Dude Man

Hi all, I am new to this forum so HI.

After that being said, I am a young electrician from South East Wisconsin. Completed my 5 year apprenticeship and have 2 years under my belt as a journeyman primarily doing commercial/industrial.

Here is my problem. On my future father-in-law's farm he got a new conveyor and wants it hooked up. OK. Look at the nearest panel that controls all the motors and inside is all 2 pole breakers. I think OK, this is easy. Go to the supply house get a 2 pole breaker and a 1 horse motor starter.

Yesterday I go to install. Pipe everything in using PVC and then I change to Seal Tite after my 2 pole disconnect switch near the motor. Pull the wire and get to the panel... scratch my head.. no ground bar seems weird being a sub panel. Being a farm you pop of the panel cover and holey smokes there is so much wire in there, I never noticed at first. Put my Fluke meter on, 240 between a-b (or what I think is ab) and then I go a-n 240 b-n 240. WTF!! Never seen this before... so I go home come on line and came to the conclusion it is a corner grounded delta after a bunch of researching.

So I think I need a little help understanding this system if anyone could help me. I understand how it works I think. But my question is can you use a single phase motor on this system just like on any other 3 phase system.

Can I put in a 2 pole breaker rated for 240V and feed a manual single phase motor starter and then go to a single phase motor and hook it up for high voltage 230V. 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.

This comes in off the pole in the yard to a fused disconnect. Black and Red are fused. The white goes to a neutral bar that is going to a grounding electrode I believe, may have to take a second look at that. Then its a service entrance cable black/red with the uninsulated grounded conductor wrapped around it under the outer sheath. This travels down and goes to the neutral bar in the panel and the black and red go to a main lug. All 2 pole breakers. All the starters are 3 phase with the two hots and the neutral being used feed 3 phase motors.

Oh yeah, I went back to the farm today and told him what I found out and then informed that the single phase motor he has might not work. Then he told me that that was just temporary to get the thing running. Has it plugged into a extension cord for now 120v feed from a different panel.

I could use this panel but it would be nice to keep all the motors out of one panel and the starters grouped together. Also the other panel is getting pretty full and I need to add some lights and receptacles.

I know I need help on this. I plan on asking some older electricians at work cause all the younger guys have never heard of it or seen it that I called. However any suggestions or thoughts/direction would be great.

Thanks
ps sorry for the length on this.

nolabama

i cant help ya

BryanMD

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."

Attached Images

cornerG-Delta.jpg (7.3 KB, 301 views)

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waco

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.

InPhase277

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.

nolabama

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

nolabama

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

Dude Man

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.

InPhase277

Nope.

Yep.

You got it

micromind

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.

waco

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?

jwelectric

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

Does this farm have livestock?

InPhase277

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.

waco

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.

frenchelectrican

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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InPhase277

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.

InPhase277

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.

jwelectric

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?

InPhase277

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.

Dude Man

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?