Bi-Polar Reverse Polarity Light

[Golden Echo]

Currently in the water at Delaware City Marina.

Yesterday morning, my wife woke up to make coffee, and from the V berth I hear "Huh, What's this?" Then "Uh oh, The Reverse Polarity light is on, on the panel!". This reaction is due to the fact that the light has not been on since we arrived here last November 2013.

Checked the connection at the power tree, no problem there. Moved the cord to another socket (same tree) same condition. I used a polarity tester at all plugs in the boat and they all read OK. Now I know the wiring is fine because last spring I installed a new DC/AC panel so I have all new wire through out the boat, and again as I said the lights been off all this time.

The plot clots. It snowed here last night, so today I was shoveling off the dock when I noticed one of the 30 amp cords for the boat behind us was unplugged laying on the dock. So I plugged it back in not really thinking about it. Came back inside from shoveling to discover my Reverse Polarity Light is no longer on.

So, What happened here? Any tips, tricks or suggestions would be appreciated.

[sailinglegend]

Was the reverse polarity light FULLY on or just glowing dimly?

If there is enough of a voltage between the earth and the neutral it will cause it to glow slightly. This voltage is caused by heavy loads on the shorepower AC system from cables or connections that can't carry the loads. Turn off all your loads and see the difference. The more loads you put on the more the reverse polarity light will glow. If you add more cables and connect to a shorepower box closer to the land you may bypass a boat taking a heavy load or bypass faulty connections on the pontoon. It's a marina problem, but they will of course deny any problem exists.

[Golden Echo]

Dimly glowing. This happened once before over the summer when we were on Long Island Sound. We were surrounded by very large yachts. The marina did not have a 30 amp outlet so they split a 50. This is the only other time it has done this.

So just because the light is on (glowing dimly) does not necessarily mean I have a problem?

[CharlieJ]

This may help you: Reverse Polarity Indicators - Blue Sea Systems

[smac999]

Originally Posted by Golden Echo

Dimly glowing. This happened once before over the summer when we were on Long Island Sound. We were surrounded by very large yachts. The marina did not have a 30 amp outlet so they split a 50. This is the only other time it has done this.

So just because the light is on (glowing dimly) does not necessarily mean I have a problem?

it wouldn't be a reverse polarity problem. but instead a voltage drop problem on most likely the N wire. somewhere between your panel and the start of the dock.

you end with a small votage between the white and green wire. (ideally you'd see 0v. in practice you see a few volts. not sure how many you'd need to make the light start to light up. maybe 5+.

if you see 120v between white and green then you have reverse politiry. (and 120v on the bulb making it go full bright)

[FlyingCloud1937]

What you describe is an out of balance on a split phase load, with what is probably a high Resistance Earth to Neutral on one of the pedestals.

On a split phase system(220-240) volt system you end up with circulating currents, when the load phases are out of balance.

Because the phases are 180 out, when a large imbalance on the lines, a dangerous current can flow on the neutral.

In some cases you could see enough voltage difference between earth and neutral on systems distant from the earth ground rod, that it could be dangerous, when a fault exist.

You would be well advised to alert the Marina Management, that a potential significant Ground Fault exists.

Lloyd

Originally Posted by Golden Echo

Currently in the water at Delaware City Marina.

Yesterday morning, my wife woke up to make coffee, and from the V berth I hear "Huh, What's this?" Then "Uh oh, The Reverse Polarity light is on, on the panel!". This reaction is due to the fact that the light has not been on since we arrived here last November 2013.

Checked the connection at the power tree, no problem there. Moved the cord to another socket (same tree) same condition. I used a polarity tester at all plugs in the boat and they all read OK. Now I know the wiring is fine because last spring I installed a new DC/AC panel so I have all new wire through out the boat, and again as I said the lights been off all this time.

The plot clots. It snowed here last night, so today I was shoveling off the dock when I noticed one of the 30 amp cords for the boat behind us was unplugged laying on the dock. So I plugged it back in not really thinking about it. Came back inside from shoveling to discover my Reverse Polarity Light is no longer on.

So, What happened here? Any tips, tricks or suggestions would be appreciated.

[sailinglegend]

Originally Posted by FlyingCloud1937

What you describe is an out of balance on a split phase load, with what is probably a high Resistance Earth to Neutral on one of the pedestals.....

What he describes is exactly what happens in thousands of marinas all over the Med which is where we have been for the last 7 years.

In a single phase feed to a pontoon the Neutral and Earth wire are joined at the main transformer supply so should be at the same potential. Under a heavy load there’s a voltage drop along the neutral wire, but because no current is flowing in the earth wire there is no voltage drop along the wire, so at the pontoon pedestal there is now a voltage difference between the neutral and the earth which is enough to dimly light the polarity detector; this should never be more than 5 volts. Above this earth leakage breakers or RCDs may keep tripping, it depends on your AC installation. All pedestals on a pontoon on the same phase will show the same problem, the ones closer to the transformer will have a lower Neutral/Earth voltage. Anything above 8 volts causes ours RCDs to trip. In winter months the problem is much worse because the more power that is taken by other boats then the higher the earth/neutral voltage difference will be. Constant AC tripping could be a problem if heating or charging is left on whilst away from the boat, so try and arrange for someone to check that AC is always present.

Stray low voltage currents in a marina can cause destructive galvanic corrosion that eats away zinc anodes and can destroy outdrives propellers and through-hull fittings.

[FlyingCloud1937]

Well, the Op is in the US.

Second, the neutral should never be daisy chained, niether for that matter should the Earth.

So Ideally what we should see is a feeder for line, and Neutral that should carry the load...ie balance.

In Europe, they are not a split phase 220/240, so the only time we would see an imbalance on he neutral is if it was high resistance neutral, and the fault followed earth.

In the US we are split phase, so any imbalance will show up first on the neutral, and if a high resistance earth is in the path, then we could have life threatening voltage between, neutral and real earth. That is the fault that can kill you.

Lloyd

Originally Posted by sailinglegend

What he describes is exactly what happens in thousands of marinas all over the Med which is where we have been for the last 7 years.

In a single phase feed to a pontoon the Neutral and Earth wire are joined at the main transformer supply so should be at the same potential. Under a heavy load there’s a voltage drop along the neutral wire, but because no current is flowing in the earth wire there is no voltage drop along the wire, so at the pontoon pedestal there is now a voltage difference between the neutral and the earth which is enough to dimly light the polarity detector; this should never be more than 5 volts. Above this earth leakage breakers or RCDs may keep tripping, it depends on your AC installation. All pedestals on a pontoon on the same phase will show the same problem, the ones closer to the transformer will have a lower Neutral/Earth voltage. Anything above 8 volts causes ours RCDs to trip. In winter months the problem is much worse because the more power that is taken by other boats then the higher the earth/neutral voltage difference will be. Constant AC tripping could be a problem if heating or charging is left on whilst away from the boat, so try and arrange for someone to check that AC is always present.

[FlyingCloud1937]

Originally Posted by sailinglegend

What he describes is exactly what happens in thousands of marinas all over the Med which is where we have been for the last 7 years.

Above this earth leakage breakers or RCDs may keep tripping, it depends on your AC installation. All pedestals on a pontoon on the same phase will show the same problem, the ones closer to the transformer will have a lower Neutral/Earth voltage. Anything above 8 volts causes ours RCDs to trip. In winter months the problem is much worse because the more power that is taken by other boats then the higher the earth/neutral voltage difference will be. Constant AC tripping could be a problem if heating or charging is left on whilst away from the boat, so try and arrange for someone to check that AC is always present.

Stray low voltage currents in a marina can cause destructive galvanic corrosion that eats away zinc anodes and can destroy outdrives propellers and through-hull fittings.

An RCD should only measure current deferential between Line, and neutral.

Earth is not in the circuit.

An RCD only faults, because the current is deferential between line, and neutral.

But it never measure the the voltage differential between neutral and Earth.

It must be faulting on the earth wire, or through seawater-to-shore to cause an RCD trip



Lloyd

[sailinglegend]

Originally Posted by FlyingCloud1937

An RCD should only measure current deferential between Line, and neutral.....

Many thanks for your quick responses.

In many installations in the med several live - neutral and earth cables may feed one pontoon and then split to several pedestals each or be daisy chained. On many pontoons there is just one feed cable and I have had to connect several showpower cables to the first pedestal to get an increase in voltage from 185 volts to 220 volts. At 187 volts my shorepower charger cuts out. There are many readers on this excellent forum from all around the world so replies should try to cover all areas, not just the OPs.

Yes you are correct that RCDs measure the difference between Live and Neutral currents - about 30 mV will cause a trip - its printed on the breaker. Maybe mine needs changing - they do get too sensitive sometimes.

But if I had an earth leak on my boat why should my breaker trip ONLY when I have a voltage of 8 volts between Neutral and Earth? We have a Victron Charger/Inverter that sits in series with the shorepower, and I have always assumed that this is somehow causing the tripping. Friends with Victrons have had the same problem.

Old ELCBs (20 years?) worked differently and used to trip with a voltage between Neutral and Earth, which is why I said in my post "...it depends on your AC installation."

The last time we had a problem was when we were lifted out of the water and I found 24 volts on the prop shaft when I went to clean it!!! It took me two hours to finally persuade the marina that it was their fault not my boat.

[FlyingCloud1937]

Originally Posted by sailinglegend

Many thanks for your quick responses.

In many installations in the med several live - neutral and earth cables may feed one pontoon and then split to several pedestals each or be daisy chained. On many pontoons there is just one feed cable and I have had to connect several showpower cables to the first pedestal to get an increase in voltage from 185 volts to 220 volts. At 187 volts my shorepower charger cuts out. There are many readers on this excellent forum from all around the world so replies should try to cover all areas, not just the OPs.

That would be thread drift, and fails to the OP, in that it fails to correspond.

It most likely would, and should deserve it's own topic, as the solution is specific.

Yes you are correct that RCDs measure the difference between Live and Neutral currents - about 30 mV will cause a trip - its printed on the breaker. Maybe mine needs changing - they do get too sensitive sometimes.

An RCD measures current not mV.

An ELCB is mV., A fault in the earth line could cause a safety issue.

But if I had an earth leak on my boat why should my breaker trip ONLY when I have a voltage of 8 volts between Neutral and Earth? We have a Victron Charger/Inverter that sits in series with the shorepower, and I have always assumed that this is somehow causing the tripping. Friends with Victrons have had the same problem.

An earth leak from an RCD means current is flowing between unintended paths.

An inverter that is acting as power source at least in the US is required to be tied to neutral to earth. So it could be a fault bc of the tie, paralleling with the earth shore connection, all it takes is a high resistance connection boat side.

Old ELCBs (20 years?) worked differently and used to trip with a voltage between Neutral and Earth, which is why I said in my post "...it depends on your AC installation."

Yep, but that was early twentieth century.

The last time we had a problem was when we were lifted out of the water and I found 24 volts on the prop shaft when I went to clean it!!! It took me two hours to finally persuade the marina that it was their fault not my boat.

It may of been the yard, it could of also been the potential between earth/neutral faults on-board. Especially if you have any ac/dc devices like a battery charger, ac/dc refer.

Lloyd

[sailinglegend]

Originally Posted by FlyingCloud1937

That would be thread drift, and fails to the OP, in that it fails to correspond.

It most likely would, and should deserve it's own topic, as the solution is specific.

I don't understand what you are talking about.

Originally Posted by FlyingCloud1937

...An RCD measures current not mV.

An ELCB is mV., A fault in the earth line could cause a safety issue.

Sorry I made a mistake - and I did an Ohms Law calculation with 30 mA and found the resistance would be 330 ohms at 10 volts Neutral to earth. My mega test shows 1.4 Mohms as earth leakage.

Originally Posted by FlyingCloud1937

An inverter that is acting as power source at least in the US is required to be tied to neutral to earth. So it could be a fault bc of the tie, paralleling with the earth shore connection, all it takes is a high resistance connection boat side.

You haven't read my post properly, or understood what I was talking about!!!!
The Victron, as you should know, is an Inverter/Charger, so always in series with the AC. In charger only mode it doesn't tie to earth, but in inverter mode it does.

Originally Posted by FlyingCloud1937

It may of been the yard, it could of also been the potential between earth/neutral faults on-board. Especially if you have any ac/dc devices like a battery charger, ac/dc refer.

Please read the posts properly. As I said "It took me two hours to finally persuade the marina that it was their fault not my boat." This says that they finally admitted it was their problem not mine.

Do I have to spell it out for you all the time - or is it just the case of two countries divided by a common language!!!!!