Reverse Polarity with load only

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L

Lober

.
Jan 22, 2008
8
Beneteau 473 Annapolis, MD
Encountered on 2000 Ben 361 during survey.

Reverse polarity light on. After further look, it only comes on when the 110 is drawing current - ie water heater on or microwave running. It goes off when these breakers are off. The battery charger does not seem to trigger the RP indicator - maybe current draw was too low.

Related to current draw or does this mean batt charger is wired OK and rest of boat is not.

Shoe power checked OK but the GFI at the shore power station was not working...
 
L

Lober

.
Jan 22, 2008
8
Beneteau 473 Annapolis, MD
Encountered on 2000 Ben 361 during survey.

Reverse polarity light on. After further look, it only comes on when the 110 is drawing current - ie water heater on or microwave running. It goes off when these breakers are off. The battery charger does not seem to trigger the RP indicator - maybe current draw was too low.

Related to current draw or does this mean batt charger is wired OK and rest of boat is not.

Shoe power checked OK but the GFI at the shore power station was not working...
 
KD3PC

KD3PC

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Sep 25, 2008
1,069
boatless rainbow Callao, VA
I seem to remember that the 99-2000 36CC and 361 had an issue with the inverter that would cause the reverse polarity...you might check what is "on" the inverter circuit or where the feeds for those two breakers come from...

it could be as simple as mis wired shore power or isolator...

Not sure how the shore power would be OK, if it's GFCI was not..that could be the problem as well...neutral
 
Bill Roosa

Bill Roosa

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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Three wire AC 101

There are three wires in a 110 volt AC service. Hot, neutral, and ground. The ground is where your problem is. For marine use ALL circuits must have a ground that is only connected to the neutral at the source. non marine gensets are wired with the neutral connected to only the genset case and not the neutral. There are a number of reasons for this but they are complicated. The key point is your boat genset must act like an independant stand alone generator that provides a ground return to the source not a ground return to the ground proper. You might have notice your boat does not have a real ground rod like your house. the ground rod in your house returns current to the power station through the dirt. You can't do that on a boat so you have to return the ground to the neutral.
Is the genset a factory option or an owner upgrade? If a factory option it is surly wired correctly and the problem is the GFI shorting the neutral to ground. If it is a owner upgrade then it may or may not be wired correctly.
Fix the GFI box first and see if that corrects the problem.
 
L

Lober

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Jan 22, 2008
8
Beneteau 473 Annapolis, MD
Re: Three wire AC 101

No inverter on this model and no genset. Just AC into the panel. Strange that when all 110V breakers are off (except the main feed), there is no problem. When a breaker is turned on and load applied (say the outlets with microwave on) the polarity indicator comes on. I would not think reversed polarity is dependent on the load applied...
 
J

JohnShannon

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Jan 4, 2010
1,037
Farr 30 San Francisco
I would guess, and the word is guess that you have a high impedance in the neutral.

I think the polarity indicator works by measuring a voltage between neutral and ground.

In a residential case the neutral and ground are tied together at the service entrance to the house. So you have 3 wires a hot, a neutral and ground. There should be no voltage between neutral and ground, if an outlet gets miswired and the hot and neutral get swapped then you get 120V at that socket between neutral and ground and a polarity error would result. In your case it seems some voltage is being developed between neutral and ground as load current increases. Resistance and current will develop voltage. So I would check the voltage at one of your boat outlets when the high current load is on and off. You should get 120V between the two narrow slits and (here I may be wrong) 120V between one of the slits and the big ground hole and 0V between the other slit and the ground hole. If you don't i.e see more than a few volts then that could explain the RP.
 
L

Lober

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Jan 22, 2008
8
Beneteau 473 Annapolis, MD
John-

Just came to the conclusion after drawing out things... I bet that is it given we are going through about 150 feet of extension cords during the survey... Probably developing about 5 or 10 volts on the nuetral when under load - enough to light the diode...

Thanks
Rick
 
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