# 480 3phase corner ground? heard of it?



## RePhase277 (Feb 5, 2008)

pimpin electrician said:


> im in this old industrial building, and for the first time have come across this older electrical system that is new to me.
> 
> 480 volts from ground to phase A and C. no voltage from ground to B phase.
> 
> ...


Sure it works. Grounding a phase does nothing to change how it operates electrically. It is grounded so that fault current has a place to go in order to trip breakers or blow fuses.

A grounded B phase follows all the NEC rules of a neutral, except that it isn't a neutral. It should not be switched unless all other conductors are switched. It should not be fused. It should, however, be white in color. Other than that, none of the theory changes.


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## pimpin electrician (May 2, 2009)

*thanx*

thanks for the reassurance!

if B phase is grounded, wouldn't that cause the panel to have voltage capability. so if i was grounded, or touching metal, then touch the panel. could i get zapped?


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## brian john (Mar 11, 2007)

B phase to ground and nothing A or C phase to ground and you get 480.

Earth and/or the metallic structures that serve in place of earth could care less about the which leg you ground on a 3 phase 4 wire system you can ground any phase if you do not ground the neutral, NOT LEGAL but it will work.


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## pimpin electrician (May 2, 2009)

*white in color*

the panel actually has B phase colored orange.

and all the branch circuits are brown, orange, yellow, i believe.

i also believe that the existing disconnect that is down the line (which i will be using to protect my motor) is not grounded. 3 wires just go to main lugs. i plan to keep it that way. should be alright. there are many disconnects already in use that way. do you think i should stick a ground lug on the disconnect? use B phase?

i understand that i should get a breaker that is rated for straight 480.

and i plan to use fast acting fused in my disconnect. for A,B and C phase.

sound good?


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## brian john (Mar 11, 2007)

Are you sure the B phase is intentionally grounded or accidentally grounded?

It is possible to have an ungrounded system and a short on one phase grounds that phase. I think I would look around a bit to determine this.


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## RePhase277 (Feb 5, 2008)

pimpin electrician said:


> thanks for the reassurance!
> 
> if B phase is grounded, wouldn't that cause the panel to have voltage capability. so if i was grounded, or touching metal, then touch the panel. could i get zapped?


No. This is a common misconception about grounding. The earth doesn't have some magical electrical property. If B phase is grounded, and the panel can is grounded, then no current can flow, because there is no difference of potential. Current only flows when there is a difference of potential.

And Brian is right. You should inspect this system a little closer, to be sure that it is in fact an intentionally grounded system. The ground should take place at the service, just like a neutral. There should be a bonding jumper of some sort from B phase to ground. It could also be that it was originally installed as an ungrounded system, and later changed to grounded. This may explain the colors.

In any case, if you verify it is truly a corner grounded system, then in order to do things right, you need to pull colors appropriately. So, colors should be brown, white, yellow, and green. At disconnects, I would not land the B phase on a fuse. I would connect A and C phases to the disconnect, and pass the B phase straight through. Unless the motor or application required all lines to be disconnected.


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## CraneTech (May 2, 2009)

Just recently i wired a 480 test station for a crane at our new(actually old) plant 4 facility. The box itself was ground. I installed a grounding lug to the box and wired in the 3 phases as normal and all works fine.


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## pimpin electrician (May 2, 2009)

*delta corner grounded system. 1 more ?*

thank you to the few that helped me out the other day with my uncertainty of the delta corner grounded system. thanks, because of your replies it gets my mind moving. i've been thinking alot about it over the past day or so.

this is what i believe is going on with this system.

1. it is a 3 wire 3 phase system. (if it were a 4 wire, there would be no need 
to ground the B phase, 4th wire would be your ground)

2. you get 480 voltage all around, except when you test B phase to ground. 
i need to double check, but i'm not sure if i had voltage at A to B and B to 
C. The reason you get no voltage from B to ground, is because it is like as 
if you touch B phase at main lug to B phase at breaker buss. same phase.

2a. the reason grounded B phase acts as a ground. if A or C phase touch 
the B phase, it will short out circuit. touching 2 different phases together 
is just like touching 1 phase to ground. hench your grounded phase as 
opposed to seperate ground wire or nuetral. Right? 

3. you can have a 3 pole breaker at panel for your circuit. But should not 
fuse the B phase at disconnect. (grounded phase)
- if there is a short on your branch circuit, it should trip all 3 phases at 
circuit breaker.
- At your fused disconnect, if you were to fuse the grounded phase, 
and that fuse were to go out. motor could keep running, and circuit after
the disconnect would have not ground fault protection on other 2 legs.
(is that the reason for not fusing the grounded phase? thats my thought

so that's what i've come to believe about the corner grounded system. which leads me to my last question.

this motor that i'm installing is going to be operated by a seperate motor controller, which has the motor go in forward and reverse. this unit has a cord on it to plug into a 110 outlet. that is where it gets it's power from. 

then you bring in the 3 phase power to unit, and then back out going to motor. these wires land on terminal strip. this unit wants L1,L2,L3 and then a protective equiptment ground. im thinking of using a ground from the 110v. receptacle circuit as opposed to the B phase of my motor circuit. not sure if grounded B phase is a good idea for my ground on small motor controller circuit.

i think i'm playing it safe, what do you think. motor controller unit is going to be mounted right next to receptacle outlet box anyway. easy install, and wont look funky. The grounded B phase that acts as a ground but also provides voltage doesn't sound good around computer chip motor controller.

any feed back would be great... thanks


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## micromind (Aug 11, 2007)

A lot of the grounded B systems I've worked with have a single phase panel and two pole breakers. The B phase is grounded at the panel, just like a single phase system. This is the only place where phase B is connected to ground, just like the neutral of a single phase system. 

When connecting 3 phase equipment, there are 4 wires. The 3 phases, and a ground. The fact that phase B is already grounded is of no consequence. Since it carries current, it must be isolated from ground at every point downstream of the bonding jumper. Same as the neutral in a single phase system.

If a disconnect switch is used, only two poles can be fused. The B phase cannot contain any overcurrent device unless it is arranged to open all 3 phases simultaneously. A 3 pole circuit breaker would be an example. 

In medium-voltage switchgear (over 600 volts), usually there are potential transformers. These reduce the bus voltage to something more manageable, like 120. They supply a voltage signal to various instrumentation. There are almost always two transformers connected open delta. Phase B is almost always grounded. Usually, there is a fuse block of some sort, with fuses in phases A and C, while phase B has a slug in it. No short-circuit or overcurrent protection is needed (or allowed) in phase B, because it is grounded. 

In a single phase system, you have 120 from either hot to neutral/ground, and 240 between the two hots. In a 480 volt grounded B 3 phase system, you have 480 from either hot to neutral/ground, and 480 between the two hots. The B phase is treated just like the neutral of the single phase system. 

If you're dealing with a panel and breakers, be careful. All breakers must be rated for 480 volts, not 277/480. The reason being, if you have a ground fault, the breaker will be interrupting 480 volts across one pole, not 277. 

Rob


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## brian john (Mar 11, 2007)

pimpin electrician said:


> 1. it is a 3 wire 3 phase system. (if it were a 4 wire, there would be no need
> to ground the B phase, 4th wire would be your ground)


 
The 4th wire would be your GROUNDED CONDUCTOR not ground.



> 2. you get 480 voltage all around, except when you test B phase to ground. I need to double check, but I'm not sure if i had voltage at A to B and B to C. The reason you get no voltage from B to ground, is because it is like as if you touch B phase at main lug to B phase at breaker bus. same phase.


Well if you took in a 3 phase 4 wire system and ground the B phase then from B to ground you have "0" volts, from neutral to ground you would have 120 Vac and from A and C yu would have 208 VAC.



> 2a. the reason grounded B phase acts as a ground. if A or C phase touch
> the B phase, it will short out circuit. touching 2 different phases together
> is just like touching 1 phase to ground. hench your grounded phase as
> opposed to seperate ground wire or neutral. Right?


YES


> 3. you can have a 3 pole breaker at panel for your circuit. But should not
> fuse the B phase at disconnect. (grounded phase)
> - if there is a short on your branch circuit, it should trip all 3 phases at
> circuit breaker.
> ...


I need to check on this. Someone else may be ale to answer this. BUt I think you could use a 3 pole CB and a 3 pole disconnect withn a dummy fuse on B phase.

See 240.22


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## RePhase277 (Feb 5, 2008)

pimpin electrician said:


> 3. you can have a 3 pole breaker at panel for your circuit. But should not
> fuse the B phase at disconnect. (grounded phase)
> - if there is a short on your branch circuit, it should trip all 3 phases at
> circuit breaker.
> ...


The motor would likely burn out because it has lost a phase if the fuse blows, unless the controller has provisions against this.



> then you bring in the 3 phase power to unit, and then back out going to motor. these wires land on terminal strip. this unit wants L1,L2,L3 and then a protective equiptment ground. im thinking of using a ground from the 110v. receptacle circuit as opposed to the B phase of my motor circuit. not sure if grounded B phase is a good idea for my ground on small motor controller circuit.


Do NOT do this. There is no guarantee that the 120 V ground is connected in any meaningful way to the 480 V B phase ground. The only real ground you have is the ground from the 480 V panel.



> i think i'm playing it safe, what do you think. motor controller unit is going to be mounted right next to receptacle outlet box anyway. easy install, and wont look funky. The grounded B phase that acts as a ground but also provides voltage doesn't sound good around computer chip motor controller.
> 
> any feed back would be great... thanks


The grounded phase acts as a ground because the potential between it and other grounded objects is the same. This is identical to the neutral of any other system. You are still not fully picturing how grounding works. Grounding a line doesn't magically make the voltage go away, it simply equalizes the voltage between it and surrounding objects. BUT, the voltage between that line and other lines remains.

Look at an un-grounded 120 V transformer. There will be 120 V between the wires, and anything connected to it will work fine. If there is a short to a conduit, let's say, nothing will happen, because that conduit is not connected to either side of the transformer, so no current will flow to blow a fuse. Now, pick a wire from the transformer (doesn't matter which), and connect it to the conduit. You now have a "grounded" system, but nothing has changed between the two wires. If a short occurs to the conduit from the other wire, the fuse will blow. The neutral in your house is just as "hot" as the hot wire, as far as the hot is concerned. They are electrically identical.

Look at your 480 system. Grounding one phase doesn't change anything between the phases, but it does give fault current somewhere to go. This is not going to destroy any microchips. They don't know the difference. Grounding has little to do with the Earth, and is mostly concerned with bonding.

To be safe, pull four wires: brown, white, yellow, and green, from your 480 panel. It doesn't matter one bit electrically that the green wire is connected to the B phase somewhere in the service. You want and need this.


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## brian john (Mar 11, 2007)

While you should not do what he is suggesting a properly sized EGC should be installed be it the conduit or copper.



> Do NOT do this. There is no guarantee that the 120 V ground is connected in any meaningful way to the 480 V B phase ground. The only real ground you have is the ground from the 480 V panel.


Ground is ground and other that minimal impedance differences this would not be damaging though it would not be per the NEC.


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## Chris Kennedy (Nov 19, 2007)

pimpin electrician said:


> im thinking of using a ground from the 110v. receptacle circuit as opposed to the B phase of my motor circuit. not sure if grounded B phase is a good idea for my ground on small motor controller circuit.


There is no direct electrical connection between the 120V circuit and the 480V motor circuit. Therefore no way to facilitate the opening of the motors OCPD. You need to use an EGC tied to the grounded point of the tranny.


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## RePhase277 (Feb 5, 2008)

brian john said:


> While you should not do what he is suggesting a properly sized EGC should be installed be it the conduit or copper.


Huh? Do what who is suggesting? My suggestion is the proper way to install a circuit on a corner grounded system.



> Ground is ground and other that minimal impedance differences this would not be damaging though it would not be per the NEC.


It may be damaging if there is no direct electrical connection between the two system grounds. I'd hate to rely solely on old building steel to complete my fault path.


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## brian john (Mar 11, 2007)

Chris Kennedy said:


> There is no direct electrical connection between the 120V circuit and the 480V motor circuit. Therefore no way to facilitate the opening of the motors OCPD. You need to use an EGC tied to the grounded point of the tranny.


 
Chris GROUND IS GROUND the connection exist but cannot be used as the sole EGC per the NEC, additionally the OP cannot use a grounded conductor as a EGC.

In this system there are four conductors A, B, C with B phase grounded, A and C ungrounded and an equipment grounding conductor that is common with the B phase ONLY at your transformer or common point of the ground to B phase bond.


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## pimpin electrician (May 2, 2009)

*1 more look 2morrow*

i will be going to look at this job again tomorrow.

i believe that i will be installing a ground wire through my conduit to the disconnect. i will just throw a bonding lug on the panel. this is a 3 phase panel with 3 pole breakers in it. 

i am also going to look at other disconnects that are fed out of this same panel. i am going to look at what they have done with the B phase in the disconnect. i know that they did not run any equiptment ground conductors to any of the disconnects from the 480 panel.

i appreciate all of the feed back. i will let you know what i find tomorrow...

you guys are a great help..........thanks


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## sparkyboys (May 3, 2009)

This guy does not sound to competent to do this kind of work. I think you need to get a new job before you get yourself killed or BADLY burned! 480 is nothing to play around with! Maybe you should get a desk job answering phones. Sorry moderator if i sound mean but this guy is going to pimp himself into a coffin. Sorry pimpin. Or at least go back to residential.


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## brian john (Mar 11, 2007)

InPhase277 said:


> Huh? Do what who is suggesting? My suggestion is the proper way to install a circuit on a corner grounded system.[/quote}
> 
> It was nothing against your post.


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## brian john (Mar 11, 2007)

sparkyboys said:


> This guy does not sound to competent to do this kind of work. I think you need to get a new job before you get yourself killed or BADLY burned! 480 is nothing to play around with! Maybe you should get a desk job answering phones. Sorry moderator if i sound mean but this guy is going to pimp himself into a coffin. Sorry pimpin. Or at least go back to residential.


This guy has a legitimate question regarding a power system he is not familiar with. Have you never run into something you are not familiar with?

Unusual distribution system.
Grounding one of the more confusing items in our line of work for some.


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## Bob Badger (Apr 19, 2009)

sparkyboys said:


> This guy does not sound to competent to do this kind of work. I think you need to get a new job before you get yourself killed or BADLY burned! 480 is nothing to play around with! Maybe you should get a desk job answering phones. Sorry moderator if i sound mean but this guy is going to pimp himself into a coffin. Sorry pimpin.


That is mean and makes no sense at all. (Well I do agree that 480 is nothing to 'play' with)

But here is a guy that realizes what he does not know and decided to ask questions about it instead of just guessing.

Why would you want to chase people off from asking questions? :001_huh:



> Or at least go back to residential.


I have been doing commercial work for 25 years and have only run across corner grounded systems a few times. Around here 480Y/277 is much more common and if that is what your used to working with seeing B phase grounded is an odd thing.


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## pimpin electrician (May 2, 2009)

hey there brian john... thanks for your feedback on my topic.

i went back to this job the other day. i know that i need to install a egc. there are only 3 conductors comming into my 480 panel. ABC phase. they are just using conduit as the ground. in the panel, there is ground buss bar installed. 2 ground wires comming off of it already. do you think that it is cool enough to just tap off of this ground buss, even though there is no ground wire comming in to feed it? or else i was planning on driving a ground rod right under the panel.

other than that, i pretty got everything else figured out. i always run ground wires through my conduit. in san francisco they just use the raceway as ground. i was very tempted to just keep my conduit run the way it is. it already has the hot wires in it, with no ground wire. i'm gonna install a ground wire, just wondering if its cool to just hit the existing ground buss.


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## RePhase277 (Feb 5, 2008)

pimpin electrician said:


> hey there brian john... thanks for your feedback on my topic.
> 
> i went back to this job the other day. i know that i need to install a egc. there are only 3 conductors comming into my 480 panel. ABC phase. they are just using conduit as the ground. in the panel, there is ground buss bar installed. 2 ground wires comming off of it already. do you think that it is cool enough to just tap off of this ground buss, even though there is no ground wire comming in to feed it? or else i was planning on driving a ground rod right under the panel.
> 
> other than that, i pretty got everything else figured out. i always run ground wires through my conduit. in san francisco they just use the raceway as ground. i was very tempted to just keep my conduit run the way it is. it already has the hot wires in it, with no ground wire. i'm gonna install a ground wire, just wondering if its cool to just hit the existing ground buss.


I'm not Brian, but I'll take a stab. I've worked on a number of old corner grounded systems, and think I understand them pretty well.

You really need to study up on grounding theory. Not a dig at you, but you still don't have a fundamental understanding of the subject. Ground rods have (almost) nothing to do with running an EGC. The ground bar in your panel is bonded to the can, and the can is bonded to the conduit, which gets its ground at the service equipment, which gets its ground from the grounded B phase.

So, yes install a ground from the ground bar. Also, I can't stress enough proper color coding of the B phase conductor. By code, it has to be white or grey.


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## pimpin electrician (May 2, 2009)

*thanks*

thanks...

i'm comfortable now with this... got my plan worked out, and ready to work it.

this site is cool. i'm glad i came across this system, and this site!

i've bee pluggin away for 10 years now, and still love it. 

2 years residential, and 2 years working for a protroleum contractor doing re-pipe and ground ups at service stations. the rest of my time doin commercial, mostly new construction..... helped on a jail project also.... 

its all the same, everything is a power or a switch... 

once again... thanks....................


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## sparkyboys (May 3, 2009)

Bob Badger said:


> That is mean and makes no sense at all. (Well I do agree that 480 is nothing to 'play' with)
> 
> But here is a guy that realizes what he does not know and decided to ask questions about it instead of just guessing.
> 
> ...


Sorry pimpin. Sorry bobthebuilder. I do work with 480 277 for power and lighting control as new construction. as well as 120 208. I mostly work with vfds that control motors. I do all commercial, jails, hospitals, schools, fire pumps, heat pumps, cooling towers, chiller pumps and have never ran across this. 

My apologies, truly, to both of you. I did some homework on it though.
That is some wild stuff


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## brian john (Mar 11, 2007)

pimpin electrician said:


> hey there brian john... thanks for your feedback on my topic.
> 
> i went back to this job the other day. i know that i need to install a egc. there are only 3 conductors coming into my 480 panel. ABC phase. they are just using conduit as the ground. in the panel, there is ground buss bar installed. 2 ground wires coming off of it already. do you think that it is cool enough to just tap off of this ground buss, even though there is no ground wire coming in to feed it? or else i was planning on driving a ground rod right under the panel.


If the conduit is a legal EGC in your area, then there is nothing wrong with the above.



> other than that, i pretty got everything else figured out. i always run ground wires through my conduit. in San Francisco they just use the raceway as ground. i was very tempted to just keep my conduit run the way it is. it already has the hot wires in it, with no ground wire. I'm gonna install a ground wire, just wondering if its cool to just hit the existing ground buss.


Sure I would hit the ground bus. Something to remember when grounding and I tell this to electricians over and over GROUND IS GROUND.

There is so much metal in commercial building it is almost impossible to isolate grounds. Re-bar, ducts, water piping, sprinklers, metal studs, EMT, MC, it is all connected, even isolated grounds are common with all these systems when properly installed and in most cases FEW if any ISO Grounds are properly installed.


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## tiffeetiff (May 8, 2009)

*New electrician*

Good morning everybody i am currently a student training to become an elctrician. I was wondering if any one had any advice. I also have lots of questions so please feel free to reply.


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## brian john (Mar 11, 2007)

Probably should have started a new post BUT, Are you working and in an apprenticeship program.


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## RePhase277 (Feb 5, 2008)

brian john said:


> Sure I would hit the ground bus. Something to remember when grounding and I tell this to electricians over and over GROUND IS GROUND.
> 
> There is so much metal in commercial building it is almost impossible to isolate grounds. Re-bar, ducts, water piping, sprinklers, metal studs, EMT, MC, it is all connected, even isolated grounds are common with all these systems when properly installed and in most cases FEW if any ISO Grounds are properly installed.


Brian, I agree that ground is ground, due to the very reasons you state, however, I personally try to keep it along an intentional path. I like to think that if a circuit I install faults, then it has a direct path back to the main bonding jumper through a conductor installed just for that purpose.

I'd hate to think of someone having a slack attitude thinking "Oh well, that duct foil, and rusty metal framing members will get the current where it needs to go..."


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## pimpin electrician (May 2, 2009)

*all comming together*

okay, i got it now.... everything is making sense.

just one more thing. 

what is the reason for not fusing the B phase at disconnect.

will have a 3 pole breaker at main panel. this will kill all 3 legs simultaniously.

so at disconnect. the only reason that i can think of why not to fuse the B leg, would be, that you are not supposed to fuse a nuetral?

i would think that you want to protect all hot legs going to the motor. the frequency inverter that i am installing has overloads in it, so i guess that is enough protection for my motor..

my customer actually ordered the wrong size inverter, so i think i am going to talk him out of using one anyways.. all he wants to do is run the motor in 1 direction anyways. 

i'm gonna talk him into letting me install my own motor starter with a start, stop push button setup instead. so then, i will be getting motor protection at all 3 hot legs from my motor overloads. 

so then, if B phase was not fused at disconnect, motor will still be protected at all 3 legs from motor overloads. and if anyone needed to work on the circuit, they can just kill the 3 pole breaker feeding the circuit...

i see why it will be okay to not fuse B phase, but why?

and i will pull brown, white, yellow and green...


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## brian john (Mar 11, 2007)

InPhase277 said:


> Brian, I agree that ground is ground, due to the very reasons you state, however, I personally try to keep it along an intentional path. I like to think that if a circuit I install faults, then it has a direct path back to the main bonding jumper through a conductor installed just for that purpose.
> 
> I'd hate to think of someone having a slack attitude thinking "Oh well, that duct foil, and rusty metal framing members will get the current where it needs to go..."


As electricians we need to do as you state my point is, that there are millions of paths, the copper conductor and/or metallic conduit should be the primary path. As I understand it, most current will remain close to the supply conductors during a fault.


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## brian john (Mar 11, 2007)

pimpin electrician said:


> okay, i got it now.... everything is making sense.
> 
> just one more thing.
> 
> ...


NOT SUPPOSE TO FUSE THE GROUNDED CONDUCTOR, in a 208/120 or 480/277 system this grounded conductor is the neutral.



> i would think that you want to protect all hot legs going to the motor. the frequency inverter that i am installing has overloads in it, so i guess that is enough protection for my motor..


THINK fused= hot=ungrounded conductors and no fuse=grounded conductor= not hot to ground.


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## RePhase277 (Feb 5, 2008)

pimpin electrician said:


> okay, i got it now.... everything is making sense.
> 
> just one more thing.
> 
> ...


Because if the fuse protecting the grounded leg blows, the load will not work. This may lead someone to believe that there is no power to the load, while in reality, the hot legs are still energized.


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## electron john (Oct 9, 2012)

*Floating Gound*

Sounds to me like your working with a floating ground system that has one leg grounded. 
I work for a major brewery and we have an occasional switchgear that will have 480 on one phase to ground 480 on another phase to ground and anywhere from 0 to 30 on the other phase but between all phases reads 480.
Our utilities Dept conducts test daily to look for grounded hot legs then make repairs. After that each phase will read 277 to ground and 480 between phases. This floating ground system allows the hot leg to be grounded without blowing fuses or single phasing motors. The first time I saw it I thought the entire line was about to burn up drives and motors. The old timers said nothing to worry about, utilities will correct it in the morning, and they did.


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## BBQ (Nov 16, 2010)

electron john said:


> Sounds to me like your working with a floating ground system that has one leg grounded.
> I work for a major brewery and we have an occasional switchgear that will have 480 on one phase to ground 480 on another phase to ground and anywhere from 0 to 30 on the other phase but between all phases reads 480.
> Our utilities Dept conducts test daily to look for grounded hot legs then make repairs. After that each phase will read 277 to ground and 480 between phases. This floating ground system allows the hot leg to be grounded without blowing fuses or single phasing motors. The first time I saw it I thought the entire line was about to burn up drives and motors. The old timers said nothing to worry about, utilities will correct it in the morning, and they did.


John, welcome to the forum, this thread is from 2009.

What you have at your plant is an ungrounded system which is common in industrial places. 

What the thread is about is corner grounded delta which is also fairly common.


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## big2bird (Oct 1, 2012)

BBQ said:


> What the thread is about is corner grounded delta which is also fairly common.


Yep. Common? Not so much anymore. The higher voltage to ground is not such a good thing, and discouraged by most engineers these days.


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## BBQ (Nov 16, 2010)

big2bird said:


> Yep. Common? Not so much anymore. The higher voltage to ground is not such a good thing, and discouraged by most engineers these days.


I have no idea how things are where you are but in my area there are tons of old buildings that are completely unchanged by new thoughts and preferences of engineers.

Beyond that as recently as 10 years ago we installed corner grounded 480 supplies because that was what the customer wanted.


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## big2bird (Oct 1, 2012)

BBQ said:


> I have no idea how things are where you are but in my area there are tons of old buildings that are completely unchanged by new thoughts and preferences of engineers.
> 
> Beyond that as recently as 10 years ago we installed corner grounded 480 supplies because that was what the customer wanted.


Then I will tell you. I only know of one such old installation around here at a saw mill. It is eons old. The only ungrounded delta and ungrounded wye service I knew of has been torn out. 
I have yet to hear of any corner grounded delta 480v install around this locale. The only delta high leg I installed for years was for general power in a sub station I worked on, doing all the controls, while 28 lineman did the HV work.I do see ungrounded delta on VFD outputs servicing wet areas ocasionally.
There is just no real reason to use it anymore.


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## brian john (Mar 11, 2007)

Big,

I know of at least 10 corner grounded deltas and all of these have been installed in the last few years. 

Was trouble shooting a PQ issues on a chiller last week 280 wye to 480 delta.

Many EC do this on jobs were the distribution is 208/120 wye and they need 480 for a machine.

Not my favorite system but it is done.


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## brian john (Mar 11, 2007)

electron john said:


> Sounds to me like your working with a floating ground system that has one leg grounded.
> I work for a major brewery and we have an occasional switchgear that will have 480 on one phase to ground 480 on another phase to ground and anywhere from 0 to 30 on the other phase but between all phases reads 480.
> Our utilities Dept conducts test daily to look for grounded hot legs then make repairs. After that each phase will read 277 to ground and 480 between phases. This floating ground system allows the hot leg to be grounded without blowing fuses or single phasing motors. The first time I saw it I thought the entire line was about to burn up drives and motors. The old timers said nothing to worry about, utilities will correct it in the morning, and they did.


I don't think ground ever floats. What is sometimes called a floating neutral is a wye or single phase 3-wire system with XO/Neutral not bonded to ground.


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