Shore power reverse polarity

M

menos22

Member
May 26, 2009
165
Colonial Beach, VA
Boat Info
1994 Sea Ray 350 Express Bridge
Engines
Twin 454 Mercruiser With V-Drives
Going crazy trying to figure out this problem. Here is the situation: Just had a new Kohler 5e installed on the boat, replaced a 7.5kw quicksilver. All went well, Kohler is doing fine. When I got back to my dock and plugged in my shore power, line 1 had about 60volts and Line 2 showed about 30volts and reverse polarity, My dock set up is 50Amp receptical, 50Amp splitter to two 30 amp cables to boat line one and two. Have used this setup for 5 years no problems. Swapped out the splitter, same problem. Replaced the 50 Amp receptical, no help. Cleaned all cable contacts, same problem. Here is the kicker. When I plug one 30 Amp cable into a 30 amp outlet it works fine. Find it hard to beleive I have two bad splitters.
Could the new generator installation have anything to do with it. Nothing was changed in the power panel on the boat. They used the existing AC power cables from the boats power panel to the new generator. A new remote start/stop switch was added.
Again all seems good when using the two 30 Amp cables, its when I try to use the 50Amp outlet with the 50Amp splitter. Any thoughts and or suggestions would be greatly appreciated. Thanks in advance. Mike
 
Maybe the 50 amp outlet on your dock has some corrosion or other issue.
 
I would test the cables where they plug into the boat with a voltmeter and check each leg (both disconnected from the boat). That would eliminate the pedestal, splitter, and cables. That would isolate the issue to the boat.
Was the generator a replacement or an addition? It should be isolated via breakers on the panel that allows a choice of shore power or generator.
 
Sounds like this issue originated immediately after the new genny install? My inclination is that it has something to do with the new genny wiring even though it should be isolated from the shore power. Here is where I think the problem is. Your boat systems are all 120 volt. The genny only produces 120 volt so no issue. When you plug in your 30 amp. power cords, all will be fine “IF” both power cords are on the same power leg on the pedestal. When you use the 50 amp. power cord (2 separate power legs that produce 240 volts) those 2 legs maybe getting connected on the boat somehow creating the issue.
 
Yes, the issue originated after genny install, it was a replacement, using the same 120ac lines from power panel to new genny. All cables have been metered out, 120vac on the two ends of the 30amp cables coming off the 50amp splitter. 240vac between the two 30amp cables, all seems good. No issues when I use the 30 amp cables directly into a sepearte 30 amp receptical on the dock. The 50amp receptical has been replaced. Everything seems to point to the splitter, but I borrowed one and it did the same thing, 2 bad splitters unlikely.
 
If the cable ends metered correctly it has to be the boat not the power feed. Something is wrong with the installation.
 
Not sure exactly what happened, but I would be looking at the neutral connections and grounds. I don’t recall which way it has to be off the top of my head, but the neutrals from the genny and shore power should all be connected, or not. On a Genny, they typically bond the neutral to ground. On shore power, typically an electrician by code would keep them separate. It’s been a while since I did that type of work, but the issue is in those connections at your panel
 
menos22 said:
Yes, the issue originated after genny install, it was a replacement, using the same 120ac lines from power panel to new genny. All cables have been metered out, 120vac on the two ends of the 30amp cables coming off the 50amp splitter. 240vac between the two 30amp cables, all seems good. No issues when I use the 30 amp cables directly into a sepearte 30 amp receptical on the dock. The 50amp receptical has been replaced. Everything seems to point to the splitter, but I borrowed one and it did the same thing, 2 bad splitters unlikely.
Click to expand...

Agreed with 2 bad splitters unlikely. More likely the issue is with the new genny hook up since it wasn’t a direct replacement. Just because there is no issue with the genny running doesn’t mean there isn’t something getting back fed thru the genny hook up when you hook up to shore power. Should be completely isolated from shore power but it seems that the issue has occurred with the new hook up. Thinking out loud here but are there 2 separate feeds from the genny to the Panel? If so, were those isolated on the old genny and now they are combined on one terminal on the new genny? I would suggest disconnecting the power feeds to the genny and see if it solves the problem.
 
There should have been a transfer switch installed and if so I would check at that for proper routing of hot, neutral and gfi connections.

If there was not a transfer switch installed then there is a much larger problem.
 
Have you checked (with a meter) what the dock side 50amp circuit is providing? While the outlet may have been replaced - it could be the circuit itself, or something upstream on the dock.
 
With dual 30A plugs your electric panel is wired for two legs of 120v that are independent of each other tied together through the neutral (white wire) and the ground from the dock tied to the bonding system and that tied to the neutral through a zinc saver. That is the very typical general setup.

Most generators are all 120v, no two legs of 120v, only one. That is handled via the cross over switch. The newer cross over switches feed both legs of 120v with one leg of 120v. So while on generator 220v is not possible, while on shore power the boat is fed with 220v split between the two power cords going to the panel.

The above is very common in the way most boats are setup. Now is it possible to have the generator supply 220v, absolutely. The way to tell visually without opening up the panel is to see if you have a rotating switch that selects shore-off-generator, that will then feed the the breaker panel. Another way of the generator feeding the panel is to have two sets of double breakers (sometimes only a single lever) with a slide that prevents both sets of breakers from being on at the same time.

If you have a selector switch that could be wired wrong for the way the generator is strapped (wired). The generator usually has four phases of 60v ac that are strapped together to create 120v or 240v ac in multiple or single phase. Getting an electrician in most cases will not help you unless they understand how marine generators work.

So, what to do? - first is there a selector switch or just breakers or both? Then use a multi-meter to see how the generator is wired meaning, measure the 3-4 wires exiting the generator so you know what the generator is supplying the boat with. Next look at the electric panel and verify the wiring. If you have a selector switch there should be a manual that shows many different wiring models. You need to verify how that is wired.

My guess is that you have a selector switch and it is wired incorrectly for your setup. But just a guess based on what your describing. If your not comfortable measuring and re-wiring the switch, you should find a very knowledgeable mechanic/electrician to do the testing and re-wiring.

EDIT: It is possible to remove the selector switch if you have two double breakers and make the wiring much more simple.

Blue Sea double breaker switch(s)

Blue Sea selector switch - see schematic link
 
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I have breakers, no selector switch. I have 2 120vac panels, line 1 and line 2. Line one is for stove, water heater, microwave, fridge, etc. Line two is dedicated to the two air conditioner units. Each panel has two breakers, one for genny and one for shore power with a slide switch to prevent having both on at same time.

The new genny was installed using the existing 120vac line from the boats power panel, nothing was touched in the boats power panel. The existing 4 wire ac connection from the old genny was simply connected to the new genny.

If I connect shore power using the 2 30amp power cables all is good. When I use the 50amp splitter I get 60volts on line 1 and about 50volts on line two with reverse polarity. Changed splitters same problem. I tried turning the breaker off on the genny no help, guess I should try disconnecting the power cables from genny to power panel see what happens. Thanks for your help.
 
The “breakers” with the slide switch for the shore power/genny are actually the transfer switches so you are good there.
Basically 1 hot and 1 neutral make 110-120. 2 hots and 1 neutral makes 220-240.

I suspect 1 hot from shore pwr is wired to to both line 1 and 2 which would result in 110-120 if both neutrals are properly wired. Which means 1 hot is not properly connected.

The hot wires should be black and the neutrals should be white.

Before opening the pwr panel for inspection insure all pwr to the vessel is disconnected.
 
Copy that. I disconnected the White, Black and green from the generator control box. These are ther 3 wires going to the boats power panel. Same results however, what i had not noticed before is when I apply power to line one it reads about 60v and normal polarity; when I apply power to line 2 with line 1 still on, line one tries to peg the voltmeter and both lines read reverse polarity. It sure seems line the splitter to me. Tomorrow I am going to move the boat over to a different 50amp outlet just to elimanate the wiring from the dock power panel to the splitter. Will advise..
 
I love a good mystery.

Just curious.....normally a Kohler or Westerbeke requires a new control harness to go from the generator to the remote control panel. When you said they didn't touch the remote control panel......I wonder how the new generator was wired in.

It sure seems somebody crossed a hot and a neutral someplace during the installation.

Keep in mind that while you have two 30 amp cords in bound......they are directly wired to two sections of the remote panel: HVAC and everything else. At that point they are isolated from each other. The generator only provides one connection to the panel which when power is transferred provides AC to the HVAC AND Everything else through a single connection. They accomplish this with isolated transfer switches.

When they wired the Kohler in I'm speculating they got this wrong. That may explain why single cords work and using a 50 amp splitter does not. Disconnecting the wires at the generator will not solve this if they swapped the wrong wires at the panel or one of the transfer switches has gone bad.
 
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Think the mystery is solved. Took boat over to another marina and using my existing splitter and two 30Amp cables I plugged into a 50Amp breaker and everything was working just fine 120vac on both line one and line two and normal polarity.
OK, back to my dock. Ohmed out the wires from the breaker panel to the 50Amp outlet, every now and then would get erractic reading on the ohm meter between hot and netural. Further investigation found that one of the hangers supporting the conduit running under the dock had broken lose and was in the water. Dont know how long it has been in the water but looks like one or more of the wires from the panel to the plug is corroded or nicked. The 50Amp breaker has been removed and will replace with new wire run and secure conduit. Believe this will take care of the problem. Thank you all very much for your input. Will advise what wiring replaced and final results.
 
Does that mean there could have been electrical current in the water?
Why wouldn’t a breaker in the shore panel open?
Dangerous situation?
Another reason why you shouldn’t swim in marina?
 
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