to bond or not to bond

[della li]

Hi All-- I have installed a galvanic isolator, but I do not beleive the elec. system itself is bonded to an external zinc. I have zincs on the shaft and rudder that are barely corroded after ove half a yr. (though none on the hull). So is the isolator doing its job? Do I really need to bond the system to an external zinc as well? I am in a small marina Maybe 20 boats, some smaller, and not a lot of heavy AC use I think. I imagine many of the other boats not bonded as well, though just guessing).

The zincs in the engine (there are 6) do not seem to have corroded much over past few months as well.

 

[CharlieJ]

I can argue bond or not bond convincingly. When asked, I tell an owner that a bonding system is just that, another system that requires periodic maintenance in order for it to perform as required. If this maintenance is done a bonding system will keep all underwater bits at the same potential, thus eliminating own boat caused stray DC corrosion.

Back to basics: If your boat was wired to be ABYC or ISO 13297 compliant then the AC safety ground (green) wire is connected to the AC grounded bus and the battery B- is connected to the DC ground bus. These two busses are connected in one, and only one, place. Also relevant is that when you open the shore pedestal breaker, you do not open the safety ground (green) wire in your AC shore power supply. Therefore, your safety ground (AC) bus is tied to your DC ground (B-) bus and you are electrically connected to all of the boats’ safety ground buses and therefore their B- buses.

Finally, a GI is installed to block galvanic current (catchy name, huh) that is generally driven by about 1.2VDC max while still providing a fault path back to the source (xfmr on the land side) to clear a fault in the AC system.

So the scenario is if all boat owners maintain their boat’s anodes, there is no need for a GI. However, if a boat that is relatively close to your berth (galvanic current is a field effect and follows a 1/R^2 function) doesn’t maintain his anodes then your boat’s anodes will protect his and your underwater metal bits.

Here is the path:
AC safety ground bus > DC B- bus > engine block > transmission (poor path but it is conductive) > shaft > propeller > shaft anodes > water column that contains the derelict boat. Since the derelict boat is electrically connected to your cathodic protection system, and you are in the same electrolyte, the circuit is there for your boat’s anodes to protect his metal bits.

With regards to the engine anodes, they exist in a different “ocean”. Galvanic current can only travel a few diameters in a pipe, hose or annular space.

 

[DDW]

The only reason I can think of to bond a boat's systems is if some underwater metal is not protected by its own anode. Then maybe you need to bond it to something that does. And then maintain that series of connections which the pundits say must be less than 1Ω resistance to be effective. Many bonding systems as implemented have a daisy chain of wires and lugs down in the bilge subject to corrosion so the 1Ω becomes unlikely with time. For these reasons I prefer to have anode protection bolted directly to those things needing it.

 

[Comodave]

Read Steve Ds articles on bonding.

https://stevedmarineconsulting.com/wp-content/uploads/2014/03/BondingSystems138_05.pdf

 

[della li]

I can argue bond or not bond convincingly. When asked, I tell an owner that a bonding system is just that, another system that requires periodic maintenance in order for it to perform as required. If this maintenance is done a bonding system will keep all underwater bits at the same potential, thus eliminating own boat caused stray DC corrosion.

Back to basics: If your boat was wired to be ABYC or ISO 13297 compliant then the AC safety ground (green) wire is connected to the AC grounded bus and the battery B- is connected to the DC ground bus. These two busses are connected in one, and only one, place. Also relevant is that when you open the shore pedestal breaker, you do not open the safety ground (green) wire in your AC shore power supply. Therefore, your safety ground (AC) bus is tied to your DC ground (B-) bus and you are electrically connected to all of the boats’ safety ground buses and therefore their B- buses.

Finally, a GI is installed to block galvanic current (catchy name, huh) that is generally driven by about 1.2VDC max while still providing a fault path back to the source (xfmr on the land side) to clear a fault in the AC system.

So the scenario is if all boat owners maintain their boat’s anodes, there is no need for a GI. However, if a boat that is relatively close to your berth (galvanic current is a field effect and follows a 1/R^2 function) doesn’t maintain his anodes then your boat’s anodes will protect his and your underwater metal bits.

Here is the path:
AC safety ground bus > DC B- bus > engine block > transmission (poor path but it is conductive) > shaft > propeller > shaft anodes > water column that contains the derelict boat. Since the derelict boat is electrically connected to your cathodic protection system, and you are in the same electrolyte, the circuit is there for your boat’s anodes to protect his metal bits.

With regards to the engine anodes, they exist in a different “ocean”. Galvanic current can only travel a few diameters in a pipe, hose or annular space.

Thx fot the detailed resp. So if after connecting the AC and B- buses, I can ground to the engine and that will carry through to tranny--shaft--collar zinc on the shaft? Do metal (bronze) hull-thrus need to be looped (hard-wired) into the system as well, or the other anondes and bonding will protect them?

 

[Comodave]

I would not count on the transmission having good continuity through to the shaft. I bond everything metal underwater. I just removed the old shutoff for the black water overboard discharge. I had it capped and shutoff but I discovered that the shutoff would leak if turned on so I got rid of it. I put a bronze cap on the through hull. But first I drilled and tapped the edge of the cap. Then used a bronze screw to hook up the bonding wire to the cap.

 

[Don L]

Bonding almost sunk my first boat if not for caulking

some things need bonding, but anything that should never see a current should not be bonded IMO

of course this debate just rages on

 

[DDW]

Some things for sure don't want to be bonded. A Volvo saildrive for example, is isolated from the engine, the installer is to check that isolation as part of commissioning and the warrantee will be void if not isolated.

 

[CharlieJ]

OP #5:
"So if after connecting the AC and B- buses, I can ground to the engine and that will carry through to tranny--shaft--collar zinc on the shaft? Do metal (bronze) hull-thrus need to be looped (hard-wired) into the system as well, or the other anondes and bonding will protect them?"

The short answer is no as the transmission is a poor conductor and shouldn’t be counted on to reliably pass 1.2VDC. I included it in my summary to show how the circuit can work. DC stray current corrosion (my example) is caused when a B+ (12VDC, 24VDC or higher) is in contact with a non-bonded underwater metal component. With SCC, the driving voltage is at least 10x greater than the galvanic potential.

If a bonding system is installed, all of the underwater bits will be connected and at the same electrical potential. Connecting the bonding system to a transom anode will protect all of these underwater components within reason.

That said, a quality bronze fitting that is not bonded will literally outlive you. As I said in my original post, I can make an argument for or against installing a bonding system.

 

[Don L]

That said, a quality bronze fitting that is not bonded will literally outlive you. As I said in my original post, I can make an argument for or against installing a bonding system.

And one that is poorly bonded and has a issue in the loop will corrode through to the point of danger. I say this as 100% real life experience.

I will never bond stuff together together again! Things that need bonding such as metal fuel tanks get their own loop.

 

[CharlieJ]

And one that is poorly bonded and has a issue in the loop will corrode through to the point of danger. I say this as 100% real life experience.

Don L: I don’t doubt your experience but that failure was not caused by poor/inadequate bonding. There was another corrosion mechanism in play.

 

[Don L]

Don L: I don’t doubt your experience but that failure was not caused by poor/inadequate bonding. There was another corrosion mechanism in play.

Yes there was 2 problems. BUT if not for the poor bonding it would not have caused a through hull valve to corrode to the point that only caulking was hold it in. That valve should never have been in that loop to start with.

So it is loop everything together and keep it perfect to prevent a "problem" that is by far only on paper, but if you don't keep perfect it becomes a problem. Or just don't do it.

There are things that are required bonding. Don't bond things that aren't required to be into those.

 

[l00smarble]

I'm sorry but I have to chime in here because I feel Don L is doing a disservice to this forum. I have no personal thing with Don but he dispenses advice with authority that may not be correct.

To OP: Read this thread:

Bonding connection to thru hull, question please

Hello, I just had the SB engine thru hull & seacock replaced at a boatyard. The original unit was a Groco and it was attached to a bonding wire that also was connected to the corresponding strainer. The tech did a great job installing the new Groco unit but after he left I discovered that he...

www.trawlerforum.com

 

[Don L]

I'm sorry but I have to chime in here because I feel Don L is doing a disservice to this forum. I have no personal thing with Don but he dispenses advice with authority that may not be correct.

To OP: Read this thread:

Bonding connection to thru hull, question please

Hello, I just had the SB engine thru hull & seacock replaced at a boatyard. The original unit was a Groco and it was attached to a bonding wire that also was connected to the corresponding strainer. The tech did a great job installing the new Groco unit but after he left I discovered that he...

www.trawlerforum.com

I have no authority!!!!!!!!!!!!!! It isn't a disservice to provide my 100% personal experience. People can do anything they want on their boat. Please note lots of non US builders do not bond thru hulls. Not even all US boats have thru hulls bonded (my last 2001 didn't). You can find any article on the internet to support anything and I didn't read the link above and sure wouldn't use a forum thread to support some other forum thread

 

[l00smarble]

Hi Don. You keep blaming the concept of bonding on your incident but the reality is that bonding did not *cause* the problem and in fact if the bonding were right it would not have happened.

You post above exclaims: "Bonding almost sunk my first boat." This fear mongering and may lead a member here to make incorrect decisions about wiring on his/her boat.

My understanding is your problem was caused by:

1. Fault current from a poorly designed or improperly installed tank sender system which was putting DC fault current on a bonded metal tank rather than having a dedicated DC negative cable for return current.

2. An incomplete/failed bonding connection which did not allow this fault current an intact, proper bonded path back to battery negative.

The existence of the bonding system in this scenario is not the cause of the problem. Bonding did not almost sink your boat. I'm not sure why you want to blame bonding for this but it does not make sense to "solve" this problem by elminating the bonding system.

 

[l00smarble]

The only reason I can think of to bond a boat's systems is if some underwater metal is not protected by its own anode. Then maybe you need to bond it to something that does.

The "main" reason for bonding is to protect from stray current issues which can be catastrophic. Protection from galvanic corrosion is secondary.

A DC fault to a non-bonded underwater metal can case the metal to become an agressive anode and fizz away to nothing in a matter of hours or days. This can destroy expensive running gear or sink a boat.

A AC fault to a non-bonded underwater metal can kill a swimmer. Not hypothetically, but kill...dead. Often a child.

 

[l00smarble]

Hi All-- I have installed a galvanic isolator, but I do not beleive the elec. system itself is bonded to an external zinc. I have zincs on the shaft and rudder that are barely corroded after ove half a yr. (though none on the hull). So is the isolator doing its job? Do I really need to bond the system to an external zinc as well? I am in a small marina Maybe 20 boats, some smaller, and not a lot of heavy AC use I think. I imagine many of the other boats not bonded as well, though just guessing).

The zincs in the engine (there are 6) do not seem to have corroded much over past few months as well.

to comment on OP post....Great that you installed a GI. This lets you be in control of your own destiny by isolating you from things you can't control on the dock. And yes you can usually expect your anodes to last longer once you decouple galvanically from the dock.

As others have mentioned the underwater metals are likely connected. You should keep the anodes as the boatbuilder specified unless you made some major change to the size/quantity of the underwater metals. You don't need to add a hull anode if you system is very small and simple.

Anodes in engine area completely separate matter unaffected by the installation of hte GI.

 

[Don L]

hey, not interested in other people people explaining MY experience and I don't care to win

So ............. this is over for me

 

[DDW]

The "main" reason for bonding is to protect from stray current issues which can be catastrophic. Protection from galvanic corrosion is secondary.

A DC fault to a non-bonded underwater metal can case the metal to become an agressive anode and fizz away to nothing in a matter of hours or days. This can destroy expensive running gear or sink a boat.

A AC fault to a non-bonded underwater metal can kill a swimmer. Not hypothetically, but kill...dead. Often a child.

The problem is, a DC fault to the bonding system - not at all unheard of - can fizz away everything underwater. Should not happen if the bonding system is maintained in good condition, but many I have seen do not fit that description. Yes, you can maintain it and hope to keep it in good condition. On the other hand, you can maintain your DC system in good condition and not need the bonding system. I'm with Charlie on this, I think it is a mixed bag.

 

[SteveK]

Thx fot the detailed resp. So if after connecting the AC and B- buses, I can ground to the engine and that will carry through to tranny--shaft--collar zinc on the shaft? Do metal (bronze) hull-thrus need to be looped (hard-wired) into the system as well, or the other anondes and bonding will protect them?

@CharlieJ explained it well, but may not have answered directly your question (bolded). The engine is already connected (bonded) to the battery negative either directly or on a buss bar. If it was not then the starter would not work.
The use of the word bonded for the bonding system which connects any thru hull metal to the anode (zinc) on the transom is not the same when the word bonded is used for ground connections whether battery negative or AC green ground wire
A metal tank should be grounded back to the DC negative and not bonded to the bonding system as the latter would only serve to create stray current into the water should a sending unit DC+ shorts to the body of the tank.

 

[SteveK]

The "main" reason for bonding is to protect from stray current issues which can be catastrophic. Protection from galvanic corrosion is secondary.

A DC fault to a non-bonded underwater metal can case the metal to become an agressive anode and fizz away to nothing in a matter of hours or days. This can destroy expensive running gear or sink a boat.

A AC fault to a non-bonded underwater metal can kill a swimmer. Not hypothetically, but kill...dead. Often a child.

IMO, if the bonding system is not grounded to the battery negative then there could not be stray current unless a hot wire lands in bilge water also with any part of the bonding system.
It has already been shown that DC+ that escapes the boat through the bonding system does not trip a DC fuse and any AC hot connected to the bonding system will go into the water looking for the easiest route to earth ground. Don't count on the green wire as being the easiest route.
Shore power cables have been found connected to pedestal while the boat is on a day trip and the hot end is in the water without tripping an old style breaker, thus ELCI was introduced.

 

[CharlieJ]

To clarify and return to fundamentals: bonding all of the underwater metal components with connections that are less than one Ohm each will keep all of these components at the same electrical potential. If there is no difference of electrical potential between two points in a circuit, no current can flow. Ohm’s law applies.

Therefore, a compliant bonding system, when inadvertently connected to a boat’s B+, cannot initiate and support DC stray current corrosion

I recommend that members of this forum that have an interest in this relatively complex subject purchase and study the applicable sections of Nigel Calder’s “Boatowner’s Mechanical and Electrical Manual”. It is written for the layman and progresses to some complex areas.

 

[l00smarble]

IMO, if the bonding system is not grounded to the battery negative then there could not be stray current unless a hot wire lands in bilge water also with any part of the bonding system.

I am not following what you are trying to convey but maybe you are not thinking about it correctly. Bonding IS connected to battery negative. If it were not it would be a "floating" bonding system without a ground reference? Not sure what the use of that would be especially when major components like engine block, shaft, propeller are likely already connected to DC negative. You would have to isolate your floating bonding system from the major components that are ground referenced.

This would set up the exact situation to sink the boat. A DC postive fault to your floating bonding system wants to get back to battery negative. You have isolated the bonding system so there is no low resistance copper path. So the full fault current will exit your floating bonding system into seawater to get to the prop/shaft to get to engine block and back to battery. The supposedly "safe" floating bonded fitting can fizz away and fall out of the boat.

Hot wire into bilge water is not as uncommon as you would think. Bilge pumps and their float switches often have DC connections very near or submerged in bilge water.

It has already been shown that DC+ that escapes the boat through the bonding system does not trip a DC fuse

Whether it trips a fuse or not it is still important to prevent the current from exiting into seawater via a metal fitting.

and any AC hot connected to the bonding system will go into the water looking for the easiest route to earth ground. Don't count on the green wire as being the easiest route.

AC hot fault to bonding system should not enter the water. Bonding should be connected to DC negative which should be connected to AC ground so AC hot to bonding is a dead short of the circuit and should instantly trip the AC branch breaker. I guess the point is we DO count on the properly designed and installed "green wire." Of course we don't design a system to intentionally put current on "the green wire" but in a fault situation we do "count on" the green wire (AC Ground or Bonding) to reliably carry the fault current. We make green wire connections on board with every bit of care and attention as current carrying conductors because we may one day count on them.

Shore power cables have been found connected to pedestal while the boat is on a day trip and the hot end is in the water without tripping an old style breaker, thus ELCI was introduced.

 

[CharlieJ]

AC hot fault to bonding system should not enter the water. Bonding should be connected to DC negative which should be connected to AC ground so AC hot to bonding is a dead short of the circuit and should instantly trip the AC branch breaker. I guess the point is we DO count on the properly designed and installed "green wire." Of course we don't design a system to intentionally put current on "the green wire" but in a fault situation we do "count on" the green wire (AC Ground or Bonding) to reliably carry the fault current. We make green wire connections on board with every bit of care and attention as current carrying conductors because we may one day count on them.

+1
The bond between AC grounding bus and the DC B- in one and only one location provides a secondary or backup water path for fault current to return to the shore source, usually the xfmr servicing the docks. This water path was added because of the demonstrably poor safety ground system on docks that led to a lack of fault clearance capability.

Of course, solving one problem creates others; ESD and galvanic corrosion

To combat ESD, the NEC started mandating 30mAAC/100mS residual current devices (RCD's) for shore power pedestals in about 2013. Over the years, there have been many changes as technology and knowledge improved.

About the same time, the ABYC realized that marinas were not going to adapt the new, and expensive, RCD requirement quickly and mandated that equipment leakage current interrupters (ELCI) be installed in recreational vessels’ shore power supply. The ELCI also has a 30mAAC/100mS trip specification.

The safety ground (green) wire is not opened by a circuit breaker. Therefore, Boat A in a marina is electrically connected via the safety ground wire to Boat B in an adjacent slip. If Boat B has no anodes, and Boat A does, Boat A’s anodes will protect Boat B’s underwater metal equipment and Boat A will experience accelerated anode wastage. This effect fostered the adaptation of a galvanic isolator from the pipeline industry. The GI blocks galvanic current which, by definition, has a maximum voltage of about 1.2VDC but provides an AC fault path from the boat back to the AC shoreside source.

Here is a an excellent video by my colleague, Nigel Calder:

 

[DDW]

Therefore, a compliant bonding system, when inadvertently connected to a boat’s B+, cannot initiate and support DC stray current corrosion

Between its own elements, true. But it can certainly be anodic to something nearby, as a circuit connection often exists through the shore cord.

 

[SteveK]

Man made problems solved!

-Dissimilar metals sitting in an electrolyte (salt water) will eat each other so bond them to a sacrificial anode circuit, problem solved.

-Add AC appliances to a boat with an extension cord, a green ground wire will return to shore any AC fault current and trip the pedestal breaker, problem solved.

-Should AC hot touch the engine it could shock a person, connect green ground to DC negative. That should trip the breaker, problem solved.

-But now DC can travel through green ground to other boats, add a galvanic isolator, problem solved unless the voltage is greater than 1.2VDC. The 12VDC can travel between boats in salt water at a reduced voltage greater than 1.2VDC and bypass the Galvanic Isolator. Install an isolation transformer. Problem solved.

Both DC and AC wants to return to the source, to create a circuit (a circle).

JMO
Keep AC faults on the boat, install an ELCI main breaker and/or GFI plugs, maybe an isolation transformer.

Keep DC faults on the boat, eliminate bonding DC- to galvanic protection anode bonding system, stop the circuit into water, into another boat and back to your boat via green ground.