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Shore power (120) electrical issue on boat

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Catalississippi
1st Mate

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USA
40 Posts

Initially Posted - 01/18/2021 : 14:06:56

So my C-25 is tripping the shore power breaker (20A, I believe) as soon as I plug my cord into the boat. I'm in the US, so this is 120v issue. I've isolated it (somewhat) to my boat - in other words, I've eliminated my cords or other boats on that same circuit as possible causes. Haven't started exploring the wiring inside the boat just yet, but I thought I'd start here until I can get out to her to poke around.

I typically only run a dehumidifier and a (dehumidifying) fan on the shore power - never a space heater. Haven't ever had a problem, though I've only had the boat for a few months. This just popped up a week or so ago as an issue. Both 120 electrical outlets on board are the GFI type - and I believe that is all that the shore power actually powers (everything else is on the 12v system). Though I haven't explored the boat wiring in detail yet, I have tried unplugging everything before hooking back up to shore power, and I've also tried the GFIs in various settings. As soon as I plug my twist-lock cable into the boat, it trips. I don't believe there is a separate breaker on board, other than the GFI outlets themselves.

It may be something basic and obvious once I get the chance to look more closely, but until then ..... any ideas?

1980 Catalina 25 TR/SK #2098 ?????
Former owner of 1982 Catalina 25 TR/SK #3081 Suzy-Q

SKS
Navigator

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USA
161 Posts

Response Posted - 01/18/2021 : 14:34:55

The wiring is very simple for shore power. Here is the wiring set up.
Maybe there's a short in the inline switch ??

http://catalina-capri-25s.org/manbro/pictures/pc39.gif

"Lady E" 1986 Catalina 25: Fin Keel, Standard Rig, Inboard M12 Diesel, Sail No. 5339
Sailing out of Norwalk Cove Marina, Connecticut

Catalississippi
1st Mate

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USA
40 Posts

Response Posted - 01/18/2021 : 15:28:38

quote:
Originally posted by SKS

The wiring is very simple for shore power. Here is the wiring set up.
Maybe there's a short in the inline switch ??

http://catalina-capri-25s.org/manbro/pictures/pc39.gif

Thanks. I don't believe there is a separate breaker on board, other than the GFI outlets themselves. Looks like a previous owner removed the breaker. This is my second C-25, and both have had this modified setup.

1980 Catalina 25 TR/SK #2098 ?????
Former owner of 1982 Catalina 25 TR/SK #3081 Suzy-Q

Voyager
Master Marine Consultant

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USA
5231 Posts

Response Posted - 01/19/2021 : 07:18:18

Check for a dead short with a Digital Volt-Ohmmeter. Disconnect the boat from shore power. Disconnect any 120VAC item on your boat including your dehumidifier, fans, fridge and any 120VAC lighting you may have.
Out at the twistlock plug with all power off and disconnected, test continuity with the ohmmeter between the hot and neutral, hot and ground, and the neutral and ground pins.
All should read as open circuits. If you have some connectivity, like 100K ohms, there may be some corrosion somewhere in a component. That won�t typically blow a fuse. But it could create a ground fault. If you read 1K ohm then you�re getting into short circuit territory. Finally, if you read zero ohms between ground and neutral, that�s bad wiring. If you read zero ohms between hot and either other wire, then you have a short.
From there, I�d check for a bad outlet. They�re cheap enough to just replace them.
All this said, once you do some checking on your own, I�d advise that you hire a licensed, insured electrician to check out your wiring. While a service call may cost a few $100, it�s cheap insurance. You don�t want to endanger yourself or your guests with lethal voltage.
Another common problem is when there are multiple boats on one circuit. If ground and neutral are switched, or if hot and neutral are switched on any nearby boats, deadly currents can run between the boats through the water. This is a major cause of electrocution of swimmers around docks.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 01/19/2021 : 22:25:04

I'm not a fan of amateur 120V or 240V wiring... 12V is tricky enough--I've been aboard a smoke filled boat out in the Pacific where we managed to keep it from turning into a fire--that was a 12V problem. 120V is capable of instantaneous ignition (not to mention killing people) before a breaker can shut it down. I like to know the wiring is done to code (or a problem resolved) by a licensed electrician.

However, if you want to see a spectacle, try an electrical fire in a fiberglass boat. We had one at a dock in my town just a few months ago--shore power--lots of excitement!

Curmudgeon out.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 01/19/2021 22:28:41

Voyager
Master Marine Consultant

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USA
5231 Posts

Response Posted - 01/20/2021 : 20:57:24

Dave, all I�d add to your comment is to make sure you find a licensed, insured electrician who�s knowledgeable about boat wiring.
A residential electrician will definitely be able to repair your ground fault or dead short problem, since that�s self-contained on your boat.
But they might not understand that two adjacent boats using the same source power circuits, where one has a ground fault or reversed polarity could cause a short between two boats connected only by water. That kind of problem would be very uncommon in a residential electrical setting.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 01/20/2021 : 21:46:04

Agreed, Bruce! I omitted the term "marine" before "electrician." A marina should have at least a line on one.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Catalississippi
1st Mate

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USA
40 Posts

Response Posted - 01/29/2021 : 13:08:46

Thanks, all. Turned out it was the outlet wired incorrectly by a (professional, licensed) electrician hired by my YC to do ongoing marina electrical work. They were called and came out and fixed it. Had neutral on the wrong terminal and wires incorrectly switched. It was self-shorting every time anything would be plugged in.

1980 Catalina 25 TR/SK #2098 ?????
Former owner of 1982 Catalina 25 TR/SK #3081 Suzy-Q

islander
Master Marine Consultant

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USA
3992 Posts

Response Posted - 01/29/2021 : 15:22:28

So the pro wired the outlet wrong....yeah that would give me a nice warm secure feeling.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Voyager
Master Marine Consultant

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5231 Posts

Response Posted - 01/29/2021 : 18:34:48

For $9 you can buy a 110VAC polarity detector at the local hardware store. Freakin� amazing that electrician didn�t bother to check their own work!

https://www.homedepot.com/p/Power-Gear-3-Wire-Receptacle-Tester-50542/206212329

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - Voyager on 01/29/2021 18:38:17

islander
Master Marine Consultant

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USA
3992 Posts

Response Posted - 01/30/2021 : 05:32:52

I was thinking about one of those testers but I didn't know what kind of outlet the shore power was. That tester will work with a 15 or 20amp post but you'll need an adapter if the power is 30amp.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Voyager
Master Marine Consultant

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USA
5231 Posts

Response Posted - 01/30/2021 : 08:14:51

You�re right Scott.

Catalississippi, that�s exactly why I mentioned doing your own pre-check above. I�m doing some construction projects at my house and I don�t care how many years experience the technician has, I always check the work. Right now I have a 3-way switch that works perfectly on one end of the hall, and is a NAND gate on the other end. Hey! is this thing even hooked up?

The other thing this points out is that if you boat was �grounded�, the current from the 120VAC power would run through the water around your boat and potentially be lethal if anyone fell in or swam in summer.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.