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Old 02-05-2021, 02:42   #1
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Reverse Polarity - Adapter?

Hello everyone - recently I had an issue with reverse polarity. It was a one off event where we came into a new marina in Greece plugged into shore power and our warning light came on. After trouble shooting on the boat we tried rewireing our shore power lead and that fixed the problem. Now I expect that when we travel to the next marina we may have the same issue and have to rewire the lead again.

Question - does anyone know if it is possible to purchase an adaptor that will switch the polarity at the shore power pedestal or at the boat?

I would prefer not to have to rewire my shore cable every other time I plug it in!

Thanks in advance!
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Old 02-05-2021, 03:50   #2
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Re: Reverse Polarity - Adapter?

Just get a plug, a connector and 50 cm of cable to make yourself a reversing adapter. If you run across other strange settings, you can always adjust this one without having to mess with our good cable. Depending on the kind or connectors you use, it's just a few Euros.

Same goes for adapting to other plugs in case they have 32A connectors but you just use 16A.
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Old 02-05-2021, 05:30   #3
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Re: Reverse Polarity - Adapter?

We have a set of I guess three or four one foot long this-to-that adaptors we made up from hardware store plugs and sockets, as Joh.Ghurt suggests. Our most common use is plugging our small portable generator into the shore power cable to supply power while at anchor and not wanting to run the big noisy diesel genset. Another is getting 240v from the dockbox to the welder. We don't have a bunch of money invested in this.
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Old 02-05-2021, 11:49   #4
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Re: Reverse Polarity - Adapter?

I try to check new shore power before power up on board devices. Simple 3 light receptacle tester in dedicated outlet. Great idea about having a plug-in adapter. Just label it so no mistakes if a crew member gets helpful. Also never store vinegar in a soda bottle....don't ask me how I know that is a bad idea.
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Old 03-05-2021, 14:16   #5
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Re: Reverse Polarity - Adapter?

Quote:
Originally Posted by HurricaneWally View Post
Hello everyone - recently I had an issue with reverse polarity. It was a one off event where we came into a new marina in Greece plugged into shore power and our warning light came on. After trouble shooting on the boat we tried rewireing our shore power lead and that fixed the problem. Now I expect that when we travel to the next marina we may have the same issue and have to rewire the lead again.

Question - does anyone know if it is possible to purchase an adaptor that will switch the polarity at the shore power pedestal or at the boat?

I would prefer not to have to rewire my shore cable every other time I plug it in!

Thanks in advance!
If you have a warning light chances are you already have a diode unit that automatically switches the polarity. The light just comes on to warn you the incoming power is reversed so you know.

Check the owners manual and it should tell you.

If not then it isn't a difficult job for a marine electrician to fit a reversing diode to your incoming mains feed which negates the need for any adapters or rewiring.

Hope that helps
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Old 04-05-2021, 02:05   #6
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Re: Reverse Polarity - Adapter?

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Originally Posted by kas_1611 View Post
If you have a warning light chances are you already have a diode unit that automatically switches the polarity ...
Wrong!!!
There’s no “automatic switching” in a typical reverse polarity INDICATOR circuit.

See ➥ https://www.bluesea.com/support/arti...lse_Indicators




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Old 04-05-2021, 02:20   #7
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Re: Reverse Polarity - Adapter?

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Originally Posted by GordMay View Post
Wrong!!!
There’s no “automatic switching” in a typical reverse polarity INDICATOR circuit.

See ➥ https://www.bluesea.com/support/arti...lse_Indicators
Gord, note I did say "chances are" I did not say "you WILL have".

On my boat we do have a diode that automatically switches the polarity if the supply from the mains is reversed. Yes a light comes on to warn us the circuit is reversed but everything running on the mains works perfectly happily, battery charger being the main item as everything else on our boat is 12v.

That is also why I said "check the owners manual" to make sure what it is, either a simple warning circuit or actually a correcting circuit before you assume anything as we all know what happens when we assume don't we
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Old 04-05-2021, 03:51   #8
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Re: Reverse Polarity - Adapter?

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Originally Posted by kas_1611 View Post
If you have a warning light chances are you already have a diode unit that automatically switches the polarity. The light just comes on to warn you the incoming power is reversed so you know.



Check the owners manual and it should tell you.



If not then it isn't a difficult job for a marine electrician to fit a reversing diode to your incoming mains feed which negates the need for any adapters or rewiring.



Hope that helps


I would love to see a photo of this “reversing diode” that is able to supply mains power in the correct orientation.
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Old 04-05-2021, 04:15   #9
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Re: Reverse Polarity - Adapter?

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Originally Posted by Sailmonkey View Post
I would love to see a photo of this “reversing diode” that is able to supply mains power in the correct orientation.
I don't think this can be done in an alternating current circuit, with a diode. I will be glad to be educated if I'm wrong about this.

In any case, reverse polarity is dangerous and worth being careful to avoid. My boat has a "Polarity Correct" indicator light and we don't switch on shore power without seeing this.

We do from time to time encounter incorrectly wired outlets. We just find another socket normally. If that's not possible, then shore power plug can be rewired in 5 minutes. Or if it's a low powered outlet (as per usual), that is, 12 amps or less, a somewhat kludgy but simple and effective solution is to use a blue plug < Schuko socket adapter with a Schuko plug < blue socket adapter (both of which we keep on board for various purposes such as plugging into Schuko sockets (common in smaller marinas in Germany and Sweden). Just flip the Schuko plug around in the socket to change the polarity -- they can be plugged in either way.


And as other have mentioned, a polarity-reversing adapter is simple and cheap to make. I've never been inspired; the problem is fairly rare where I sail.
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Old 04-05-2021, 05:26   #10
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Reverse Polarity - Adapter?

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Originally Posted by Dockhead View Post
as other have mentioned, a polarity-reversing adapter is simple and cheap to make. I've never been inspired; the problem is fairly rare where I sail.


I coincidentally got warned by a pontoon neighbour of the increasing risk of erroneous re-wiring in our and close-by marinas.

Could someone be kind enough to explain me in lay language what this means and the consequences for a small boat (ie no complex systems, just 230v and battery charger/boiler/fridge working in that voltage)?

What is the simpler solution ? Is it to have ground and 1 of the other wires swapped in a small cable extension? Is this after the pontoon plug or should it be done elsewhere?

Thanks in advance
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Old 06-05-2021, 17:32   #11
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Re: Reverse Polarity - Adapter?

you should be telling the marina to fix it. and not using that plug. not changing your boat...

it could be wired wrong in a few differnent ways. so you'd need a few adapters... and first figure out how it's wired wrong and which one might fix it...

the best thing to do is get yourself an isolation transformer on the boat. then you will never have reverse pol on the boat even if the dock is.
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Old 06-05-2021, 17:36   #12
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Re: Reverse Polarity - Adapter?

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Originally Posted by kas_1611 View Post
Gord, note I did say "chances are" I did not say "you WILL have".

On my boat we do have a diode that automatically switches the polarity if the supply from the mains is reversed. Yes a light comes on to warn us the circuit is reversed but everything running on the mains works perfectly happily, battery charger being the main item as everything else on our boat is 12v.

That is also why I said "check the owners manual" to make sure what it is, either a simple warning circuit or actually a correcting circuit before you assume anything as we all know what happens when we assume don't we
ummm no. you are probably just continuing to use the boat with the reverse polarity. which will work just fine, just less safe. especially if you have single pole breakers.
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Old 06-05-2021, 23:57   #13
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Re: Reverse Polarity - Adapter?

in regards to 'reversing diode' for AC...... does not exist. The only gadget that can make a reverse connection 'good' is an isolation transformer. All the LEDs and little lights show what is wrong with the shore connection, they do not rectify the issue. (pardon the pun, was not intentional).

Here is a diagram that can show you what is wrong with the power connections (at the dock or at home), borrowed from https://theorycircuit.com/phase-neut...rcuit-diagram/

Four Red colour LEDs are used here, and resistors are 56KΩ / 1W.
LED1 is connected between Phase and Earth through Resistor.(here you can connect LED in any polarity).
LED2 is connected between Phase and Neutral.
LED3 is connected between Earth and Neutral.

These three LEDs will show the condition of AC power supply.

LED Indication
LED1 LED2 LED3 LED4 Status
ON ON OFF - Phase Neutral Earth wired correctly
OFF ON ON - Wrong Polarity of Phase/Neutral
ON ON ON - Open Earth or Neutral
- - - ON Blown fuse
LED 4 connected parallel to the fuse and it glows when fuse blown and appliance being connected the power source.
Another word for 'Phase' is 'Active'.

Note, if you were to built something like this, be aware that 220-240 volt is dangerous and can kill.
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