is there an electrical engineer in the house?

[Guest]

have heard much about polarity problems in french marinas. is there anyone who can tell me if the following is correct?

i had an electrical problem on my boat in france this summer, and the skipper of the boat next door kindly came round to help. he said he was an electrical engineer, and explained the polarity issue in france in the following terms

in the uk the neutral wire is at or about earth potential, and the voltage difference is the same earth to live and neutral to live at 240 volts in both cases. in france, they operate with a split voltage ie the difference between neutral and live is 240 but the difference between earth and either live or neutral is 120v. this is claimed to be much safer, since you cannot get a fatal shock from 120v (hence the widespread use in the uk of 110v electrical tools in e g the building industry)

the split in voltage is not absolutely precise, so in different locations either the neutral / earth or live / earth will have a slightly higher figure. if it happens to be the neutral / earth, then the polarity detector circuits you find in some uk boats will light up. however, all the electrical equipment should still work o k without changing round the plug.

the rcd detects slight current mismatches between neutral and live (ie current leaking away to earth or through you). it should be unaffected by the above polarity situation.

once we were told the above, we ignored the whole issue and never had a problem in either france or spain even when other boat owners were saying there was a polarity problem. all our equipment worked correctly including the rcd

 

[Bergman]

I don't know anything about French electricity supply, but I would strongly recommend that you don't take it for granted that 110V cannot kill.

In the words of the old saying "Its Volts that jolts, but its mils (milliamps) that kills.

Treat it with just the same respect you would show 230V

 

[ccscott49]

I do believe it has something to do with the way the alternators in the power stations are connectd, either star wound, as in UK or delta wound as in france or the other way round, but I agree 110 volts has killed a lot of people in America!

 

[Guest]

Useless bit of information number 3003.........

Don't know electrical details of the French system but understand that when France went from 110 volts to 240 volts the national death rate from "electrical faults" fell by about 50% in a year!

Watts divided by volts = Amps = load on circuit.

Therefore:
o 3000 watt fire divided by 110 volts = 27 amps.
o 3000 watt fire divided by 240 volts = 12.5 amps.

Much less load on domestic circuits apparently resulted in many less home fires (and deaths) caused by burned out wiring.

Moral of the story - "Never trust a French electrician."

Best regards )

Ian D

 

[VMALLOWS]

Firstly, yes I am an Electical Engineer (C.Eng MIEE)

I also completely endorse the point that 110v will kill you just as easily as 240v. The 110v (construction industry) system refered to for use in the UK is (or most certainly should be) a center tapped 55-0-55 transformer meaning that the maximum voltage to ground can only be 55v. Even that can kill if for some reason you cant disconnect. (and please don't catch hold of both wires at the same time!)

The 'polarity' question is interesting. I think we should be talking 'phase/neutral'......polarity (+/-) belongs to DC. (don' t even think about a 200 volt DC shock ... you can't release yourself from it very easily)

The only relevance of so-called 'polarity' that I can see is that any ON/OFF switch should probably have been wired in the live(phase) side of the circuit on any appliance. Why not unplug it if your worried. The vast majority of domestic items sold in Europe/US have 2-pin plugs that go in either way round.

Just install an RCD (residual current Device). They used to be called 'Earth Leakage Breakers' which I think was a better term. They typically detect 30 milliamps or less. (yes 30mA can kill you, but not very likely).

If your RCD is tripping, then probably your propeller/seacock/anode is wasting away.

 

[oldharry]

Ever had a shock off a 24v wired boat? Quite nasty enough in the wet to realise 110v (even splt 55-0-55 for our construction industry) is potentially lethal.

But bear in mind that even if the French voltage to earth is only 110volts, the potential across the pos and neg lines is still 240 volts, so if you are unfortunate (or stupid) enough to connect yourself across + and - , rather than to earth, then you get an even worse and probably fatal shock.

 

[VMALLOWS]

Reost by 'oldharry'

I thought that was exactly the point I was making....that almost any voltage can be lethal in certain circumstances.

I stand by my comment that the best protection you are likely to get - assuming you want AC onboard - is an RCD. Just to expand my last comment, an RCD should NEVER trip unless something is faulty either by design or deterioration. I have had examples of battery chargers and electric kettles in particular.
A two-wire appliance (without an earth connection) will never trip an RCD unless something (you?) touches it and creates a leakage path to somewhere.

Incidentaly, have always found Marina supplies in France to be 230v phase/neutral,
though don't doubt that some may differ.

A final safety plea ...... dont forget the current when working on 12/24v. I will not wear a wedding ring or any jewelery ANY TIME. Have witnessed the consequences and don't trust myself to remember to take them off.

 

[LadyInBed]

Re: Wedding Ring

Yes – I tell my wife that’s the reason I don’t wear a ring as well!!

 

[chas]

I can rememeber being given a similar explanation when I lived in Holland some years ago.

 

[Guest]

thread seems to have got slightly de-railed, or perhaps i didnt word it very well.

am not so much concerned about the safety of 120v v 240 (though i take the point about the center wound transformer) but as to whether the explanation of how the french system worked was correct

have met dozens of people who have busily rewired their plugs in french marinas. the explanation i was given suggest they are wasting their time. are they?

 

[Guest]

f a o mr v mallows

interesting comment ref rcd. yes, mine does trip out particularly if the circuit is loaded when connecting to shore power, or if shore power has not been used for some time.

all there is on the circuit is an rcd, a battery charger and two sockets. after taking advice from the charger maker who assured me that there was no connection whatsoever between mains earth in and negative dc out, i took the decision not to connect mains earth to boat negative.

so why does my rcd trip out - only to then work when re-connected.

 

[oldharry]

VM - I Agree! Agree! Agree! In my simple (according to Mrs O'H) way, just thought I'ld reinforce this important point, as the posts seemed to have got bogged down in the probable safety or otherwise of 110v supplies, with the implicit suggestion that the French mains is in some way less lethal than ours....

Bottom line is that the instant electricity 'escapes' from its insulation it is likely to become lethally dangerous, either directly by electrocution at much lower voltages than most people realise, or indirectly by setting fire to things.

Even the humble and familiar 12volt lead acid battery can create a life threatening fire situation in a matter of seconds. 3 or 4 good lungfuls of toxic smoke from burning insulation, GRP and fabrics, and you are just another statistic.

 

[Jean]

Sounds like you had some good advice. A couple of points though, I think France aims for 220 volts line to neutral, ie, 110 volts from either to earth if it is an earthed centre tapped supply. I think that their appliance switches are generally double pole (ie, a contact in both line and neutral) whilst UK may generally just switch in line circuit (probably main reason you need to get polarity right in UK). Using a single pole switch in France can therefore leave your appliance circuits at around 110 volts above earth potential, whichever way round you connect your supplies!
Someone mentioned star/delta supply alternators; I think that the earth point in UK tends to be at nearest star connection back down the line, the “neutral point” (not so easy to earth a delta system as we know it). If France uses earthed centre tap, this is probably a lot nearer the consumer, but either way, a shock is a shock! RCD’s well worth considering and if in doubt, unplug when not in use.
Does anyone know if Spain uses a similar supply system to France?

 

[HaraldS]

Howard, quite a complicted matter to explain, but I'll try:
First, I have no experience with the french system, but what you have been told seems plausible and it's not different to two phase systemsin other places.
Not sure it's really saver that way, since assuming you have a one to two better chance of surviving a 120V shock versus a 240V shock, then this is offset by your chance of 50:50 of touching neutral instead of the hot wire in the UK.
Back to why your RCD may be tripping: It shouldn't have anything to do with the french system. In any system, be it 3-phase, two phase like in your France example or single phase and neutral like in the UK, the load carrying wires go through the RCD. It could be two or thre or four.All that matters to the RCD is that the current going in and the current going back is the same. The voltage potential relative to earth or ground does absolutely not matter. What maters is a potential leakage to ground in which case some current is returned via ground and the balance in vs. out isn't the same in the RCD.
Inside the RCD there is something like a small transformer which is wound in a way that the field that is generated by the one wire, is offset by the field of the return wire. If the current in the two wires isn't the same, the magnetic field isn't neutralized and the residual field induces a voltage in a thrid coil that drives the release solenoid.
So if the RCD trips, you need to think about what could case a difference in the current in the two wires.
You also mention that it is happening under load only.

In an asymentric system, where you ahve neutral and phase, the neutral wire is connected with the ground in one and ONLY one spot, which usually is at the power transformer. While neutral is run through the RCD, the same potential ground wire isn't. If this ground wire is connected with neutral, after neutral passes through the RCD, you will have a scenario in which the RCD will only trip when there is some load. This is because the return current is split between the neutral wire and the ground wire and only the neutral part will pass back through the RCD. Deoending on the resistance of this faulty connection, you may need different levels of load before the RCD trips.

Note that if the faulty connection was between the hot wire and ground, rather than neutral and ground, the RCD will trip immediately, no matter if there was any load.

You would have the described tripping under load, if your charger would have a leak between neutral and ground. If that was the case you could proove that by reversing the 'polarity' on the charger, meaning swapping neutral and hot wire. Now, if ther was this leak, the RCD would now trip immediately, regardless of load. Where I come from, that could easily be veryfied by just turning the plug around, UK plugs don't allow this, but you could still swap the wires to test it.

So if that leads to immediate tripping you have a leak in the charger.

More likely, swapping the wires will not change anything and the problem isreally differnt.

As I said, the RCD has a little transformer and just some phase shift between in and return would be enough to cause a problem. Very unlikely you would have a phase shift due to cable inductance at the low 50Hz or 60Hz, but at higher frequencies you could easily have that.

Unfortunately, modern power supplies and chargers can cause current shapes that are far from a true sine wave and hence contain high frequency components. Most common reason are silicon diodes used as a rectifier, that would would not start conducting until voltage following the 50Hz curve reaches a level higher than the buffer capacitor. The result is a narrow current spike near the upper and lower maximum of the voltage curve. Now depending on your wireing, this can be phase shifted enough between in and out to induce current in the RCD that would trip it.

Try to put a long cable between your RCD and the charger, and the problem might go away.

Probably the best thing you can do to prevent many of this problems and also prevent elecrolysis problems, is to instal an insulation transformer. In this case you just run the two wires hot and neutral or two phases like in France to the primary side, and leave shore ground unconnected. On the secondary side you would usually have one side of the output connected to your AC ground, and your neutral and ground wire would start there. With a switachble transformer you can also select differnt shore voltages and convert them to whatever you have chosen inside your boat.

You could also opt to run an ungrounded AC system in your bout, an RCD is then useless, but you would also not get a shock when you touch either of the two AC wires. By some standars that s illegal wireing, but it has a lot of pros.

When you go grounded on the secondary side, you still can decide whther you want to connect AC ground and DC ground. I wouldn't. But here we would get into the difficult topic of grounding, bonding, lightning protection and so on.

Again, best recommnedation is an isolating transformer. Has only very few draw backs, like limited peak current. An example of that is that I can only get my dive compressor started fron the generator, but not from shore power.

Hope I haven't confused you too much, but you asked...

 

[Artimes]

It is not correct to speak of the french system having a neutral in the same sence as britain. The supply transformer in france is a single phase unit with one secondary which is centre tapped to earth. This give 110 volts to earth (call it neutral) from each end of the transformer secondary winding. In UK if the transformer has a single secondary winding, one end of that winding is normally grounded giving 240 V from the other end to the neutral but the neutral should not be regarded as earth for protection purposes. also at each consumer the neutral is not earthed. See the difference??? The UK earth is the metalwork of the transformer and appliances and possibly a seperate earth wire.There may or may not be a potential between the neutral conductor at the consumer and true earth, it depends on the impedance of the earth at the transformer and other factors.

in some Europian countries the transformer winding is grounded at one end, and the neutral wire is grounded at each consumer where this applies its called "protective multiple earthing"

 

[Guest]

Appropos........

You would have the described tripping under load, if your charger would have a leak between neutral and
ground. If that was the case you could proove that by reversing the 'polarity' on the charger, meaning swapping
neutral and hot wire. Now, if ther was this leak, the RCD would now trip immediately, regardless of load.
Where I come from, that could easily be veryfied by just turning the plug around, UK plugs don't allow this, but
you could still swap the wires to test it.......



I would point out that most /all switched mode DC power supplies which includes most modern battery chargers have a significant amount of inductive / capacitive filtering on their mains inputs, some of these capacitors are connected to ground / earth. When powering up these units it is possible that initial inrush currents can cause a significant instantaneous earth leakage currents until the unit stabilises.

I have experienced this and yes it does matter that it is connected the right way round. The 12v Switch Mode PSU I use to supply my boat with shore power was original connected inverted, worked fine except that if mains power was applied when the ouput was connected to the batterys the ELB (RCD) tripped, the ELB could be reset and all would be fine until the next time. When I discovered that the the mains supply was apparently inverted I crossed it over, after that the ELB never tripped when mains power was applied with the batteries connected to the supply.

In this case this was proven on a UK 240V marina system, the charger was not connected to mains earth, in fact mains earth does not exist on my vessel I believe this to be far safer both inrespect of personal safety and anode errosion.

DC negative does go to ground (water!) via the engine.

 

[HaraldS]

Definitely another quite valid point. I have seen leaking filters too, I would just not think that this is an ok state. If switching the wires helps, there's obviously a leak. So far all input filters I have seen have been symetric, and as you point out they do have capacitors towards ground. However the current through those is generally very small and far from the 30mA that trip an ELB. No matter whether powering up or not, there will always be a small current since it's AC. Surges with a steep flank can cause higher currents, but the duration is then usually too short to trip the slow ELB.
More likely, and I have seen that, is a bad varistor, a surge protection device that looks much like a capacitor and is supposed to short against ground when you get a high voltage surge. They sometimes short or leak towards ground at the regular 240V. If one of the two does that, you get a clear polarity dependance.