Shore power polarity

[tom52]

I am new to the luxury of shore power.
When I connect at a starnge marina and my incorrect polarity light goes on, I know I am not supposed use that source of power but what am I supposed to do ?
Rewire my shore power plug altering the positive and neutral ? Or is there some kind of adaptor or some other cleve rsolution ?

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[AIDY]

Yup. swapping the wires is the answer.

We are always doing this, we solved this by making up a short adaptor for about a tenner. Buy a male and female set of plugs a short length of wire and wire up with the polarity reversed and add it onto the shore power end saves messing about with wires at every marina.

<hr width=100% size=1>/forums/images/icons/wink.gif <font color=blue> Regards Andy </font color=blue>

 

[Robin]

There is a clever device (cannot remember where I saw it adverised) that will detect incorrect polarity and you can chose to reverse it, but like you we just have a tester. I haven't found a wrong one for a long time now since our French friends rewired with blue sockets like ours, if I do I would probably just try a different outlet. Otherwise you could easily make up and carry a short cable with the relevant plug & sockets and the connections reversed internally.

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[tugboat]

I've also seen a device advertised and I'll do another post if I can find it. In the meantime PBO did a series of very useful articles in issues 394-399 covering all aspects of boat electrics - AC and DC. 399 is the one you want which refers to the polarity issue and is worth a read if you can access it. I'm not really a saddo surrounded by mags , it's raining that's all!

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[robp]

I know the question has come from you Tom but I need to ask one. OK, it's correct to have live and neutral the right way round but what is the worst scenario envisaged by any of us being supplied incorrectly? The RCD might not like it but what else? Obviously safety but I'm trying to think how, unless we grab what we think is neutral and something else too? But that would hurt anyway. In any case general supplies in Continental Europe are not polarised. (I don't know if marinas and camp sites tie one side down to "earth" or not?) Galvanic corrosion? I've never checked and perhaps I ought to? My installation doesn't have a polarity checker.

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[Birdseye]

You shouldnt find this problem in the UK, and if you do so either your boat or the marina has a wiring problem. Obviously, if it repeatedly happens it makes it more likely its your boatin which case professional investigation is needed.

What follows was what I was told by a Brit electrical engineer when I had this problem in France. I have no way of knowing whether he was right, but he ceratinly was plausible.

Abroad, some countries have live and neutral wires that are, in effect, 2 live wires each at 110 volts either side of the earth - so there is 220v between these 2 "lives" but only 110 between each of the "lives" and the earth wire.. But this is never exactly balanced equally and can be, say 100v on one and 120 on the other, so you can get signals telling you the polarity is wrong. Best solution is a simple polarity reversing cable of the sort described above.





<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[Vara]

Aah!! its something I've always been puzzled by,why are French and German plugs ambidextrous,at last an explanation./forums/images/icons/smile.gif.

<hr width=100% size=1>If it can't be fixed with a lump hammer dont fit it!

 

[petersto]

What bidseye is describing is the same sort of thing as the yellow transformers used on building sites for 110v supplies where the secondaries of the transformer is centre-tapped to earth only in the foreign case it is 220v. The out of balance between phases is that the centre tap is not quite centre tapped. As far as the RCD is concerned it only monitors the phases i.e. what goes out must come back or you have leakage and it trips. Which way round should be of no interest.


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[snowleopard]

most AC equipment has a power switch only in the live line. when correctly wired and switched off, the only part that is live is the wire between switch and socket. if polarity is reversed, the whole thing remains live when switched off.

under normal domestic use that isn't too much of a problem, the switch still turns the appliance off and its insulation protects you from shock. the main dangers are (a) dampness causing the insulation to pass current and (b) a short circuit inside the appliance could cause a fire. these problems can be overcome by unplugging all equipment when not in use!

bear in mind that some countries have symmetrical plugs so the polarity is always random!

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[tom52]

Thanks everyone.
It was a French marina; next time I go to France I will make up a short "polarity switching" extension cable.



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[robp]

Thanks Chris. Yes that was all I could see happening. So using the 230V outlets isolator achieves all that is needed really. Given that the French etc., supply alternates symmetrically between the "poles", it's irrelevent there.

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[jkim1]

The idea of centre tapping the main supply is to reduce the shock you may get if one side goes to earth, Its done on 110 volts as it possible to survive a shock of 55 volts. If you reverse the plug leads and you have a centre tapped 220 volt supply your rccd may still not like it. It may be that you will require an isolation transformer to make the whole thing work. Just as a point of interest you will still get a 220 volt shock if you touch the live wires its just that there are two of them now. rccds are getting "smarter" it would be an idea to contact the manufacturer to find out exactly what it detects or you may well be making a new changeover lead for nothing

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[ongolo]

It does not really matter in most cases. Continental Europe with its two prong plugs can be used either way. If the Germans use it that way, it will be safe for the rest of the word.

Further, if you have some of the double adaptors, or female coupling with two sockets, opening them up, you will find they are reversed on one side as well.

Dont worry be happy.

regards ongolo


<hr width=100% size=1>So what......... it floats

 

[Rick]

This subject always scares me, as here in Australia as in the US it gets people killed. I'm unsure how the description of the continental supplies works, however ROBP posed "what is the worst scenario envisaged by any of us being supplied incorrectly? The RCD might not like it but what else? Obviously safety but I'm trying to think how, unless we grab what we think is neutral and something else too?"

Lots of boats have an onboard DC earth system, tying DC-, engine and maybe thru hulls together. When installed with AC, people inadvertantly, and naturally (as you'd do elsewhere) tie the AC earth to the boat grounding system. This can be a cause of galvanic corrision, but all is more or less okay, until somewhere in the marina, ashore or on someones boat, or at a power post, a fault develops - result? Everyboat in the water with tied earth system just went live - somebody walks along the marina finger, and grabs a shroud to pull themselves aboard - doesn't bear thinking about.

I'd make very sure that the polarity was correct, and wouldn't use the power unless I was satisfied.

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[ongolo]

No people you have it wrong. Proper apliances do not have an internal connection between between life and earth.

Consider this. What would be the case if the neutral of the plug or where your power originates were disconnected faulty or burned away? The result would be that the 220 voltage has a path via life from the plug, throught cable, through the appliance back down the neutral wire to the disconnected or faulty or free dangling neutral. If you were to measure the voltage at this point (the Neutral) you would have full 220V. Yet touching the appliance, you would still not get a shock unless the device is faulty, but the earth leakage protaction shuld have come in already. Even if the Neutral is connected and the device is faulty, the earth leakage would disconnect. So either way, no matter which way round you connect neutral or life, the current/voltage passes through insulated wires in a device. When people die in Australia, then they must have done something really dumb like swopping earth and neutral or disconnecting earth. At the same time, many power tools do not even have an earth wire in todays machines.

One tip an old electrician told me 45 years ago and I have never forgotten and passed on many times.

If you are not sure whether anything carries lethal voltage, touch it with the back of you fingers. If you get an electric shock and you hand closes from it, the fingers PULL AWAY from the danger, rate then locking your fingers around it and you cant let go. Touching with the back of you hand/fingers, the shock is so slight that I dont mind testing when I am in a hurry, also after switchng things off just to make double sure.

regards ongolo

PS if anyone does not follow my explanation, make a drawing with two wires and a lamp, then disconnect on paper any one point and consider the reversal at all times. You will find that it does not make one Iota off difference to the safety or danger.

<hr width=100% size=1>So what......... it floats

 

[MainlySteam]

<<<tie the AC earth to the boat grounding system>>>

If in your post you are saying that the ac earth conductor on board should not be grounded to the boat then you are dangerously incorrect. In all codes the grounding is required and in many places it would also be illegal.

It is possible that you are confused with where when a shore cable is connected then the neutral on board should be disconnected from the boat's own ground but when the shore cable is disconnected then the neutral on board must be restored to the boat's ground if there is an on board means of producing AC eg from an invertor or a generator. The switching is normally done by means of a "Shore/Ship" switch or some invertors do it automatically.

John

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[robp]

Rick, have you ever known of anybody die in that way? (The shrouds thing I mean). If the "tied earth" thing works, then yes water in the immediate vicinity might hold some potential relative to real earth. However when you grab the shrouds, you need to be touching power "relative to" a different potential. If the tied earth system goes back to the pontoon source and the pontoon is earthed as it should be, you will be at the same potential.

I'm not claiming to be an expert but it seems to me that you do have to have a "difference" in potential of say more than 50 Volts to damage yourself. All IMHO of course.

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[snowleopard]

beware of gining advice

this topic has come up before - the inadvisability of offering advice that could result in injury. probably not a good idea to advise people to touch live wires on a boat. while internet anonymity may protect you there is a chance the widow might track you down and sue you!

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[snowleopard]

worst case scenario

<what is the worst case scenario?>

imagine you have a power tool plugged into a 240v socket. the switch on the socket is in the 'off' position. you splash some sea water on the tool.

you look at the switch - it's off - so you consider it safe to pick up the tool. with reversed polarity, the tool is actually live and when you put your hand in the water, bang.

mike mcmullan's wife was killed by a wet power tool when preparing for the 1976 ostar.

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[pelissima]

Re: worst case scenario

sorry, but to my understanding a splashed tool, even with proper polarity set, is lethal.
Rgds
George

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