electrolysis

[the kuz]

Maynard, I have been reading all this with much interest, but reluctant to comment since my knowledge as an electician is 40 years old and limited to shore based stuff. My 77 36C also has 2 30 AMP, 110/120 volt inputs, one for the ships service and one for the A/C. The Hatteras wiring diagrams show all the grounds/neutrals for these 2 panels and the 12V tied to each other and the bonding system (that's the way it is still on the boat). All my wiring is OEM, and there is no isolation or polarity transformer, just a light to warn of reversed polarity. We don't have a zinc problem (shaft zinks last 6 months, rudder zincs are fine after a year). Never been stung , but GFIs are always a good idea. IMHO you don't have much of a safety risk if you use common sence (like unpluging before you go under /swim around to clean, and using extra care not to ground yourself when things are wet). WRT your electrolysis, check your 12V stuff also, especially be sure your bilge pumps are wired right (positive to float switch). Not sure what else to suggest. Good luck. Regards, Bob K

 

[REBrueckner]

Maynard posted "...OK I lifted all the wires off the case ground pin on the iso. amp. 2 of the three had continuity to my shoreline ground pin..."

According to Nick's post, that's because shore ground and boat ground are connected via the (polarization) transformer case.

If you are getting a few volts reading here, that is, when you lift shore ground and measure voltage from shore ground to boat ground, and get, say, 3 or 4 volts dc, that's the likely source of your stray currents (electrolysis). If you did your measurements according to Yandina's website, then you checked it correctly. I haven't read that in at least five years, but their procedural description I do remember is excellent.

 

[TedZ]

I don't want to belabor this in the slightest but 1.1mvac is not a voltage measurement it is a radio or maybe a TV! You cannot isolate radio frequency (RF) from the wiring that is acting like an antenna when you make such a measurement. Another words, you will never read zero if you are using a millivolt scale on AC with any length of wire.

I don't know what the ABYC is doing but if the term "balanced" is not used for isolation transformers with shields, we will continue to be confused. Everyone has valid points depending on what type of transformer you are discussing. Balanced iso's were rare years ago, now they are the rule...for obvious reasons.

Ted

 

[Maynard Rupp]

I will dig this thread up once more. I talked with an electrical expert at Hatteras. He pulled a copy of my blueprint from their file.(Try that with any other boat builder after 20years; I am impressed). He said that our 36 is wired exactly the same way as every new Hatteras is today. They do not believe in isolating the shore grounds from the ships bonding system. They do isolate all ac neutrals from those grounds. They also don't recommend galvonic isolators. They claim that the galvonic isolator will help make zincs last longer but if the diodes fail, as they do, you no longer have an ac ground. That is bad. They also say that normal zinc consumption in Florida is 3 sets per year. They also don't like adding more zincs, they don't even approve of the fish we hang over the side.
This folks is the word from our friendly manufacturer.

 

[REBrueckner]

"...They do not believe in isolating the shore grounds from the ships bonding system...."

Comment: I've never heard of anybody who doesn't follow this ABYC practice. To do otherwise introduces shock hazards.


"..They do isolate all ac neutrals from those grounds..."

Comment: To do otherwise introduces unwanted stray current possibilities.


"...They also don't recommend galvonic isolators. They claim that the galvonic isolator will help make zincs last longer but if the diodes fail, as they do, you no longer have an ac ground. That is bad.

Comment: That's an uninformed, very poor answer. ABYC now recommends galvanic isolators with continuity indicators...in other words, an open due to a failed diode is signalled. (An isolater without any indicator could pose a shozk hazard if the diode fails).


"..They also say that normal zinc consumption in Florida is 3 sets per year... "

Comment: That seems rather high, but then I don't boat there..." On a fiberglass boat there is nothing wrong with a guppy type zinc, especially if hung at the stern near underwater gear.

 

[Trojan]

A guppy is only a band aid for someone who does not want to or does not know how to resolve the real problem. Sorry!


What if you don't see the warning when the diode fails in the isolater? No thanks.




BILL

 

[Boatsb]

3 sets a year in Fl? Seems a bit high. I do not live aboard but stay on the boat almost every weekend and we do run her at least 3 x a month.

I pulled to clean the bottom after 9 months and had 90% of the zincs intact. I have 2 1/34 shaft zincs on each shaft. 1 R5 i believe on each rudder and an R3 on each strut. Pencils are changed too but not showing excessive loss. It may depend on those around you and the power issues at the marina but I recomend looking into the stray power around you or could it be something with the bottom paint and the metals? One set as i have the boat set up will last a year.

 

[TedZ]

???

Now everyone agrees you are NOT supposed to isolate the ships ground/neutral from shore ground/neutral???

I thought there were adamant posts that spoke to the contrary??

We ought to state it clearly:

If you use an isolation transformer that does not have a potential between neutral of the transformer and neutral of the dock supply i.e. a balanced iso, you cannot do any better than put the whole world and your boat at the potential of the earth which is the potential of the dock supply. Don't use isos that produce any potential between their neutral and the dock's neutral and you can never have a problem.

Crystal clear to me. Are there those that still disagree??

Ted

 

[Genesis]

Well, I've said my peace on this, Calder has said his, ABYC has said THEIRS, and there are multiple ways to deal with it which meet "the rules."

If you're in a marina where you have no problems with stray current caused by other people (or at your own private dock where its under your control) none of this matters much.

If not, then it can matter a great deal.

I happen to like the GFI solution WITH the transformer, running with shore ground lifted. It will absolutely prevent stray current leakage (and cut off the power if it occurs) and in conjunction with even a "non-isolation rated" transformer is both safe and in accordance with the NEC, which permits a GFI in place of a ground to prevent current leakage. There is a solid argument for a GFI being SAFER, in that if you bridge a hot and ground without one you'll get electrocuted (even with a "safety ground") but with one you won't.

In salt water I am also comfortable with a bare isolation-transformer setup. In fresh I'd put the GFIs in even with the isolation setup because there the risk of electrocuting SWIMMERS is real and needs to be dealt with.

If you're not running into stray current issues then "as factory done" is fine. I personally do not like diode-based ground isolators AT ALL and won't have them on any boat I own; they are like putting a bandaid on a sucking chest wound.

 

[Trojan]

When did it change. With an isolation transformer the boat ground is never connected to the shore ground. That's why it's called an isolation transformer it isolates everything on the boat from shore. That includes the ground. Any connection to the shore stops at the isolation transformer.


BILL

 

[Beckytek]

I think a lot of this confusion about how our boats are wired is due to the fact that we don't have isolation transformers, we have polarization transformers. At least my boat, 88 40' DC does. It's clearly stated on the wiring diagrams I have. I always assummed it was the other way until this discussion came up and I checked. So I think I'll leave everything as is and make no changes for now. GFI's are in my future though as per Genesis. Ron

 

[Genesis]

If you add GFIs on BOTH sides of the polarization transformer you don't need shoreside ground to come on board. It is not possible for you to have leakage past the GFI's outlet; ergo, no need for the shoreside ground to come on board.

Were I running into leakage problems from shoreside that'd be how I'd go after it.

 

[Beckytek]

My boat already has GFI's on the output of the transformer. Are these the type you are talking about, or are these something different? Ron

 

[Genesis]

That's half of it and covers the onboard risk. That one should be on the output of the polarization transformer.

If you add a GFI at the shore inlet then shoreside ground need go no further than that GFI, as any current flow that is not symmetrical down the shore cord (that is, any ground fault) will cause the GFI to trip.

You then have a totally isolated system yet it is impossible for a ground fault to electrocute someone. The only remaining risk of electrocution is one that exists with ALL systems; if you bridge hot and neutral there is no ground fault and you will die. That risk cannot be removed, no matter how you wire the system.

 

[TedZ]

I'm not clear on what is being said here. If you bond the boat's neutrals/grounds to the dock's power supply is it being suggested that a hot to neutral/ground leak or fault on the boat will not trip the dock GFI's?

That is not correct. Those GFI's will trip if the phase of the moon is wrong let alone a leak to ground. Even an older hand tool with a grounded case is likely to trip them. Hasn't everyone had nuisance trips of marina's GFI's? I certainly have.

More GFI's on the boat are wonderful for underway protection and when on the dock. Simply added protection.

Stray currents go away by definition if the boats and the marina are solidly at the potential of earth. Offenders trip GFI's. a first clue.

Ted

 

[Genesis]

What's not clear?

A GFI's action is absolutely what you want. They do not trip because of a "phase of the moon" - they trip because there for every milliamp of current that flows in one direction downstream of the GFI, there must be a milliamp of current flowing back to the energy source upstream of the GFI.

If those two flows are not exactly equal, then the GFI trips. This is not a "nuisance" - it is how they are designed and supposed to operate.

Grounded-case handtools trip GFIs because there is leakage to the case! The trip is what prevents you from becoming the ground. That the leakage is below what would kill you isn't the point - its not supposed to be leaking at all!

With a GFI, you do not need to bond the shore to ship's ground. With GFI protected shore inlets you can use your polarization transformer as an isolation transformer safely, because the function of the shield in an isolation transformer - to protect against the fault of a short in the transformer itself that could energize ship's ground - is covered.

If you are getting "nuisance" trips on your GFIs, then you need to find the leakage downstream from them and fix it. When you do, your "nuisance" trips will cease.

So will your zincs disappearing.

Gigabite had two GFI breakers in its AC panel from the factory, which fed all of the outlets in the boat (that is, basically everything not hard-wired.) I added one more to feed the service outlets in the engine room (a particularly dangerous place for leakage currents.) During the time I owned the boat I never had a "nuisance" trip - not one.

Lots of people dislike GFIs because they seem to trip when a phantom passes the panel. The truth is that there's a potentially dangerous electrical fault downstream of the GFI, and its doing its job.

 

[TedZ]

Well on that theory the GFI's on the dock are not supposed to protect the boat, they are to protect the dock wiring.

Please understand, I respect completely your right to wire your boat any way you want. I'm simply trying to understand your thinking.

And when you say:

"With a GFI, you do not need to bond the shore to ship's ground. With GFI protected shore inlets you can use your polarization transformer as an isolation transformer safely, because the function of the shield in an isolation transformer - to protect against the fault of a short in the transformer itself that could energize ship's ground - is covered."

All i do is shake my head. In this scenerio and no bond from the ship's to shore ground, what event on the boat trips the "GFI protected shore inlets?"
The GFI on shore has to be a mind reader!

Could you also explain to me why we are talking about phase changing/correction transformers (polarization transformers)? That is another thing i am not getting but i'm sure there is an explanation. What i do know is their neutrals will not be close to the same potential and, i understand, in your wiring, it does not make a difference.

Anyway, a good learning discussion.

Ted

 

[Maynard Rupp]

The reason for a polorization transformer is to make your boat not care if the guy that wired the shore stand swapped the hot and neutral wires. Boats that don't have these transformers usually have a red warning light to advise you, when you hook up to shorepower, that a "reverse polartity" exists. If you don't have either a transformer or a warning light, you can buy one of those yellow outlet checkers at Home Cheapo and permanently plug it into one of your on board duplex outlets. look at it each time you plug in. A better idea yet is to make sure you own a Hat.

 

[Genesis]

Well on that theory the GFI's on the dock are not supposed to protect the boat, they are to protect the dock wiring.

Incorrect. A GFI protects against wiring faults downstream from it.

Therefore a GFI on the PEDESTAL protects from that point onward into the boat. A GFI on the BOAT at the inlet protects from the inlet onward, but does not protect the cable itself.

However, if the cable ITSELF has a green wire (but it extends no further than the inlet) then the cable itself is protected from shorts in the cable itself to the water.

Please understand, I respect completely your right to wire your boat any way you want. I'm simply trying to understand your thinking.

And when you say:

"With a GFI, you do not need to bond the shore to ship's ground. With GFI protected shore inlets you can use your polarization transformer as an isolation transformer safely, because the function of the shield in an isolation transformer - to protect against the fault of a short in the transformer itself that could energize ship's ground - is covered."

All i do is shake my head. In this scenerio and no bond from the ship's to shore ground, what event on the boat trips the "GFI protected shore inlets?"
The GFI on shore has to be a mind reader!

Incorrect again.

Current that would return to ground via a fault in your boat (which can happen if your transformer has a fault on the PRIMARY side, or in the wiring between the inlet and primary side) will trip the GFI.

Could you also explain to me why we are talking about phase changing/correction transformers (polarization transformers)? That is another thing i am not getting but i'm sure there is an explanation. What i do know is their neutrals will not be close to the same potential and, i understand, in your wiring, it does not make a difference.

Anyway, a good learning discussion.

Ted

Correct, "neutrals" do not need to be at the same potential provided that the reference is not shared. The point of using a transformer is to create a bifilial supply on board.

 

[TedZ]

I'm aware that the GFI's protect downstream. To think otherwise would be nonesense.

Hatteras and others go through the trouble to bond everything in the boat and to continue that bonding to the shore power. Most of us operate in that mode.

For some reason when using isolation transformers you advise abandoning that philosophy when it is unnecessary and can be dangerous. It is simply based in a misunderstanding the role of the modern isolation transformer.

Electrolysis, which is the subject of this thread, is not prevented by unbonding the boat from shore power in any scenerio and attempting to make an "electrical island" out of your boat when docked at a marina is doomed to fail in some way.

Using an isolation transformer to protect against stray currents can work as well as protecting against transients, but it has nothing to do with the bonding of the neutral or lack thereof.

Ted