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Thread: Isolation transformer for residential dock power

  1. #1
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    Isolation transformer for residential dock power

    For a freshwater residential dock with convenience receptacles, lights, and boat lift: Is it possible to connect an isolation transformer (such as Charles Marine ISO-G2) to conform to NEC bonding requirements AND to have a true isolated grounding conductor? Issue is stray voltage on the existing grounding conductor that causes a mild “tingle” to swimmers when exiting the water.
    Recommendation to use the isolation transformer comes from the utility.

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    Correct the wiring that is energizing the water, before someone is electrocuted!!!

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    There will be a connection to the primary grounding system via the primary EGC. That will be connected to the secondary grounded conductor and EGC in an installation that complies withe the NEC rules.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

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    As mentioned you need to find the source of this stray voltage and correct the problem. Try turning off all the power at the source and see if there is still current flow on your ground conductors---as a start.
    May the force be with you

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    Quote Originally Posted by don_resqcapt19 View Post
    There will be a connection to the primary grounding system via the primary EGC. That will be connected to the secondary grounded conductor and EGC in an installation that complies withe the NEC rules.
    Exactly, and this negates the establishment of a new isolated GEC and does not eliminate the issue.

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    Quote Originally Posted by ghostbuster View Post
    As mentioned you need to find the source of this stray voltage and correct the problem. Try turning off all the power at the source and see if there is still current flow on your ground conductors---as a start.
    That has been done. Utility admits the problem is on their end and recommends the isolation transformer as a solution.

  7. #7
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    Quote Originally Posted by normel View Post
    That has been done. Utility admits the problem is on their end and recommends the isolation transformer as a solution.
    Kick that issue up to the state authority that regulates the utility.

    Assuming that the elevated voltage is from their primary neutral, you might be able to get them to install a neutral blocking device between the primary and secondary neutral at the transformer that serves the dock, and not have any grounding electrode at the transformer that connects to the primary neutral.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

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    Quote Originally Posted by normel View Post
    For a freshwater residential dock with convenience receptacles, lights, and boat lift: Is it possible to connect an isolation transformer (such as Charles Marine ISO-G2) to conform to NEC bonding requirements AND to have a true isolated grounding conductor? Issue is stray voltage on the existing grounding conductor that causes a mild “tingle” to swimmers when exiting the water.
    Recommendation to use the isolation transformer comes from the utility.
    Looking at this, I would be hesitant to install this per their instructions. They are showing connecting the neutral and ground together on the feed side of the isolation transformer. That is a no-no to the NEC.

    It also says it is designed to be installed in the engine room, I was under the impression you were installing it on shore.

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    I had a similar situation once, and the source of the voltage to water was coming in on the PoCo neutral conductor (U/G service). Turning off the main breaker did not reduce the voltage (1.2-volts). The only way we got rid of it was to lift the incoming neutral.

    PoCo said we had a grounding problem.

    It went to the homeowner's board for discussion and I never heard about it again.

    One thought was to drive ground rods down near the waterway and make it part of the grounding system. While that should mask the symptom, are we just transferring the problem out into the water? That makes me nervous.

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    It would appear this lake water maybe energized from another nearby electrical source and the utility neutral return current is using this ground system to "get back" to the utility primary neutral/ground side.

    This is an extremely dangerous situation and can get much worse really fast.

    A similar situation has already been fully documented on this website.
    May the force be with you

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