Correct grounding and bonding

[bazzer]

Ok, this might open up a whole can of worms, but here goes. What is the correct way to ground and bond my Hans Christian? I have read reports that say the 110 volt ground should be tied to the DC ground and others that say not. Some reports say to bond all metal thru hulls and others that say not. It would seem that UK regs say to connect the grounds and the US suggest to do so, but many pundits say don't do this. So what is the correct way? I want to be safe and at the same time comply to the US boating standards as well as to ensure my thru hulls do t get eaten up. Some of my thru hulls are bonded whilst others are not.
I would appreciate your help.

[donradcliffe]

Try the search function--there is no right answer and this topic has been beaten to death several times.

[Andina Marie]

Connecting the shore power ground to the (12 volt negative) under water metal is the MAJOR source of electrolysis damage to the metal. If you isolate them you don't need a galvanic isolator or an isolating transformer.

BUT,

If there was an accidental short between the AC power and any DC circuit you risk putting AC voltages into the water that can kill people swimming in the vicinity or shock people boarding the boat (depending on situation). In particular the most vulnerable item is the battery charger that links between the two systems.

The chance of a faulty battery charger or a connection between the systems is nearly zero. The chance of killing someone if you do is also rare. "Nearly zero" multiplied by "also rare" is STILL NOT ZERO and the consequence are extreme. "Still not zero" multiplied by "extreme" is sufficiently high that most jurisdictions insist on the ground connection to the underwater metal so you either blow a fuse or remove any voltage from underwater metal. (Assuming your shore power is wired correctly which is 100 times more likely!).

On the bonding or not bonding of underwater metal, my preference is only bond if needed. Electrolytic corrosion only occurs if current is flowing in the water. An isolated piece of metal in the electrolyte is like a charged battery but it has no current flowing until you connect it to a load. If you never connect it, no current flows and no damage occurs. Once you bond it and complete the electrical circuit you have to make sure it is on the receiving end of electrolytic currents by providing sacrificial zinc anodes (or equivalent). I suggest an annual inspection of all unbonded underwater metal. Only if you see evidence of electrolytic corrosion should you bond it.

[bazzer]

I'm moored at a new marina. Recently a diver was about to go in the water to inspect a large cat when he got a large shock whilst reaching into the water to rinse his face mask. I checked the metal edge of the dock and found it to be at six volts AC. The marine later said that the main ground to the AC system had be disconnected by a contractor. The boat in question a couple of weeks before had a connector on the shore power cable replaced due to it getting overheated to the point it was smoking. I am left wondering if the new connector was wired incorrectly. But either way the diver was lucky. He refused to go in the water until the fault was fixed.

[Andina Marie]

The ABYC in their wisdom require the AC ground be connected to the underwater ground so if there is a short, for example between the AC and DC of a battery charger, then the AC ground will protect a swimmer from electric shock.

I've maintained for many years that the probability of a shore power cord or dock being mis-wired is an order of magnitude greater than the possibility of a faulty battery charger or other appliance linking between AC and DC.

Unless your boat has sufficiently sophisticated shore power monitoring, you would appear to be better off not following ABYC specifications.

[fstbttms]

Originally Posted by bazzer

I'm moored at a new marina. Recently a diver was about to go in the water to inspect a large cat when he got a large shock whilst reaching into the water to rinse his face mask.

What diver? What marina?

[bazzer]

Why are the names so important? I saw it happen.
Incidentally I just found out that the shore power outlets are not GFI protected.
I have been checking my boat with a reference diode and found it all to be adequately protected. So I am going to leave well alone.

[Richard_W]

Originally Posted by bazzer

Incidentally I just found out that the shore power outlets are not GFI protected.

That could be a major problem ... not for the boat but for people. I would ask marina to correct this right away ... this ain't a joke.

I am myself confused like hell about the DC and AC grounding, but if you look at ABYC Standard E-11, Figure 18 ... you will notice that DC main negative ground bus which is connected to grounding bus (bonding) is also connected to AC grounding bus.

Go figure!

Originally Posted by Andina Marie

The ABYC in their wisdom require the AC ground be connected to the underwater ground so if there is a short, for example between the AC and DC of a battery charger, then the AC ground will protect a swimmer from electric shock.

I've maintained for many years that the probability of a shore power cord or dock being mis-wired is an order of magnitude greater than the possibility of a faulty battery charger or other appliance linking between AC and DC.

Unless your boat has sufficiently sophisticated shore power monitoring, you would appear to be better off not following ABYC specifications.

I can see the logic here, but how do you eliminate the "potential" connection between AC and DC grounds on engine, genset, battery charger, inverter, etc?

[FlyingCloud1937]

Originally Posted by fstbttms

What diver? What marina?

As a diver I'm suprised you don't take you're own precautions. A simple $200.00 tool that you use before you ever hit the water could and would save your life.

Lloyd

Every Pro-Diver I know won't go in the water with out one.

[goboatingnow]

My personal approach is to follow RCD reccomendations , fit an all boat RCD, and don't connect DC negative to AC protective earth. This prevents AC and DC currents intermingling as AC earth can be notoriously noisy.

Furthermore I not sure what " UK " regs you mention are valid, as the EU RCD is the only regulation set , unless you wish to use your boat on inland UK waters , where the boat safety scheme applies

Dave

[boatpoker]

I suggest you read the BoatUS article about the "electric shock drowning" of Lucas Ritz.

Then read the documents section on Captain David Rifkin's website of his study funded by USCG.

Then reconsider your position on AC/DC bonding.

[fstbttms]

Originally Posted by bazzer

Why are the names so important? I saw it happen.

Because I work in the water and I'd like to talk to the diver in question. I probably know him. Further, this is information all local hull cleaners need to be made aware of.

[boatpoker]

Originally Posted by bazzer

Why are the names so important? I saw it happen.
Incidentally I just found out that the shore power outlets are not GFI protected.
I have been checking my boat with a reference diode and found it all to be adequately protected. So I am going to leave well alone.

I think you mean a "reference electrode". A diode won't tell you anything in this application.

[David M]

Bonding all your metal is a two edged sword. It may introduce stray DC currents where there were none and it may do the opposite, save your metal. You just have to look at all your metal on a case by case basis and make the right choice. I have an all metal boat where the AC system is completely isolated from the DC system. It is safe and electrolysis free.

[goboatingnow]

The chance of a faulty battery charger or a connection between the systems is nearly zero. The chance of killing someone if you do is also rare. "Nearly zero" multiplied by "also rare" is STILL NOT ZERO and the consequence are extreme. "Still not zero" multiplied by "extreme" is sufficiently high that most jurisdictions insist on the ground connection to the underwater metal so you either blow a fuse or remove any voltage from underwater metal. (Assuming your shore power is wired correctly which is 100 times more likely!).

You are completely ignoring the role RCDs play in many nations regulations. Equally no safety solution offers "ZERO" chance of failure. So that point is moot.

Whole boat RCD or RCDBO, and a good mains ground back to shore is as good as you can make it. Bonding DC negative to AC earth in that case adds little , and can cause more problems then its worth. Furthermore I suggest you never plug into any shore outlet that isnt in itself protected by a RCD ( GFI)

Dave