# 480v 3 phase problem



## Scubasteve82

I just installed a new 400a 480v Eaton breaker in a 2000a piece of switchgear. I have 277v to ground on all 3 legs. Between A and C phase I have 480v between B and C I have 480v BUT!! Between A and B phase I have like 2 volts. On the line side of the breaker I have 480v between all 3 phases. I was a residential guy for more of my career and just recently started working for a commercial company.

Any help would be greatly appreciated.


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## Southeast Power

More of an argument that phase to ground won't tell you very much.


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## Scubasteve82

Phase to neutral reads 277v as well


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## telsa

Scubasteve82 said:


> I just installed a new 400a 480v Eaton breaker in a 2000a piece of switchgear. I have 277v to ground on all 3 legs. Between A and C phase I have 480v between B and C I have 480v BUT!! Between A and B phase I have like 2 volts. On the line side of the breaker I have 480v between all 3 phases. I was a residential guy for more of my career and just recently started working for a commercial company.
> 
> Any help would be greatly appreciated.


Since you didn't specify the Eaton switchgear -- I'm poking around blind...

But it smells as if you've managed to tap the same exact bus with both your A & B phases.

If this is true, everything would make sense.

Yet, just from a mechanical point of view, that ought to be impossible.

Did Eaton ship you the wrong 'feet' aka bus taps that transmit the juice from the bussing to the new breaker ?

Again, just not enough information to take this any further.

In this situation, your prior experience in residential circuits is no help at all.

It's astounding that you were put on this task. 

There are so many ways to foul these installations up. 

They are often a puzzle palace even for veterans. 

"Engineers, they're always changing things." 

Yes, it's not impossible for the factory to send out the wrong parts... even skip some parts... it's happened to me. 

[ Factory put the wrong voltage bolt switch assembly in the frame. As built it wouldn't accept the proper voltage T type Service fuse. Now, that's pretty bad! When informed that they had built it wrong -- the factory could scarcely believe it. ]

The result is that what fits -- mechanically -- is wrong electrically. :blink::no:


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## Scubasteve82

Well the strange thing is on the line side of the breaker everything is normal 480v across all 3 phases.


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## Bad Electrician

Logically I can see no reason for this BUT

Assuming you have NO LOADS ON THE LOAD SIDE, all loads are off.

You are saying you have

A-277 to GND/Neutral
B-277 to GND/Neutra
C-277 to GND/Neutral

You are sure none of the voltages is 277 millivolts 
Or that you are reading ghost voltages though this would be a high ghost voltage.

A-B 0
B-C 480
C-A 480

TUFF TO DO NOW

Are all the line side connections properly installed, no plastic or cardboard between the breaker stabs and the switchboard bus? 

Connections torqued?

Have you tried opening and closing the CB several times, with the main off preferably, if the CB is defective I would not want to be putzing with it. Then check the voltage, then replace the CB.

What model CB Eaton had some issues with some 400 amp frame molded case CBs a few years back


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## Southeast Power

Scubasteve82 said:


> Phase to neutral reads 277v as well


Ok then, we shall call it the grounded conductor.


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## teufelhounden91

I would take that breaker out and test continuity from the line side bus insert (where the breaker lands on the phase bus bar) to the load side terminals, for each phase. Throw the breaker handle both directions and make sure continuity opens and closes as it should. This will tell you for sure that breaker is not broken mechanically inside. If you have solid continuity from line to load at each of the 3 poles then the breaker is good and you can probably cross that off the list....but we need to see a picture or manufacturer info to make sure there's not something else that could be going on.


On another note, stop messing with a 480v 2000a 3ph switchgear if you're not qualified to work on it. It's not the place to be tinkering your first time. Residential is a bathtub in an ocean of electrical knowledge my friend. Please be safe.


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## Southeast Power

teufelhounden91 said:


> I would take that breaker out and test continuity from the line side bus insert (where the breaker lands on the phase bus bar) to the load side terminals, for each phase. Throw the breaker handle both directions and make sure continuity opens and closes as it should. This will tell you for sure that breaker is not broken mechanically inside. If you have solid continuity from line to load at each of the 3 poles then the breaker is good and you can probably cross that off the list....but we need to see a picture or manufacturer info to make sure there's not something else that could be going on.
> 
> 
> On another note, stop messing with a 480v 2000a 3ph switchgear if you're not qualified to work on it. It's not the place to be tinkering your first time. Residential is a bathtub in an ocean of electrical knowledge my friend. Please be safe.
> 
> 
> Sent from my iPhone using Tapatalk


How does one become "qualified" to work on a 2000amp switchgear?


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## wendon

jrannis said:


> How does one become "qualified" to work on a 2000amp switchgear?


Would an arc flash improve your qualifications?


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## teufelhounden91

jrannis said:


> How does one become "qualified" to work on a 2000amp switchgear?



By being trained and supervised many times on how to do it the right way and being exposed to situations many more times before being left alone to do it on their own.

All "qualified" persons does not mean all "electricians". I wouldn't trust a residential electrician to be qualified to troubleshoot a 75kva 3ph 480/208 transformer with an accidental floating neutral at a shopping mall that is burning up plugs, vacuum cleaners, and lamps getting 208v single phase to ground. It is obvious he would have no idea what's going on, therefore he would not be qualified no matter how many recessed cans and rolls of Romax he's installed in houses through the years.


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## Bad Electrician

teufelhounden91 said:


> By being trained and supervised many times on how to do it the right way and being exposed to situations many more times before being left alone to do it on their own.
> 
> All "qualified" persons does not mean all "electricians". I wouldn't trust a residential electrician to be qualified to troubleshoot a 75kva 3ph 480/208 transformer with an *accidental floating neutral* at a shopping mall that is burning up plugs, vacuum cleaners, and lamps getting 208v single phase to ground. It is obvious he would have no idea what's going on, therefore he would not be qualified no matter how many recessed cans and rolls of Romax he's installed in houses through the years.
> 
> 
> Sent from my iPhone using Tapatalk


Typically in MY EXPIERENCE the term FLOATING NEUTRAL refers to ungrounded neutral and that will not result in equipment burning up. Did you mean an open neutral possibly?

As for experience it varies with a persons mechanical ability, while I tend to agree with you on who should work in or on gear, as a electrician that specializes in maintenance and testing of distribution systems, I cannot tell you the number of times I go to sites for calls were commercial electricians have improperly operated a Bolted Pressure Switch, or improperly grounded a transformer and this list could go on and on. Often operational issues are a direct result of the electricians inability to stop and read directions.


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## ELECTRICK2

Scubasteve82 said:


> I just installed a new 400a 480v Eaton breaker in a 2000a piece of switchgear. I have 277v to ground on all 3 legs. Between A and C phase I have 480v between B and C I have 480v BUT!! Between A and B phase I have like 2 volts. On the line side of the breaker I have 480v between all 3 phases. I was a residential guy for more of my career and just recently started working for a commercial company.
> 
> Any help would be greatly appreciated.


Sounds like you've lost a leg through the breaker. I've seen it before. If it's possible, shut down the panel and (after you make sure everything is de-energized) just ohm out the breaker. 

To equate it to your experience, in a house you are checking a hot water tank that isn't working. You measure A to ground and get 120. B to ground you get 120. A to B you get zero. Only 2 real possibilities, 2 pole breaker has both poles on the same phase (very common) or the breaker is only closing one phase (rarer but not unheard of)

In a 3 phase situation it would be pretty hard to get 2 phases onto the same bus so I'd guess faulty breaker.

I'd like to know the outcome.


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## Big John

ELECTRICK2 said:


> Sounds like you've lost a leg through the breaker. I've seen it before. If it's possible, shut down the panel and (after you make sure everything is de-energized) just ohm out the breaker....


 Agreed. Open pole and the load-side is being backfed which is why it's reading to ground.

Open all connected loads and you'll lose voltage on that missing phase.


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## A Little Short

ELECTRICK2 said:


> To equate it to your experience, in a house you are checking a hot water tank that isn't working. You measure A to ground and get 120. B to ground you get 120. A to B you get zero. Only 2 real possibilities, 2 pole breaker has both poles on the same phase (very common) or the breaker is only closing one phase (rarer but not unheard of)
> 
> In a 3 phase situation it would be pretty hard to get 2 phases onto the same bus so I'd guess faulty breaker.
> 
> I'd like to know the outcome.


Are you saying it's possible and common to install a 2-pole breaker and get both stabs/connections on the same leg of the bus?
If so, how could you do that?

Or are you saying the breaker is defective and both sides are picking up the same leg?

Or are you talking about 2 single pole breakers being used for 240/208/480V but not mounted together on the bus?


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## micromind

A Little Short said:


> Are you saying it's possible and common to install a 2-pole breaker and get both stabs/connections on the same leg of the bus?
> If so, how could you do that?
> 
> Or are you saying the breaker is defective and both sides are picking up the same leg?
> 
> Or are you talking about 2 single pole breakers being used for 240/208/480V but not mounted together on the bus?


A lot of 2 pole minis can be installed so that both poles are on the same phase.


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## varmit

Are the other breakers, in this switchgear, reading voltage correctly? If so, and this breaker is installed correctly, PROBABLY the breaker is faulty. I have seen Siemens/Cutler-Hammer breakers give this problem before.


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## Bad Electrician

varmit said:


> Are the other breakers, in this switchgear, reading voltage correctly? If so, and this breaker is installed correctly, PROBABLY the breaker is faulty. I have seen Siemens/Cutler-Hammer breakers give this problem before.


We had quite a few CH, CB's with defective line side connections.


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## ELECTRICK2

A Little Short said:


> Are you saying it's possible and common to install a 2-pole breaker and get both stabs/connections on the same leg of the bus?
> If so, how could you do that?
> 
> Or are you saying the breaker is defective and both sides are picking up the same leg?
> 
> Or are you talking about 2 single pole breakers being used for 240/208/480V but not mounted together on the bus?


As an example in a federal stab lock panel, if you are using NC type, you have to make sure to have the 2 stabs go onto different phases. I've seen lots of installs where the guy put the 2 pole breaker onto the same phase.
Another thing I see a lot is a tandem breaker with both circuits using the same neutral. Some people just don't understand how the phases/neutrals work


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## ELECTRICK2

Big John said:


> Agreed. Open pole and the load-side is being backfed which is why it's reading to ground.
> 
> Open all connected loads and you'll lose voltage on that missing phase.


Back in the day you'd just take a voltage reading from load to line on all 3 breaker phases. If you get a voltage, it ain't closed. :whistling2:


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## varmit

ELECTRICK2 said:


> Back in the day you'd just take a voltage reading from load to line on all 3 breaker phases. If you get a voltage, it ain't closed. :whistling2:


This is still one of the best tests to use. An old style 'Wiggy" is usually best testing tool, since there are no problems with "ghost" voltages.


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## ELECTRICK2

Bad Electrician said:


> Typically in MY EXPIERENCE the term FLOATING NEUTRAL refers to ungrounded neutral and that will not result in equipment burning up. Did you mean an open neutral possibly?
> 
> As for experience it varies with a persons mechanical ability, while I tend to agree with you on who should work in or on gear, as a electrician that specializes in maintenance and testing of distribution systems, I cannot tell you the number of times I go to sites for calls were commercial electricians have improperly operated a Bolted Pressure Switch, or improperly grounded a transformer and this list could go on and on. Often operational issues are a direct result of the electricians inability to stop and read directions.


Pardon my ignorance but what's a "bolted pressure switch"


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## ELECTRICK2

varmit said:


> This is still one of the best tests to use. An old style 'Wiggy" is usually best testing tool, since there are no problems with "ghost" voltages.


If one leg on a 3 phase breaker is open and loads are still connected your wiggy will read the same as a real meter. It`s reading voltage that is going through a load but has no way home. Its not a ghost, just homeless.:laughing:


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## ponyboy

ELECTRICK2 said:


> Pardon my ignorance but what's a "bolted pressure switch"



It's a type of mechanical switch. Imagine the knife contacts in your basic run of the mill 3 phase safety switch, now imagine it rated for 2000 amps or so. They require regular maintenance and honestly I don't know why anyone would use them anymore


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## ELECTRICK2

Does it operate on pressure


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## ponyboy

ELECTRICK2 said:


> Does it operate on pressure



Mechanical pressure, spring pressure, maybe air pressure. I honestly don't work around them enough to give you any good info though. Other guys her like bad electrician are the ones to talk to. I find them unreliable and too often poorly maintained, our facilities don't utilize them and that's fine by me


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## ELECTRICK2

ponyboy said:


> Mechanical pressure, spring pressure, maybe air pressure. I honestly don't work around them enough to give you any good info though. Other guys her like bad electrician are the ones to talk to. I find them unreliable and too often poorly maintained, our facilities don't utilize them and that's fine by me
> 
> 
> Sent from my iPad using Tapatalk


Strange response...


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## Big John

ELECTRICK2 said:


> Does it operate on pressure


 Each pole has two knife blades and when the switch closes the two blades are actually squeezed towards each other. This sandwiches them tight onto the stationary line-side contact.

They are like a weird hybride between a disconnect switch and a breaker. I have no ideaa what criteria makes people choose them, but they aren't super common and like Pony said, the old ones are very prone to seize.


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## ELECTRICK2

Why is it called a bolted pressure switch
Been around a long time, never heard of this.
Just curious


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## Big John

Because the mechanism that applies pressure to the knife blades is similar to an acme bolt thread: The bladed are essentially "screwed tight" onto the stationary contact.


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## radio208

Just to throw my $.02 in  if a person somehow landed both load side A and B phases on the same A phase lug and C phase on C , close the breaker...no short circuit but will have the same voltage readings in the OP . But really hard to do that ....


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## radio208

But as was stated in previous posts if B phase did not close-in and there was a load on A to B..... ballast...control transformer...etc then A would back-feed to open B phase and give the same readings


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## varmit

ELECTRICK2 said:


> If one leg on a 3 phase breaker is open and loads are still connected your wiggy will read the same as a real meter. It`s reading voltage that is going through a load but has no way home. Its not a ghost, just homeless.:laughing:


Yes, probably a bad choice of words on my part. Sometimes, not often, a contact can pass enough voltage that a digital meter will read it as good, but any tiny load, such as a Wiggy, will shunt the voltage to near zero.

Well,the type meter or tester USUALLY will not matter doing an initial fall of potential test, but a solenoid tester eliminates one more variable.

If one pole of a breaker is not closing, and you test from the load to line terminal on each pole, and you read more than a few millivolts ( depends on several criteria but usually less than 100 mv) you PROBABLY have a faulty breaker. If the voltage is feeding through the connected load and back to the load side of the breaker, the faulty pole will read voltage between the breaker load terminal and the breaker line terminal on the same pole, assuming all phases are energized at the breaker line side.


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## ursus

Scubasteve82 said:


> I just installed a new 400a 480v Eaton breaker in a 2000a piece of switchgear. I have 277v to ground on all 3 legs. Between A and C phase I have 480v between B and C I have 480v BUT!! Between A and B phase I have like 2 volts. On the line side of the breaker I have 480v between all 3 phases. I was a residential guy for more of my career and just recently started working for a commercial company.
> 
> Any help would be greatly appreciated.



A and B phase have no difference in potential, but they individually have a difference in potential from C phase. This means A and B phase are sharing the same leg some how and might go back to where the transformer was wired.

If A was connected to B and B was connected to B, those are the readings you would get.


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## ursus

ursus said:


> A and B phase have no difference in potential, but they individually have a difference in potential from C phase. This means A and B phase are sharing the same leg some how and might go back to where the transformer was wired.
> 
> If A was connected to B and B was connected to B, those are the readings you would get.


I misread it was a breaker but A and B are probably sharing a phase somehow.


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## Bad Electrician

ELECTRICK2 said:


> Does it operate on pressure


When the blades close a cam operates to clamp the switch close.

Hard to beat for high current, high AIC and inexpensive.

http://www.eaton.com/Eaton/Products...ndDisconnects/BoltedContactSwitches/index.htm

http://products.schneider-electric....tenance-and-testing/bolted-pressure-switches/

http://www.boltswitch.com/products.html


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## Big John

Bad Electrician said:


> ...Hard to beat for high current, high AIC and inexpensive.


 I've never priced one. How does the total cost plus fuses stack up against an insulated case main?


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## Bad Electrician

Big John said:


> I've never priced one. How does the total cost plus fuses stack up against an insulated case main?


3000 BPS 12,000
3000 CB 28,000 and up

Just a WAG from my limited memory


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## Big John

Bad Electrician said:


> 3000 BPS 12,000
> 3000 CB 28,000 and up
> 
> Just a WAG from my limited memory


 That explains it. I would've figured the pressure-switches for being much more expensive.


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## JRaef

Bad Electrician said:


> When the blades close a cam operates to clamp the switch close.
> 
> Hard to beat for high current, high AIC and inexpensive.
> 
> http://www.eaton.com/Eaton/Products...ndDisconnects/BoltedContactSwitches/index.htm
> 
> http://products.schneider-electric....tenance-and-testing/bolted-pressure-switches/
> 
> http://www.boltswitch.com/products.html


The other issue is that a BPS is like a Power Circuit Breaker, in that you have a handle that "charges" a spring, then the spring operates the mechanism that "bolts" (forces) the contacts closed. It's used on switches over 800A, because the amount of physical force required to DIRECTLY close the contacts gets to be too extreme, unless the amount of closing pressure is reduced. When you get into the larger sizes like that, the amount of physical force from the magnetic fields of a fault gets very hairy and will want to force things like the contact mechanisms apart. The spring charged mechanism also means you can use GF relays and Shunt Trips for them as well.

If you look into it, you will see a simple knife blade disconnect switch WITHOUT fuses only has a withstand rating of something like 10kA. The 200kA rating is ONLY when used with current limiting fuses, because the switch itself is protected by the fact that the fuse will limit the current, and the amount of mechanical force, involved in a fault. Pringle Switches (the older name for BPS) are often used _as _the main disconnect in a switchboard or service entrance, so they have to be able to withstand everything that's available. So a BPS will have a much higher withstand rating, with or without the fuses. Pringle Switches (now owned by Eaton) are 200kA withstand, no qualifiers.

The "bolted" term refers to the fact that the strength of the connection is equal to that of a piece of bolted bus bar by the way.


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## ELECTRICK2

ursus said:


> A and B phase have no difference in potential, but they individually have a difference in potential from C phase. This means A and B phase are sharing the same leg some how and might go back to where the transformer was wired.
> 
> If A was connected to B and B was connected to B, those are the readings you would get.


He was talking about the load side of the breaker where he was getting wonky readings. Line side reads fine. This would eliminate your transformer idea. I'll go back to the hot water tank analogy. Take one wire off the 2 pole breaker feeding your hot water tank and put a marrette on it. This imitates an open side on the breaker. If the hot water tank is calling for heat, at the tank you will get 120 A to ground or neutral, and you will get 120 B to ground/neutral as well. A to B will read zero volts. 
Same scenario.


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## A Little Short

ELECTRICK2 said:


> I'll go back to the hot water tank analogy. Take one wire off the 2 pole breaker feeding your hot water tank and put a *marrette *on it.


We're not allowed to use those in the US, we have to use wire nuts!
Plus we can't spell it either!:laughing:


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## mikestoner38

Maybe I'm a nube but why did noone suspect a phase to phase short in an equipment down range from the breaker? That is exactly what's going on here. It's not the breaker at all. It's the wiring or equipment installed on the crkt there is a phase to phase short likely through a contactor or motor some place


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## backstay

Seven years.


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## Almost Retired

mikestoner38 said:


> Maybe I'm a nube but why did noone suspect a phase to phase short in an equipment down range from the breaker? That is exactly what's going on here. It's not the breaker at all. It's the wiring or equipment installed on the crkt there is a phase to phase short likely through a contactor or motor some place


they either fixed it or replaced SEVEN YEARS AGO
check the dates on these things please, they are in various places in the thread


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