# Help!! Corner Grounded Delta 3 Phase



## nolabama (Oct 3, 2007)

i cant help ya:no:


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## BryanMD (Dec 31, 2007)

I've never worked on one and I don't think I've seen one either. But I did some googling maybe some of this will help.

You mentioned reading a-b and a-n and b-n...
what about the others?

"In a corner grounded delta system, one of the three phase legs is intentionally grounded. If the leg chosen is the B phase, then the voltage to ground for A and C will be 240 volts, while for B it will be zero."


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## waco (Dec 10, 2007)

I'm interested to see what others say about this, but from what you described, it doesn't sound like a kosher three-phase setup. Is there any way the farm could be getting two service feeds and they have become intermingled?

I don't know. Glad I don't have to work it.


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## RePhase277 (Feb 5, 2008)

Of course a single phase motor will work with this system. As long as the voltage is correct, and the breaker is rated for it, you could run the motor on either a single pole or double pole breaker. You need to read 240.85, which addresses the issue of breaker selection for corner grounded systems. It basically says that a breaker can't be used on this system unless it is marked as suitable as a 3-ph breaker. And because the voltage to ground is 240, you must use a breaker rated for 240 V only. Not a 120/240 V. 

If you use a single pole 240 V breaker, remember that the grounded conductor still needs to be white, even though it is a phase conductor. There is nothing else really special about a corner grounded system except that there is no neutral but there is a grounded conductor, and the breakers used must be straight rated, not /.

The bar in the panel is not a neutral bar. It is the ground bar, and this is where your EGC comes from as well as the white grounded phase. And there is no C phase. So one leg of the three phase feed to a motor is white and not protected by any OCPD. It can be switched but not fused.

Edit: The service entrance conductors should all be insulated. A bare wire for the grounded phase is a no no.


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## nolabama (Oct 3, 2007)

the what about the others led to my edit of my first post 
i was wondering were "c" was 
looking in my ugly book - i dont see a c phase on a corner grounded system
looking in my new book on grounding it says
3-ph, 3-wire,240v delta system
ph a to b 240v
ph b to c 240v
ph a to c 240v
ph a to ground 240v
ph b to ground 240v
ph c to ground 0v

see 250.26(4) 
multiphase systems were one phase is grounded - one phase conductor

which seems to tell me the c is your n 

is the n - the grounded conductor feeding a lug in the main breaker of this panel or the main lug of this panel 

this is how the illustration indicates how the line side of your service equipment to be made up

if this is the case i dont know if you can use a two pole on this system 

"While pulling a ground wire from I guess the neutral bar??? that seems wrong, but the existing panel well its probably all wrong. Betting other people didn't under stand either."

edit :this does not sound like a safe way to ground this :edit this may be the only way to ground the motor??

pulling another equipment grounding electrode does not sound like a code compliant way to do this either 

please note i have never worked on this system and like i said in my first post ...

on another note - i bet the guys who installed this did know what they were doing 

do a little more research on the subject 
and some smarter guys around here may be able to help


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## nolabama (Oct 3, 2007)

pull the circut for the single phase motor from the 120v panel seems like the easy choice


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## Dude Man (Dec 15, 2008)

thanks for the replies.

my grounded conductor goes to the ground bar.
If I would use a single pole, would that mess up the blancing of this system?

So I could use a single pole breaker rated 240v run say the black and white to my motor starter and also pull a green off the ground bar, and then to the motor and wire it for the high voltage side on the single phase motor? I would also put the Heater in the manual starter on the Black conductor.

Or I could I use a two pole and pull black and red threw the starter to motor and pull a green of the ground bar? 

Is this all correct/legal/safe?

Thanks.


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## RePhase277 (Feb 5, 2008)

Dude Man said:


> thanks for the replies.
> 
> my grounded conductor goes to the ground bar.
> If I would use a single pole, would that mess up the blancing of this system?


Nope.



> So I could use a single pole breaker rated 240v run say the black and white to my motor starter and also pull a green off the ground bar, and then to the motor and wire it for the high voltage side on the single phase motor? I would also put the Heater in the manual starter on the Black conductor.


Yep.



> Or I could I use a two pole and pull black and red threw the starter to motor and pull a green of the ground bar?
> 
> Is this all correct/legal/safe?
> 
> Thanks.


You got it:thumbsup:


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## micromind (Aug 11, 2007)

Either of your choices would work, but you'll likely have a hard time finding a single pole breaker rated for 240 volts that will fit the panel. 

When I install a single phase motor on a corner grounded system (known as grounded B around here), I simply use a 2 pole breaker that's 240 volt (not 120/240), and use the ground bus as the ground. Same as a single phase panel, but with a 240 volt breaker. 

Rob

P.S. 3 phase motors need 4 wires, 2 of them go to the ground bus. One carries current and goes to a motor lead, and is the same size as the two hots. The other doesn't carry current, and goes to the motor frame, and is sized for a ground.


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## waco (Dec 10, 2007)

I don't understand the distinction between a "240 volt" breaker and a "120/240 volt" breaker. Seems obvious to me, any 240 volt breaker would handle 120 volts.

I'm also not sure I understand how a "grounded corner delta" can be ungrounded, but the confusion probably comes from using the letters to designate the corners of the delta and the "phases."

So, how is the farm metered?


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## jwelectric (Sep 28, 2008)

Dude Man said:


> . On my future father-in-law's farm......


This just don't sound right. A corner grounded systen on a farm?????????

Does this farm have livestock?


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## RePhase277 (Feb 5, 2008)

waco said:


> I don't understand the distinction between a "240 volt" breaker and a "120/240 volt" breaker. Seems obvious to me, any 240 volt breaker would handle 120 volts.
> 
> I'm also not sure I understand how a "grounded corner delta" can be ungrounded, but the confusion probably comes from using the letters to designate the corners of the delta and the "phases."
> 
> So, how is the farm metered?


A 120/240 breaker is intended for use on a system where the maximum voltage to ground is 120, and the maximum voltage line to line is 240. In the setup the OP describes, the maximum voltage to ground would be 240, so he must use a straight 240 V breaker.

A corner grounded delta is not ungrounded. It has one phase tied to ground. It is similar to how a neutral is tied to ground, except there is no neutral. Basically the idea was you only needed 240, but you also wanted a grounded system. How can you do this with a delta secondary? You can either center tap one transformer (more expensive), or you can ground one phase (cheaper). Now you have a grounded 240 V 3-phase system.


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## waco (Dec 10, 2007)

Good explanation, but I don't see how a breaker can know if it is looking at line to line voltage or line to ground voltage. I'll take your word for it.

"A corner grounded delta is not ungrounded." I agree, so somewhere in there, the voltage should have been voltage to ground. Maybe I didn't read it closely enough.


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## frenchelectrican (Mar 15, 2007)

jwelectric said:


> This just don't sound right. A corner grounded systen on a farm?????????
> 
> Does this farm have livestock?


 
I ran into few farms like that set up and I am not  crazy with it and few farms I have to rewired to run in Wye format and slove the issue for once at all.

One very large farm not far from me used 480Y277 in there so I am not suprised about that and what more mine POCO don't allowed delta service to new customers but exsting one they can stay and only match the transfomer to main breaker size nothing more.



waco., It was expained in the NEC about the straght votlage and dual voltage.

However.,,It kind common error when someone used standard 120/240 volt breaker on CGD system.

Yes you can order straght 240Volt breaker they should be about the same or little more on costwise.

Merci,Marc

* CGD = Corner Grounded Delta


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## RePhase277 (Feb 5, 2008)

waco said:


> Good explanation, but I don't see how a breaker can know if it is looking at line to line voltage or line to ground voltage. I'll take your word for it.
> 
> "A corner grounded delta is not ungrounded." I agree, so somewhere in there, the voltage should have been voltage to ground. Maybe I didn't read it closely enough.


The voltage to ground is 240 V. If you ground the B phase, then A to ground is 240 V, and C to ground is 240 V, and A to C is 240 V. You get 240 all the way around.


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## RePhase277 (Feb 5, 2008)

jwelectric said:


> This just don't sound right. A corner grounded systen on a farm?????????
> 
> Does this farm have livestock?


I don't see how that is an issue. I have read the IEEE report on this, well part of it anyway. I'm not convinced. I don't see how grounding a corner of the delta could be any different electrically than grounding any other part. Or grounding a 120/240 V center tap, or the star point of a wye. Stray currents occur after the distribution equipment due to faults, not due to what kind of ground is provided. I mean a stray current can travel through the earth from a wye connected system just as easily as it can from a CGD, the physics is no different.


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## jwelectric (Sep 28, 2008)

InPhase277 said:


> I don't see how that is an issue.


 240 volts pushes twice as hard as 120 volts. Should the phase fault that is grounded then we have earth as the return path. It would take a second fault for the overcurrent device to open would it not?


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## RePhase277 (Feb 5, 2008)

jwelectric said:


> 240 volts pushes twice as hard as 120 volts. Should the phase fault that is grounded then we have earth as the return path. It would take a second fault for the overcurrent device to open would it not?


If the phase that is grounded faults to earth, no current will flow, because it is already at ground potential. There is no overcurrent device in the grounded phase, exactly the same as a neutral. The only difference between a grounded phase and a grounded neutral is that the neutral is literally the neutral point in the system. A delta has no neutral point, but it can still be grounded just the same. The same physics applies.


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## Dude Man (Dec 15, 2008)

Went to two supply houses. One is Square D. so they didn't have much.

The other sells cuttler hammer. They say they don't make a CH 2 Pole 15 Amp 240Volt straight rated breaker. Where to find these?


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## jwelectric (Sep 28, 2008)

InPhase277 said:


> If the phase that is grounded faults to earth, no current will flow, because it is already at ground potential. There is no overcurrent device in the grounded phase, exactly the same as a neutral. The only difference between a grounded phase and a grounded neutral is that the neutral is literally the neutral point in the system. A delta has no neutral point, but it can still be grounded just the same. The same physics applies.


 
So does not these same physics say, A higher line-to-ground voltage exists on two phases than in aneutral-grounded system? 
 
Is this not more push of current for the dollar?


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## RePhase277 (Feb 5, 2008)

jwelectric said:


> So does not these same physics say, A higher line-to-ground voltage exists on two phases than in aneutral-grounded system?
> 
> Is this not more push of current for the dollar?


Yes, 240 pushes harder than 120. 277 to ground pushes yet harder. 347 harder still. My point is, since the physics is the same, how is a corner grounded delta less suited to farm use than any other system? What makes a grounded neutral system safer for use with livestock? I'm serious, I'm not trying to be a pain, but from what I know about electricity it shouldn't matter what conductor gets grounded.


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## nolabama (Oct 3, 2007)

now finding something for sale thats something i can help you with 
i dont know the specific style cb your looking for other than 15 amp 2 pole 240v 
http://www.baybreakers.com/catalog/search.html

shop till you find what you need 
i still say pull it out of the other panel


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## nap (Dec 26, 2007)

nolabama said:


> i still say pull it out of the other panel


if this is a typical farm, the motor is 12 miles from the panel (slight exagerration) and the higher voltage will allow for a lesser voltage drop due to the reduced current so they can use smaller wires= less cost.


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## nolabama (Oct 3, 2007)

op said it was plugged in with extension cord temp like - probably not further than 100 ft
but op has already ran condiut to corner grounded panel.....


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## Dude Man (Dec 15, 2008)

Yeah it is all piped in already to the corner grounded delta system.

Also the 120/240 panel is of course on the opposite side of the barn like 200' away. It is plugged into a extension cord... but I said this is a barn and old. The receptacle comes off the lights that feed half the barn not good either. And its ran on 14s. This place needs to get re wired badly. I will do this for now but I will be talking to him about getting in contact with the power company to put in a newer service 120/208. He could use a bunch more circuits anyway.

Thanks for all the replies guys.


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## jwelectric (Sep 28, 2008)

Dude

Are you saying that this system has both 240 and 120 volts?


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## Raverill (Aug 30, 2008)

*Grounding*

I think you have a grounding problem.
1.Check with your utility to verify the type of service to the barn. A corner-grounded delta service is extremely unlikely.
2. What is the source for the 120 volt panel? Is it really a 120/240 3 wire panel?
3. Do the two panels in the barn have a common source?
4. Is there a grounding electrode anywhere in the barn connected to any of the electrical panels, or at the source(s) of these two panels?

I'm betting that your electrical service is 120/240 single phase and that you have an open on the neutral conductor feeding the neutral bus in your motor panel. Or you could have a "floating neutral"; an ungrounded neutral. You should look into this first. 
If there is no grounding electrode system in the barn you should install one as per Art. 250. This is important for proper electrical functioning and personal safety.
Correct grounding issues and I'll bet your voltage will make sense.


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