Galvanic Isolator

[Anomaly]

My head hurts.....

BUT I think I have it figured out---- SELL the boat and just stick to the plywood stitch-and-glue sailing dinghy with no metal parts anywhere....

[goboatingnow]

PS dockhead, one of the problems, is that if you have a whole boat bonding system, these can cause more problems then they cure, whoch is why you do not find them in European boats. These only applies to fibreglass boats obviously.

dave

[DotDun]

Originally Posted by fairbank56

That drawing is not in accordance with ABYC rules. Shore power ground should be connected to the transformer shield.

11.17.5
Isolation Transformer System with Single Phase 240 Volt Input, 120/240-Volt Output with Boat Grounded Secondary. Transformer Shield Grounded on the Shore. Transformer Metal Case Grounded on the Boat.
11.17.5.1
Each ungrounded shore current carrying conductor is connected from the shore power inlet to the primary winding of the isolation transformer through an overcurrent protection device that simultaneously opens both current carrying shore conductors. Fuses shall not be used instead of simultaneous trip devices.
11.17.5.2
The shore grounded (white) terminal of the shore power inlet is not connected on the boat.
11.17.5.3
The shore grounding (green) conductor is connected, without interposing switches or overcurrent protection devices , from the shore power inlet to the transformer shield.

Hmm, I'm not the only one wrong. Take a look at page 6....

http://www.charlesindustries.com/mar.../12i%20kva.pdf

stated to be reprinted from ABYC.

IMO, my boat is safe. As stated by others, RCB/ELCI are very safe/reliable devices.

[goboatingnow]

Yes you are, if you have a RCB/ELCi in th efeed to the primary, then all faults that can reasonably happen are covered.

Dave

[donradcliffe]

Hey, if you aren't confused now, you will be if this thread continues. The grounding systems have to deal with three potential threats--stray AC currents, lightning, and electrolysis. They are conflicting requirements and, as a result, the experts disagree. IMHO, it would take at least a couple of months of study for the average electrical engineer to come up to speed on this issue. I'm by no means an expert, but if I wanted a job, this is a field where a real expert would have more work than they wanted.

Modern technology, in terms of the residual current devices, is changing the equation, but the whole question of what to do for retrofitting an individual boat is a can of worms.

[SvenG]

Originally Posted by goboatingnow

Only by you , in the water , coming in contact with a lower earth path then the water.

You do not have to come in contact with anything but the water. By being in the water you become part of the conductor between the higher and lower potentials on either side of you.

I don't know how to explain that in simpler terms.



-Sven

[goboatingnow]

You do not have to come in contact with anything but the water. By being in the water you become part of the conductor between the higher and lower potentials on either side of you.

you do , it occurs when you enter the electric field in the water and the water is fairly pure, your body offers a better path to ground then the water. Its a simple resistance issue.

ist also very rare and completely protected by th existence of a RCB or ELCi. ( which should be required anyway).

[SvenG]

Originally Posted by goboatingnow

you do

"you do" what ?

It isn't clear if you are finally agreeing or still claiming that:

The notion that currents circulating in the seawater are entering through one underwater metal and leaving through another are not possible,

-Sven

[goboatingnow]

Hey, if you aren't confused now, you will be if this thread continues. The grounding systems have to deal with three potential threats--stray AC currents, lightning, and electrolysis. They are conflicting requirements and, as a result, the experts disagree. IMHO, it would take at least a couple of months of study for the average electrical engineer to come up to speed on this issue.

NO its not , its a simple issue , made confusing by mixing up different things.

There are basically two types of corrosion ( a) Stray Current or "impressed" corrosion and Galvanic corosion. Both generate electrolysis.

Galvanic corrosion occurs becuase metals are immersed in an electrolyte. this is a normal slow process, that can be stoped by using a lower nobility metal, like zinc as a sacrifice

Bonding is primarily used for (a) SHock protection and (b) Lightening , both of which it isnt very good at. Last of all its used to eliminate the need for multiple zincs.

In fibreglass boats, theres no need to bond at all. Thats the European perspective. Safety is better handled by the fitting of RCB , which are mandatory both on the boat and on the marina supply pillar.

So thats leaves stray current corrosion, This problem is made worse by the conflicting needs of protective earth requirements and the need to isolate the stray currents.

AC stray currents happen becuase ( amongst other things) the protective earth connects all boats in the marina and carries such currents onto your boat , where the bonding system happily distributes it to all the underwater metals!. The only really safe way is to disconnect your boat electrically and couple it magnetically , hence the traffo. This make for enhanced personal security from shock primarily but allows a discontinues ground that protects you from external stray currents.

That then leads internal stray currents, or which DC is the worst. Again bonding ( which is tied to the dc ground and sometime the AC neutral). works against you.

The best system in my view is isolation traffo, RCB/ELci on the shore power feed just inside the boat. No ground connection to the traffo. No bonding and no connection between the AC neutral and the dc GROUND. This often requires al isolated starter on the engine ( and perhaps an alternator). Essentially keep everything isolated from each other.

This is typically the system used in the EU. ( with some debate as to the A/C neutral connected to DC ground being had).

Dave

[fairbank56]

Originally Posted by goboatingnow

Just to reiterate,

The notion that currents circulating in the seawater are entering through one underwater metal and leaving through another are not possible,

I have seen firsthand, a demonstration of the destructive effects of stray current from another source on a test vessel with underwater metal fittings bonded together. Current meters were placed in line with the bonding wires to show this action in progress. This is not only a problem for boaters, it's a problem for any underwater metal structure such as pipelines, bridge structures, etc. that may be in an area where stray currents can be problematic. I have seen a boats underwater fittings being eaten away by a nearby ship that had an impressed current cathodic protection system on board that was causing this. This boat did not have a shore power connection or even batteries on board at the time.

Eric

[fairbank56]

Originally Posted by DotDun

Hmm, I'm not the only one wrong. Take a look at page 6....

That drawing no longer exists in ABYC standards. It was in a previous version of standard E-8 which is no longer used. E-8 was incorporated into E-11 7 years ago. The current version of E-11 does not have "method 2" in the Charles manual. I wouldn't worry about it. I don't see the need to have the shield connected either. The RCB's are a great idea and I hope they become standard in the U.S. but even with them, you can still have up to 30ma of leakage before they trip.

Eric

[GordMay]

Originally Posted by fairbank56

... I have seen a boats underwater fittings being eaten away by a nearby ship that had an impressed current cathodic protection system on board that was causing this. This boat did not have a shore power connection or even batteries on board at the time.
Eric

From whence came the (impressed) current, if not from shore power nor battery?

[SvenG]

Originally Posted by GordMay

From whence came the (impressed) current, if not from shore power nor battery?

From the nearby ship that had shore power.



-Sven

[GordMay]

Originally Posted by SvenG

From the nearby ship that had shore power.
-Sven

Oops, my bad. You did say that.

[SvenG]

Originally Posted by GordMay

Oops, my bad. You did say that.

At least Fairbank56 did

But feel free to credit me with anything good and accurate.



-Sven