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Old 12-07-2018, 04:36 PM   #1
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Shorepower short - help diagnose?

Dear all;

I was out on overnight winter cruise this week when a bad evening surprise hit me. Nordic Tug 32 2008. When I plugged into another marina's shore power and switched on - my entire shore power cord started smoking and smoke coming into the interior. Immediately unhooked from shore power and smoke cleared. The shore breaker never tripped but the shore outlet was badly charred on the ground terminal as was my shore power inlet on the boat. The entire shore power cord is burned in a helical pattern (see photos).

Next day opened up the boat to find the main power cable from the power inlet to the main 110V board is also burned (see photos) all the way the the 110V box; where I can follow the individual wires. Only the green (ground) wire is charred up to the main ground terminal.

Anyone up for telling me what could cause this? Any why no breakers stopped it from happening?
Thanks -
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Old 12-07-2018, 05:46 PM   #2
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I can't diagnose the system fault or tell you why the breakers didn't protect you, but I'm glad that you are okay and the boat suffered only 'minor' damage. Thanks for sharing your misfortune so that others might learn something.

I assume you regularly use shore power at other locations with no problems? Since you have damage to repair, possibly due to someone else's error, involving an insurance claim, I recommend you get an expert to do a forensic analysis of the damage and likely cause.
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Old 12-07-2018, 09:57 PM   #3
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An interesting failure mode. The ground wire got overloaded, but not the hot or neutral wires. Even with a full short to ground, the ground wire in a good cable should have the same ampacity as the hot and neutral wires.

Seems like you had a short to ground combined with a sticking breaker in the pedestal and undersized ground wiring.

Any inverters, generators, big loads like heaters running while you connected the shore power?

Have you found where the short is in your boat? With everything turned off, measure resistance between hot, neutral and ground, while turning on breakers one at a time.
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Old 12-07-2018, 10:48 PM   #4
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What marina? I want to be sure to not plug in there.
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Old 12-07-2018, 11:07 PM   #5
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What marina? I want to be sure to not plug in there.
Same here. Would you be willing to tell us?
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Old 12-08-2018, 05:13 AM   #6
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I can understand this happening for several reasons.
The short to ground was not of enough amps to turn off the breaker but it was close and you had high resistance bad connections in the plug-wire which caused it to get real hot. I had a yellow power cord develop a bad spot inside itself, salt water got in there and corroded the wires. Corroded wires cant carry the current load. So maybe the ground wire was bad.

You can have too much current flowing on the ground, if the neutral wires not working and you have a ground fault. Say you had both 30 amp wires plugged in, and had short to ground, the ground wire might be having to deal with 40 or 50 amps when designed for only 30 amps, like having a shared neutral, too much current can flow back on a single neutral wire versus the other wire. But that would take a double fault of both shore wires. All grounds are shared on boats.
Having a GFCI breaker would have stopped that burning immediately.


I assume your breakers are double pole on al power wire going into the boat? If the marina had reversed polarity and you had a short to ground and there were single pole breakers, no breaker would trip off.

A GFCI breaker on your boat at the inlet or on shore at the dock would have prevented miswired and shorts to grounds. But not do any good for high resistance wires or connections.
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Old 12-08-2018, 05:44 AM   #7
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I noticed your photo of the power inlets shows a couple of breakers there and they appear to be ELCI breakers? if they are, they are set to detect a 30 ma ground fault and then trip off, so were they working? They have a test button.

If the burned wire is the ground wire, well they could not have been working as any current flowing on the ground wire would have turned them off.

Other thing is is one saying 20 amps??? Do you not have 10 gauge shore wires? Maybe your ground fault sent 30 amps through a 12 gauge ground which would explain why the entire wire overheated and burned like that.

That would be really bad to have the boat built with wrong gauge wires, it clearly shows a 20 in there alongside 30 amps. Whats going on here?
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Old 12-08-2018, 07:33 AM   #8
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You are very lucky. I note you are in Seattle. A really good guy to look things over is Dan Heyl at Emerald Harbor Marine. Your insurance company will know of him. Has any recent work been done on vessel’s electrical system. BTW, your cord’s male end looks odd for 30 amp, what brand and how old?
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Old 12-11-2018, 04:16 PM   #9
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Thank you

thank you all for these suggestions. For clarity in response - I was at the Port of Poulsbo Marina guest dock - but I do NOT have any information yet that the marina faciities caused this (I also do not have any diagnosis that it didn't). I did not have any 110V electric loads running when I connected to shore power. I have a marine electrician coming to look at my boat this Friday morning - I'll post back here when I have something more to understand about the likely cause(s) - but still I'm very surprised and "shocked" that the circuit breakers didn't prevent this.
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Old 12-11-2018, 04:26 PM   #10
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HI - thanks for your reply. It sounds like you know a lot about these things. My yellow power cord may have been damaged a year ago when we backed out of our slip without disconnecting first - could that have caused an internal damage that only surfaced later? But I still don't understand how a short within the cord - say from one of the power cords to ground - would not have tripped a breaker. And I can't understand how a short within the shore cord could still have caused the ground wire circuitry inside the boat to overload and heat up - wouldn't it just short back to the shore breaker?
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Old 12-11-2018, 04:26 PM   #11
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Originally Posted by sdowney717 View Post
I noticed your photo of the power inlets shows a couple of breakers there and they appear to be ELCI breakers? if they are, they are set to detect a 30 ma ground fault and then trip off, so were they working? They have a test button.

If the burned wire is the ground wire, well they could not have been working as any current flowing on the ground wire would have turned them off.

Other thing is is one saying 20 amps??? Do you not have 10 gauge shore wires? Maybe your ground fault sent 30 amps through a 12 gauge ground which would explain why the entire wire overheated and burned like that.

That would be really bad to have the boat built with wrong gauge wires, it clearly shows a 20 in there alongside 30 amps. Whats going on here?


The 20 amp breaker is most likely for the pedestal bonnet light and a 110v "service outlet" on exterior of the pedestal or in one of the internal socket bays.

The 2 30amp breakers service the twist lock connections.
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Old 12-11-2018, 04:40 PM   #12
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Looks like short at the boats shore plug right? The shore power supply breakers should have tripped - if they are bad/stuck from corrosion ext. that's the likely reason the wires melted as much as they did I think. Glad you are ok!
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Old 12-11-2018, 05:05 PM   #13
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I agree that it looks like the 20 amp breaker is probably for the pedestal light. If I had to guess I believe that this is a case of two separate faults. The ELCI breaker should have blown if it sensed a differential in current flow between the hot and neutral sides, which it did not. Also, it looks like there was also a short internal to the boat between the hot and ground at the 110V box. Without the boat short you would never know, without testing, it the breaker was working or not.


This might be a good reminder to test the ELCI breakers before connecting. Sorry for your headache.
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Old 12-11-2018, 05:46 PM   #14
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Sorry for your misfortune. It has happened to me as well. Glad only and short span of wiring was damaged and nothing more.
Now, what you experienced was not so much a “short” as it was an arcing through your ground wiring, probably beginning in your shore cable plug-in. The break could have occurred when you pulled away from the dock with it still plugged in. While it didn’t break fully then, it weakened the wire/connection and through corrosion and vibration, caused the short, increasing resistance and making the wiring hotter, to the point of the burn out. You did not have an increase in amperage, only resistance, thus not tripping any of the circuit breakers. Hope this answers your questions. Thankfully you were there to take immediate action.
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Old 12-12-2018, 08:27 AM   #15
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Wow, a lot of guesses here. The bottom line is you have significant damage that needs to be carefully and thoroughly investigated and repaired. Part of that investigation needs to uncover WHY this happened. Otherwise, it could happen again. If you are not VERY familiar with how a boat should be wired, I strongly suggest you get a pro in to perform the complete repair.


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Old 12-12-2018, 08:33 AM   #16
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It is true his GFCI-ELCI breakers set to detect a 30 ma ground fault ground breakers failed him if the ground wire burned up. If you look at the incoming shore line inside the boat it is burnt in a spiral pattern indicating one wire overheated. That means the yellow shore cord is probably ok of itself. The yellow shore cord ends may have high resistance bad connections, likely the wire is still ok of itself.

A digital ohm meter can tell you a lot, but some of this is common sense, like check for overheating plugs when your plugged into shore power, and exercise your boat breakers see if they are working ok. Those breakers may be in a spot exposed to sea water and rain, maybe they corroded and can no longer break the circuit open.

My own system, I have twin 30 amp, almost never run both together. I have typical SS shore inlets, but I wired them to 8 gauge wire for overkill, and have standard 30 amp GE double pole breakers mounted in a NEMA weather tight metal grey box and it is out of the weather so never gets wet. I even put in a 30 AMP double pole switch to join both 30 amp lines together for convenience as some places only have one 30 amp power to plug into, that way the whole boat still has power.

I run 8 gauge wire all the way to my old Square D distribution panel, and in that panel have 5 out of 8 circuits (its a small panel ) GFCI-AFCI protected breakers. Its been like that over 15 years with not a single problem, except one time my shore power cord got damaged and burnt up 6 feet of cord. If the problem is the yellow shore cord, it wont be burning up the interior boat wiring.
Look at picture 4 and 5, you will the interior incoming shore wiring had one of the 3 wires burnt up, not all of them.

So either high amount of amps with bad deficient wires, or high resistance burnt the wire..
A high amp power supply with too much resistance somewhere in the wiring creates a ton of heat.

And there is another weird possibility, if your running both shore cords, and you get a severe ground fault, and you have a bad ground on one of the shore cords, double the amps will flow on the remaining ground wire severely overloading it and it will burn up. You could get 60 amps on a wire designed for 30 amps. But that scenario is unlikely but could happen, lots of bad things would have to happen.

The load will be under 30 amps on each incoming shore cord, so breakers wont trip, but up to 60 amps flowing on a ground returning wire. Power is not always shared equally on wires, this is how shared (joined )neutrals across incoming shore wires can cause wires to burn up. Because the resistance on one white wire is not the same as the other, you might get 20 amps on one and 40 amps on the other overloading it.
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Old 12-12-2018, 09:35 AM   #17
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This is a time to use your insurance. hey will have experienced surveyor inspect the damage an tell you what went wrong. In my experience their surveys are free as that is how they determine if you have a covered situation.
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Old 12-12-2018, 10:01 AM   #18
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A little over a year ago I pulled into Poulsbo. I'd heard they were one of the first marinas to re-wire to GFCI "standards in WA. I was curious as to how my vessel would work on the new dock wiring as I'd had problems earlier in AK on new GFCI wiring. Sure enough, the pedestal breakers popped.

So the next day I went to Emerald Harbor Marine (already planned) and had their electric wizard, Dan Heyl, check into things. Dan is well aware of the issues boats and docks face in the new GFCI era. He says a very high percentage of WA boats fail the 30ma criteria, especially those older than 10 or so years and without an isolation transformer.

Upon checking our vessel is was quickly determined that we failed the 30ma stray current test. Two options were available to fix things. One, install an isolation transformer or two, rewire the vessel's grounds. ITs take up a lot of space and are not cheap. Installing one does not fix the underlying problem, it only keeps the boat from tripping the breaker. Redoing the grounds would not be a small task either.

We elected to re-do all the AC grounds up to current standards. The DCs were fine. Without belaboring the work done, the ground re-do was relatively quick, successful and necessary. This approach was more cost effective and was required once it was found that the vessel now passed the 30ma test.

Foregoing the IT route does make it necessary to plug into 30ma GFCI outlets in a very careful fashion, with power off and inverter shutdown. This technique is boat specific and marina specific we have found.


I recommend two things:
  • Throw away your 30 amp cord. Ignore advice on TF, do not repair it. I bought a new one at West Marine last year for $90
  • Have your vessel with new cord checked out on a proper 30ma GFCI outlet. Do it next time at Poulsbo or check at Emerald Harbor Marine at Elliot Bay.
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Old 12-12-2018, 10:27 AM   #19
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Definitely in insurance territory. 10 gauge wire hot enough to char the inner and outer insulation should have tripped the shore power 30 amp breaker.
Yes something on your boat failed which initiated the fault but the pedestal breaker failed too. Call your ins co yesterday.
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Old 12-12-2018, 10:46 AM   #20
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I recommend two things:
  • Throw away your 30 amp cord. Ignore advice on TF, do not repair it. I bought a new one at West Marine last year for $90
  • Have your vessel with new cord checked out on a proper 30ma GCFI outlet. Do it next time at Poulsbo or at Emerald Harbor Marine at Elliot Bay.

It doem't appear that his vessel had a problem tripping the breaker but not having the breaker trip caused the problem.... Because the wiring in the boat from the shore power connector to? (galvanic isolator , power selector switch, breaker or perhaps inverter) where ever it goes after it enters the boat. Something upstream caused the short....
I've always found the power connections at Poulsbo to be heavily used and not in the best of condition.The shore side breaker could be compromised..

The ground wire is fried but if the neutral was intact it should have taken half the current load so it was either open,or high resistance. I think that there were a few issues, compromised breaker at the power pedestal, compromised or failed neutral connection and a dead short somewhere upstream of the shorepower connection in the boat most likely prior to boats main disconnect.....again I agree with the prior post that said get your insurance company involved let them sort it out....
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