Reverse Polarity Light came on suddenly - What happened?

smokey73

smokey73

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Oct 26, 2010
2,214
Hunter 40.5 Beaufort, SC
Long story follows but to describe accurately (not worrying about complete sentences)

Working on boat yesterday (no electrical work) hooked up to shore power at yacht club. Checked polarity before hooking up (pushed test button with no beakers closed on boat - light comes on) - everything fine - turned on A/C heat (reverse cycle heat pump), battery charger and AC outlet (plug in) breakers. Still everything fine. Plugged in a household vacuum (Dyson) and began cleaning up and vacuumed for about 5 minutes, everything fine - after awhile vacuum stopped and I noticed Reverse Polarity Light on. Immediately tripped AC Main breaker, and switched AC Power Surce rotary switch to OFF. Turned all AC breakers off and rotary switch back to Shore Power. Pushed Reverse Polarity test switch and light came on "dimly". Closed AC main, no light. Then closed various AC load breakers. Each time I closed a load breaker the Reverse Polarity light came on brightly. Tripped Main AC breaker off and AC source switch to OFF.

Then I started the Generator and switched the AC Power Switch to Generator Power. Pushed Reverse Polarity Switch and light came on brightly. Closed AC main breaker, no light. Closed Battery Charger, A/C heat, AC plug breakers. No Reverse Polarity Light, everything worked fine, including the vacuum - no problems noted. This would seem to indicate to me that everything on the boat was okay and the problem was probably at the Yacht Club power source? Does that sound right?

I went up to the Yacht Club yard and asked around to see if anyone had changed up there in the last half hour - everyone answered no? I did notice that there was a hand held power saw plugged into an outlet up by the pool but it was not being used.

WHAT THE HECK HAPPENED?

Heading back to the boat today to do some more work. Won't hook up to Shore Power other than to see if the problem is still there. Will update as I sort this out but any thought are welcome. Hopefully Mainesail will add his thoughts.

Thanks in advance
 
B

Benny17441

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May 24, 2004
7,213
CC 30 South Florida
Yes, it sounds like it is a shorepower fault and unfortunately it seems to happen quite often in marinas across the Country.
 
BigEasy

BigEasy

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Jun 21, 2004
3,111
Beneteau 343 Slidell, LA
Can't say what your issue is with info available. Had a reverse polarity issue last year. Started checking at dock power pedestal, & power cord with no problem detected. The power inlet on the transom was the source of the problem. Took the opportunity to convert to a smart plug, problem solved. One of the best upgrades that I have done.
 
Gunni

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
This kind of thing happens when your shore power cord comes loose at the dock plug.
 
agprice22

agprice22

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Aug 3, 2012
2,542
Performance Cruising Telstar 28 302 Watkins Glen
Gunni said:
This kind of thing happens when your shore power cord comes loose at the dock plug.
Click to expand
I would guess “loose” could be worn prongs, corrosion, etc.
 
smokey73

smokey73

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Oct 26, 2010
2,214
Hunter 40.5 Beaufort, SC
I have a new (2 year old) Smart Plug on the boat and a "Factory" Smart Plug shore power cable. (Marina end is an old style plug though). I checked the voltage and resistance at the shore side pedestal. I'll have to figure out which of the plugs prongs is supposed to be hot and which is neutral and which is ground. I'll make some sketches this evening and post my results. I plugged in a tester to an AC outlet on the boat with shore power connected. It showed "Hot and Neutral reversed". When I started the generator and used the the same plug it showed "all normal". I'll post some more info this evening with pics, etc.
 
SG

SG

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Feb 11, 2017
1,670
J/Boat J/160 Annapolis
This is the diagram that should tell you, Smokey73
upload_2018-1-20_17-42-53.png
 
Gunni

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
smokey73 said:
I have a new (2 year old) Smart Plug on the boat and a "Factory" Smart Plug shore power cable. (Marina end is an old style plug though). .
Click to expand
At the marina end. Loose plug will set off a reverse polarity signal. Been there.
 
SG

SG

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Feb 11, 2017
1,670
J/Boat J/160 Annapolis
It can also be a corroded connection that is not allowing consistent flow. I'd make sure your shore power connections are clean inside the box. Did they get flooded in the Hurricane(s)? They may still have issues.

I've seen shore power "towers" burn out. Pretty scary while standing on a rain soaked dock ;^)))
 
LeslieTroyer

LeslieTroyer

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May 20, 2016
3,015
Catalina 36 MK1 94 Everett, WA
Here is a short write up on the reverse polarity led from blue sea https://www.bluesea.com/support/articles/AC_Circuits/85/AC_Reverse_Polarity_False_Indicators.
Basically it’s telling you that neutral has > 0.7vac when compared to ground.

This can be caused by either your boats circuits ( high impedance on the neutral line) or from the dock for various reasons. A simple check with a vom will tell you how much. If on the marina side notify the management with your findings.

Mahalo
 
smokey73

smokey73

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Oct 26, 2010
2,214
Hunter 40.5 Beaufort, SC
Thanks all. I used a Volt Ohm Meter on the shore side AC plug. I found the diagram from SG and checked it against the shore side AC plug On the diagram from SG, going clockwise from the Ground (G) it is supposed to be Ground (G) - Neutral (W) - Hot. What I measure indicates it is actually wired clockwise from Ground (G) - Hot - Neutral. So it would seem that the Hot and Neutral are reversed. This is consistent with what I showed on my handy-dandy plug tester. The pic of the tester is blurry but the two lights corresponds to Hot - Neutral reversed. I notified the Yacht Club manager this evening. Not sure how it got that way though since it was working properly earlier in the day?

0120181308d.jpg 0120181309.jpg
 
smokey73

smokey73

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Oct 26, 2010
2,214
Hunter 40.5 Beaufort, SC
Thanks, I hadn't thought about that. I'll have them check the polarity elsewhere at the club to see if its the pedestal plug or the incoming to the Yacht Club.
 
peacheykeen

peacheykeen

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Dec 8, 2013
33
Hunter / Aragosa 34 / 32 831 Toronto
Having had the same problem recently I would suspect your cable, either end, or the boat input pins.
What you're trying to do is reassure yourself that the problem isn't your equipment, it must be the shore side.
The best way to test that is to go to another outlet on the dock and test it/them.
Best quess at this end is if it is the shore side - was that a 15 amp duplex outlet?- there's either a bad pin (corroded, misaligned), or connection in the box.
Also, if you're using a 15/30 amp adaptor, the connections would heat up just from the loads you've been drawing.
Mine was a 15/ 30 adaptor that overheated and burned out. First warning was crackling noise due to poor connection at 15 amp pins. No breakers went off. The power went out, the reverse polarity light was on
dimly and I found the adaptor completed melted out at the return pin. lesson learned: all connections are a potential weak point.
When powered by a duplex outlet, I now use an 15a extension cord with #12 conductors, 15amp male at one end and a female 30 amp plug on the working end; NO adaptors.
 
smokey73

smokey73

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Oct 26, 2010
2,214
Hunter 40.5 Beaufort, SC
Resolution - After carefully checking the cables and connections on board I found no problems there. I cleaned the spades on the shore power cable and everything is fine now. I can only conclude, as others have suggested that the extra resistance leads to the reverse polarity light coming on. When the contacts were cleaned there were no further problems.
 
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