Shore Power Problem

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BigTime

BigTime

Senior Member
Joined
Nov 15, 2018
Messages
133
Location
United States
Vessel Name
Shady Grove
Vessel Make
TMC Custom 41 Trawler & S-2 10.3 Sail
My new to me Taiwanese Trawler has two 30amp power receptacles. One feeds the main (original) panel and the other feeds an added panel. The 5 months I have owned the boat I have had 2 cords plugged into the shore power pedestal and all has been well. I just moved to a larger slip which has a single 50amp outlet instead of the double 30amp my old slip had. I purchased a new Marinco splitter that plugs into the 50 and y's into two 30's. When I plug my boat in and flip the breaker on it immediately trips the breaker, tried the next pedestal over and same thing. Using only one cord in ANY position ( either side of splitter or either boat receptacle or either cord) all in well. Plug the 2nd cord in and immediate breaker trip when powered on. Once I tried to plug in the 2nd cord to the boat while the breaker was on and huge bang!&pop!. This is not some quirky gfci issue.
ANY IDEAS ?
 
Sounds like L1 on one cord and L1 on the other are somehow tied together. If they are by chance in phase, no problem. If they are out of phase as they certainly would be on a 50A through a splitter, dead short.

Sounds like you have some funky wiring.

Plug in one cord, then test the receptacle for the other cord (not connected) and see if there are volts. Should be none, but suspect there are.
 
Thanks
I will check for voltage when I go to the boat Thursday evening.
 
Checking for voltage as Ski said is a good thought.

Another thought......In the event that you have only one cord plugged in do you have the option of connecting the 2 ac panels together? Sometimes there is a switch that would allow this so that you can supply 30 amps to both panels with one 30 amp cord. If that switch could be accidentally left on (normally their is a lock out to prevent this from occurring) that would cause your problem.
 
Is the pedestal 50A 240V or 120V?
Same for splitter.... 2 different 50A "Y" splitters and they arent interchangable.
interchangeable.
 
Last edited:
My guess is that the two 120V services are tied together on the hot sides in the boat. I'm pretty sure they can be tied together on the neutrals, so I would say it's probably just a polarity issue. With the boat completely disconnected from shore power and no inverter or genset operating, check continuity between the hot inputs on both 30 amp inlets. They should not be connected.



That said, my boat has a switch that combines the two panels in case I want both panels fed from one source and that switch left on would cause the issue you are experiencing. If you have a switch that does this, make sure it's off.

shore_power_plug_30_amp_125_volt.png
 
Thanks very much for the help. I slipped down to the boat last night and this is what I found.
With one plug plugged in I had full voltage on the hot of the unused receptacle and everything from both panels was working. I then started thinking about a switch.

Last week , before I changed slips, I had discovered an issue with the selector switch for GEN-OFF-SHORE. I had been trying to get my generator to operate the boat I would start the genset with selector on SHORE and every time I would switch to GEN the main breaker physically located on the genset would trip. I accidentally discovered that if I first powered down the boat by turning off the power pedestal then bringing on the genset by selecting GEN all was fine and the generator would run everything on the boat.
So with this in mind I discovered that by switching from SHORE to OFF I no longer had voltage at the unused receptacle and could plug my second cord in without issue. I did note that with only one cord plugged in it would always power both panels on either SHORE or OFF position.

I will investigate further when I have both daylight and a clearer mind, but a resolution may have to wait for my next month visit to the yard, I'm not sure I have the understanding to work this out.
Thanks again for the help.
 
Just a quick read without full understanding of your issue...


My boat had twin 30A that were separate on the shore power setting on the selector switch.


When on genset, a jumper carried power to both 30A panel sections.


Where your selector switch (rotary or slide over breakers) is, look for a set of jumpers (power and neutral).


Take some pics of the back of this area and it may be easier to help in diagnosing your issue.
 
I think Ski & Psneeld are on the right track.

120-volt boats that have two 30-amp cords or single 240/50 will typically have the AC generator wired straight 120 (versus 240). The transfer switch on the generator side will have a jumper between the two hot legs. The shore side should not. Sounds like in your case the shore side has the jumper too. No problem in phase. You get more power. Out of phase you get something else!
 
BigTime said:
Thanks very much for the help. I slipped down to the boat last night and this is what I found.
With one plug plugged in I had full voltage on the hot of the unused receptacle and everything from both panels was working. I then started thinking about a switch.

Last week , before I changed slips, I had discovered an issue with the selector switch for GEN-OFF-SHORE. I had been trying to get my generator to operate the boat I would start the genset with selector on SHORE and every time I would switch to GEN the main breaker physically located on the genset would trip. I accidentally discovered that if I first powered down the boat by turning off the power pedestal then bringing on the genset by selecting GEN all was fine and the generator would run everything on the boat.
So with this in mind I discovered that by switching from SHORE to OFF I no longer had voltage at the unused receptacle and could plug my second cord in without issue. I did note that with only one cord plugged in it would always power both panels on either SHORE or OFF position.

I will investigate further when I have both daylight and a clearer mind, but a resolution may have to wait for my next month visit to the yard, I'm not sure I have the understanding to work this out.
Thanks again for the help.
Click to expand...


Seems like somebody re-purposed your GEN-OFF_SHORE switch to tie the two panels together when in either GEN or SHORE. It would be a great use of your time to make a wiring diagram of how it is right now and make some new labels for the switch.
 
Mischief Managed said:
Seems like somebody re-purposed your GEN-OFF_SHORE switch to tie the two panels together when in either GEN or SHORE. It would be a great use of your time to make a wiring diagram of how it is right now and make some new labels for the switch.
Click to expand...

Yes
Next rainy day I will make a wiring diagram.
Thanks all
 
Does the slip with the 50 amp service have the new GFI? Maybe the slip with the 2 30 amp outlets does not. It sounds like maybe your neutrals are comingled on the boat. How experienced are you with marine electrical systems? If you don’t have a good handle on it maybe you should call in a certified marine electricial to diagnose the problem. If you don’t get it right it could cause a fire or worse.
 
Comodave said:
Does the slip with the 50 amp service have the new GFI? Maybe the slip with the 2 30 amp outlets does not. It sounds like maybe your neutrals are comingled on the boat. How experienced are you with marine electrical systems? If you don’t have a good handle on it maybe you should call in a certified marine electricial to diagnose the problem. If you don’t get it right it could cause a fire or worse.
Click to expand...



I think you are on to something with regards to the newer marina power systems. We have the new pedestals in neighboring marinas with ELCI. We were tripping 30A breakers when connecting our 50A cord to 2x30A with a Y adapter. Our boat electrician told me that I can't use the Y adapter with the 30A pedestals with ELCI. straight 50A to a single 30A is fine.
 
I have twin 30s on my boat. I had to replace my main electrical panel and separate all the neutrals which took several days of tracing wiring. I have a 50amp to twin 30s adapter but I have not tried it on a GFI equiped dock yet. A lot of people are having problems around here since the marinas are upgrading to the GFIs on the docks. So many of the boat owners with tripping issues will insist that their boat does not have a problem but it trips the GFIs...
 
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