Shore power polarity

[snowleopard]

Re: worst case scenario

not so, it's only lethal if you switch on the power (as long as the polarity is correct).

likewise, condensation on a plug is dangerous, even if you switch off the socket before unplugging it, but only if the socket polarity is wrong.

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[ongolo]

Re: worst case scenario

If a power tool is wet, if there is water in the handgrip where the switch is located, there are also the exposed cable connection from the incoming cable, to the switch input and to the switch output and if this switch input terminal is wet with a saltwater path to the outside of the housing, it nakes no difference whether the switch is on or not you get a shock.

You people mention RCD or something like it waht is this thing? I only know earth leakage relays that are set to 20 or 30mA error current when they trip. Is this the same thing? An RCD different name only?

wondering ongolo


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[Bejasus]

Re: worst case scenario

Same thing

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[MainlySteam]

Re: worst case scenario

Snowleopard is irrefutably correct and I find it surprising that he appears to be doubted by some.

He is saying that if the switch at the plug end (not the one on the tool) is off and the polarity is reversed then the tool is still alive through the neutral conductor in the tool's cord. I cannot see how that can be disputed at all. That means if you come into contact with the electrical parts directly or by means of salt water splashing, etc and you are grounded, you will be electrocuted.

Whether the risk is of concern is perhaps a matter of how cavalier one is, but I believe that it is of much concern as do all electrical authorities I have come across.

John

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[ongolo]

Re: worst case scenario

You should apply some logic here. Why do you plug in a power tool? To use it obviously. And to use it you have to switch it on. Or would you deliberately plug in a wet tool into a socket and not switch it on because it is wet? Under the circumstances I would not even plug it in.

Snowlepard talks in the second part of his post of plug and socket. Fisrt he only talks about switches.

And it has been insinuated that I suggest touchng a life wire. That is nonsese. Touching a wire with the back of my hand is the last test to convince me after all other precautions, that there is no voltage present between that wire and yourself.

Measuring with a meter will not give any indication at all under circumstances.

Switching a cct breaker off which you think is the right one is not good enough. An electrician might have swapped wires since the last time.

If both earth and neutral are off at any connection, you will measure no voltage between live and N or gnd, yet that is when all three wires might be live incase of a fault, or in the absence of a fault and a devices is on or off, you will not detect a voltage unless you stick a probe into the ground next to your foot and test the other wires against that. Ever seen anybody do this? Of course not. So the las test for me is after I made sure I can not detect any voltage with an instrument, touch it with the back of my hand.

Since mainly staem like to quote other authorities he has come across, I mention some too. Germany does not have switches on their plugs and these plugs can be plugged in any way. All CE approved devices must and have in any case followed this standard. But then I suppose Germany is technologically inferior to NZ and electrical Giants like Siemens (300000 employees when I begun working for them as a young engineer, now having 500000 employees) and Kloeckner-Moeller switch gear manufaturers could be taught a lot by NZ authorities.

Why dont you rather use your own knowledge?

<hr width=100% size=1>So what......... it floats<P ID="edit"><FONT SIZE=-1>Edited by ongolo on 02/07/2004 05:50 (server time).</FONT></P>

 

[ongolo]

Now that is utter nonsense. Either you did not understand or he did not know what he was talking about.

The Neutral comes from the centre of a 3 phase generator. Phases against each other 380V , each phase against neutral 220V. At this point it was logically decided to save one wire (and a lot of complication in step up and step down transformers), to ground Neutral at the generator. So only three phases and neither neutral or earth come from the powerstation. Then on the other side, the consumer side, from the earth (a plate in the ground) a neutral is made to "carry" the current. Usually in underground cables the earth (in the form of a shield) is carried along, but this is not essential.

Only if you have 220V will you have a Neutral running to the next 3Phase board which is certainly not far away.

ongolo

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[MainlySteam]

Re: worst case scenario

Not sure why you are quoting Germany at me as Germany and a number of other European countries do not have protection from reversed polarisation at the appliance plug (in Germany the Shuko plug). Thought it was pretty obvious that they did not care which way you put the plug in, but the fact remains if the polarity is reversed what is being said about the danger is correct.

If you know of any important country that has a polarised system right through to the appliance but does not care whether you protect the polarity or not I would appreciate you telling me of it.

John

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[ongolo]

Re: worst case scenario

it is obvious you dont follow what I am saying.

What is the reverse polarity protection you are talking about? Is it that RCD thing? If it is an earth leakage with another name it neither detects nor protect against reverse polarity.

That is simply a device that checks the amount of current in one wire against the current in the oposing wire, if there is more than 20 or 30mA difference, it means that some current goes somewhere else, that is to ground or if you touch the faulty device through you to ground.

Now we have to define what is "an important country". One which did the first successful heart transplant? Or builds his own jets? Or has Atomic bombs? Or has its own high industrial standard like BS or DIN?

All this applies to South Africa, and although every plug is marked L/N/E and every body sticks to it while wiring, the system changes the moment you put a multiplug, or doubl adaptor on. I would almost bet, if you have these couplings with two female plugs and open one up, in that plug that system changes. What is neutral on the one side of the coupling is L on the reverse side of it. From an internal safety point of the coupling this is safer as no connections overlaying and crossing one another, they simply run parallel inside. All acceptable under SABS.

Does NZ have a standard like BS. DIN or SABS? Builds Jets? Made atom bombs? No?

So NZ is not an important country (I am applying you criteria), so what is your basis of discussion. ))

I am not normally backing out of a discussion, but this is getting too stupid.


regards and have a nice weekend

ongolo


BECAUSE IT DOES NOT MATTER AT ALL.


ongolo


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[Birdseye]

Re: worst case scenario

I dont understand what Mr Ongolo is saying. If I have no problem in the UK and sometimes but not always have to "reverse polarity " in France or my RCD trips out, what can be the cause?

Is there no really well qualified electrical engineer on this forum who can give the definitive answer?

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

 

[halcyon]

Re: worst case scenario

Back in the 1990 when we first started fitting RCD's to the switch panels, we started getting tripping for no reason when the owner first plugged in. After a lot of head scratching I realised that the reverse polartiy light was after the RCD. If you had a reverse polarity it supplied a neon between neutral and earth, this caused some of the current to be blead off to earth. The RCD then saw a inbalance between live and neutral and tripped out the RCD. We moved the reverse polarity neon to before the RCD, end of problem as the loss of current was before the RCD. Only possible problem then is the Marina supply RCD.
Thus if the current drawn by the reverse polarity neon is close to the trip current of the RCD, supply voltage variation may give a trip or not trip, or for that matter the condition of the earth.

Brian

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[claudio]

Re: worst case scenario

Most equipment sold in the U.K. only has single-pole switching. This means that the on-off switch is only connected in the Live wire to the equipment. This is perfectly safe provided everything is connected correctly.

Reversed polarity will mean that the switch is now in the Neutral line, and even if the equipment is switched off, the Live line is still connected.

This sets up the situation that even though the equipment is apparently turned off, inadvertently touching either the Live or Neutral wire will result in an electric shock.

Perhaps more seriously, most installations only have fuses in the Live side of the supply. In the event of a fault, even if the fuses blow, they will not isolate the equipment from the mains, allowing the fault condition to continue with possibly disastrous results. In a domestic situation, a polarity reversal is unlikely to occur unless some rewiring has been carried out. On a boat however, you are totally dependent on the power hook-up being correct, and that is by no means certain.



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[boatless]

Re: worst case scenario

What Ongolo is asking is "What is an RCD?"

Residual current device IIRC.

<A target="_blank" HREF=http://www.tlc-direct.co.uk/Book/5.9.2.htm>http://www.tlc-direct.co.uk/Book/5.9.2.htm</A>

Corrected - thanks Halcyon, more reading to do..

<hr width=100% size=1>my opinion is complete rubbish, probably.<P ID="edit"><FONT SIZE=-1>Edited by boatless on 02/07/2004 22:51 (server time).</FONT></P>

 

[halcyon]

Re: worst case scenario

RCD and ELCB are totally differant.
RCD measures current in live and current in neutral, if there is a error greater than there set trip level , 10, 30 60, 100 200 ma, depending on unit.
Earth leakage breaker messure current in the earth cable, thus if the flow is not to earthe via the mains cable it will not trip.
RCD's are sometimes described as earth leakage protection, which is a general term for leakage somewere to earth, as opposed to earth leakage cicuit breaker.

Brian



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[MedMan]

Re: worst case scenario

I had this problem with a new commercially-made panel which had a 'Polarity Correct' neon between live and earth. It was before the panel's own RCD so it did not trip that, but it did keep tripping the shore-side RCD making me very unpopular with the marina management. I solved it by moving the neon to run between neutral and earth - i.e. a 'Polarity Incorrect' warning. It can still theoretically trip a shore-based RCD, but only if the marina supply is incorrectly wired, so I don't feel too bad about that!

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[claudio]

Re: worst case scenario

Shouldn't the panel have two neons, one to indicate 'correct polarity' and one to indicate 'incorrect polarity' ?
Problem with using a single neon is that if its not lit it could be because there's a fault somewhere and its not working.



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[MainlySteam]

Re: worst case scenario

When polarity is protected right through to the appliance then the regulations governing electrical wiring in the nation set out which conductor in the supply is "live" and which one is not eg the grounded neutral in UK, Australia, USA (which in the distribution to the house has 2 live conductors and a grounded neutral), etc. It then specifies the orientation of all connections through the supply right to the appliance itself - all sockets and plugs and plugs are polarised (ie they are not reversable like the German Schuko and Euro plugs are, for example).

Most nations outside of some continental European countries use systems with polarised plugs and I would assume that the majority of them, if not all, regulate the protection of that polarity right through to the appliance ie the conductors cannot be swapped in the appliance's own cord set nor in extension leads (UK, USA, Australia, etc all certainly do). In Europe Switzerland, France, Belgium and Ireland, for example, have polarised systems but how rigorously it is protected by regulation I do not know.

You mention South Africa - South Africa uses polarised plugs but I could not comment on whether they have regulations in place protecting polarity from supply right through to the appliance but as an ex British colony I would be quite confident that they would have. For that same reason, I suspect that of the European nations I mention, Ireland protects polarity right through to the aplliance by regulation.

So nothing to do with RCD's, heart transplants, jets or atomic bombs at all I am afraid. And I have to agree with you that it is not much to do with New Zealand either, as it just followed the practice of the "more advanced" nations.

I trust that has made what I have previously said clearer. It can be easily seen that such a system is inherently much safer than a non polarised one but that that safety is compromised if there is inadvertent swapping of the polarity to an appliance through the house/marina/whathaveyou wiring, the appliance's cord set or an extention lead.

John

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[halcyon]

Re: worst case scenario

We used to fit reverse polarity, power to boat, and power on warning lights.
Correct polarity is realy odd, and will trip every RCD it meets.

Brian

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[MainlySteam]

Re: worst case scenario

<<<...if you have these couplings with two female plugs and open one up, in that plug that system changes>>>

Ongolo, your comment aroused my curiosity. I have now checked some of the ones we have in the house here (some are strip boards, some are the ones with two female sockets) and the correct polarity is maintained through them all.

Of course, one may find this not the case in more advanced countries also having polarised plugs /forums/images/icons/smile.gif.

Regards

John

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[Rick]

John wrote:
"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."

I didn't mean to imply that, however under US NEC regulations it is illegal to tie the shoreside earth to a ground connected to the water.

What I was really trying to point out is that where we have a polarity system, including the neutral and earth tied together at the distribution panel, a reverse polarity situation becomes deadly in the event of a fault.

Two simple solutions remove the risk - solution one: bring an extension lead on baord, plug an appliance in, use, and then disconnect when finished - solution two: if you need installed AC on board, then use an isolation transformer to remove you from the upstream risks.


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[Mike21]

Re: worst case scenario

ELCB's and RCD's are the same thing, they measure current leakage between live and earth.
The main reason as Claudio pointed out for ensuring it's correct is the fact that most sockets in uk have single pole switches that disconnect only the live when switched off. and also any fuses fitted are on the live side. If live and neutral reversed then appliance could still be live or in fault condition not blow the fuse.
Since most continental europe and USA don't used switched sockets, you'll find that most appliances that are sold worldwide tend to be fitted with a 2 pole switch and disconnect both live and neutral when switched off.

There is no polarity with ac systems, most ac appliances will work regardless whether live and neutral are reversed, it's only from a safety point it needs to be correct.

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