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Old 05-09-2014, 02:05 PM   #1
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Odd Reverse Polarity Issue

Hello. I have a rather peculiar issue involving the reverse polarity light on my Blue Sea AC distribution panel.

Reverse polarity light is faint (but lighted) when shore power is plugged in and the AC switch is off. Meter on the AC panel also reads around 35-40 volts AC.

HOWEVER, when I turn the AC switch on the reverse polarity light is off and I read nominal voltage (~120 VAC).

I plugged in a polarity tester to all my AC outlets and there was nothing out of the ordinary. I checked the wiring at the AC panel and all looks good--neutral, hot, and ground are wired correctly.

This has happened at three marinas. Perhaps my Blue Sea panel is defective?
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Old 05-09-2014, 02:23 PM   #2
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Working on control panels that used LED lights we would occasionally see dimly glowing LEDs that should have been dark. The fix would have required installing diodes all over the place so we instead mentioned the phenomena in the operating manual. They can backfeed and light easily because they draw so little current.
If your light is incandescent, then you might have a problem, but LEDs can light (dimly) from tiny stray voltages or one ground being more negative than another ground, it's one of those little problems that pop up with LED indicator lights sometimes.
What exactly does your AC switch do?
I have no experience with the subtleties of marine grounding schemes.
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Old 05-09-2014, 02:35 PM   #3
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Hi, Bluto. Yes, the light is LED. I'm not sure about your question--the AC switch I mentioned was referring to the "AC main" switch.

Shore power plugged in and AC main off = dim light and 40 volts AC

Shore power plugged in and AC main on = no reverse polarity light and ~120 volts AC

The 40 volts AC is what has me particuarly baffeled.
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Old 05-09-2014, 02:40 PM   #4
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I had a similar situation. It ended up being shore power! There was 30Vac across ground (green) and common (white). Once they traced the problem they found a shorted meter.

Disconnect shore power and make sure you don't have any bleed over....
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Old 05-09-2014, 03:18 PM   #5
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Thanks! I Googled 30VAC and "shore power" and found several references related to this issue. Most appeared to be as you noted: stray voltage on a marina's neutral and ground. I've also gathered from my findings that this could be the result of AC noise and I'm not really measuring "true" 30-40VAC. I'm going to bring one of my high end voltmeters to the marina and conduct a test.

I'm fairly certain now that the problem is not on my end.
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Old 05-09-2014, 04:19 PM   #6
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It looks like some real boaters are chiming in, so I will defer to their experience.
It would seem like the shore power wiring in some marinas can cause weird problems. It doesn't take much 'noise' to dimly light a small LED.
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Old 05-09-2014, 06:12 PM   #7
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Quote:
Originally Posted by Bluto View Post
It looks like some real boaters are chiming in, so I will defer to their experience.
It would seem like the shore power wiring in some marinas can cause weird problems. It doesn't take much 'noise' to dimly light a small LED.
Bluto is most probably correct but a check is worth while.
disconnect from shore power
Close (turn on) all your circuit breakers
Set multimeter to ohms/resistance
insert one probe into the neutral slot in an outlet
and one probe into the ground slot
There should be no continuity between ground and neutral

a few intricacies ...
If you have an inverter make sure it is turned off
If you have a generator make sure its off and its breaker is open
If you test at a GFCI protected outlet you are permitted no less than 25megohms resistance (ABYC).

If you see continuity (less than 25megohms) between neutral and ground the problem is on your boat and it is significant.
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Old 05-09-2014, 06:47 PM   #8
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This may help you sleep better at night. It did me.

http://www.bluesea.com/resources/85
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