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Old 02-04-2019, 06:42 AM   #1
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Random reverse polarity

Here’s a new one to me.


Over the Christmas holiday I took a trip to a new marina. When I arrived at the marina and plugged in one of my lines showed reversed polarity. I unplug this line and plugged it back in and everything was good.

When I arrive to my home marina I again plug back in and a line showed reverse polarity. I figured this line was a culprit so I swapped it with a different line.

Yesterday we took a short trip and when I came back in I plugged everything back in the way it was. Again I showed reverse polarity. After unplugging and plugging back in twice, the reversed polarity light went out.

I was able to troubleshoot a little bit more and saw that this reversed polarity would follow the line.

All of my powerlines are brand new with less than six months of use.

What would cause such an intermittent polarity issue? I have two lines connected to form 100 feet of line.
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Old 02-04-2019, 07:07 AM   #2
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Quote:
Originally Posted by k9medic View Post
Here’s a new one to me.


Over the Christmas holiday I took a trip to a new marina. When I arrived at the marina and plugged in one of my lines showed reversed polarity. I unplug this line and plugged it back in and everything was good.

When I arrive to my home marina I again plug back in and a line showed reverse polarity. I figured this line was a culprit so I swapped it with a different line.

Yesterday we took a short trip and when I came back in I plugged everything back in the way it was. Again I showed reverse polarity. After unplugging and plugging back in twice, the reversed polarity light went out.

I was able to troubleshoot a little bit more and saw that this reversed polarity would follow the line.

All of my powerlines are brand new with less than six months of use.

What would cause such an intermittent polarity issue? I have two lines connected to form 100 feet of line.
you seem to have a hot ground or an open neutral .what does you line voltage meter read when the reverse polarity light is on?
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Old 02-04-2019, 09:10 AM   #3
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You may have a loose or damaged wire where shore power plugs into your boat. I had similar issue last year, I removed the outlet and cleaned a corroded wire and the problem went away.
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Old 02-06-2019, 06:28 AM   #4
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I thought about this but it appears to follow the line when I swapped the lines from 1 to 2
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Old 02-06-2019, 01:30 PM   #5
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Take the suspect line and start performing continuity tests between all 6 end points.
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Old 02-07-2019, 11:42 AM   #6
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You may also need a megger to test the cord. Megohmmeter

It is a small, in my case, handheld mechanical voltage generator of 250V: 500V : 1,000V. I have seen ohmmeters not show any leakage from one conductor to another with an ohmmeter because they only use 9V , not nearly enough.

A leak can occur from damaged conductor insulation or contamination such as salt crystals that will show only at a higher voltage, maybe 60 or so.

You may need to contact an electrician to test the cord for you as these are not inexpensive tools. Mine was $500 20 yrs ago and the electronic units were north of $1,000.

I will temper that by looking at Amazon and I see now that some are available for less than $100. I also see that Amazon does not really know what a megger is since they are also calling a clamp on ammeter a megger when from the description it clearly is NOT. They are NOT the same. If you go that route be carefull that what you are getting is indeed a megger.

If you get one yourself they can do damage if misused. Do NOT test while the cord is plugged into the boat or anything else as that voltage, 250 or more, will be applied to the boat system and blow something. They can also shock you if misused.

You will simply attach the leads to the cord at one cord end, two conductors at a time and test untill you have done all three conductors between each other. If there is leakage it will tell you.
You won't need the higher voltages, the 250V setting will be enough.

Just be carefull or get it done by an electrician.
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Old 02-07-2019, 03:19 PM   #7
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What is the make/model of the device that has your reverse polarity indicator?

The way many of those reverse polarity indicators work is to wire a resistor in series with an LED from the neutral side of the load to earth ground wire going back to shore. In other words, coming off of the load neutral, there is a path through an LED and resistor to the ground wire and to ground.

Under normal circumstances, since the neutral and ground are tied together on shore, current doesn't (significantly) flow through this path -- there is no (significant) voltage across it, no (significant) potential to drive current flow.

In a reverse polarity situation, what should be neutral turns out to be hot and now there exists 120V of potential between what should be neutral and ground, which drives current flow through the LED and resistor.

The role of the LED is to light up. The resistor is current-limiting -- but, more importantly, it builds a tolerance into the system. Wiring is designed to be low resistance, but none is zero resistance. This is especially true of aging connections that may exist along the way. The voltage drop is equal to current* resistance (i=v*r ==> v = i*r). So, under load, the resistance of the neutral wire matters more in the sense that it causes more voltage drop on that wire than on the ground wire, which isn't carrying any current. Now we have a potential difference across the resistor-LED path, which drives current through that path, potentially saturating the LED and turning it on.

The same thing can happen if the neutral line becomes high-resistance for some reason unrelated to load. For example, a bad connection between the shore box and the shore-side plug, or a bad connection between the shore power inlet on the boat and the inlet side plug, or a bad connection at the back of the shore power inlet or where the neutral line connects to the main panel or ELCI, etc. This often manifests itself with other symptoms, e.g. lower AC voltage on the meter, or fluxuation as the bad connection is stressed by vessel movement, etc.

In older systems where, instead of an LED, there is a light bulb, either of these situations most often shows up as a less dimly lit bulb than a true reverse polarity situation. You can sort of tell it isn't the same "bright light" that exists with a true reverse polarity situation. But, in LED systems, some times the difference in brightness just isn't as noticeable.

Where am I going with this? If I had to take one blind guess, I would guess that the problem lies with your shore power cable, shore power inlet, or the wire between the inlet and the reverse polarity circuit. I would guess that current is leaking from hot to neutral.

If I had to lay a more detailed guess, I would guess that corrosion, debris, salt water, or dirt and water exist on the plug that goes into your shore power inlet or the inside of your shore power inlet that were serving as a path for leak current. I'd clean them out, dry them off really well, check the back of the inlet for moisture/corrosion/grime and clean it as necessary, and then see what happens. In your situation, not being able to see things, I wildly speculate that there is a good chance that this will fix it.

If it didn't turn out to be a shore-side hot-neutral leak, and I got a second guess, I'd guess that it was a high-resistance neutral. I'd check and clean all of off the connections along the way, paying particular attention to trying to find corroded connections, brittle broken wires, things pulled out of crimps, etc.

If that still didn't turn out to be it, and I got a third guess, I'd start inquiring about the load at the time and how it effected the situation, e.g. air conditioners, etc. If the load on the system was particularly high, my next guess might be that the load was too high for the wiring and that the natural resistance of the neutral wire was overcoming the resistance of the reverse polarity circuit, causing that LED to light up.

Wild guesses from the peanut gallery.

-Greg
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Old 02-08-2019, 06:44 AM   #8
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When you plug in, do you do so with the power post breaker off, then turn the breaker on? Or do you plug in hot?


In general it's better not to hot-plug. But in this case I'm wondering if the order in which the conductors make contact in the plug(s) might be causing this apparent problem?
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