Ferretti winter updates

[baylabayla3288]

I'm surprised that you find it surprising (sort of), because here in IT I think that single contact breakers are even illegal!
Do you mean that in the UK, boats aside, it's normal to have AC lines where breakers cut just one wire?

Also here in Finland the normal way is to cut one wire only. There are some exceptions but in the majority of cases only the phase or the live is cut. On the Fairline the main circuit breaker next to the shore power input did cut both, all other were single contact I believe but the polarity light system never cased any issues for me. This reminds me of the world travel adapter I just bought...

 

[MapisM]

In UK (and fwiw USA I think), the neutral is positively grounded

I see, thanks for enlightening me.
Then again - apologizing in advance if I misunderstood something - what's the point of the 3rd GND pin in the center of UK sockets/plugs...

 

[mlines]

I see, thanks for enlightening me.
Then again - apologizing in advance if I misunderstood something - what's the point of the 3rd GND pin in the center of UK sockets/plugs...

Depending on the exact local wiring (there are more than one standard depending on age) the neutral pin (2nd pin) on a UK plug can be "Power station earth" whilst the Earth Pin (3rd pin) is "Local Earth".

Therefore there can be a small voltage between neutral and earth due to ground resistance/distance etc. I am sure someone more technical will be along to describe "Protective Multiple Earth" systems etc.

 

[Deleted User YDKXO]

Thanks to jfm and baylabayla for the electricity tutorial. Much appreciated!

 

[jfm]

I see, thanks for enlightening me.
Then again - apologizing in advance if I misunderstood something - what's the point of the 3rd GND pin in the center of UK sockets/plugs...

I totally see why you're asking that question, but it's hard one! There is an explanation but I'm going to get out of my depth soon. Basically, as mlines said, the UK neutral is connected to earth some distance away, up river so to speak. The earth pin is connected directly to ground locally, and the (eg) metal casing of your toaster is connected to that.

So if we abandon the 3rd earth pin and, say, your toaster had a malfunction and the live wire inside it got connected to the metal casing of the toaster, and the neutral was also connected to the casing (because there was no earth system using the 3rd pin), then you touch the toaster while you are standing in bare feet on the ground, the toaster casing would have a potential relative to the earth so you could still get a shock. Why? - Because the downstream resistance in the neutral wire between the toaster and the place where the neutral and the ground are connected together would result in some voltage still remaining between the toaster casing and the earth, so you could still get an electric shock.

There is probably better explanation that that and the maximium I would claim here is that I'm possibly along the right lines. Back in ancient history, in UK at least, we did have 2-wire installations where the neutral did the same job as the earth

 

[BartW]

…….. Basically, as mlines said, the UK neutral is connected to earth some distance away, up river so to speak. The earth pin is connected directly to ground locally, and the (eg) metal casing of your toaster is connected to that.

So if we abandon the 3rd earth pin and, say, your toaster had a malfunction and the live wire inside it got connected to the metal casing of the toaster, and the neutral was also connected to the casing (because there was no earth system using the 3rd pin), then you touch the toaster while you are standing in bare feet on the ground, the toaster casing would have a potential relative to the earth so you could still get a shock. Why? - Because the downstream resistance in the neutral wire between the toaster and the place where the neutral and the ground are connected together would result in some voltage still remaining between the toaster casing and the earth, so you could still get an electric shock.

There is probably better explanation that that and the maximium I would claim here is that I'm possibly along the right lines. Back in ancient history, in UK at least, we did have 2-wire installations where the neutral did the same job as the earth

I think your explanation is perfect, at least I can’t do it any better 

But here; I think this is not completely correct:

……
If you bring a Uk boat to France/IT as I have done, it is perfectly fine to have a breaker just on the live side because the neutral is grounded on board the boat. There is no "incompatibility" problem in plugging a UK boat with a grounded neutral into a French/IT electrical system with an ungrounded neutral

IF on a UK boat, neutral is grounded to earth, you could have potential problems in certain situations / places

1) There are still regions in Europe (in Belgium fe) where you have 3phase networks of 3x230V (not the more common 3 x 380 + neutral)
Your 2 pole shore power connection is than connected to two phases, and your boat would make a short cirquit between one pole (neutral) and ground

2) If the grounding in the marina is not good, you could potentially place a dangerous voltage on the grounding of your neighbour boat

Of cause “behind “ the isolation transformer one pole can or should be connected to ground

happy to be Corrected on this,

 

[MapisM]

Thanks all for your explanations, an interesting reading indeed.
As they say, every day is a school day...!

 

[baylabayla3288]

Yep.
...If you bring a Uk boat to France/IT as I have done, it is perfectly fine to have a breaker just on the live side because the neutral is grounded on board the boat. There is no "incompatibility" problem in plugging a UK boat with a grounded neutral into a French/IT electrical system with an ungrounded neutral

Actually shore power neutral N and safety ground G are never connected on the boat, it vould cause an immediate short if the polarity would be wrong. The uk boat is allways compatible provided that the polarity indicator is working. The G to N connection is done normally at the closest junktion/ distribution box on shore. Safety ground is there like jfm stated earlier to protect a user in case of an isolation fault, it helps to make the ground fault breaker to trip before anybody touches the faulty device. But the N and G are ( should be) connected at the genset and the inverter on the boat which are the source when in use. On all my boats DC negative, G and the bonding system have been connected. This is a trade off between safety and electrolytic corrosion i favour for safety. To prevent corrosion a galvanic isolator on the G works very well as the galvanic corrosion is caused normally by DC currents.

 

[jfm]

1) There are still regions in Europe (in Belgium fe) where you have 3phase networks of 3x230V (not the more common 3 x 380 + neutral)
Your 2 pole shore power connection is than connected to two phases, and your boat would make a short cirquit between one pole (neutral) and ground,

Bart, I'm happy to be corrected too!

I wasn't aware that there were European systems with 3x230v, where the 230v is the difference between any 2 phases. In such a case there is no neutral, or rather there is (the star centre of the 3 phases together of course) but no-one would use it. I think that is what you are saying.

But yes, if that system exists, I agree that you would not want to connect a Uk boat with an on board "neutral to ground" connection. You would then be connecting one of the phases (132volts) to ground, exactly as you say. That would blow lots of circuit breakers BANG! And make for some interesting electrolysis effects under the hull!

 

[baylabayla3288]

Actually shore power neutral N and safety ground G are never connected on the boat, it vould cause an immediate short if the polarity would be wrong. The uk boat is allways compatible provided that the polarity indicator is working. The G to N connection is done normally at the closest junktion/ distribution box on shore. Safety ground is there like jfm stated earlier to protect a user in case of an isolation fault, it helps to make the ground fault breaker to trip before anybody touches the faulty device. But the N and G are ( should be) connected at the genset and the inverter on the boat which are the source when in use. On all my boats DC negative, G and the bonding system have been connected. This is a trade off between safety and electrolytic corrosion i favour for safety. To prevent corrosion a galvanic isolator on the G works very well as the galvanic corrosion is caused normally by DC currents.

Here is a good picture about the above

http://lnvt.wdfiles.com/local--files/electricalsafety/groundfault.jpg

 

[BartW]

Yep. In continental Europe the neutral isn't grounded and so it can (I think!) have a voltage difference relative to earth (if the voltage drop across the three phases that must exist - somewhere across town or up the street - isn't perfectly matched. So both L and N need to be isolated. ......

In Europe, in a three phase + neutral network, the neutral IS grounded in the power station, or in the transformer station,
but at a distance from this grounding point, you can have a "small voltage" between neutral and ground, when ground resistance is not low / good enough.

fe Interference supressing capacitors, on the mains input (between the 230V poles and ground) on a applience fe a computer,
can pass a voltage on the metal housing, when the housing is not grounded correctly

 

[jfm]

@ Baylabayla, thanks. That's a v helpful picture. I'm happy to stand corrected ref the on board G-N connection

I'm wondering if your picture changes when there is an isol transformer on both the hot and the neutral. I'm inclined to think it doesn't, but not sure, and have to run to airport so no time to think about it

 

[baylabayla3288]

@ Baylabayla, thanks. That's a v helpful picture. I'm happy to stand corrected ref the on board G-N connection

I'm wondering if your picture changes when there is an isol transformer on both the hot and the neutral. I'm inclined to think it doesn't, but not sure, and have to run to airport so no time to think about it

In case of an isolation transformer the G and N should be connected at the transformer, because this becomes the source and if not, the ground fault breakers would not work either. The boat G sould not be connected to the shore G as the galvanic corrosion prevention would be lost ( a bit guessing here now, correction is welcomed...)

 

[BartW]

I'm wondering if your picture changes when there is an isol transformer on both the hot and the neutral. I'm inclined to think it doesn't, but not sure, and have to run to airport so no time to think about it

when your boat is isolated with a transformer, you schould ground the secondary side of the transformer,
actually you are like a galavanically isolated power generator, and for safety reasons, one phase of your boat network should be grounded (and becomes the boat network neutral then) This neurtral has nothing todo with the shore connection neutral
that's how it is done on your Fairline I think.

On BA there is no Isolation transformer, BUT
when the Victron invertors notice that they are floating, there is a relay inside that connects One phase to ground.