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Old 05-10-2016, 01:13 AM   #1
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Boat trips shore power GFI breaker?

All, thanks for the great advice and knowledge thus far! This forum is amazing and generous.

We brought our new to us trawler home and plugged it into power on our dock. We have power to the dock from a 60amp GFCI breaker in the main panel at the house which goes to a sub panel on the dock. I installed two 30amp breakers and corresponding 30 amp 125v plugs for shore power.

With the two 30amp breakers on the sub panel off and the main 50amp shore power breaker on the boat switched off I can plug in the shore power cords and the 60amp GFCI on the main panel will immediately trip.

My electrical knowledge is limited to the basics. My understanding is that the GFCI is measuring the positive against the negative and if there is a mismatch, i.e. Current dissipating through a ground, then it trips. This would often happen if the ground and negative were linked. But how can the GFCI trip with the sub panel breakers off and the 110v system/breakers on the boat off? Does this mean there is some residual current, perhaps leaking 12v current, getting into the 110v negative? How can the GFCI be triggered?

I've got a multimeter and would like to try to eliminate the simple (and safe) stuff before throwing money at an electrician. Any suggestions for how to begin the process of elimination?

Thanks!
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Old 05-10-2016, 01:26 AM   #2
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Check your cord and where it plugs into the boat. I was tripping the GFCI and found a terribly loose connection was the issue. Am convinced that GFCI outlet tripping kept my boat from burning down and taking the marina with it.
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Old 05-10-2016, 05:49 AM   #3
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Here are some things to check:
  • If you don't understand any of the following you need a marine electrician.
  • Buy a 30 amp adapter and check your cords and outlets are wired properly.
  • Does your boat have double pole breakers? It should so hot and neutral are disconnected when switched off aboard.
  • Unplug your boat and see if the neutrals are connected using your multmeter between the pins on the shore power inlet. The neutral busses should be separate.
  • Unplug your boat and see if the neutrals are grounded aboard using your multimeter between the green ground and neutral pins. They should not be. You will not be able to perform this test if you have galvanic isolators. You would have to check at the AC busses.
I suspect you have more than one problem or nothing would have happened when you plugged in. Your neutrals and possibly grounds are connected aboard and you may not have double pole breakers on your shore power supply aboard. In addition possibly reverse polarity on one or both of your cords.

Good cords plugged into properly wired inlets with breakers switched off aboard is a dead end and should not trip a GFP breaker. Even with no main breakers all loads off should not trip a GFP breaker. I think you need some help...



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Originally Posted by Panhandler View Post
All, thanks for the great advice and knowledge thus far! This forum is amazing and generous.

We brought our new to us trawler home and plugged it into power on our dock. We have power to the dock from a 60amp GFCI breaker in the main panel at the house which goes to a sub panel on the dock. I installed two 30amp breakers and corresponding 30 amp 125v plugs for shore power.

With the two 30amp breakers on the sub panel off and the main 50amp shore power breaker on the boat switched off I can plug in the shore power cords and the 60amp GFCI on the main panel will immediately trip.

My electrical knowledge is limited to the basics. My understanding is that the GFCI is measuring the positive against the negative and if there is a mismatch, i.e. Current dissipating through a ground, then it trips. This would often happen if the ground and negative were linked. But how can the GFCI trip with the sub panel breakers off and the 110v system/breakers on the boat off? Does this mean there is some residual current, perhaps leaking 12v current, getting into the 110v negative? How can the GFCI be triggered?

I've got a multimeter and would like to try to eliminate the simple (and safe) stuff before throwing money at an electrician. Any suggestions for how to begin the process of elimination?

Thanks!
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Old 05-10-2016, 06:59 AM   #4
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"Good cords plugged into properly wired inlets with breakers switched off aboard is a dead end and should not trip a GFP breaker."

Right!

If no breaker pop,, plug in the items into the outlets one at a time and see what the GFI doesn't like.
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Old 05-10-2016, 07:48 AM   #5
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" But how can the GFCI trip with the sub panel breakers off and the 110v system/breakers on the boat off? "

Look into where the wires connect to breakers and sockets.
If you have the 240 vac to 120 vac split, maybe you have a bad connection to neutral, high resistance, or a floating neutral.

Or some kind of current is flowing from hot to neutral from dried salts on the terminals

Or the wires are damaged.

Or you have a POV ( previous owner virus) miswired the boat.
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Old 05-10-2016, 08:07 AM   #6
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I'm scratching my head a bit about how your boat is wired. If I'm following you, you have two 30/120V shore power cords, but a single on-boat 50A breaker? Do each of the 30A cords power different things? Or do you need to have them both plugged in?

Getting back to your issue, the 30A breakers on your dock are likely single pole, so only open the power leg. Your neutral and ground which are common on each of your power cords are connected through to the boat, so that's probably where your issue lies.

Most likely the neutral and ground are connected on your boat somewhere, and that's what's tripping the 50A GFCI.

A few tests that might help narrow down the problem would be;

1) Does the GFCI trip with only one of the two 30A cords connected? If so, is it the same with both, or just one?

2) Are your 30A cords hard wired at the boat end, or do they plug in? If they plug in, then unplug them and see if the GFCI stil trips. This will tell you whether the problem is on the boat or in the cables.

3) Check the power post wiring. Test the outlet and confirm that you have line power, neutral, and ground of the correct pins. And confirm that the line terminal on each of the 30A is different. you should get 240V reading between them.

4) Check for continuity between neutral and ground on the cable going into your boat. My bet is that you will find continuity between them, and that's your problem.
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Old 05-10-2016, 08:27 AM   #7
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Neutral to ground bonding creates great confusion, and is frequently done incorrectly. I'll apologize in advance for the side track here, but I think it's probably relevant to the issue at hand.

The rules say that neutral and ground must be bonded (connected together) at the power source, and only at the power source. They should never be bonded in two places - always exactly one place. The confusion usually comes from understanding what is the power source. On a boat there are frequently multiple power sources, and bonding must be handled differently for each. This last bit often gets skipped over and you end up with multiple or no bonding under different scenarios.

The typical power sources on a boat, and proper bonding for each are:

1) Shore power: In this case, bonding is done on-shore in the land power system. The neutral and ground should not be bonded on the boat.

2) Generator: In this case the generator is the power source, and bonding should be at the generator. The trick is that when the generator is not the source of power, the bonding needs to be removed. Typical approaches are break the neutral from the generator with some combination of a selector switch or multi-pole breaker. That way if your switches are aligned for power from the generator, the boat is connected to the generator's neutral which is in turn bonded to ground. And when the switches are aligned for a different power source, the generator's bonded neutral is disconnected.

3) Inverters: When you are running on inverter power, the inverter is considered the power source and neutral to ground bonding must be done there. Once again, there needs to be some mechanism to bond when powered from the inverter, and un-bond when a different source is used. This becomes even trickier when shore power feeds into the inverter and is passed through to the inverter loads. In this case shore power is the power source and the inverter bond must be disconnected. Some inverter companies make "mobile" versions of their inverters to handle this. These models automatically connect and disconnect the neutral ground bond based on the presence or absence of "shore" power. Note that you have the same challenge when you are running on generator and that is feeding through the inverter. Once again, the inverter bonding needs to be removed.
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Old 05-10-2016, 08:30 AM   #8
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Indeed, Corrosion inside the power cord connections is common and causes GFCI to trip.
If you don't know the history of the cord and boat connection opening and cleaning both ends of the cord is the first place I would look.
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Old 05-10-2016, 08:57 AM   #9
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I cannot justify a rumor I heard about galvanic isolators causing problems with GFIs. Since there is a lot of knowledge and experience here could someone explain how and why a galvanic isolator would cause a GFI to ghost trip or not work? They are just expensive diodes, right?
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Old 05-10-2016, 09:08 AM   #10
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Thank you, all. I really appreciate the information. I'll triple check my wiring job at the post, will disassemble the shower power cords to check for problems, and then check the shore power inlets.

If that doesn't work, I'll start going more in depth but I have a feeling I may be calling a marine electrician.

I see that I need to do some serious reading before buying and installing an inverter to avoid creating more problems....

Again, thanks.
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Old 05-10-2016, 09:11 AM   #11
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Go to Amazon and buy Nigel Calder's marine electrical book as it's the bible on this subject.
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Old 05-10-2016, 10:12 AM   #12
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Originally Posted by Panhandler View Post
All, thanks for the great advice and knowledge thus far! This forum is amazing and generous.

We brought our new to us trawler home and plugged it into power on our dock. We have power to the dock from a 60amp GFCI breaker in the main panel at the house which goes to a sub panel on the dock. I installed two 30amp breakers and corresponding 30 amp 125v plugs for shore power.

With the two 30amp breakers on the sub panel off and the main 50amp shore power breaker on the boat switched off I can plug in the shore power cords and the 60amp GFCI on the main panel will immediately trip.

My electrical knowledge is limited to the basics. My understanding is that the GFCI is measuring the positive against the negative and if there is a mismatch, i.e. Current dissipating through a ground, then it trips. This would often happen if the ground and negative were linked. But how can the GFCI trip with the sub panel breakers off and the 110v system/breakers on the boat off? Does this mean there is some residual current, perhaps leaking 12v current, getting into the 110v negative? How can the GFCI be triggered?

I've got a multimeter and would like to try to eliminate the simple (and safe) stuff before throwing money at an electrician. Any suggestions for how to begin the process of elimination?

Thanks!
If I understand correctly, you installed the electrical system (from the house to the dock) yourself and it's not working properly. You're not "throwing money at an electrician", you are paying him for his knowledge and experience to fix something that you are not capable of fixing.

My suggestion is to hire a qualified electrician to inspect your work and fix the problem.

I will say this about supplying a boat through a GFCI breaker or receptacle:

The way a reverse polarity indicator works is, a red light is connected from the neutral to ground. With normal polarity in the supply, there is no voltage difference between neutral and ground and the light does not light. If the polarity is reversed, there is a 120 volt difference between the neutral and ground and the light lights.

There is another light (a green one) wired between the "hot" conductor and ground. If the polarity is correct, this green light lights. This is where the reverse polarity lights and the GFCI come into conflict. The green light causes an imbalance in the current between the hot and neutral conductors and the GFCI thinks there is a fault and it trips.

Most of us are not yet faced with this problem because most marinas do not have GFCI protection in the circuits that power the boats. This protection is provided in the boat's electrical system beyond the reverse polarity indicators.


If you have followed this this far and think you are capable of doing this safely, disconnect the reverse polarity indicators and see if the problem goes away.
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Old 05-10-2016, 04:29 PM   #13
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If I understand correctly, you installed the electrical system (from the house to the dock) yourself and it's not working properly. You're not "throwing money at an electrician", you are paying him for his knowledge and experience to fix something that you are not capable of fixing.

My suggestion is to hire a qualified electrician to inspect your work and fix the problem.

I will say this about supplying a boat through a GFCI breaker or receptacle:

The way a reverse polarity indicator works is, a red light is connected from the neutral to ground. With normal polarity in the supply, there is no voltage difference between neutral and ground and the light does not light. If the polarity is reversed, there is a 120 volt difference between the neutral and ground and the light lights.

There is another light (a green one) wired between the "hot" conductor and ground. If the polarity is correct, this green light lights. This is where the reverse polarity lights and the GFCI come into conflict. The green light causes an imbalance in the current between the hot and neutral conductors and the GFCI thinks there is a fault and it trips.

Most of us are not yet faced with this problem because most marinas do not have GFCI protection in the circuits that power the boats. This protection is provided in the boat's electrical system beyond the reverse polarity indicators.


If you have followed this this far and think you are capable of doing this safely, disconnect the reverse polarity indicators and see if the problem goes away.


Sorry, I should have been more clear. The power to the dock was checked by an electrician and is up to code. We have been using it for two years with the boat lift and other things. I simply added two 30a circuits to the sub panel on the dock.

I appreciate the suggestions regarding the reverse polarity indicator and the green light. I'll look into that as well.

Thanks, all!
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Old 05-10-2016, 06:10 PM   #14
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try this. Switch off all the breakers on your boat. Then plug in. If it trips it is probably between your pedestal and your inlet plug. If it doesn't trip turn on one breaker at a time to see which circuit is tripping. Then turn that circuit off again, and try each one in a similar fashion. That may isolate your problem, and tell the circuit(s) that need correction.
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Old 05-10-2016, 06:33 PM   #15
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try this. Switch off all the breakers on your boat. Then plug in. If it trips it is probably between your pedestal and your inlet plug. If it doesn't trip turn on one breaker at a time to see which circuit is tripping. Then turn that circuit off again, and try each one in a similar fashion. That may isolate your problem, and tell the circuit(s) that need correction.

I couldn't recall in my earlier post how we diagnosed my issue. This is exactly how we did it.

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Old 05-10-2016, 08:08 PM   #16
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Most of us are not yet faced with this problem because most marinas do not have GFCI protection in the circuits that power the boats. This protection is provided in the boat's electrical system beyond the reverse polarity indicators.
Come south and you will.
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Old 05-11-2016, 09:19 PM   #17
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By design & code, the ground and neutral are normally connected ONLY at the source of the power- e.g. the shore power, the generator, or the inverter. If you're on shore power, the ground and neutral are connected at the source (the main panel); the generator will have the ground and neutral connected at the generator and your selector switch will reconnect the power leads in the appropriate configuration.

If you have an inverter on board, it's possible that the inverter is causing the trip, particularly if the neutrals for the inverter and those on the shore power supply that the inverter is NOT wired to- are interconnected. What happens is that when the inverter's pass-thru relay closes, it creates a connection between the ground and the neutral, and depending on how the boat is wired, it could create an ELCI trip.

It's also possible that neutrals from shore 1 and shore 2 are commingled somewhere on the boat, or that a ground and neutral connection exists when it should not, perhaps a miswired selector switch, there are many potential sources.

When connecting to a ELCI supply, it sees any connection between ground and neutral downstream of the shore power connection and it trips out because it's not supposed to see any connection between the neutral and ground other than its connection at the panel.

Jim Healy has several well-written articles on his blog, one explains in detail the ELCI issues that are becoming more of a problem with the mandated upgrade to the new technology as dockside electrical systems are brought up to current standards. He offers some insight into solving problems aboard. You may want to have a qualified MARINE electrician help with troubleshooting. A residential electrician will not be familiar with the requirements of ABYC standards and likely will do considerable head scratching.

We're only beginning to scratch the surface of these problems, you'll be hearing more about it as the technology is implemented.
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Old 05-12-2016, 03:41 PM   #18
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try this. Switch off all the breakers on your boat. Then plug in. If it trips it is probably between your pedestal and your inlet plug. ....................... .
The reverse polarity indicator circuitry may or may not be before the main breaker. So - this could still be the problem with all the boat's breakers turned off.
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Old 05-12-2016, 03:46 PM   #19
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Come south and you will.
I spent a month or so in several different marinas in FL last May/June. Also a few in GA.

No electrical issues.

In my experience, the 15/20 amp receptacles are GFCI protected while the 30 amp and 50 amp boat receptacles are not. GFCI protection is supposed to be provided by the boat. The reason being that it's difficult to plug tools, heaters, etc. into the 30 and 50 amp receptacles.
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Old 05-12-2016, 03:50 PM   #20
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By design & code, the ground and neutral are normally connected ONLY at the source of the power- e.g. the shore power, the generator, or the inverter. If you're on shore power, the ground and neutral are connected at the source (the main panel);............
Not the main panel on the boat, the main panel at the marina (or your home if it's a home dock).
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