# Transformer Voltage Problem or NOT???



## Pete m. (Nov 19, 2011)

What is the configuration on the secondary (460 volt) of the transformer? Delta, Wye? 

Pete


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## shwadaddy76 (Apr 28, 2013)

Yes - Delta Wye.


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## BDB (Jul 9, 2008)

shwadaddy76 said:


> Yes - Delta Wye.


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## Big John (May 23, 2010)

I assume you mean this a wye primary, delta secondary transformer?

If that's the case, it's very likely the secondary is ungrounded. It's normal to have erratic line-to-ground voltages on those systems.


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## SteveBayshore (Apr 7, 2013)

If it is a standard 480x208/120 transformer using the 208 side as the primary, the neutral tap MUST not be connected to anything. Was called to a project quite a few years ago, standard 480x208/120 transformer wired with the primary connected to the 208 side and creating 480 for some type of x-ray machine. The owners called me as a last resort. The original contractor had replaced the 75kva transformer three times in seven years. I called SquareD for help. Solution, isolate the neutral tap when using the 208 side as the primary. It causes some sort of circulating currents and kills the windings prematurely. Also, if secondary is ungrounded delta, ground fault detectors are required.


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## micromind (Aug 11, 2007)

As noted, the 480 side is very likely a 3 wire ∆. There is no ground reference; the phase to ground voltages are determined by capacitive coupling. 

If the unit it feeds has a VFD or anything else that has MOVs, then you'll need to either disconnect the MOVs or install some sort of grounding system. Or, if the equipment can tolerate it, simply ground one of the 480 phases, I'd recommend B.


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## brian john (Mar 11, 2007)

Lets get a few issues out of the way

1. Is the transformer Primary DELTA 208 with a WYE secondary 480/277?

2. Is the transformer Primary WYE 208 with a DELTA 480 secondary?

Or am I really missing something

Lastly where does the autotransformer come in?

I would bet this transformer is a Primary WYE 208 with a DELTA 480 secondary and the secondary is not grounded, and to be fair others have pointed this out as I am not an electrician but I slept at a HOliday Inn last night.:laughing:

If this is a WYE Primary, verify the XO was not bonded at the factory and no neutral is installed to the XO


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## shwadaddy76 (Apr 28, 2013)

SteveBayshore said:


> If it is a standard 480x208/120 transformer using the 208 side as the primary, the neutral tap MUST not be connected to anything. Was called to a project quite a few years ago, standard 480x208/120 transformer wired with the primary connected to the 208 side and creating 480 for some type of x-ray machine. The owners called me as a last resort. The original contractor had replaced the 75kva transformer three times in seven years. I called SquareD for help. Solution, isolate the neutral tap when using the 208 side as the primary. It causes some sort of circulating currents and kills the windings prematurely. Also, if secondary is ungrounded delta, ground fault detectors are required.



Steve and everyone - Thanks for the input so far. I don't know if the 208V Pri (wye) has a bonded neutral. It is a standard 480x208/120 setup. Sec is delta. They have a maint time coming up and I'll be able to pull the cover. As far as the ground fault comment, are you saying that if the sec is ungrounded, I need to provide a GFCI breaker as OP for the 480 output?


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## Big John (May 23, 2010)

shwadaddy76 said:


> ...As far as the ground fault comment, are you saying that if the sec is ungrounded, I need to provide a GFCI breaker as OP for the 480 output?


GFCIs are protection against electrocution. Ground fault detection is a separate device designed to alert someone to a single fault in a distribution system. 

The idea is to prevent fires caused by dual faults, but it is not necessary for a 480V ungrounded delta. See 250.21(A)(4)


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## shwadaddy76 (Apr 28, 2013)

Big John said:


> GFCIs are protection against electrocution. Ground fault detection is a separate device designed to alert someone to a single fault in a distribution system.
> 
> The idea is to prevent fires caused by dual faults, but it is not necessary for a 480V ungrounded delta. See 250.21(A)(4)


I read the section, and that looks right. Can you tell me what you mean by dual faults?


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## Big John (May 23, 2010)

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shwadaddy76 said:


> ...Can you tell me what you mean by dual faults?


 You can safely ground any electrical system one time. When you ground it twice, you've completed a circuit and current will flow.

In an ungrounded system, the first ground fault will not by itself cause a failure. If it is allowed to continue until a second ground fault occurs, then you will have a short circuit and the potential for damage.


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## shwadaddy76 (Apr 28, 2013)

Big John said:


> You can safely ground any electrical system one time. When you ground it twice, you've completed a circuit and current will flow.
> 
> In an ungrounded system, the first ground fault will not by itself cause a failure. If it is allowed to continue until a second ground fault occurs, then you will have a short circuit and the potential for damage.



I see (at least I think I do!). By grounding twice you could possibly create a potential difference that could allow current to flow. Makes sense that the 1st fault wouldn't cause failure.


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## Ultrafault (Dec 16, 2012)

Sounds like you should get an engineer to consult with you on transformer jobs. They are very dangerous and take quite some time to learn.


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## SteveBayshore (Apr 7, 2013)

micromind said:


> As noted, the 480 side is very likely a 3 wire ∆. There is no ground reference; the phase to ground voltages are determined by capacitive coupling.
> 
> If the unit it feeds has a VFD or anything else that has MOVs, then you'll need to either disconnect the MOVs or install some sort of grounding system. Or, if the equipment can tolerate it, simply ground one of the 480 phases, I'd recommend B.


If the secondary (480) side of the transformer is truly ungrounded delta, you won't have any real potential from any of the three phase legs to ground. You must use a solenoid type tester for this because a digital meter doesn't have enough load to pull down any stray voltages. After confirming that it is ungrounded delta by visually checking the connections and testing voltage, the next step to make it safe and code compliant is to (A) install a ground detector system (not GFCI) or (B) ground one of the phase legs, as mentioned by MICROMIND. Anyone not familiar with type of system will think that I am nuts telling you to install a grounding electrode conductor to one of the 480v phase legs. (B) is usually the easiest way to make the system safe. The ground detection system is used in large process facilities to prevent process shut down on the first fault in the system. For non critical applications, grounding one phase leg is the solution. The first time that you build one of these grounded systems, no one wants to be the first one to turn the power on to the transformers. GROUNDED PHASE LEG, NO WAY!! :no:
If you don't ground a phase leg or use a ground detection monitor, you have the potential to have one of the phases short to ground and never know it because it will not blow a fuse or trip a CB.


We build 240 volt delta power systems the same way.


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## brian john (Mar 11, 2007)

Ultrafault said:


> Sounds like you should get an engineer to consult with you on transformer jobs. They are very dangerous and take quite some time to learn.


I agree engineers are very dangerous and a well read expierenced electrician will know more about an ungrounded distribution system than a college full of engineers.


Actually transformers are no more dangerous that any other component of a distribution system, Do some googling and ask a few more questions and you should be well armed to tackle this.


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## brian john (Mar 11, 2007)

SteveBayshore said:


> If the secondary (480) side of the transformer is truly ungrounded delta, you won't have any real potential from any of the three phase legs to ground. You must use a solenoid type tester for this because a digital meter doesn't have enough load to pull down any stray voltages. After confirming that it is ungrounded delta by visually checking the connections and testing voltage, the next step to make it safe and code compliant is to (A) install a ground detector system (not GFCI) or (B) ground one of the phase legs, as mentioned by MICROMIND. Anyone not familiar with type of system will think that I am nuts telling you to install a grounding electrode conductor to one of the 480v phase legs. (B) is usually the easiest way to make the system safe. The ground detection system is used in large process facilities to prevent process shut down on the first fault in the system. For non critical applications, grounding one phase leg is the solution. The first time that you build one of these grounded systems, no one wants to be the first one to turn the power on to the transformers. GROUNDED PHASE LEG, NO WAY!! :no:
> *If you don't ground a phase leg or use a ground detection monitor, you have the potential to have one of the phases short to ground and never know it because it will not blow a fuse or trip a CB.
> *
> 
> We build 240 volt delta power systems the same way.


While you need to control where you ground the delta secondary for a variety of reasons. But an ungrounded system thet has a 1st fault is grounded system, Not so bad (EXCEPT THE LOCAtioN OF THE GROUNDING.


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## Ultrafault (Dec 16, 2012)

brian john said:


> I agree engineers are very dangerous and a well read expierenced electrician will know more about an ungrounded distribution system that a college full of engineers.
> 
> Actually transformers are no more dangerous that any other component of a distribution system, Do some googling and ask a few more questions and you should be well armed to tackle this.


My opionion was this gentelman was too far from the anwser to get there with a Google and a question. 
In my experience only a small percentage of people have the skills to self teach from the internet.


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## micromind (Aug 11, 2007)

brian john said:


> I agree engineers are very dangerous and a well read expierenced electrician will know more about an ungrounded distribution system that a college full of engineers.


This is by far the most accurate statement I've seen in many years. 

As others have stated, make sure that the 208 side neutral connection is isolated, even if you need to remove the factory bond strap. 

As to the fear of energizing a 3 wire ∆ transformer with an intentionally grounded phase, consider this; with the transformer ungrounded and energized, and no ground faults present, placing a solenoid type Wiggy from one of the phases to ground results in zero voltage across the Wiggy. This is because you have grounded that phase. And nothing bad happened. 

Nothing bad will happen if one of the phases is solidly grounded as well.


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## brian john (Mar 11, 2007)

Ultrafault said:


> My opionion was this gentelman was too far from the anwser to get there with a Google and a question.
> In my experience only a small percentage of people have the skills to self teach from the internet.


While I do understand your point, I tend to disagree. Having been stymied more than once in my life (like all the time), I find common sense a bit of reading and logic goes a long way. And believe me I am far from the smartest. 

But I think the average electrician that has little to no expierence with an ungrounded system would be well armed to attack the problems posted by just asking a few questions here.

And an average electrical engineer is one of the last people I would ask. Not because I do not respect engineers, I just doubt many engineers would have any more expierence then the OP.


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## Jlarson (Jun 28, 2009)

brian john said:


> I agree engineers are very dangerous


:laughing: :laughing:


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## Ultrafault (Dec 16, 2012)

I see your piont. 
The only electrical engineers I have contact with here work with industrial power systems. I dont have experience with the less experienced variety. 
I do have experience with electricians that dont know how to tie there shoes properly. I think its my area anyone with any skills and knowledge travels north to work in the city.

I was depressed about the state of our trade as a whole before I came to this site.


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## shwadaddy76 (Apr 28, 2013)

Ultrafault said:


> My opionion was this gentelman was too far from the anwser to get there with a Google and a question.
> In my experience only a small percentage of people have the skills to self teach from the internet.


Calling it self teaching from the internet is a little misleading. I am seeking advice from qualified professionals, and admittedly, haven't worked with an ungrounded system like this before. I do appreciate all of the advice, and may eventually consult an engineer before any changes are made. I try to be very cautious, especially with new issues, without underestimating my own ability to learn. This site is proving to be a great resource, made so by everyone's willingness to share knowledge and the recipient's responsibility in weighing it all . . .


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## shwadaddy76 (Apr 28, 2013)

brian john said:


> I agree engineers are very dangerous and a well read expierenced electrician will know more about an ungrounded distribution system than a college full of engineers.
> 
> 
> Actually transformers are no more dangerous that any other component of a distribution system, Do some googling and ask a few more questions and you should be well armed to tackle this.


Thank you Brian john


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## shwadaddy76 (Apr 28, 2013)

SteveBayshore said:


> If the secondary (480) side of the transformer is truly ungrounded delta, you won't have any real potential from any of the three phase legs to ground. You must use a solenoid type tester for this because a digital meter doesn't have enough load to pull down any stray voltages. After confirming that it is ungrounded delta by visually checking the connections and testing voltage, the next step to make it safe and code compliant is to (A) install a ground detector system (not GFCI) or (B) ground one of the phase legs, as mentioned by MICROMIND. Anyone not familiar with type of system will think that I am nuts telling you to install a grounding electrode conductor to one of the 480v phase legs. (B) is usually the easiest way to make the system safe. The ground detection system is used in large process facilities to prevent process shut down on the first fault in the system. For non critical applications, grounding one phase leg is the solution. The first time that you build one of these grounded systems, no one wants to be the first one to turn the power on to the transformers. GROUNDED PHASE LEG, NO WAY!! :no:
> If you don't ground a phase leg or use a ground detection monitor, you have the potential to have one of the phases short to ground and never know it because it will not blow a fuse or trip a CB.
> 
> 
> We build 240 volt delta power systems the same way.



I'll verify more when I'm able to de-energize the xfmr and examine. Until then, I'll check phase to ground with a Wiggy and see if there is really a reading. And yes, it does sound crazy to connect the GEC to a phase for those of us used to everyday wiring practices. It's one this to see the little dotted line on paper coming off of the corner of a delta diagram, and another to connect it yourself and energize . . . !


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## Big John (May 23, 2010)

While there's a lot of good information in this thread, let's go back to the title: Voltage problem or *not.

*As best as I can tell this all started because the HVAC guy got some funny phase-to-ground voltages, and there are no other operational issues, is that correct? 

If that is the case, I would not do anything to this system. It works and it's code compliant. Having strange line-to-ground readings is not automatically a problem.


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## shwadaddy76 (Apr 28, 2013)

Big John said:


> While there's a lot of good information in this thread, let's go back to the title: Voltage problem or *not.
> 
> *As best as I can tell this all started because the HVAC guy got some funny phase-to-ground voltages, and there are no other operational issues, is that correct?
> 
> If that is the case, I would not do anything to this system. It works and it's code compliant. Having strange line-to-ground readings is not automatically a problem.


Yes - I told the customer that I wasn't convinced that there is a problem. I think the HVAC scared the guy (plus he told him that his xfmr was too hot - not the case - it is mounted over another heavily loaded xfmr, and heat rises, as he should know . . . ). This A/C unit serves a critical data center, so I def. want to check out all possibilities. A/C unit has never had a prob, other than several condensate pumps burning up that were fed from a factory-mounted autotransformer. I was told that once the auto xfmr was changed several years ago, no more problems. Your point = Occam's Razor.


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## brian john (Mar 11, 2007)

shwadaddy76 said:


> I'll verify more when I'm able to de-energize the xfmr and examine. Until then, I'll check phase to ground with a Wiggy and see if there is really a reading. And yes, it does sound crazy to connect the GEC to a phase for those of us used to everyday wiring practices. It's one this to see the little dotted line on paper coming off of the corner of a delta diagram, and another to connect it yourself and energize . . . !


You can take an ungrounded wye and ground any leg you want. Then if you grounded the "A" phase you have 

A-GND "0" VAC
B-GND 208 VAC
C-GND 208 VAC
N-GND 120 VAC


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## SteveBayshore (Apr 7, 2013)

brian john said:


> You can take an ungrounded wye and ground any leg you want. Then if you grounded the "A" phase you have
> 
> A-GND "0" VAC
> B-GND 208 VAC
> ...


I thought that we were discussing the 480 side of the transformer. I'll go back and look.


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## brian john (Mar 11, 2007)

SteveBayshore said:


> I thought that we were discussing the 480 side of the transformer. I'll go back and look.


I was just saying, that Earth or "GROUND" could care less, not suggesting anyone do this.


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## shwadaddy76 (Apr 28, 2013)

*Voltage Problem or NOT?*



SteveBayshore said:


> If the secondary (480) side of the transformer is truly ungrounded delta, you won't have any real potential from any of the three phase legs to ground. You must use a solenoid type tester for this because a digital meter doesn't have enough load to pull down any stray voltages. After confirming that it is ungrounded delta by visually checking the connections and testing voltage, the next step to make it safe and code compliant is to (A) install a ground detector system (not GFCI) or (B) ground one of the phase legs, as mentioned by MICROMIND. Anyone not familiar with type of system will think that I am nuts telling you to install a grounding electrode conductor to one of the 480v phase legs. (B) is usually the easiest way to make the system safe. The ground detection system is used in large process facilities to prevent process shut down on the first fault in the system. For non critical applications, grounding one phase leg is the solution. The first time that you build one of these grounded systems, no one wants to be the first one to turn the power on to the transformers. GROUNDED PHASE LEG, NO WAY!! :no:
> If you don't ground a phase leg or use a ground detection monitor, you have the potential to have one of the phases short to ground and never know it because it will not blow a fuse or trip a CB.
> 
> 
> We build 240 volt delta power systems the same way.



I returned to this job friday and removed the transformer cover. Found no neutral conductor installed on the 208V side, factory bonding strap connected to XO, and EGC from both pri and sec conduits landed on XO. Used a Wiggy this time to check phase-to-ground voltage, and the solenoid didn't move when checking any of the phases. Thanks for the good advice:thumbsup: I'll be consulting an engineer before recommending changes.


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## SteveBayshore (Apr 7, 2013)

I would suggest talking to an OEM engineer from the manufacturer of the transformer. That is where I got my first information about the detrimental effects of the grounding of the XO terminal. Let them know the specific connections for your installation, the 208 side being the primary and the 480 being the secondary. Tell them that there is a factory grounding strap on the XO terminal and ask them if it should remain in place or should it be removed. The one I had encountered in the past was from Square D.


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## Jlarson (Jun 28, 2009)

XO needs to be floating. Loose the XO strap and the bonds to XO and corner ground the 480 side.


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## SteveBayshore (Apr 7, 2013)

Jlarson said:


> XO needs to be floating. Loose the XO strap and the bonds to XO and corner ground the 480 side.


My suggestion was just in case he doesn't trust us 100% to make changes.


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## shwadaddy76 (Apr 28, 2013)

SteveBayshore said:


> My suggestion was just in case he doesn't trust us 100% to make changes.


There's liability/exposure in all electrical jobs, but this one is in a high profile law office that occupies 7 floors in a major banking HQ bldg. I trust the advice, and have used it in my recommendations, but will put the ultimate burden on the engineer, for a change!:thumbup: I'll call the mfr (fed pac) as well for their recommendations . . .


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## SteveBayshore (Apr 7, 2013)

Let us know what decisions are made. Thanks


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## noarcflash (Sep 14, 2011)

:detective:


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