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Old 18-09-2020, 11:23   #1
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Marinco 50 amp shore plug shorted

I've been chasing down an intermittent issue where 120v breakers on the boat and marina pedestals would all trip at once. It didn't matter the load we were pulling and it seemed random.

Today I started testing things (I'm at anchor) and found continuity at the ship side plug between ground and neutral. After opening breakers and still seeing it, I removed the plug and still saw it (photo attached)

I couldn't see anything making contact even after completely disassembling the plug. I've now installed a Smartplug and will test that next time we're in a marina.

I'm curious if anyone has seen this issue or knows what may have caused it.
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Old 18-09-2020, 11:49   #2
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Re: Marinco 50 amp shore plug shorted

2.4 mega ohms? That is open. No issue there.
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Old 18-09-2020, 11:53   #3
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Re: Marinco 50 amp shore plug shorted

Even at 120v, that would only leak 0.5 milliamps. That's highly unlikely to be the issue. And between neutral and ground, that amount of resistance is probably even less of a concern. Certainly not enough to trip a GFI.
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Old 18-09-2020, 11:59   #4
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Re: Marinco 50 amp shore plug shorted

Moving the probes around resulted in higher values. It was pretty intermittent and everything tripped when there was a heavy load on the Marina's system.

Also, at one point, while trying to figure out why things were tripping and the marina said I was pulling 15 amps when I know I should have only been pulling 5 or less.

I also say the reverse polarity light in the panel dimly lit.
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Old 18-09-2020, 12:03   #5
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Re: Marinco 50 amp shore plug shorted

Spray some contact cleaner and blow it out with compressed air. It’s just some dirt, grease. 2.4MOhm or even more is not the cause of 30A breakers flipping, you are on the wrong track.
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Old 18-09-2020, 12:04   #6
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Re: Marinco 50 amp shore plug shorted

The ground and neutral are joined on the dock anyways.
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Old 18-09-2020, 12:09   #7
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Re: Marinco 50 amp shore plug shorted

I started taking the end of the 50 amp shore power cable apart and found that the cord has started pulling out. Now I'm thinking there was just a partial connection being made so it may have been pulling more amps than I thought. Possible?
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Old 18-09-2020, 12:20   #8
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Re: Marinco 50 amp shore plug shorted

Quote:
Originally Posted by crayiii View Post
I also say the reverse polarity light in the panel dimly lit.
You sparked a memory with that. I read somewhere (I'm no expert) that some reverse polarity lights are simply connected to neutral and ground. If there's current there, they'll light. But they also present a path between those and will themselves cause a GFCI to trip.

That said, I imagine that light would also indicate an actual voltage difference between ground and neutral by dimly lighting. So in your case it could be the cause, or a symptom, or both.

It can be difficult to find an unwanted bond between ground and neutral. On my boat I discovered one of the neutral wires to an outlet had broken, so some wanna-be electrician simply wired the outlet to ground, instead. It worked fine until the boat was plugged into a GFCI. That took a while to track down!
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Old 18-09-2020, 12:24   #9
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Re: Marinco 50 amp shore plug shorted

Quote:
Originally Posted by crayiii View Post
I started taking the end of the 50 amp shore power cable apart and found that the cord has started pulling out. Now I'm thinking there was just a partial connection being made so it may have been pulling more amps than I thought. Possible?
Absolutely.

There is a correct procedure for dealing with those Marinco plugs and sockets:

1. Carefully detach the cabling.

2. Place entire assembly in an opaque plastic bag; seal up tight.

3. Deposit in marina trash skip.

4. Purchase SmartPlug.

This is the only correct solution to any of the various failure modes of the Marinco connectors, and in fact is strongly recommended for non-failed ones as well.
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Old 18-09-2020, 12:32   #10
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Re: Marinco 50 amp shore plug shorted

Are these tripping breakers GFCI?
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Old 18-09-2020, 12:33   #11
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Re: Marinco 50 amp shore plug shorted

Installed today! It will be awhile before we're in a marina to test it though.





Quote:
Originally Posted by Dockhead View Post
Absolutely.

There is a correct procedure for dealing with those Marinco plugs and sockets:

1. Carefully detach the cabling.

2. Place entire assembly in an opaque plastic bag; seal up tight.

3. Deposit in marina trash skip.

4. Purchase SmartPlug.

This is the only correct solution to any of the various failure modes of the Marinco connectors, and in fact is strongly recommended for non-failed ones as well.
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Old 18-09-2020, 12:47   #12
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Re: Marinco 50 amp shore plug shorted

Quote:
Originally Posted by Dockhead View Post
There is a correct procedure for dealing with those Marinco plugs and sockets:

1. Carefully detach the cabling.

2. Place entire assembly in an opaque plastic bag; seal up tight.

3. Deposit in marina trash skip.

4. Purchase SmartPlug.

This is the only correct solution to any of the various failure modes of the Marinco connectors, and in fact is strongly recommended for non-failed ones as well.

It is my observation that all outdoor electrical connectors have a limited life. It will be interesting to see how the SmartPlugs fare when there is a larger installed base of older ones. I note that SmartPlug now have "service kits" on their website so perhaps they don't last forever either.


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Old 18-09-2020, 12:50   #13
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Re: Marinco 50 amp shore plug shorted

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Originally Posted by Thumbs Up View Post
Are these tripping breakers GFCI?
These are the two breakers that trip in addition to the pedestal (this only happens at some marinas)

The first one is inside and the second one is in the engine compartment near the shore power (only the left one trips).
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Old 18-09-2020, 12:56   #14
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Re: Marinco 50 amp shore plug shorted

Quote:
Originally Posted by crayiii View Post
I started taking the end of the 50 amp shore power cable apart and found that the cord has started pulling out. Now I'm thinking there was just a partial connection being made so it may have been pulling more amps than I thought. Possible?
Back when I went through USCG ET school, current was equal to voltage divided by resistance (I=E/R), maybe Y2K changed this , but I still believe a poor connection can't cause higher current.
Since both pedestal and boat breakers, I would suspect an intermittent short on the house side of the breaker
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Old 18-09-2020, 13:01   #15
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Re: Marinco 50 amp shore plug shorted

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Originally Posted by Bill Seal View Post
Back when I went through USCG ET school, current was equal to voltage divided by resistance (I=E/R), maybe Y2K changed this , but I still believe a poor connection can't cause higher current.
Since both pedestal and boat breakers, I would suspect an intermittent short on the house side of the breaker
I've tried tracking it down but I would have thought that if it was downstream of the shore power, it would trip on generator and inverter. Planning on setting up a time with an electrician as soon as we're someplace long enough.
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