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Go Back   SailNet Community > On Board > Gear & Maintenance > Shorepower and Reverse Polarity
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Thread: Shorepower and Reverse Polarity Reply to Thread

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Topic Review (Newest First)
12-03-2007 10:46 PM
sailingdog Layer 1 is always important to check...
12-03-2007 10:03 PM
oft UPDATE: As it turned out, our neighbor, while unplugging from shorepower, had bumped our cable causing it to pull out somewhat from the connection and this, in turn, resulted in the reverse polarity situation. So, checking connections and terminations is not a bad place to start.
06-13-2007 06:14 PM
bestfriend Please forgive my naivete with electrical systems on the water. There is a button marked "test polarity" and then a light next to it that says "reversed". I think I misunderstood that as "push this button to test your polarity". I am guessing that it means "push this button to test the polarity light/alarm system". So, you push the button and the light goes on telling you that your check system is operative. My light is not always on. Thinking on it more now, I would think that the light would go on automatically if there was a problem.
Update: I got the confirmation that I needed. The button is a check system. Thanks all.
06-13-2007 03:45 PM
capthor Oft Junior member! I think,that this system your boat is connected to,is a 240 120 V system.Which means that you have two or three wires in to the distrybution box on the dock +groundwire.If you measure between one of them two or three wires and the ground you get 120 Volts.The ground and the neutral wire are the same thing.Red light on your switchpanel means leak to ground on your outlet.Since here in America you donīt have groundleak breakerswitch,this light is in stead.
06-13-2007 07:18 AM
sailingdog Yes, but I doubt it. Get one of the dongles that allows you to plug a regular extension cord in to your shorepower outlet and then get a regular household polarity checker... keep them both aboard the boat, and use whenever you're at a different marina—to check the wiring status before you plug your boat in.
06-13-2007 02:25 AM
bestfriend Well, she survived through the night. The only way I could get the polarity light to go off was to unplug the shore power. I didn't have time to check the dock receptacle with a meter, that will be tomorrow. Watch the news for "sailor electrocuted". If the dock receptacle is not reversed, could the problem be on board?
06-12-2007 01:10 AM
Oh Crap!

I just happened to push the "test polarity" button today on the boat and it lit up like a christmas tree. I didn't think much of it, everything was working fine and has been since we moved to the new slip a month ago(yikes!). Not being much of an electrician, I figured I would check out sailnet for the answer. Not the answer I was hoping to hear. Now I am across the Bay for the night, 40 minutes away with a couple (read half a bottle) of glasses of red wine in me. So, stay tuned for tomorrow's local fire report! Wish me luck.
06-08-2007 11:19 AM
bhcva Thanks for the post by Art Richards....I've had exactly that problem for 12 years and no one has been able to explain it except to say "don't worry"...the light glows very brightly when the water heater is on and very faintly at other times.

06-08-2007 10:03 AM
phaiakian credit goes to Art Richard IP32 #34 "Lagniappe" (St. Petersburg, FL) for the following dialogue:

A low-level reverse polarity light on an IP when there is heavy current draw (like a heater or air conditioner) is not unusual. The reason is as follows:

1. The reverse polarity light is connected between the AC neutral (white) and AC ground (green) wires inside the distribution panel. If there is a voltage between these two lines, the light lights in proportion to the voltage.

2. When using shore power, the neutral and ground wires are connected together somewhere on the shore at a power distribution box. Between that point and your boat load (heater) are many feet of wire. Normally the AC current flows through the hot (black) wire to the load (heater) and back through the neutral (white) wire to the aforementioned distribution box (of course the current also flows through the black and white wire back to the power generator, but that is not pertinent to this discussion).

3. When current flows through a wire, the small resistance of the wire causes a voltage drop which is proportional to the length of the wire and the resistance of the wire. You see this on your AC voltage meter when you turn on a high current load (heater). Depending on the load and the length of wire, this voltage drop is sometimes 10 or more volts.

4. The reverse polarity lamp is effectively measuring the voltage between the neutral and ground wires at the boat. Since the ground wire is not (normally) carrying any current, there is no voltage drop in this wire. The neutral wire however is carrying current and does have a voltage drop. This voltage drop in the neutral wire appears across the reverse polarity lamp, causing it to glow, the brightness depending on the actual voltage drop in the neutral wire. This glow is not an indication of reverse polarity, and will not normally cause a problem.

When you have a bright glow in the reverse polarity here is what happens:

1. In order for the bright glow to happen, there must be a high (about 100+ volts) voltage difference between the neutral and ground wires in your boat.

2. When the polarity is reversed, the power source's hot (black) wire is connected to the boat's neutral distribution, and the white (neutral) wire is connected to the boat's black wire. This can cause electrolysis and lots of other problems as well as being very unsafe. NEVER IGNORE A BRIGHT REVERSE POLARITY LIGHT! "

( Art continues with the following - not pertinent to your problem, but included anyway )

Just because the generator does not light the reverse polarity light on another (non IP boat) does not prove that you do not have reverse polarity. It is hard to determine your problem without measuring voltages, but here are some possible causes:

1. Your generator has a reversed internal polarity. You need to measure the AC voltage between the neutral and ground pins on the generator output connector to verify this. On a "standard" (wall type) socket) the neutral is the wider flat slot and the ground is the round hole. If you get over 100 volts, the generator has reverse polarity. If you get a fluctuation in voltage, you probably have a floating ground.

2. Your generator has a floating ground (This can cause the reverse polarity light). If this is the case, you need to connect the neutral line to the ground (case) of the generator."

now back to sailnet:

for the problem you have of the indicator light, a question would be : is it totally off, low, or bright?

Clues to your situation are:
1) you're always plugged in at the dock - so with your batteries constantly topped, there would not even be a low glow (very faint perhaps) of the light.

2) when you replaced a dead battery and plugged in again, the system started working harder to get the bank up to specs. A low glow would be normal and actually shows everything is working OK. But the low glow would be a change from no light before and begs an explanation. Hopefully this is it.

3)before sailing, you have no light (batteries are topped, there's little draw), then after sailing, and perhaps using more amps than you made while underway, you plug in again - if a low glow is seen this is normal because you need to draw on you system to get back to full banks.

good luck. all the advice in the world doesn't mean you shouldn't get a reverse polarity tester and plug it in. cost is about 10 dollars at a hardware store.
06-08-2007 08:51 AM
sailingdog Did you check with the marina to see if they had done any work on the wiring over the winter? If so, they may have accidentally reversed the polarity on the system.
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