ungrounded service

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Dean Vermont

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Forgive me for not having every detail. I hope I have enough to share.

I recently toured a farm that put in a co-generation plant to feed back onto the power companies grid.

When looking at the main power panel that supplied the 480 volt 3 phase power, I noticed that there was no neutral brought to this main panel. I asked the electrician, "why"? He said that the power company was going to give them a closed delta system (no neutral). To run the equipment they didn't need a neutral(all three phase motors).

The electricians installed a step down transformer off two legs of the main to supply lighting and receptacle loads. They also installed 10 ground rods outside in a large loop. I believe the power company did not want to supply this customer with a neutral because they were afraid of stray voltage coming from their lines and affecting the cows? That is only my opinion, because I don't have that great an understanding of the distibution of power as far as the power company is concerned. My concern is that if there were a fault to ground,that the earth would be the path back to the source and that is not good.


I have not yet talked with anyone from the power company, but I would like to. It also appears that there is some voltage flowing on the center tap of this generator that supplies power back to the utility. Probably because the three phases are somewhat unbalanced. This voltage is tied to this ground grid of rods. Since they turned this generator on the cows have been acting a little "funny".

I am interestd to here thoughts on this. Thank you.
 
Re: ungrounded service

Dean,

I suspect that the delta is grounded at the pole. The neutral and EGC of the low voltage service is grounded with the rods. A fault to neutral or EGC would not cause significant current in the earth.

Question for Charlie the poco man: With a corner grounded delta, can you bring an EGC to that corner ground? If so, a fault to the EGC would produce no earth currents.

As for cows, they are goofy anyway. They are probably reacting to the noise of the generator. I doubt that it has anything to do with ground currents, electromagnetic fields, or anything else. Some cows are paranoid. Anything new or different will cause them to go berserk.
 
Re: ungrounded service

With a corner grounded delta, can you bring an EGC to that corner ground?
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If the customer has taken a corner grounded service or you have grounded a corner of the delta in the service equipment, the EGC is required to be brought to that point.
 
Re: ungrounded service

More questions for Charlie:

Could the corner ground be connected to the neutral of the 120/240 service?

Is delta service ever provided without a ground of some sort?
 
Re: ungrounded service

Could the corner ground be connected to the neutral of the 120/240 service?
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Let me see if I understand what your asking.

The delta corner ground is grounded to earth.

The neutral of the single phase service is supposed to be grouded to earth.

So the two grounds are connected via the earth.

The question is can you connect those two grounding points with a conductor?
 
Re: ungrounded service

If you have a corner grounded system, you can't have a 124/240 volt system and meet the Code requirements of 250.20(B). Also, if I am reading your question correctly, it will blow up.

An ungrounded delta system is fairly common but not for a farmstead. :D
 
Re: ungrounded service

I am confused here... so I will ask a question.

From the original post on this thread, we are talking about a 480 volt corner grounded delta. Now, let's say we install a xfmr that is 480 delta primary to 240/120 high leg delta. Any problem with the grounding? The grounded phase of the 480 will be connected via MBJ to equipment grounds and GECs to SBJ to the neutral of the 240/120 and I don't see a problem with that.

Am I missing something?

On the other hand, if the service is 240/120 high leg delta which is required to have the neutral grounded, and then we also try to ground the corner, yep, it blow up big time!
 
Re: ungrounded service

I'm not sure if it is a corner grounded delta or not? I didn't look at the connections at the pole, just listened to what others were telling me. There is only three conductors coming from the pole to the service though.

As for the transformer, it is a single phase transformer fed 480 volt with 120/240 volt single phase, XO bonded to building steel and ground rods.
 
Re: ungrounded service

I was inquiring about the farmstead with the second xfrmr which provided 120/240 with the CT tied to earth ground. Obviously you could not ground two points in the secondary or primary of any xfrmr.
 
Re: ungrounded service

This system is actually seperate from the barn service. This is a seperate building located about 300 yards from the barn that houses the cows and milking parlor. The buildings do have a plastic water line that brings hot water down to the milking parlor. Hope that answers your question?
 
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