Reverse polarity

[Largslout]

Looking for technical advice please. My yacht is a newish Beneteau and is connected to shore power for battery charging and dehumidifier etc. A recent visit revealed a very faintly glowing reverse polarity light. Can't say I noticed this before and am confident that the a/c side of the boat is new and ok. As I recall this light is sensing a leak between neutral and earth or of course pos and neg reversed although I am sure an expert on the forum will correct me. I also suspect it could be a pontoon supply fault. Anyone seen this before? Many thanks.

 

[Richard10002]

I have a short shore power cable which re-reverses the polarity when added to the longer shorepower cable.

You could get one of those 3 pin plugs with a series of lights to test the supply at the actual sockets on the boat aswell.

I would have though a leak to earth would throw the switch and cut your power.

 

[VicS]

I think you will find your faintly glowing reverse polarity light is telling you that there is a small voltage difference between the neutral and the earth (where normally there should not be one of course) rather than that there is a leak between the two.

This could come about because the whole pontoon or marina system is loaded with battery chargers, dehumidifiers and no doubt heaters to close to bursting point or because somewhere there is a poor neutral connection. That could even be at one end or the other your own shorepower lead.

I suggest you switch off all your load and if the indication clears the fault is yours but if it persists it is some thing to do with the pontoon or marina as a whole.

You could check your "polarity" by cautiously checking that you have the full mains voltage between your live and your earth using a voltmeter or a low wattage neon (anything over 7 watts will trip the RCD)

Anything moe than a small neutral to earth fault will, as Richard says probably trip the RCD.

 

[Peanuts]

Hi
Not quite sure if this is going to help or confuse matters but here is my story. I was working on a new Beneteau, and the owner wanted UK style socket fitted in place of the factory fitted french one, not a problem until I checked the socket with my tester and all of the wiring was reversed, live and neautral only of course not earth, that was correct! Although all of the factory fitted items were working I went through the boat ensuring all to UK spec so that at a later date when an item gets plugged in that is polarity sensitive it did not blow a fuse or just blow up
I hope I have not confused you even more from your original question.

 

[Largslout]

Oh, thats interesting because it was after I changed one socket to uk style on Sunday that I noticed the problem. So just to be clear I double checked live to live neutral to neutral on the back of the new uk style socket. Are you saying the remaining french sockets are wired wrong in the factory or my new uk socket is marked in reverse. There is a danger here I could get confused! The bar heater and dehumidifier seem to work ok from this new uk style socket but the reverse polarity light shines faintly. Many thanks.

 

[robp]

I have experienced differentials between neutral and earth. They are often tied together further back in the distribution system. I think this can result in very small potential differences. I guess it depends on the installation within the marina supply.
I've often wondered about "European" boat wiring though, because don't they have a 230V supply on the continent that is not tied to earth at all? I have to admit that I'm not sure.

 

[Largslout]

Thats also interesting as even though I changed a socket the light is on with no load on any of the sockets, which would tie in with your marina supply suggestion.

 

[NormanS]

First thing to do is lash out a fiver for a test plug. I found that my Cromarty shore supply plug (the one installed on the boat) had been wired wrongly. It was an American fitting, which instead of being marked + and -, was marked "B" and "W". Whoever did the original installation had assumed that the "B" was negative. Oh no it's not!

 

[Dann]

I believe most French distribution systems use double pole switches and require the installation of double pole mains MCBs, unlike UK which only requires the live to be switched. Thus, most French installations do not require specific pins to be used for live or neutral. Therefore, as many visitors to French Marinas can testify, this can lead to live and neutral being reversed and be a problem with a UK type system and be potentially dangerous.

 

[Largslout]

Yes I did notice the french socket whilst marked for earth the other 2 pins had no live or neutral marking, however the wiring is standard colours ie blue, brown and earth.

 

[Peanuts]

Hi
As we say at work when something goes wrong there is normally a story and in your case it is regarding the changing of the socket. The way I look at it you have wired the new socket correctly but I think you will find that the other 'french' sockets on the boat will be wired the other way round. Of course I stand to be corrected but I can't help feeling this is the problem.

 

[VicS]

[ QUOTE ]
The way I look at it

[/ QUOTE ]

I assume that the OP refers to a reverse polarity light on his incoming shorepower panel. This wont be affected by the socket outlets around the boat will it?

It is unsatisfactory and in fact potentially dangerous perhaps if there is a reverse polarity situation anywhere as the fuse in the British style plugs will be on the "wrong" conductor.

I agree 100% with the suggestions to invest in a test plug. Test all the sockets on the boat.

 

[Largslout]

Yes I agree because with nothing plugged in the sockets they are open circuit and therefore with no load their polarity matters not.

 

[VicS]

[ QUOTE ]
their polarity matters not

[/ QUOTE ] I did not mean to imply that it does not matter, just that it wont affect the reverse polarity warning light.

Already mentioned the fuse business but also the socket switch will be on the wrong side and probably switches in appliances.

 

[Largslout]

Quote:- I did not mean to imply that it does not matter, just that it wont affect the reverse polarity warning light.

Yes, thanks I understand.

 

[dk]

The safest way to have shorepower on board is via an isolation transformer. Direct connection to any shore AC supply will always be risky, particularly in Europe where they have no polarity rules and rarely even have switches on their sockets. A transformer will also eliminate any risk of stray current corrosion, which is very common in poorly wired marinas.

 

[footsoldier]

Just to add an observation. My technical knowledge is zilch, but I am very familiar with France and I can confirm, as an earlier post remarked, that the French do not seem to pay much attention to polarity.

My long-time understanding was always that in a French power socket (female), when viewed from the front, the positive should be on the right. I had some domestic re-wiring done (by a qualified electrician) and subsequently was bemused to find that half of the sockets had the positive on the left. It seemed to be a purely random choice.

 

[philby]

when visiting camp sites in Europe we always checked polarity with a tester and if reversed had a separate connector to the electricity point "wired the wrong way"

 

[pollygonforty]

please we have had this thread before and i have asked time and time again please explain to me why reverse polarity is a problem in the UK whilst in the rest of europe all connections are optional ie , a two pin plug that can be connected in either polarity and it never causes aproblem??

 

[VicS]

My understanding is that it's because in the UK it is common, but not universal, practice for appliances to have only a single pole switch, which is in the incoming live wire, whereas elsewhere double pole switches are used that isolate both live and neutral. If a UK appliance with a single pole switch is connected to a supply with live and neutral reversed then even when switched off all off its insides will be live.

Someone will correct PDQ if that's wrong no doubt