Reverse Polarity - Galvanic Isolator

[Bora]

Spent the afternoon digging through all of the posts to see if I can finally piece together the mystery that is the reverse polarity indicator.

Does anyone remember seeing a definitive answer (in sailor speak?)  In my current marina I have the galvanic isolator showing around 0.9v and the reverese polarity light is faintly lit but still noticeable. 

I have the Aquafax galvanic isolator installed, the needle can go in two different directions, towards the boat's earth connection, or the shore connection.....does this show which side is causing the leak?

[Trevor]

Hi findhorn,

Have a look at this thread.

jeanneau.proboards.com/thread/1440/reverse-polarity-warning-light

Many times the issue is the voltage drop on the neutral conductor. Earth and Neutral are connected back at the distribution point. The reverse polarity light looks for voltage between neutral and earth. If the neutral cable has a slightly high resistance (like a corroded neutral connector on the shore power plug) as the boat draws current a voltage is developed in the neutral circuit, thus making the light glow a dull red. The more things you turn on in the boat the brighter the light glows.

Sometimes spraying the connector with electrical spray can resolve the problem. Other times the shore power connector needs replacing.

I don't think the voltage drop across the galvanic Isolator will be the problem.

I hopes this helps a bit

Regards,

Trevor

[Bora]

Thanks for the post Trevor, it’s becoming a bit clearer. Definitely prefer to understand these things rather than simply getting an electrician in.
Going to look at cleaning up the shore power connections or maybe replace it, see how it goes.

[rc sail]

Well understand frustration with the Reverse polarity light. Some easy attempts first, if you have not yet tried:

if you share dockside pedestal with dockside power outlets briefly turn off power to other boat on your shared
pedestal and see if reverse light goes out.

Next plug your shore power into another pedestal/outlet. If no fix, try a different shore power cord.

good luck.

[Bora]

My galvanic isolator was showing around 0.9v so was blocking current (blocks up to 1.1v). I unplugged the cable from my boat and stuck a multimeter between the neutral and ground, it showed 2v, not sure how accurate it is as the ground and live was showing 254v.

I then plugged in to another shore connection point on the same pedestal and the galvanic isolator now shows 0.0v. Again I put the multimeter on my shore power cable and it still shows around 2v.

The reverse polarity light is faint with both shore connection points.

I think I’ll order a new shore power cable as the one that came with the boat is a bit ragged and the connection on the boat side has a very bent/stressed entrance in to the plug to get it past the deck hatch if it needs opened.

There’s no one around on the boat next to me so a bit hesitant to unplug their connection brielfy in case I trip something or it resets something they may have on.

[Don Reaves]

Do you never experience power failure? Briefly disconnecting power to your neighboring boat would be interpreted that way.

Personally, I check to see if power has been lost since I was last on my boat. The microwave indicates this by virtue of having been reset. It doesn't happen often, but it does happen occasionally. Nothing on the boat suffers as a result.

Don

[ForGrinsToo]

Findhorn,

I have to say your observations are weird, if I understand correctly.
Plugged into one outlet on the pedestal, you find 2.0 V between the neutral and earth on your shorepower cable, but the isolator says 0.9.
Plugged into a different outlet on the same pedestal, you find 2.0 V between the neutral and earth, but the isolator says 0.0?

First, did you probe the pedestal outlets with your multimeter? Voltage between line, neutral, earth, and case? The marina probably discourages opening up the pedestal to check relatively protected connections, but outlet components can accumulate dirt and corrosion - you have salt air, after all.
Second, is the pedestal-mounted breaker a double-pole? Ideally, the voltage drop across a breaker is 0, but they do develop problems with age, use, and exposure.
Third, a 2 volt difference is a lot between neutral and earth. That would trip a typical GFI breaker.
Fourth, if your multimeter has a resistance function, you might check your shorepower cable for conductivity end-to-end, and for the resistance between neutral and earth, neutral and line, line and earth (which should be infinite - or something larger than 2 M ohm).

As for the accuracy of your meter, it's probably 1% of full scale unless you paid a good bit for it. I think I'd take it indoors and probe a known-good outlet to be more confident of its readings, then go check out that pedestal.

Geoff

[Bora]

I’m on the boat most evenings doing something or other so I’ll have another go on the shore power tomorrow.

I’ll take some photos of the multimeter and the galvanic isolator on the different plugs shoreside.

[Bora]

So i checked the shore power pedestal, all connections (including my neighbours), all were showing around 2 volts across neutral/ground.

Dock reading neutral/ground - imgur.com/c3EYctF


The shorepower cable onboard shows a similar reading.
Shorepower cable boat side - 

Galvanic isolator seems to be doing its job.....just.
Galvanic isolator - imgur.com/HLNbjaB


Spoke to the marina so they're going to look in to it.

[Trevor]

Just to add some meat and potatoes.

The active and neutral cables back to the supply source are in balance. In other words the current down the active is the same as the current down the neutral. If we have a fault the current can flow to earth and then the currents are out of balance. Out of balance currents trip core balanced earth leakage breakers.

The current flowing down the neutral conductor can develop a voltage drop. If the cable back to the supply point is thin, compared to the current it is carrying, a significant voltage will be developed. If the cable back to the supply point is thick compared to the current it is carrying, less voltage will be developed.

The 2 volts difference you are seeing between earth and neutral is the result of the combined neutral currents of all of the boats sharing the return path to the distribution point. That may be the boat sharing your pedestal or it may be all of the boats on the arm. Depending upon where the distribution point is and the size of the marina it could be all boats in the marina. If the currents are in balance you would see the same voltage drop on the active conductor. You can see the voltage drop on the neutral conductor because you have a convenient reference, the earth conductor (it hopefully has no current flowing so has the same potential as the distribution point.)

It is not unusual or a fault and it has nothing to do with your boat. It is a function of the neutral current of combined boats. You expect some voltage drop over long lengths of cable distribution when current flows. Unfortunately it is simply the laws of physics. Electrical Standards do outline what is acceptable voltage drop. I have forgotten he exact spec but in Australia 2 volts is absolutely fine. Provided no current is flowing to earth, the earth leakage breakers will not trip and all is perfectly safe.

Now for the galvanic isolator. It is simply there to disconnect dissimilar metals between boats that are connected to the same earth point. You expect to see some voltage drop across it because that is the extent of its DC blocking ability to stop these dissimilar metals creating a lovely battery cell to eat away your very expensive underwater metal boaty bits.

I hope this helps.

Regards,

Trevor

[uli057]

hi.
here are example from ship...



and pdf from galvanic isolator.


media1.svb-media.de/media/snr/2583/pdf/manual_multi_2014-10-07.pdf

regards uli