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Thread: Mobile home service (utility supplied)

  1. #1
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    Mobile home service (utility supplied)

    Hello everyone. I recently went to a mobile home/RV park where the utility supplies their own 200 amp mobile home services/meter combos. The utility installs these combo units to the pole and blanks out the meter bases until we get in and install the RV 50 amp receptacles and service grounding, then call for inspection. The utility does not provide grounding themselves. So, while I was installing the wiring to one of the units, my sweaty arm touched the side of the enclosure and I felt a nice jolt. I was working on the load side of an opened 200 amp breaker so it wasn't that I connected a conductor incorrectly. I continued connecting the unit (with gloves) and when I was finish, I drove two ground rods. The first ground rod went in with no issue connecting the grounding conductor but when I tried to connect the grounding to the second ground rod, there was a visible arc. I then became reassured there was voltage on the grounding system. I pulled out my meter and there was 78 volts on the ground rod ( which is terminated at the source neutral bar in the service enclosure). So, am I correct to assume there is stray voltage on the neutral, from the utility line? What could (likely) cause this? Thanks
    Chris Hill, EE,ME,GA-CR
    Power Factor Correction

  2. #2
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    If your ground rod is terminated to the neutral bar, to what are you measuring 78 volts?
    I will have achieved my life's goal if I die with a smile on my face.

  3. #3
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    I'm more than a little perplexed, maybe worried, that someone whose signature line includes EE: electrical engineer, and ME: mechanical engineer (two engineering degrees) is installing mobile home service grounds and can't find an open neutral or stray power...really?

    As in the previous reply, which two points are you using to measure this difference of potential?
    Kirchoff and Ohm...the only laws that make sense

  4. #4
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    Quote Originally Posted by cuba_pete View Post
    I'm more than a little perplexed, maybe worried, that someone whose signature line includes EE: electrical engineer, and ME: mechanical engineer (two engineering degrees) is installing mobile home service grounds and can't find an open neutral or stray power...really?

    As in the previous reply, which two points are you using to measure this difference of potential?
    First of all.....Mr. Pete. that refers to my licensing numbers in the state of KY One refers to electrical license and the other refers to masters license. I "am" an Electrical Engineer but that's not what it's referring to and it is not that I can't find it, I'm not allowed to even work on the pole because again...its utility supplied. My question was not how to find it, nor is it as perplexing as you would like to make it. I asked a simple question, if you don't want to provide a helpful answer, keep to yourself please. The question was simply looking for a sanity check since I am unable to dig any further. Perhaps someone has seen this with utilities or mobile home parks (was where I was going with this). To answer your question, I measured, using a Fluke with a low impedance adapter, that provided a low impedance load to the rods, desensitizing the meter to low energy so we could get an accurate reading. Since the measurement points were energized with a “hard” voltage, the meter simply displayed the voltage reading. Measurements were taken between the ground to the ground rod (10 -20 feet away). We split the grounding from the utility neutral as well and measured the potential difference there. We also measured 2 other ways to come up with virtually the same readings.
    Chris Hill, EE,ME,GA-CR
    Power Factor Correction

  5. #5
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    Quote Originally Posted by aelectricalman View Post
    ... I measured, using a Fluke with a low impedance adapter, that provided a low impedance load to the rods, desensitizing the meter to low energy so we could get an accurate reading. Since the measurement points were energized with a “hard” voltage, the meter simply displayed the voltage reading. Measurements were taken between the ground to the ground rod (10 -20 feet away). We split the grounding from the utility neutral as well and measured the potential difference there. We also measured 2 other ways to come up with virtually the same readings.
    If you lifted grounding from the utility supply, you may have 'floated' the transformer secondary... depending on how the POCO wired it. They usually do not rely on service grounding to ground their transformers. A comprehensive troubleshooting scheme should reveal the problem. What you are providing us with is just enough to indicate you or the POCO have a problem. It's far from enough for us to tell you what the problem is.
    I will have achieved my life's goal if I die with a smile on my face.

  6. #6
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    Is possible someone got grounded and ungrounded conductors switched around in the meter combo or somewhere between it and the source and the entire frame of that is energized.

    Take readings at that equipment, if one of the ungrounded conductors appears to be at ground potential this is likely what has happened.

  7. #7
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    Quote Originally Posted by aelectricalman View Post
    First of all.....Mr. Pete. that refers to my licensing numbers in the state of KY One refers to electrical license and the other refers to masters license. I "am" an Electrical Engineer but that's not what it's referring to and it is not that I can't find it, I'm not allowed to even work on the pole because again...its utility supplied. My question was not how to find it, nor is it as perplexing as you would like to make it. I asked a simple question, if you don't want to provide a helpful answer, keep to yourself please. The question was simply looking for a sanity check since I am unable to dig any further. Perhaps someone has seen this with utilities or mobile home parks (was where I was going with this). To answer your question, I measured, using a Fluke with a low impedance adapter, that provided a low impedance load to the rods, desensitizing the meter to low energy so we could get an accurate reading. Since the measurement points were energized with a “hard” voltage, the meter simply displayed the voltage reading. Measurements were taken between the ground to the ground rod (10 -20 feet away). We split the grounding from the utility neutral as well and measured the potential difference there. We also measured 2 other ways to come up with virtually the same readings.
    Yeah, well...based on the criteria for this forum I just thought I would ask.

    It seemed entirely odd that you would drive a ground rod in an apparent attempt to bond an energized enclosure with the hopes of...what?

    Good luck with that.
    Kirchoff and Ohm...the only laws that make sense

  8. #8
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    Quote Originally Posted by cuba_pete View Post
    Yeah, well...based on the criteria for this forum I just thought I would ask.

    It seemed entirely odd that you would drive a ground rod in an apparent attempt to bond an energized enclosure with the hopes of...what?

    Good luck with that.
    I think he was driving ground rods because he needed them to meet code, not because he was trying to mitigate stray voltage.

    I myself would have likely been trying to figure out why I got shocked touching the enclosure before doing much else work though. If no load is connected to it yet (which seemed to be the case) it about has to be a POCO problem though.

  9. #9
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    Quote Originally Posted by cuba_pete View Post
    Yeah, well...based on the criteria for this forum I just thought I would ask.
    Good luck with that.
    Does being snarky along with contentious hostile, inconsiderate comment, the primary principle that describe the order of business of this forum?

    Or you just need to hone your communication skill. Don't forget that we are not third graders or predators just waiting to devour someone who slips and falls into their feeding frenzy.
    That, or you are in the wrong place.

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