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

nigelmercier said:
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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What you have defined is a floating system and is used in some countries. The US is one I think but the supply voltage in most domestic case is 110 VCD

That is not the system in the UK it is the E/N unbalanced system. In fact it is the E/N connection that defines the neutral so connecting the "line" to Earth now makes it neutral so if you connected both sides if supply to earth you would have a very big bang.

The point of having an IT is to not have an electrical connection between the boat and supply but only have a magnetic through only AC power can flow so no DC. If you want a balances system, the type used on building sites is to have a centre tap IT and a person is only exposed to half the supply voltage but again in this set up the RCD would not work.

In you view if there was a short to equipment case of the live connector in a balances system what would happen and if there was no danger how would you know that there was an internal short inside the equipment.
 
ISOLATING TRANSFORMER

when an isolating transformer is installed it is wired like this

Image6.gif
( diagram from tb-training)


Note there is no connection of the shorepower earth to any part of the boat or its electrical systems .

A "neutral" is created on the boat by bonding one side of the transformer output to the boat's internal "earth". This includes anodes, engine block, DC negative when the DC system is not isolated, hull in the case of metal hulls and other large metal structures that could come into contact with 230V AC system.

An RCD would still be fitted between the transformer and the on board AC installation and for it to be fully effective the above earthing is necessary.


Because there is no connection between the boat or its systems and the shorepower earth a galvanic isolator is not required.

I am personally not convinced that a 1:1 isolating transformer makes a significant improvement in electrical safety for those on board the vessel. Risks to nearby swimmers from on board faults though should be eliminated.
 
I agree 100%.

The only thing I would add is that the RCD must be boat side of the neutral/earth connection point NOT transformer side.
 
Rogershaw said:
What you have defined is a floating system and is used in some countries...
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There are two issues here: GI and safety. Using an IT with an E/N bond will act as a GI, but it will be no safer than the system without it.

BTW, I wasn't suggesting that both L and N could be connected to E, just that the labels are meaningless on the output of an IT.
 
nigelmercier said:
There are two issues here: GI and safety. Using an IT with an E/N bond will act as a GI, but it will be no safer than the system without it.

BTW, I wasn't suggesting that both L and N could be connected to E, just that the labels are meaningless on the output of an IT.
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In fact, by definition the wire that you bond to E becomes N
 
VicS said:
ISOLATING TRANSFORMER

when an isolating transformer is installed it is wired like this

Image6.gif
( diagram from tb-training)


Note there is no connection of the shorepower earth to any part of the boat or its electrical systems .

A "neutral" is created on the boat by bonding one side of the transformer output to the boat's internal "earth". This includes anodes, engine block, DC negative when the DC system is not isolated, hull in the case of metal hulls and other large metal structures that could come into contact with 230V AC system.

An RCD would still be fitted between the transformer and the on board AC installation and for it to be fully effective the above earthing is necessary.


Because there is no connection between the boat or its systems and the shorepower earth a galvanic isolator is not required.

I am personally not convinced that a 1:1 isolating transformer makes a significant improvement in electrical safety for those on board the vessel. Risks to nearby swimmers from on board faults though should be eliminated.
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so there is no way a path exists through the metal parts of the machinery, shafts, props etc that are under water, the water and through the soil for the "earth" to complete a circuit; not even for a very tiny current? - I find that hard to believe.
 
Marsupial said:
so there is no way a path exists through the metal parts of the machinery, shafts, props etc that are under water, the water and through the soil for the "earth" to complete a circuit; not even for a very tiny current? - I find that hard to believe.
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That is not a complete circuit.. that is only half of one!

The circuit that can cause the problematic galvanic corrosion associated shorepower installations consists of the path you describe AND the shorepower earth connection back to the boat to complete the circle.

When a galvanic isolator is fitted it breaks that shorepower earth half of the circle (for the low voltages associated with galvanic corrosion).

If people chose not to bond the shorepower earth to the anodes and DC negative etc etc then that means the circle is not completed.

When an isolation transformer is fitted the shorepower earth is not connected to any part of the boat so the circle is not completed.
 
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VicS said:
That is not a complete circuit.. that is only half of one!

The circuit that can cause the problematic galvanic corrosion associated shorepower installations consists of the path you describe AND the shorepower earth connection back to the boat to complete the circle.

When a galvanic isolator is fitted it breaks that shorepower earth half of the circle (for the low voltages associated with galvanic corrosion).

If people chose not to bond the shorepower earth to the anodes and DC negative etc etc then that means the circle is not completed.

When an isolation transformer is fitted the shorepower earth is not connected to any part of the boat so the circle is not completed.
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Thanks Vic

I get a bit paranoid about this as a few feet from my plastic boat there is a aluminium boat and a steel boat both have lots of zinc wired to stanchions dangling in the water - my galvanic isolator says there is no stray current and my anodes are good so perhaps I should relax a bit.
 
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My view on this and some people disagree on this is :-

On a GRP boat without all the metal bits bonded there is no need to have the mains earth connected to any metal unless there is a danger of any one on board touching and exposed metal case of a mains powered equipment. Without bonding and no earth boat connection there will be little if any galvanic corrosion. Once you start bonding and connecting DC negative and mains earth you have created current paths for galvanic corrosion. As there is no bonding and no galvanic corrosion current paths hull anodes are not needed. Where you have dissimilar metals in electrical connection you do need anodes to protect the less noble metal like prop shafts and may be bow thrusters. These are protected by local anodes (shaft anodes).

On a metal boat like my steel boat and you have a mains installation as you will have mains powered items bolted to the metal hull there is a distinct possibility that if there is an internal mains short in some equipment the hull could become live so it is very important to have a proper earthed hull. Anodes are also very important as the chance of dissimilar in electrical contact is much higher. IMHO if the DC negative is also connected this adds to the possibility of having DC leakage currents flowing through the hull inducing additional galvanic corrosion and the rapid erosion of any anodes. This is much more important on aluminium boats than steel due to aluminium's position on the galvanic table.

On my boat I have lots of mains equipment most with metal cases bolted to the hull so mains earthing is very important to me. I have 3 mains power sources on my boat. Shore power, inverter and inbuilt diesel generator. The latter 2 I have added the earth/neutral connection to the equipment because as supplied there were not connected. My 12 VDC system is totally isolated from the hull yet my engine like most has the DC negative connect to the block. I took great care to isolate the engine from the hull. flexible couplings rubber mountings but also all the mechanical controls like gearbox, throttle and stop cables.

I also have a GI fitted connected as in VicS posting type 2

All of my sea cocks are 316 stainless and I even fabricated my own prop from stainless last year to get rid of the bronze prop I had. My hull ahodes are bolted to 316 stainless studs welded to the hull and my prop shaft have shaft anodes. Even my steel rudder has its own anodes.

Below are pics of my anodes last year 2012 boat first launched 2009 need to clear some pics to upload new ones.
 
Rogershaw said:
My view on this and some people disagree on this is :-
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For anyone concerned this link gives reasons for bonding Shorepower earth to DC negative etc http://www.shorelineproducts.co.uk/marine_earthing.php

It should be pointed out that the version of ISO 13297 referred to has now been superseded by a new (2012) version which came into force approx a year ago.

I expect to find that the new version does not contain the concession not to bond shorepower earth to DC negative. Maybe one of the professionals can confirm this or otherwise.
 
Unless you have a metal boat then there is no reason to fit a galvanic isolator, the only metal that a GRP boat has in the water is a prop and the anodes protect that. Stray current corrosion occurs when there is an earth leak from pontoon shore power or where salt water mixes with fresh water, the latter is really damaging.
 
KellysEye said:
Unless you have a metal boat then there is no reason to fit a galvanic isolator, the only metal that a GRP boat has in the water is a prop and the anodes protect that. Stray current corrosion occurs when there is an earth leak from pontoon shore power or where salt water mixes with fresh water, the latter is really damaging.
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My boats (GRP) have metal keels, hull valves, p brackets, cutlass bearings and rudder stocks. Oh, and propellers. In the water.
 
KellysEye said:
Unless you have a metal boat then there is no reason to fit a galvanic isolator, the only metal that a GRP boat has in the water is a prop and the anodes protect that. Stray current corrosion occurs when there is an earth leak from pontoon shore power or where salt water mixes with fresh water, the latter is really damaging.
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The galvanic isolator's main purpose is to protect the anodes. That is why they are sometimes called "zinc savers"

These "stray currents" as you call them arise not from electrical leakage from the shorepower supply but from the variety of metals structures in the vicinity

By virtue of the connections created by the shorepower earth conductor your anodes can be attempting to protect the hull of a nearby steel boat or even the surrounding steel pilling of the marina
 
VicS said:
The galvanic isolator's main purpose is to protect the anodes. That is why they are sometimes called "zinc savers"

These "stray currents" as you call them arise not from electrical leakage from the shore power supply but from the variety of metals structures in the vicinity

By virtue of the connections created by the shore power earth conductor your anodes can be attempting to protect the hull of a nearby steel boat or even the surrounding steel of the marina
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1st statement is correct but if the shore power is not connected to the anodes GI is not needed.

"stray currents" on a metal boat can come the connection of the 12v negative system to the hull of a steel or via the interconnection of metal fittings on a GRP boat. If no connection of 12v negative to interconnected items no stray currents.

If you don't have the shore power connected to the isolated metal items on a GRP boat no galvanic interaction with outside metal structure.

As far as the link you posted the RCD is not the only safety device in the UK you have at least the fuse in the 13 A plug or in my case the MCB which you may have also. The shore power installation will also have a RCD at the marina box.

The drilling on the engine shorting the mains to the 12 v system is a bit of an exaggeration as most power tools ard double insulated hence no earth wire in their power lead or if not double insulated they have an earth lead which if shorted would cause either RCD to trip or the MCD of fuse to blow/trip.

Just note what shore line products and anode suppliers wish is to sell more of their products and if they can suggest that their product will make a boat safer or protect the boat they will.

I in fact have a shore line GI and lots of anodes as there is no way I can insulate all the dissimilar metals below the water line. What I have done is to reduce the dissimilar metals below the water line as much as possible to my anode wastage is now minimal but there is still some and no sigh of hull corrosion damage.

Capnsensible
What is the likelihood of any mains live power coming into contact with the external metalwork on your steel boat. If it is unlikely less to worry about.
What is the likelihood of any person in the normal cause of usage of your boat coming into contact with any metal item on your boat that could also have mains live power connected to it. If also unlikely.

I look at earth connection/protection and inter bonding like insurance the less likely the less you need it. In the case of a metal hull boat it is IMHO much more likely that on a GRP boat without interlink bonding

The problem with standards are they have to take all possibilities and all construction types no matter how remote into account and do not consider cost.

A friend of mine has a jen/ben with 15 underwater sea cocks and was told he must bond then all together with anodes. So he did ans within 3 months the sea cocks started to corrode. He then removed the bonding cleaned to sea cocks and had no further problems. I sailed with him along the South African coast he then left went to Brazil, Caribbean and back to US with out any further sea cock corrosion problems. Several boats in our marina have had high anode wastage without having permanent shore power on removing bonding and 12- connection, the high wastage was eliminated.

KellysEye and I both have metal boats and so are very concerned with corrosion and I looked into this greatly as possibly KellysEye has but in saying that if anyone wished to boat with mains earth 12v- bonded with anodes all connected to underwater fittings and GI go for it your choice.
 
>These "stray currents" as you call them arise not from electrical leakage from the shore power supply but from the variety of metals structures in the vicinity

They certainly are caused by electrical leakage from shore power (look it up on the Internet) the only exception could be a Aluminium boat near a steel boat.
 
KellysEye said:
>These "stray currents" as you call them arise not from electrical leakage from the shore power supply but from the variety of metals structures in the vicinity

They certainly are caused by electrical leakage from shore power (look it up on the Internet) the only exception could be a Aluminium boat near a steel boat.
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In the context of the protection that a galvanic isolator gives to the anodes the currents we are considering come from low voltage galvanic sources. such as nearby steel boats or other steel structures
A GI offers no protection from leakage current from shorepower supplies , or for that matter from defective 12/24 volt installations. Leakage currents from these, and the electrolysis they could cause, is a different matter altogether and potentially more serious because the GI offers no protection.

It is quite wrong to suggest that there is no reason to fit a GI to a GRP boat, at least if the shorepower is normally connected.
 
Is there a point at which a GI is worth it? My new (to me) boat is about to get a minimalistic shore power set up, but I only expect to stay I'm marinas and on shore power for about 30 days, spread over the year. The rest of the time she'll be sat on a trot, or anchored.
 
>A GI offers no protection from leakage current from shorepower supplies , or for that matter from defective 12/24 volt installations. Leakage currents from these, and the electrolysis they could cause, is a different matter altogether and potentially more serious because the GI offers no protection.


Again that is wrong which is why metal boat that have a GI don't get stray current corrosion and those that haven't got one have been known to get corrosion from (as I mentioned) shore power, normally caused by a bad earth, and where salt and fresh water mix. We also had a GI on our 12v system.

I wouldn't bother to fit one to a GRP boat but everyone to their own.
 
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