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Old 08-12-2021, 06:08 AM   #1
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120 240 wiring.

The current issue of (PBB ) Pro Boat Builder has a good easy to understand article on correct dock wiring and bringing the power on board.

As some cruisers are having hassles with GFI in different marinas this might be a good current source of info.

PBB can be had by subscription.Paper, electric or both.

No connection with company , just delighted subscriber.
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Old 08-12-2021, 06:35 AM   #2
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To add on about the GFI troubles, almost every time I've seen GFI issues with a properly wired boat, it's been water getting somewhere it shouldn't (in a connector, or into a power pedestal). And I've seen a few faulty GFI breakers as well that just trip randomly, even with nothing connected to the breaker output.
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Old 08-12-2021, 06:41 AM   #3
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If anyone is having "hassles" with GFI in different marinas, they need to have their boat's wiring checked by a competent marine electrician. They don't need to understand dock wiring, that is for electricians.

A GFCI circuit measures the current on both the hot and neutral wires and if it's not the same, the circuit trips the breaker. The reason is, if the current returning from the boat isn't the same as the current entering the boat, the difference is going somewhere it shouldn't be going (like through your body to ground).

As a practical matter, many times, on an old boat, some duffus connected the neutral and grounding conductor together at some point. This is improper, a violation of the electrical code, and the cause of the ground fault (because current is returning through both the neutral and the grounding conductor).
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Old 08-13-2021, 05:29 AM   #4
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As a practical matter, many times, on an old boat, some duffus connected the neutral and grounding conductor together at some point. This is improper, a violation of the electrical code, and the cause of the ground fault (because current is returning through both the neutral and the grounding conductor).


The hassle is the neutral and grounding wires are required to be connected at the SOURCE ,

so will be connected at every generator and inverter.

Control of these sources is required.
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Old 08-13-2021, 06:47 AM   #5
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As a practical matter, many times, on an old boat, some duffus connected the neutral and grounding conductor together at some point. This is improper, a violation of the electrical code, and the cause of the ground fault (because current is returning through both the neutral and the grounding conductor).


The hassle is the neutral and grounding wires are required to be connected at the SOURCE ,

so will be connected at every generator and inverter.

Control of these sources is required.
That is the case but the transfer switch should be connecting or separating the neutral and ground as required.
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Old 08-15-2021, 05:56 AM   #6
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"They don't need to understand dock wiring, that is for electricians."


That is part of the problem many "electricians" understand houses but not the different requirements of a boat.
A bit of understanding by the boat owner might allow separating the house or car, folks from the real marine pros.
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Old 08-16-2021, 04:08 AM   #7
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Originally Posted by rwidman View Post
If anyone is having "hassles" with GFI in different marinas, they need to have their boat's wiring checked by a competent marine electrician. They don't need to understand dock wiring, that is for electricians.

A GFCI circuit measures the current on both the hot and neutral wires and if it's not the same, the circuit trips the breaker. The reason is, if the current returning from the boat isn't the same as the current entering the boat, the difference is going somewhere it shouldn't be going (like through your body to ground).

As a practical matter, many times, on an old boat, some duffus connected the neutral and grounding conductor together at some point. This is improper, a violation of the electrical code, and the cause of the ground fault (because current is returning through both the neutral and the grounding conductor).
Many years ago when this GFI issue began to be talked about, I took a look at my neutral and grou d busbars. Sure enough, there was a jumper between the two. I have yet to trip a marina's breaker.
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Old 08-16-2021, 06:04 AM   #8
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Many years ago when this GFI issue began to be talked about, I took a look at my neutral and grou d busbars. Sure enough, there was a jumper between the two. I have yet to trip a marina's breaker.
But have you plugged your boat into a GFCI breaker on a pedestal or on shore?

If you have and it didn't trip, you should really have your boat checked out because that would mean that the ground is not being carried through the cord to shore.

The National Electrical Code specifies that the neutral and ground should be tied together at the source and only at the source.

In a marina, that would be at the marina's main electrical panel. Your boat should have no connection between neutral and ground when you are receiving shore power.

When on generator or inverter power, that "source" is the generator or inverter and the neutral and ground should be connected together at that point.

It is the task of the transfer switch to take care of making and breaking these connections.
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Old 08-16-2021, 07:01 AM   #9
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But have you plugged your boat into a GFCI breaker on a pedestal or on shore?

If you have and it didn't trip, you should really have your boat checked out because that would mean that the ground is not being carried through the cord to shore.

I agree the wiring in question isn't right, but it he has a working isolation transformer or galvanic isolator, I don't think it will trip a shore GFCI.
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Old 08-16-2021, 08:26 AM   #10
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I agree the wiring in question isn't right, but it he has a working isolation transformer or galvanic isolator, I don't think it will trip a shore GFCI.
A galvanic isolator would make no difference. An isolation transformer would make a difference and if it's properly installed, no amount of miswiring on the boat would trip a shoreside GFCI.
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Old 08-16-2021, 10:34 AM   #11
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A galvanic isolator might make a difference. By intent, it introduces a voltage step between the ground on the boat and the marina. The reason connecting neutral and ground together on a boat trips the GFI is that there are then two possible return paths for neutral, and the current is shared between them depending on their resistance. The GFI interprets the current in the green wire as a fault. A galvanic isolator may add enough (effective) resistance to force the current through the white wire, and not trip the GFI.

Also, an older GFI might be failed open. Newer ones are supposed to fail closed.
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Old 08-16-2021, 10:48 AM   #12
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A galvanic isolator might make a difference. By intent, it introduces a voltage step between the ground on the boat and the marina. The reason connecting neutral and ground together on a boat trips the GFI is that there are then two possible return paths for neutral, and the current is shared between them depending on their resistance. The GFI interprets the current in the green wire as a fault. A galvanic isolator may add enough (effective) resistance to force the current through the white wire, and not trip the GFI.

Also, an older GFI might be failed open. Newer ones are supposed to fail closed.

But the galvanic isolator won't conduct current in the absent of a voltage difference. So if the shore connection neutral is healthy, I think all current will travel through that, and no current through the ground.
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Old 08-18-2021, 05:37 PM   #13
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@DDW #11
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A galvanic isolator might make a difference. By intent, it introduces a voltage step between the ground on the boat and the marina. The reason connecting neutral and ground together on a boat trips the GFI is that there are then two possible return paths for neutral, and the current is shared between them depending on their resistance. The GFI interprets the current in the green wire as a fault. A galvanic isolator may add enough (effective) resistance to force the current through the white wire, and not trip the GFI.

Also, an older GFI might be failed open. Newer ones are supposed to fail closed.
This simply is not how an ELCI functions. The safety ground (green) wire is not part of the circuit monitored by the ELCI. For 120VAC the current supplied on the line (L; black) must match that returned on the neutral (N; white) within 30mAAC. If the mismatch >30mAAC, the ELCI trips. For 50A/250VAC it is a bit more complicated, but the concept is exactly the same.
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