Hello all,
I have a dock with electrical service, on a lake with several similar docks all around. Recently, after upgrading the AC wiring on a boat (which is plugged into shorepower at the dock), I was testing various aspects of the system with my multimeter. I was surprised to get a 0.2A reading at all times on the grounding conductor even with no power applied to the boat (dockside breaker off and inside shorepower breakers off, which cut both hot and neutral).
The boat wiring is appropriate to ABYC standards (DC bonding and AC safety ground are tied, AC safety ground is fitted with a galvanic isolator, there is no neutral to ground connection anywhere on the boat). Regardless, to completely isolate the boat itself as a source of the problem, I physically disconnected it from the shorepower source/ground and moved it away. I made a test rig of a piece of copper pipe with a low gauge wire and dropped it in the water on another part of the dock. When connected to the ground on the dock, I see the same current between the dock ground and my test electrode (0.2A registered on my clamp-on ammeter, and a very small <1V but measurable deflection on a sensitive AC voltmeter set to the 5V scale).
Next, concerned that there was an electrical issue on my property, I shut off service to the main panel, totally disabling the house and dock. The same current and voltage are still present from the water to the AC safety ground at the dock. I have no idea where the voltage is coming from and I am a bit unsure who to engage next if the source is apparently not my property (or at least not past the main breaker at the utility entrance).
I feel like ANY AC potential in water is a hazardous situation no matter how small, and I was hoping someone here could give me some pointers:
- Does this likely indicate a problem with the utility service/grounding at the street or a neighbor's property?
- In my mind the most likely cause would be a fault at a neighbor's property which creates a small leakage current back to my ground through the water. If that is the case, would it have to be a neighbor served by the same transformer at the street (physically sharing a circuit)? How would an expert likely diagnose the source?
- Is it likely the small voltage is not caused by a fault at all but is capacitively or magnetically induced in the long ground wire from some other source? I don't know how, when all power is shut off to the house (although the neutral and ground are still connected)?
I'm trying to figure out if my next call should be the utility company, an electrician, my neighbors, or all three. While I may not be creating the leakage current, since I observed it I now have an obligation to figure out the source if it is potentially hazardous to swimmers.
Thank you for any input.
I have a dock with electrical service, on a lake with several similar docks all around. Recently, after upgrading the AC wiring on a boat (which is plugged into shorepower at the dock), I was testing various aspects of the system with my multimeter. I was surprised to get a 0.2A reading at all times on the grounding conductor even with no power applied to the boat (dockside breaker off and inside shorepower breakers off, which cut both hot and neutral).
The boat wiring is appropriate to ABYC standards (DC bonding and AC safety ground are tied, AC safety ground is fitted with a galvanic isolator, there is no neutral to ground connection anywhere on the boat). Regardless, to completely isolate the boat itself as a source of the problem, I physically disconnected it from the shorepower source/ground and moved it away. I made a test rig of a piece of copper pipe with a low gauge wire and dropped it in the water on another part of the dock. When connected to the ground on the dock, I see the same current between the dock ground and my test electrode (0.2A registered on my clamp-on ammeter, and a very small <1V but measurable deflection on a sensitive AC voltmeter set to the 5V scale).
Next, concerned that there was an electrical issue on my property, I shut off service to the main panel, totally disabling the house and dock. The same current and voltage are still present from the water to the AC safety ground at the dock. I have no idea where the voltage is coming from and I am a bit unsure who to engage next if the source is apparently not my property (or at least not past the main breaker at the utility entrance).
I feel like ANY AC potential in water is a hazardous situation no matter how small, and I was hoping someone here could give me some pointers:
- Does this likely indicate a problem with the utility service/grounding at the street or a neighbor's property?
- In my mind the most likely cause would be a fault at a neighbor's property which creates a small leakage current back to my ground through the water. If that is the case, would it have to be a neighbor served by the same transformer at the street (physically sharing a circuit)? How would an expert likely diagnose the source?
- Is it likely the small voltage is not caused by a fault at all but is capacitively or magnetically induced in the long ground wire from some other source? I don't know how, when all power is shut off to the house (although the neutral and ground are still connected)?
I'm trying to figure out if my next call should be the utility company, an electrician, my neighbors, or all three. While I may not be creating the leakage current, since I observed it I now have an obligation to figure out the source if it is potentially hazardous to swimmers.
Thank you for any input.
