200A neutral return grounded twice

Discussion in 'General Electronics Chat' started by tombrooks1111, Mar 12, 2013.

  1. tombrooks1111

    Thread Starter New Member

    Mar 12, 2013
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    Background of my Problem: 200Amp service comes from power company from their xformer via 2 hot wires (120VAC 180 degrees out of phase) and a 3rd neutral wire (from their center tapped xformer) which they grounded at the pole. There is a single 200A breaker switch under the meter at the pole which is 10 feet away from my house. I wired 3) 4/0 AL cables from this 200A breaker switch on the pole a distance of about 90 feet under ground in conduit to my main 200A CB panel in my garage. I treated my Garage Panel as a main household CB panel and Not as a Sub Panel. This means I have the neutral and earth ground tied together in my panel and I added an earth ground cable to an 8 foot copper electrode into the yard nearby (as an aside, all my plumbing in the house is plastic PEX).
    Now we are getting closer to my question. All unbalanced currents in my Main CB panel are expecting to return 100% back to the pole 90 feet away, where the power company installed their 8 foot electrode into the ground (why ?, because current has a tendency to return to its source, is the answer I have so far found). Lets say there is 20A of unbalanced current at some given point in time. This 20A of current reaches the point in my Main Panel where the neutral and earth ground are connected. This current has a choice of going 90 feet back to the ground at the pole via the neutral cable like it is supposed to, or some of it can choose my earth ground that is about 15 feet from the panel. (When I get back to this house in Missouri (2 months from now) I am going to put an ammeter clamp around my cable to earth ground and verify once and for all if any current does flow thru it or not and I will post the results on this site.)
    So here is my question. My conduit is under my driveway now and there is no way for me to add a 4th wire per code. Can anyone explain to me how my house is now in danger of electrical fire, or people can get electrical shocks or my TV and computers are at risk for surges etc. because of what I have erroneously done? Or can I sleep peacefully at night and forget about it? (There have been no problems so far for 2 years of continuous usage.) By the way, there are no electrical inspectors in this remote part of Missouri. 2 power company electricians were at my site giving me advice when I only connected 3 wires instead of 4.
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Disclaimer: while I am a degreed electrical engineer and have read much of "The Code" (NEC, or National Electrical Code) wiring is still my hobby. Use my opinion with caution.

    "Ground" and "neutral" should be connected (bonded is the term) at one and only one place to keep normal operation current (ie, not from any fault condition) from flowing thru two paths , one path thru neutral and another path thru ground.

    If I understand your description it sounds like you left out the ground from the pole, and made an 2nd ground inside your house. So the dual path would be literally thru the ground (and I do mean dirt) between your Main Panel and that pole 90 feet away.

    Do you get a tingling sensation while walking barefoot outside on a rainy day? That is where the problem (if it exists at all) would be.

    If you still have any concerns you might raise the suggestion with the power company electricians the possibility of removing the earth ground at their pole: you will then have one and only one truly good ground in your panel and that should be sufficient.

    Is it possible to make a sketch of your circuit? Every picture DOES tell a story and words only paint a partial picture.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Where is the electric meter connected in this setup?

    The biggest danger I would see is ground swell from a nearby lightning strike. The "Ground" over 90 feet could change by a few thousand volts, which would be a not good thing. Whether your ground stake is nearer to the actual strike or the utility ground is, there will be a difference.

    I'd suggest calling your electric company and asking them. Who originally installed your meter/house wiring, and performed the safety inspection? When was that done?
     
  4. #12

    Expert

    Nov 30, 2010
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    This is my interpretation of the verbiage in the first post. Correct if necessary.
     
  5. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    I can second what the others have said and add that you should NEVER trust the utility ground to provide the ground for your house. Having a utility ground at the service 3 wire drop transformer pole is pretty common (it's not a requirement, but most will one at the end of a long run).
    http://ecmweb.com/nec/top-50-nec-rules-1
    http://ecmweb.com/qampa/code-quandaries-august-2010
    What's of primary importance is make sure your house ground system is working correctly and to have whole-house surge protection at the utility meter (or at the main panel if a outside connection is not possible) with a direct and short connection to the grounding rod.
     
    Last edited: Mar 12, 2013
  6. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Is your panel wired as per #12 drawing in post 4?
    If not, tell us what is different.
    The service for my school (2,000 amp, 120/208Y 3ø) is located right outside my classroom door. Every couple of months the local utility company sends someone around to check the current going through the ground wire that is coming down the pole. They use a clamp on amp meter.
    I asked the tech what the reading was, and he said" nothing really, as it should be".
     
  7. tombrooks1111

    Thread Starter New Member

    Mar 12, 2013
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    Yes, Post 4 picture describes the situation. Thank you everyone for responding. The one comment about tingly feet on a rainy day: I will have to walk barefoot on a rainy day and find out (but hopefully I will not feel anything since the conduit runs under the concrete driveway 90% of the distance - and most of the dirt between my ground and their ground is all under the concrete driveway).
    The comment about a 1000V lightning strike near the ground at the pole is quite possible as we have very severe thunderstorms sometimes 2 or 3 times every week during the spring and summer and my property has been struck twice in the last 6 years. If their ground is at 1000V and mine is at 0v, there would be a lot of current traveling thru that 75 foot neutral return. I use good surge protectors for my electronic devices in the house. I would like to get an affordable house wide surge protector that actually works but dont know if there is such an affordable device (under $250).
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Actually, that would be several thousand volts across all of your outlets, due to neutral and ground tied together. :eek:

    This is one of the major reasons for having either a point ground, or a large radial mesh ground (such as radio towers use).

    I'd suggest contacting your electric company to determine the solution to the issue. You can get "whole house" surge suppressors that install at the panel which would "crowbar" that fault back to the electric company transformer and ground, but that's about it.
     
  9. tombrooks1111

    Thread Starter New Member

    Mar 12, 2013
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    It sounds like the safest thing to do is merely disconnect the cross bar in my Main and only let my earth ground be for the earth ground of all my receptacles in my house and do Not let the neutral go to my ground. Are there problems with this?
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    That can create some issues as well, due to the length of the utility ground line.

    It would be best to contact your utility for their input on this. There could be a factor we are unaware of.
     
  11. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    Don't do that. Your current wiring is safe for 99% of the most common electrical faults. If there is a near strike it's possible for a ground loop to develop between the two ground rods that might induce a spike into the house wiring but the solution to that is to have a much better ground at the house than at the pole with good shunt protection for the power wires to that ground.
     
    Last edited: Mar 14, 2013
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  12. Duane P Wetick

    Active Member

    Apr 23, 2009
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    Ground Loops can be a problem and also an electrical shock hazard. The resistivity of ground can be influenced by minerals, type of soil and water tables. The best ground systems that I have encountered are of the Star type, where a copper alloy rod is driven at least 2 meters into the ground
    and all ground wiring starts from this point. Sometimes mutiple ground rods are used in close proximity to each other and all tie to the central star rod.
    Tinned copper braid is used because of its low inductance figure.
    Also, clean the connections to the Star rod periodically. The idea is to make the ground path as low in resistance as possible.

    Cheers, DPW [Everything has limitations, and I hate limitations.]
     
  13. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    In my area, they have two neighboring houses fed by one pole pig(transformer). The houses are less than the 90Ft in this instance. Wouldn't this be the same thing? Just use a ground rod at each service entrance?
     
  14. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    As long as the ground rod wiring (bonding) is external to the house and there in only one ground wire to the main panel inside the house from the service entrance ground rod you should have pretty good protection from most types of lightning induced surge problems.

    The voltage drop between the utility rod and the house rod with a 100 foot or less drop using normal sized neutral wiring (1/0Cu or 2/0Al for 200A service) should be less than a volt so there no shock hazard if the connections are solid.
     
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