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Subject - ungrounded service
unknowingsap 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.
lctrc789 Usually they do not install a Delta system with out a nuetral for that reason alone, because some where they may need a neutral for another service.
If I am thinking right here by article 547-8(a) you cannot have a agricultural service with out a grounded service. Again the local power company engineer should be able to come and out and see what type of service they have and if it requires a grounded conductor.
Livestock requires a special grounding with all insulated ground wires as well as the buildings have to be grounded etc... They can feel way better then we can when it comes to current in the ground.
I really suggest you get an enginner out there to see what can be done, 10 ground rods is Ok, if you need them, but this doesn't sound right to me as far as the grounding for livestock and buildings by the code.
Good luck and keep us posted I am curious to see what they say.
JimmyDee Pat, I know we have been through this before but I have to ask you a question. On the 480 volt 3 phase delta system, What would the power company attach the neutral if they were to run one. These systems are totally an ungrounded system and by nature have no grounded conductor as part of the system.
If this were a 480 volt Y system, then you would definatally have added a neutral on the center tap of the system.
Jim
JimmyDee
quote:
He said that the power company was going to give them a closed delta system (no neutral).

This is not the definition of a closed delta system. It is a true statement that in a 480 volt delta system, you would not have a neutral on a closed delta but you also would not have one on an open delta system.
The difference between a closed and open delta system is the number of transformers, not whether of not it has a neutral. A closed delta is configured with 3 transformers and an open delta is configured with 2 transformers. When configuring an open delta you only get 57% -58% of the capacity than if you used 3 transformers.
I have had customers loose a huge transformer that was part of there main service at a plant and cause a complete shutdown of that plant. We have gone in and rewired the 2 existing good transformers in an open delta system so they could continue running at a reduced rate.
When you have to wait 2-6 weeks for a replacement transformer for your substation, you can reconnect at a reduced rate and that is usually the reason for using the open delta system.
At times for smaller 3 phase loads, it is more cost effective for the power company or the customer to go to the open delta system. This configuration does not allow for you to have the handy backup transformer on site that can be rewired in a few hours to have you back in service.
HERE is a good page that shows these hookup.
Jim
lctrc789 Jimmy, I do know here we have the two transformer delta systems in use and since I have done electrical work and the two major power comapnies here require a neutral for every service regardless.
We have installed delta systems in industrial jobs we finished on last year 13,200 trans. delta to 480 delta for the building with no neutral, the stipulation was this, we had to install delta to wye transformers inside for lighting, and equipment use.
Only two large motors in this building was deltas, and the rest used wyes.
The power company does have some strict guidelines in areas, and especially for livestock, I live in the country and livestock is a large part of our jobs in the farm and residential side.
I do know different areas have different stipulations, the east coast have two phase power systems which is a no no here.
We still have the old haystack configurations in the old rural areas where the secondary line is higher then the primary line, these are very very dangerous and the power company will not allow you to even touch the secondary lines at all without them being present, even in residential applications.
jagerbombme About using the earth as path back if a fault occured. Neutral or not, it would still be a emergency path back. Same as it should be in your back yard for your resi service. the ground rod and/or your main water supply would feed current into the earth back to the pole or w/e. But I believe most of the electricity flowing into the earth in a fault situation is just dissipated into the earth, hence the spacing of the ground rods certian distance apart lets the electricity dispersed in each rod disperse. er......... hehehe hope that sounds right. don't know much more than that to help you, but there shouldn't be any current on the ground anyway i believe unless something smokes.