Stray current dangers

Stray Current

I think some of this discussion would have sounded different if all of you would have take the time to view the video. After viewing the video one of the first things I did is walk down my dock and check shore power cords with my clamp style VDO as described in the video. Just as I suspected the house boat next to me was leaking 1.7 amps from each of it's shore power cords. That's 340 mil amps enough to kill in fresh water. The saving grace is this is a 50' steel house boat and the length and shape of it's hull radiates the current in a safer way than as if it was originating from a small metal part like a prop or zinc. I still would not touch the steel hull and the grounded metal dock. Also the alga and silt in our water may make it a better conductor out of the water as well. Because our bodies have approximately the same salt content sea water sea water electrocution is not a danger from stray current. Take the time to view the video all the way through it covers the danger of stray current thoroughly. My house boat neighbor who lives full time on his boat doesn't believe he has a problem because his grand-kids swim around the boat all the time. I'm going to make up a device to measure voltage in the water. Surprising of the 30 boats I checked only two showed stray current. The other next to the house boat was leaking 70 milamps from each shore cord. The other boats checked may have not had any ac current in use so the readings may not mean anything. My own boat which is a ac power hog"50amp 240v" uses isolating transformers and showed no leakage. The video highly recommended the use of isolating transformers.

Scary said:

I think some of this discussion would have sounded different if all of you would have take the time to view the video.

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Scary, My corrosion worksheet says that if there are two cords you clamp them together to check for stray current. If you clamp them separately you take the difference. In the case you mention the difference may be zero which would mean no stray current.

The metal boat can be a hazard on another basis also. If the hull, DC negative and AC green ground are not connected then it becomes a hazard. The AC system needs to have a way to tell stray current reaches the hull and can do so if it is connected to the AC green ground. If a wire chaffs or equipment has an internal short that finds its way to the hull the breaker will trip (if it is a serious enough fault). Therefore, even though the metal boat may have no fault current today in the absence of proper grounding it could change with the next problem. Another way to think of this is to view the boat hull as the frame of an appliance. To protect users appliance frames and boat hulls should be grounded.

This guy: Quality Marine Services, LLC is out in front of this and has a good number of articles on the subject.

You are right to be concerned. With a little more information you may be able to help the guy be certain he doesn't run into trouble down the road...

the video say's to add the amperage together

bglad said:

Scary, My corrosion worksheet says that if there are two cords you clamp them together to check for stray current. If you clamp them separately you take the difference. In the case you mention the difference may be zero which would mean no stray current.

The metal boat can be a hazard on another basis also. If the hull, DC negative and AC green ground are not connected then it becomes a hazard. The AC system needs to have a way to tell stray current reaches the hull and can do so if it is connected to the AC green ground. If a wire chaffs or equipment has an internal short that finds its way to the hull the breaker will trip (if it is a serious enough fault). Therefore, even though the metal boat may have no fault current today in the absence of proper grounding it could change with the next problem. Another way to think of this is to view the boat hull as the frame of an appliance. To protect users appliance frames and boat hulls should be grounded.

This guy: Quality Marine Services, LLC is out in front of this and has a good number of articles on the subject.

You are right to be concerned. With a little more information you may be able to help the guy be certain he doesn't run into trouble down the road...

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I may have misunderstood the video I'll look at it again. I thought it said to add them together. I seriously doubt his hulls are bonded to his shore power green. The professional house electrician that wired his boat may have bonded the neutral and green ground like you would do at the service of a home. I don't know how to approach him to check as he seems very defensive. He built his house boat and did a very nice job on the interior as he is a professional cabinet builder. The inside is gorgeous, but he's a trial and error guy and the engineering side of things are hit or miss. He had to add a larger outer hulls to float it as the original pontoons didn't have enough floatation, fuel, water, and holding capacities are meager and its underpowered and hard to handle. It works nicely as a dock queen and they live full time aboard. As for now I don't seem to be having any trouble with zincs and nobody is dead. I just won't be swimming near his boat.

I just reviewed the video and you are correct

Scary said:

I may have misunderstood the video I'll look at it again. I thought it said to add them together. I seriously doubt his hulls are bonded to his shore power green. The professional house electrician that wired his boat may have bonded the neutral and green ground like you would do at the service of a home. I don't know how to approach him to check as he seems very defensive. He built his house boat and did a very nice job on the interior as he is a professional cabinet builder. The inside is gorgeous, but he's a trial and error guy and the engineering side of things are hit or miss. He had to add a larger outer hulls to float it as the original pontoons didn't have enough floatation, fuel, water, and holding capacities are meager and its underpowered and hard to handle. It works nicely as a dock queen and they live full time aboard. As for now I don't seem to be having any trouble with zincs and nobody is dead. I just won't be swimming near his boat.

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Apparently you do subtract the to amperage reading when measuring two shore power cords independently. According to the video this shows a shared neutral which would make sense given he is using a house style electrical panel. Thanks for pointing that out. This makes me feel a little better about being in the water near his boat.

Scary said:

............. I don't know how to approach him to check as he seems very defensive.............

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That's understandable. I think we all are to some extent. Just read postings in this forum and you'll see evidence of people being "defensive".

Just imagine your reaction if a slip neighbor came up to you and said "Hey buddy, I think your boat is wired wrong and I want to inspect it and tell you how it should be wired".

It's probably best to let it go unless it's actually damaging your boat or shocking you. Even if it is, it might be easier to move to a slip further away.

If nothing else maybe you can pass along the link and let him do some reading on his own. I have had some spirited discussions with very knowledgeable folks who needed gentle persistent prodding to wrap their head around the topic. It is not an issue one wants to experience to gain understanding when others have already paid the price:/

It would be in his, your and the marina's interest if any electrical problem was resolved. Maybe a discussion with the marina management would help bring it to a peaceful resolution.

Since he seems to have a combined neutral for both shore power cords and that doesn't create a shock hazard for swimmers I think I'm just going to drop it and not worry about it.