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post #11 of 19 Old 05-31-2013 Thread Starter
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Re: Shore GFCI trips when plugging in boat

There are a lot of ideas here that I'll need to test over the weekend. Ebs001, the inverter automatically switches between pass-through of shore power and inverting depending on whether it senses shore power. The switch is effectively instantaneous so none of the electronics on the boat know anything is amiss -- it's great during a blackout. When shore power resumes, it verifies the stability for about 15 seconds before switching back to pass-through mode.

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post #12 of 19 Old 05-31-2013
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Re: Shore GFCI trips when plugging in boat

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There are a lot of ideas here that I'll need to test over the weekend. Ebs001, the inverter automatically switches between pass-through of shore power and inverting depending on whether it senses shore power. The switch is effectively instantaneous so none of the electronics on the boat know anything is amiss -- it's great during a blackout. When shore power resumes, it verifies the stability for about 15 seconds before switching back to pass-through mode.
That automatic switching may be your problem. GFCI specs indicate that they should trip in less than a nanosecond which may be enough to catch the auto switch. It's to bad you are not able to connect to that GFCI receptacle again because it's possible that you will get it to trip no matter what load you have on and it's not the charger at all.
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post #13 of 19 Old 05-31-2013
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Re: Shore GFCI trips when plugging in boat

Check your hot water tank. Even with the hot water turned of it would trip the shore GFI. Cleaned the contacts to the heating element and all was fine.

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Toronto in summer, Bahamas in winter.

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post #14 of 19 Old 06-01-2013
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Re: Shore GFCI trips when plugging in boat

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I do have an oscilloscope (and a logic analyzer, not that it's useful for this -- I'm an electrical engineer!). Are you suggesting that the absence of a voltage between ground and neutral will indicate a ground fault? I can't quite figure out what you're getting at. There is always a voltage present between those two lines any time a circuit is under load due to the resistance in the wires. Any other boats on my dock drawing power will result in me seeing that voltage even if I am not drawing anything. I suppose if those lines are shorted inside my boat, I might not see a voltage. Or do you mean when inverting only (no shore power)?
When the inverter/charger is OFF, and the boat is out of the water, the potential voltage difference between neutral and ground should be 0VAC, 0VDC. When it is on, the potential voltage should be ~110VAC and 0VDC. Again, assuming that the boat is out of the water.


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post #15 of 19 Old 06-02-2013
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Re: Shore GFCI trips when plugging in boat

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When the inverter/charger is OFF, and the boat is out of the water, the potential voltage difference between neutral and ground should be 0VAC, 0VDC. When it is on, the potential voltage should be ~110VAC and 0VDC. Again, assuming that the boat is out of the water.
If the boat is plugged in the potential voltage between neutral and ground should be 0 VAC as the neutral is the grounded conductor. This does not change whether or not the boat is in the water.
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post #16 of 19 Old 06-02-2013
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Re: Shore GFCI trips when plugging in boat

I'm allowing for galvanic current which may be a factor when the boat is in the water. The OP did say that this was only an issue when the boat was on the hard. The OP did not say if he had any form of ground isolation.


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post #17 of 19 Old 06-02-2013
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Re: Shore GFCI trips when plugging in boat

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I'm allowing for galvanic current which may be a factor when the boat is in the water. The OP did say that this was only an issue when the boat was on the hard. The OP did not say if he had any form of ground isolation.
Regardless, the potential between ground and neutral on the A/C side should always be zero. When plugged-in to shore power the neutral and ground must not be connected on the boat since they are connected at the source in this case the marina service but when he's connected to his inverter the neutral is grounded which is proper.

The O/Ps problem occurs with a GFCI receptacle. When he is on the hard he only had power available from a GFCI and while at the dock he is on power not protected by GFCI. Thus the ground fault only showed up when he tried to connect to a GFCI protected circuit. Without being connected to a GFCI protected circuit it will be difficult to solve the problem.
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post #18 of 19 Old 06-04-2013
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Re: Shore GFCI trips when plugging in boat

Based on this;
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My boat is on the hard right now for a bottom job. The yard provides power in the form of a standard household 15A outlet with GFCI. Whenever I plug my boat into it, either the GFCI trips or my main AC breaker trips.
I have assumed that this is a new problem which manifests itself only when on the hard.

I agree that the AC neutral and AC Ground should NOT be connected on the boat, and that AC Neutral should not be tied to the bonding circuit. This does not mean that it is true. If they are, it could explain the behavior.


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Re: Shore GFCI trips when plugging in boat

Thank you all for your input... I still haven't had a chance to do any real testing with your recommendations. I do not have any kind of ground isolation (which I assume would be the same as a galvanic isolator?). My AC and DC grounds are both tied to the engine block, and I believe the thru-hull bonding system is also tied to the engine block -- the zincs are on the prop shaft, at any rate, so I figure there must be an electrical connection there somewhere. Neutral is not connected to ground except inside the interver when it is actually inverting (supposedly).

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