service disconnect on and off.

 

[Fred B]

Not sure if applicable on 480/277 or not, but with 120/240 or 208 an open neutral will give wildly variable reading on any L/N while having a solid readings L/L. Look for open neutral?

 

[ptonsparky]

Not sure if applicable on 480/277 or not, but with 120/240 or 208 an open neutral will give wildly variable reading on any L/N while having a solid readings L/L. Look for open neutral?

It is applicable.

 

[Delta5]

Thank for your thoughts.
I do like this idea with a flick of a switch you go from a Y to a corner delta grounded service, it seems the best description.
Did not send much time on this call about and hour, meaning did not look into the building wiring lay out. As i drive away. they didn't want me to wait for the utility for who knows when they might show up. Was thinking to myself waht could be going on,was the building tranx for 208/120 some how causing this?. does the utility transformer have a winding inside going to ground.

And geting a response from the utility that's a fake neutral, does not help me explaining to my customer what they have for a service confriguration. Guessing they must have a corner delta system which makes the most sense to me. With all my years in the trade I have not heard the term "FAKE NEUTRAL"! which upsets me for my customer probably thinks i should have known that.

So gentlemen in the end my final questions are.
Your reading shouldn't change all that much under a load or not. and when they do which has happen here(which i explained above) there is some kind of problem.
How does the code handle corner delta services you just cant have 3 hots, the original installer shouid have never used a white cable but instead a green one, from point of connection then after metering kept it a 4 wire system into builing, not truning it into a 5 wire system which is what they did. giving us our fake neutral now.

Peace

 

[ptonsparky]

A grounded conductor is typically white or some other similar. Having multiple grounded systems of different voltages should change the way each are identified.

A corner ground at the SE would be white or a center ground could be white at the SE. The EG is green after that but the grounded conductor is still white. A corner grounded phase out to the plant would be identified as such. White.

I chose white as an example. It could be white/grey, white/yellow, etc.

 

[texie]

How 'bout just basics here. Did the OP even look at the serving xformer data plate or, if overhead, the configuration? This all should be pretty obvious.

 

[kwired]

If you have ~277 volts to ground it is not a corner ground system, ungrounded phase voltage to ground should be ~480 if corner grounded.

Were you using a low impedance meter when testing?

Put some 277 volt load on each line individually and see what happens to voltage. If neutral is good/solid voltage reading shouldn't change much. If neutral is open or has unacceptable resistance, adding a 277 load to just one line will make voltage drop pretty severely.

 

[synchro]

... Called out to a water department well pump station( very small building containing one large pump), where they lost power and when power came back on, the VFD drive was not operating( was powered up with display working would not operate motor, in manual or auto). Their concern was the fuses needed to be checked after checking the fuses and seeing they were good I went on to check the voltage. 480v between all phases, 280v to ground phases A.B.C. Now all these readings were taken at the motor controller compartment where the VFD drive was located off the top of its disconnect.

Then I went to the buildings main disconnect and meter a 200amp service which i shut it down for more readings. Notice it a 4 wire service one with neutral markings also terminated like a neutral through the disconnect an meter socket. Took some more readings found 480 between all phases but then(now remember that the building load is disconnected) phase A 100v to neut/ground phase b 480v to neut/ground phase c 480 neut/ground. ...

Overview
All these readings at the main service disconnect.
building powered up-480volt phase to phase.... 280 volt phase A,B,C to neut/ground
building power down-480volt phase to phase....phase A 100 to voltsneut/ground phase B 480 to neut/ground phase C 480 to neut/ground

Perhaps there's an open neutral on the 480/277V service as was suggested, and therefore when the disconnect is open the L-N voltages going into the disconnect can be way off from their normal value. But when the disconnect is closed such that the VFD is being fed, there would likely be MOV protection devices connected from line to ground that will tend to equalize the three L-G voltages, at least to some extent. The problem is that if there are any L-N loads, this could cause the L-N voltages to be unbalanced and result in excessive current through the MOVs, possibly causing them to be damaged.
In any case, an open service neutral is a prime suspect, and it should be checked as kwired suggested and corrected if present.

 

[Delta5]

Perhaps there's an open neutral on the 480/277V service as was suggested, and therefore when the disconnect is open the L-N voltages going into the disconnect can be way off from their normal value. But when the disconnect is closed such that the VFD is being fed, there would likely be MOV protection devices connected from line to ground that will tend to equalize the three L-G voltages, at least to some extent. The problem is that if there are any L-N loads, this could cause the L-N voltages to be unbalanced and result in excessive current through the MOVs, possibly causing them to be damaged.
In any case, an open service neutral is a prime suspect, and it should be checked as kwired suggested and corrected if present.

like it.
appreciate your insight.

 

[Jpflex]

Hi there gentlemen,
I like to run this troubleshooting call through your minds, that I have just been involved with. Called out to a water department well pump station( very small building containing one large pump), where they lost power and when power came back on, the VFD drive was not operating( was powered up with display working would not operate motor, in manual or auto). Their concern was the fuses needed to be checked after checking the fuses and seeing they were good I went on to check the voltage. 480v between all phases, 280v to ground phasea A.B.C. Now all these readings were taken at the motor controller compartment where the VFD drive was located off the top of its disconnect.

Then I went to the buildings main disconnect and meter a 200amp service which i shut it down for more readings. Notice it a 4 wire service one with neutral markings also terminated like a neutral through the disconnect an meter socket. Took some more readings found 480 between all phases but then(now remember that the building load is disconnected) phase A 100v to neut/ground phase b 480v to neut/ground phase c 480 neut/ground.

But then when I turn the building back on adding the load to the service, my readings go to my original readings that I had at the VFD compartment,
480 volts phase to phase--280volt each phase to neut/ground in main disconnect. With this discrepancy in mind I told them to call the power company to check the transformer out.
Overview
All these readings at the main service disconnect.
building powered up-480volt phase to phase.... 280 volt phase A,B,C to neut/ground
building power down-480volt phase to phase....phase A 100 to voltsneut/ground phase B 480 to neut/ground phase C 480 to neut/ground

miscellaneous thoughts and information.
This service feeds a motor Control Center, then off one of the compartments feeds a 3 phase transformer for 208 and 120 Volt power panel for lights and plugs.
When the power company did arrive which I was not there for,it was explained to them that they had a "FAKE NEUTRAL" and there was no issue with the power quality.
So my own thoughts tells me that they must have a 480 volt grounded delta corner service.( wish I could have confirmed this with the utility). But why am I getting 100 volts on phase A when I should get zero is this possibility a ghost voltage, did use a fluke meter. And if my memory(been in the trade since 1990) serves me correct when I troubleshooted these types of services in the past even with the building load on or off line, I would get the same readings!
And does the code permit to have a "FAKE NEUTRAL"!!!
Can a utility just provide you with just three hots and no ground reference back to their transformer??
I think the utilities faking it(lol)
If you gentlemen can help me out to understand how a delta readings should take place with building load on or off . Trying to really understand why phase to neut/ground value is changing with the building load being on/off line.

Looking forward to your feedback gentlemen.

Some voltage on phase A load side return or partial open/ high resistance can show a lower potential drop such as 100v instead of 480v expected. But it’s probably something else

 

[Jpflex]

Hi there gentlemen,
I like to run this troubleshooting call through your minds, that I have just been involved with. Called out to a water department well pump station( very small building containing one large pump), where they lost power and when power came back on, the VFD drive was not operating( was powered up with display working would not operate motor, in manual or auto). Their concern was the fuses needed to be checked after checking the fuses and seeing they were good I went on to check the voltage. 480v between all phases, 280v to ground phasea A.B.C. Now all these readings were taken at the motor controller compartment where the VFD drive was located off the top of its disconnect.

Then I went to the buildings main disconnect and meter a 200amp service which i shut it down for more readings. Notice it a 4 wire service one with neutral markings also terminated like a neutral through the disconnect an meter socket. Took some more readings found 480 between all phases but then(now remember that the building load is disconnected) phase A 100v to neut/ground phase b 480v to neut/ground phase c 480 neut/ground.

But then when I turn the building back on adding the load to the service, my readings go to my original readings that I had at the VFD compartment,
480 volts phase to phase--280volt each phase to neut/ground in main disconnect. With this discrepancy in mind I told them to call the power company to check the transformer out.
Overview
All these readings at the main service disconnect.
building powered up-480volt phase to phase.... 280 volt phase A,B,C to neut/ground
building power down-480volt phase to phase....phase A 100 to voltsneut/ground phase B 480 to neut/ground phase C 480 to neut/ground

miscellaneous thoughts and information.
This service feeds a motor Control Center, then off one of the compartments feeds a 3 phase transformer for 208 and 120 Volt power panel for lights and plugs.
When the power company did arrive which I was not there for,it was explained to them that they had a "FAKE NEUTRAL" and there was no issue with the power quality.
So my own thoughts tells me that they must have a 480 volt grounded delta corner service.( wish I could have confirmed this with the utility). But why am I getting 100 volts on phase A when I should get zero is this possibility a ghost voltage, did use a fluke meter. And if my memory(been in the trade since 1990) serves me correct when I troubleshooted these types of services in the past even with the building load on or off line, I would get the same readings!
And does the code permit to have a "FAKE NEUTRAL"!!!
Can a utility just provide you with just three hots and no ground reference back to their transformer??
I think the utilities faking it(lol)
If you gentlemen can help me out to understand how a delta readings should take place with building load on or off . Trying to really understand why phase to neut/ground value is changing with the building load being on/off line.

Looking forward to your feedback gentlemen.

I meant phase A to ground/ neutral voltage but not 480v typed earlier. I don’t recall if you wrote this was delta but if so phase B Stinger should be highest among A and C To neutral/ ground

 

[don_resqcapt19]

A grounded conductor is typically white or some other similar. Having multiple grounded systems of different voltages should change the way each are identified.

A corner ground at the SE would be white or a center ground could be white at the SE. The EG is green after that but the grounded conductor is still white. A corner grounded phase out to the plant would be identified as such. White.

I chose white as an example. It could be white/grey, white/yellow, etc.

While the code requires the grounded conductor of a corner grounded system to be identified as a grounded conductor in accordance with Article 200, I have never seen that actually done on any of the corner grounded systems I have worked on.

 

[ptonsparky]

While the code requires the grounded conductor of a corner grounded system to be identified as a grounded conductor in accordance with Article 200, I have never seen that actually done on any of the corner grounded systems I have worked on.

Wow...

 

[Jraef]

Well you have me intrigued. I don't know any way you can convert a 480V corner ground service to a 480/277 wye service just by turning the service disconnect on and off.

Inside of the VFD there are MOVs on the line terminals that are connected in Wye to ground. The VFD is essentially then acting as the Wye point, at least enough to be read on a DMM. This is a dangerous situation (for the VFD) because as soon as there is a ground fault ANYWHERE in that system, the MOVs in the drive will attempt to conduct ALL of the fault current to ground, making them explode and cause collateral damage, ie a flashover or component shorting etc. Most VFD mfrs will tell you EITHER to disconnect the ground reference to the MOVs (and common mode noise capacitors if included) when you connect to a delta service, or they just say “This drive can only be connected to a solidly grounded wye (star) service”, or words to that effect. Delta services are only used in North America, so some EU and Asian based drive mfrs do a poor job of explaining this up front.

So when you have the building load disconnected, you are reading the transformer voltages, but once the building load is connected, your meter is reading through the VFD front end. If there are any other 3 phase power electronics in the building, they will likely be the same, ie UPS, battery chargers, solar inverters etc.

What make and model of VFD is it.

 

[kwired]

While the code requires the grounded conductor of a corner grounded system to be identified as a grounded conductor in accordance with Article 200, I have never seen that actually done on any of the corner grounded systems I have worked on.

I haven't either, but most I have encountered were installed 40-50 years ago, were not inspected when new, etc. If they were installed today, I think that it would be more likely to be done properly or be cited for correction by an inspector.

 

[winnie]

The one corner grounded delta that I've worked with had the grounded conductor identified with white and red tape spiraled around the conductor, like a candycane.

-Jon

 

[ActionDave]

The one corner ground I worked on was on the edge of a hay field and all the conductors were black. I'm not trying to one up winnie just want to reinforce that they are rare and if you find one more than likely something will be odd about it.

 

[electrofelon]

The one corner grounded delta that I've worked with had the grounded conductor identified with white and red tape spiraled around the conductor, like a candycane.

-Jon

The one corner ground I worked on was on the edge of a hay field and all the conductors were black. I'm not trying to one up winnie just want to reinforce that they are rare and if you find one more than likely something will be odd about it.

I installed a 600V corner grounded SDS to re- feed an old elevator after a service upgrade once. I used a fully white conductor for the grounded conductor on the new portion, but it refed old wiring where of course they were all just black.

Recently I saw a 480 corner ground SDS that was recently installed, and they did a spiral of white tape on one of the standard BOY colors. I remember thinking that it was kind of wrong, in that it should just be a "normal" solid white conductor. But I don't know, maybe that method is good as it might make it more clear that something "weird" is going on, I e. that it's corner grounded and not split phase?