Boat electrical question

Chasin' Dreams

Chasin' Dreams

Well-Known Member
Hi guys. I have my boat on a trailer next to my home and just hooked up the shore power from the boat to the house to keep the batteries topped up. I have the shore power going to a 2500 watt inverter/generator and to a 30 amp breaker panel in the cabin. Two 15 amp breakers run the fridge, the 120 volt outlets and the cabin lights.
I've used shore power several times and have never noticed the red reverse polarity light go on before but this time after plugging it in I noticed the light go on. I checked all the wiring, extension cords, house outlet etc and can find no reverse polarity anywhere but I do notice up to 5 volts showing up on the neutral line on the extension cord coming from the house to the boat. Would 5 volts on a neutral be enough to set off the RP warning light?
I'm going to check all the neutrals on the boat tomorrow morning to make sure there's not a bad one so far and that all the grounds are tight etc.
Just concerned about this reverse polarity light. Nothing seems to be shorting out and no breakers are popping off but still wanna be sure nothings going wrong.
 
Neutral wire carries unused current back to where it was created..... Earth. Ie: If 15A leaves a breaker and your heater uses 10A, then the neural carries 5A back too the panel.when you mention polarity that is a term for extra low voltage. Positive and neg 12 or 24volt systems. Look for reversal of 12 volt devices.
 
Thanks ericl. I checked the house plug and the polarity there is fine. No voltage at all on the neutral. I think it may be the plug adapter on the extension cord going from 30 amp configuration to the regular 15 amp plug then into the shore power plug in the boat gunnel. There's been lot's of condensation in the boat over the past month cause it's been tarped to keep the snow off. I'm going to dry everything out very well today and go over all the connections I can on the boat to see where it's picking up that RP reading from. My other thought is I wonder if some voltage is jumping across the aluminum where the outlet plugs are screwed onto the boat. It's a welded aluminum boat and where the outlet hot and neutral connections are on the outlets are very close to the aluminum. I've got a voltage meter I'm going to use to go over everything really thoroughly today.
 
bones said:
Neutral wire carries unused current back to where it was created..... Earth. Ie: If 15A leaves a breaker and your heater uses 10A, then the neural carries 5A back too the panel.when you mention polarity that is a term for extra low voltage. Positive and neg 12 or 24volt systems. Look for reversal of 12 volt devices.
Click to expand...
I'm not sure but I don't think this RP light indicator is connected on the 12 volt system is it? It's on the breaker panel from where the shore power goes to the generator/inverter then to the 30 amp/120 volt pannel. When I switch the main switch to inverter/shore power that's when the RP light comes on. When I switch it to just inverter generator power the light goes out.
 
pardon, you mentioned charging batteries and have 5v on what is being called N or common. voltage on return path is usually series low voltage issues.
you cannot get voltage on a neutral in AC systems only current. is the extension cord stock or does it have a new end on it? is the extension cord reversed at the ends?
 
Dried out and cleaned up the plug adapter and gunnel connection for the shore power and that got rid of the 5 volts on the neutral but when I turned on the cabin shore power/inverter switch there was 9 volts showing up on the neutral coming out of the 30 amp main boat cabin breaker. This is right where the reverse polarity warning light is. When I turn it off from that main breaker and switch it to just using the generator/inverter power the warning light goes out. So I'm pretty sure it's that main breaker causing the RP light to go on. I watched everything closely as I had the shore power hooked up and charged up the batteries/generator and nothing shorted out, no connections got hot etc. So it seems everything is ok. I'm going to buy another breaker just to be safe though.
 
When you say voltage on a neutral, how are you metering this? Or what is the neutral?
Neutrals or common conductor or identified conductor in a 120v does not carry voltage.
 
That's how the reverse polarity light detects a problem Bones; by voltage showing up on the neutral/common line. That's correct, they are not supposed to have voltage. That's what the problem is and why the reverse polarity light is on. I am using a voltage meter to test the lines.
I think it will all be good when the breaker is replaced.
 
Are you talking ac or dc? You say neutral so ... AC. ??? I'm just try to establish where the cross is. If this is on the dc side then.... Would you be think the neg - not neutral. If it I the dc side then its very hard to track down on a computer. Your reverse has to be tracked device by device.
 
i have to agree with bones, do not buy a new breaker,it is NOT the problem! the voltage that you are reading on your neutral is called potential difference. simply put it is the voltage difference between the two lines that you have connected to. A 120 volt, 2 wire system has 120v ac on both the hot and neutral while connected loads are drawing power. What you need to verify is that you have 120v ac from your hot lead to ground (not neutral)at the boat end of your shore power while it is unplugged.
A small amount of potential difference is not unusual, emf fields caused by electrical current can induce voltage on the neutral as the neutral is run right next to the hot in a/c cable. Feel free to pm me if you need more help
 
Hoochiebob said:
i have to agree with bones, do not buy a new breaker,it is NOT the problem! the voltage that you are reading on your neutral is called potential difference. simply put it is the voltage difference between the two lines that you have connected to. A 120 volt, 2 wire system has 120v ac on both the hot and neutral while connected loads are drawing power. What you need to verify is that you have 120v ac from your hot lead to ground (not neutral)at the boat end of your shore power while it is unplugged.
A small amount of potential difference is not unusual, emf fields caused by electrical current can induce voltage on the neutral as the neutral is run right next to the hot in a/c cable. Feel free to pm me if you need more help
Click to expand...
Yes, the voltage is all correct, no RP going on from the house power to the boat. And no problem at the boat connection in the gunnel. I tested the voltage on the other side of that connection and all is good. No RP.
I think RP lights are usually wired on boats with 25K resistors. How many volts will a 25K resistor hold back before letting it through to light up the RP light at the breaker panel?
If I test the neutral line after the resistor that goes into the RP warning light wouldn't that tell me how many volts are getting to the RP light? And if so isn't there only one possibility for where that voltage on the neutral is coming from ie the breaker? Or can voltage on the ground also set off the RP light?
Like I mentioned earlier; there is only 9 volts showing up on the neutral line coming to the breaker from the shore power. So if that's the case, how can the RP light be going off?
What if the 25K resistor blew when the GFI shorted on an outlet when I was using too much power? Would that let any amount of voltage through the resistor to set off the RP light?
 
So your on the low side? Your RP light has nothing to do with resistors. Resistor is there to limit voltage. If allows voltage to flow all the time. Zeener diode has a break over voltage. Ie: A red led light runs at 3v. You put a voltage dropping resistor in series with it with enough resistance to drop 9V. Now the led light see's the difference 3v and lights up and not burns up.
A breaker is a protection device, it is there to control, overload and short circuit. When a circuit overloads amps run out of control. The breaker controlling it shut down Via thermal break the circuit before th insulation fails
Your digging to deep. Keep it simple and you will figure it. There will always be voltage on the neg - side pending where you put your probes. You can also pm me as well. A picture would help as dc voltage is .... Difficult. Ps: Its not a neutral but a neg-

My red light on my charging control turns green when the batteries are full
 
Here are something's to try. Turn ea breaker or fuse off one at a time until the light goes out. That is your dc branch circuit that has a rev polarity. Trace those wires back to each device, might be more than one.
 
Thanks Bones. I will take the breaker panel out again on Monday and take some close up pics of it to show you.

"My red light on my charging control turns green when the batteries are full"
Is that red light also your reverse polarity warning light?
 
If I've read this correctly and you can measure a voltage between ground and neutral, the problem points to a bad or corroded splice in the neutral wire somewhere.

Joe
 
Well guys thank you all for your help but turned out there was no problem. As Bones pointed out on a post "My red light on my charging control turns green when the batteries are full" This was also the case with the Reverse Polarity light on my boat. Why they use the same light to show low battery's is beyond me but sure enough when the shore power charged up the batteries to full power that light went out. And the light isn't labeled with anything mentioning low batteries. All it says is "Reverse Polarity" That was a time consuming lesson lol.
 
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