Do current rules require a galvanic isolator on new build boats?

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maby

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I recently installed one on our (nearly) new boat and mentioned it in passing to someone in the marina who usually seems to know about these things - he asked me why I had bothered since the current EC rules require one to be fitted at manufacture. I was not aware of this and could not see any GI marked on the wiring diagrams. Anyone know any better? Should I pull it out and put it up on eBay?
 
maby said:
I recently installed one on our (nearly) new boat and mentioned it in passing to someone in the marina who usually seems to know about these things - he asked me why I had bothered since the current EC rules require one to be fitted at manufacture. I was not aware of this and could not see any GI marked on the wiring diagrams. Anyone know any better? Should I pull it out and put it up on eBay?
Click to expand...


Don't pull it out unless you can find one already fitted.

Even then no harm in having two in series as far as I know
 
maby said:
I recently installed one on our (nearly) new boat and mentioned it in passing to someone in the marina who usually seems to know about these things - he asked me why I had bothered since the current EC rules require one to be fitted at manufacture. I was not aware of this and could not see any GI marked on the wiring diagrams. Anyone know any better? Should I pull it out and put it up on eBay?
Click to expand...

There was a draft proposal a while ago for the fitment to be included in the RCD (especially with respect to the current bonding requirements) but I am pretty sure that it was not adopted, it should have been really. If it ain't in the schematic it ann't there is an entirely reasonable assumption In any case seepost above.

Edit to correct appalling spelling.
 
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David2452 said:
There was a draft proposal a while ago for the fitment to be included in the RCD (especially with respect to the current bonding requirements) but I am pretty sure that it was not adopted, it should have been really. If it ain't in the schematic it ann't there is an entirely reasonable assumption In any case seepost above.

Edit to correct appalling spelling.
Click to expand...

Just to mention for the sake of completeness its worth a mention that fitting an isolation transformer where the shore power enters the boat performs the same function as a galvanic isolator. - do they do that now as a matter of routine?

From what I can understand even then there is no reason why both devices should n't be fitted - anyone know anything different?
 
A galvanic isolator after an isolation transformer is completely pointless and the other way round the inrush into the transformer could kill the diodes.

AN isolation transformer is a hell of a lot safer than a galvanic isolator.

Galvanic isolator.
Advantages
Cheap
Very simple to install
Disadvantages
Unit can fail without symptoms thus requiring regular checking. The failure could either endanger life by failing open circuit or remove the galvanic protection by failing short circuit. In fairness none of these failures are likely unless there is a large fault which blows the shorepower main circuit breaker. But the possibility does exist. The solution is to test the galvanic isolator after any problem with the AC system has been rectified, plus periodic checking.

Isolation Transformer
Advantages
The possibility of symptomless failure is almost zero. A failure will usually result in failure of the AC supply.
Disadvantages
More Expensive
Heavy
More complicated to install
 
nimbusgb said:
A galvanic isolator after an isolation transformer is completely pointless and the other way round the inrush into the transformer could kill the diodes.

AN isolation transformer is a hell of a lot safer than a galvanic isolator.

Galvanic isolator.
Advantages
Cheap
Very simple to install
Disadvantages
Unit can fail without symptoms thus requiring regular checking. The failure could either endanger life by failing open circuit or remove the galvanic protection by failing short circuit. In fairness none of these failures are likely unless there is a large fault which blows the shorepower main circuit breaker. But the possibility does exist. The solution is to test the galvanic isolator after any problem with the AC system has been rectified, plus periodic checking.

Isolation Transformer
Advantages
The possibility of symptomless failure is almost zero. A failure will usually result in failure of the AC supply.
Disadvantages
More Expensive
Heavy
More complicated to install
Click to expand...

I was thinking more of a galvanic isolator before the isolation transformer

so its one or the other not both then and both solutions are pretty reliable.

but no rules that say either MUST be fitted even though AC and DC grounds should be combined.
 
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nimbusgb said:
AN isolation transformer is a hell of a lot safer than a galvanic isolator...
Click to expand...
They perform totally different functions.

Marsupial said:
... fitting an isolation transformer where the shore power enters the boat performs the same function as a galvanic isolator...
Click to expand...
No it doesn't. It does not break the earth continuity for small voltages.
 
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nigelmercier said:
They perform totally different functions.

No it doesn't. It does not break the earth continuity for small voltages.
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Sorry to disagree if it is wired correctly the isolation transformer breaks all voltages. There is no connection between the incoming earth and the boat earth

http://www.smartgauge.co.uk/galv_tran.html

Vic is you have GI's in series the DC blocking will doubled. If they are connected in parallel it will make no difference
 
nigelmercier said:
Bonding the N and E on the output of the IT (as in your link) totally negates the point of having it.
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It does, rather, doesn't it? Depending on which side of the RCD it is fitted, it will result in earth leakage currents not tripping the breaker either.
 
nigelmercier said:
Bonding the N and E on the output of the IT (as in your link) totally negates the point of having it.
Click to expand...

Tell that to smartgauge who web site I referred to. This had been discussed several times before that for a RCD to work IT IS ESSENTIAL TO HAVE THE EARTH AND NEUTRAL BONDED. If it is not there is no where for the earth leakage to flow back to the neutral supply line and by kirchoff's law (the algrabrac sum of the current flowing at a point must be zero)

http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws

You can also have balanced systems where the earth is connected to the centre tap IT as in 110 VAC industrial site transformers to to reduce the voltage to earth to a max of 55 VAC but that is a special application.

As shown in the smartgauge site is the same way substation transformers are connected in the UK and my current country South Africa but not all countries work the same way.

I an sure VicS will cone up with the relevant standards for the UK.
 
I'm reasonably relaxed about bonding earth and neutral - it's the idea that neither is bonded to the mains earth that is the problem. With the wiring diagram on that web site, the casing of an item of equipment on your boat could be floating around at the full 240v without tripping any fuse or circuit breaker.
 
P.S. I am also very sceptical about the explanation on the web site as to why the isolation transformer is necessary. It revolves around the design of the filters installed in equipment to block RFI and goes on to say that they rely on capacitors connected from live and neutral to earth - quoting switch mode power supplies as the main example. Trouble is that virtually all the equipment we use these days is designed for sale across all of Europe (and, in many cases, across the world) - and many countries have no concept of an earth connection. I've just looked at the power supply for my laptop on the floor next to me and the charger for my tablet - both on universal plugs with adaptors to work in many countries round the world - both are two wire systems. The food processor in the kitchen? Two wire again! Manufacturers simply don't assume the presence of an earth any more - there are plenty of places where it simply is not there.
 
'casing of an item of equipment on your boat could be floating around at the full 240v without tripping any fuse or circuit breaker'

If that casing is metal of any kind it will have its case connected to the earth pin of the plug. That earth line will be connected to the neutral at the transformer. The line (brown) and neutral (blue) line will be connected to the transformer line and neutral but through the RCD and may be a MCB as well ( these could be combined). If there is an internal short to the case of the equipment making the case live (240VAC) current will flow down the earth line direct to the neutral connection on the IT bypassing the RCD. The RCD will now see of different current in the line side to the neutral side and thus trip disconnecting both the line and neutral supply from the equipment. If there is no earth connection at the IT the no current can flow back to the IT in effect there is no circuit until there is an alternate path for that current, which could be through a person touching the now live case and thus getting a shock at the path would be down through the ground earth path.

The one thing that is not shown on that diagram is the earth/neutral connection to ground through the hull of the vessel of ground spike as is the case in a substation installation
 
Rogershaw said:
Vic is you have GI's in series the DC blocking will doubled. If they are connected in parallel it will make no difference
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If the OP has in fact installed a GI in addition to an existing one they will almost certainly have ended up in series. I dont think doubling the blocking voltage will be any problem.
 
Rogershaw said:
'casing of an item of equipment on your boat could be floating around at the full 240v without tripping any fuse or circuit breaker'

If that casing is metal of any kind it will have its case connected to the earth pin of the plug. That earth line will be connected to the neutral at the transformer. The line (brown) and neutral (blue) line will be connected to the transformer line and neutral but through the RCD and may be a MCB as well ( these could be combined). If there is an internal short to the case of the equipment making the case live (240VAC) current will flow down the earth line direct to the neutral connection on the IT bypassing the RCD. The RCD will now see of different current in the line side to the neutral side and thus trip disconnecting both the line and neutral supply from the equipment. If there is no earth connection at the IT the no current can flow back to the IT in effect there is no circuit until there is an alternate path for that current, which could be through a person touching the now live case and thus getting a shock at the path would be down through the ground earth path.

The one thing that is not shown on that diagram is the earth/neutral connection to ground through the hull of the vessel of ground spike as is the case in a substation installation
Click to expand...

But the concept of "neutral" on the boat side of the transformer is not meaningful - both the output wires of the transformer are floating relative to the mains earth. Neutral is just the wire that is nominally tied to earth and should be sitting within a volt or two of earth. As you say, there is the potential of an alternative earth connection, for example through the boat's grounding plate or an earth spike.

I guess that many countries would wonder what all the fuss is about - America seems to have survived on two wire supplies for a long time and I don't hear of thousands of deaths through electrocution every year.
 
Two things. The fitting of only 2 pin plugs is based on the fact that a lot of equipment these days have a plastic non conductive case that even if there is a internal short would not cause a danger to the user. My very first Black & Decker power tools had metal cases and a 3 wire power lead including an earth wire most power tools and other equipment have plastic cases so no need to have an earth wire in the power lead.

One design project I did when I lived in the UK was the design of an all plastic mains control switch. The Chief Electrical Engineer insisted on an earth wire so I had to all a self tapping screw into the plastic case to connect the earth wire to.

The point about the filter caps to earth do as far as I understand rely on a connection to ground to allow the cap to sink any high frequency noise that may be generated.

My main expertise is in Mechanical and Electrical systems design with a little digital electronic design with very little analogue electronic design work so I stand to be corrected with regard to the exact operation of the filter caps in power supplied.
 
VicS said:
If the OP has in fact installed a GI in addition to an existing one they will almost certainly have ended up in series. I dont think doubling the blocking voltage will be any problem.
Click to expand...

You may be right I just wished to point out that there was a difference between parallel and series connection of the GI
 
"But the concept of "neutral" on the boat side of the transformer is not meaningful"

Sorry to disagree IMHO it is very meaningful in fact I think it is essential for a safe installation as I have said, without the E/N connection there is no way the leakage current could flow back to the neutral on the IT to cause a difference in the currents flowing through the 2 sides of the RCD. Before RCD's were fitted this disconnect could only happen when the fuse or CB tripped at the rated current of the fuse or circuit breaker. Now if the difference in current exceeds 20/30mA the RCD will trip so removing the danger.

Don't know about the USA only been there twice and glad to leave both times. The voltage in most of the US is 110 and I do think some supply companies do have a 3 wire system of they just rely on the ground connection for protection. I stand to be corrected
 
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The whole point of an isolation transformer is to isolate the legs of the supply so they are both floating WRT earth. Then the only way you can get a shock is by bridging both conductors with your body. If you connect one of these to your local earth, you are effectively removing that safeguard.

If the diagram showed the L wire connected to the E, you would all be saying it was crazy. In fact it makes no difference.
 
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