electrolysis

[Maynard Rupp]

I am tearing what is left of my hair out. Our "86 36C is eating its anodes quite fast. The diver says it is only our boat. The other nearby boats are OK. Of course we never had this problem in the great lakes. It has shown up since we moved the boat to Florida in Sept. I read an online article from an outfit that sells galvonic isolaters. The article has you remove the shore cords and check resistance between each pin and the bonding ground. They want no connection at all. Our hot and neutral pins on both the Ships power receptacle and he AC receptacle are wide open. Both ground pins show no resistance to the ships bonding. The article said there should be no connection. I disconnected every ground bus feed wire, both ac and dc. still no resistance to the bond. I looked at the Hat prints and it looks like they connect the white wire to the case ground on the outlet side of the isolation transformer. That would surely cause the ground to show no resistance. On the dc side they hook a wire from the engine bed to the bonding. The battery negative cables hook to the engine and the engine to the mount. Here is another connection. I disconnected the battery cables as well as all the ground busses in every electrical box. None of these actions opened that circuit. I will do the rest of their tests tommorrow. Maybe I can just install a galvonic isolater on those shore power grounds to solve the problem. I sure don't see any easy way to isolate those shore lead grounds from the boats bonding system. There goes some more of my hair.

[Boatsb]

Can you measure the potential the boat has both plugged into the dock power and disconnected. If there is a differance the ground isolators should help. On the other hand do you have other metals in contact with the water or does the bottom paint contain another metal causing the corosion?

[Genesis]

Ok, here is how an isolation transformer SHOULD be wired:

1. Shore cord hot and neutral (black/white) (or hots/black for 240V service) are wired to isolation transformer inlet lugs.
2. Shore ground is connected to isolation transformer SHIELD. NOT to the case - that risks KILLING someone. The transformer should have a shield lug that is NOT connected to the transformer case.
3. Shore cord NEUTRAL (white) on a 240V cord is NOT CONNECTED AT ALL.

1. OUTLET of isolation transformer has either two or three lugs, depending on whether the transformer is for 120 or 240V. If 240V, then it has two "hots" and one "neutral" (more correctly, "grounded conductor.") If 120V then it has two "hots".
4. The center tap on the 240V or one of the "Hots" on a 120V transformer outlet is BOLTED to ship's ground at the outlet of the transformer on board. This is NOT connected to the transformer shield and is not connected to the shore inlet ground wire! It IS connected to the physical transformer CASE, which MUST NOT be shorted to the shield referenced in #2.

An isolation transformer secondary is wired EXACTLY as is a generator. Both are "power sources" and as such "neutral" and "protective ground" must be connected together at their case and nowhere else.

A shore cord is a "power source" ON SHORE; as such you NEVER connect neutral and ground together on board. That power source ENDS at the isolation transformer inlet (if you have one.)

For a diagram of this see Calder's book on page 103. This is in conformance with ABYC standards; the diagram shows both 120 and 240V transformer setups.

If your boat is not wired like this, its wired wrong and is the source of your problem. Fix it and as long as the leakage is not on board your vessel the problem will go away.

It sounds like your SHORE ground is tied to the SHIP'S ground, even though you have an isolation transformer. This is wrong and defeats the purpose of the isolation transformer - you're hauling around all that iron for nothing!

[Trojan]

Karl is right. But you need to check the neutral connections on the transformer. Each side, to make sure that the neutrals are not bonded. Also check the transformer primary. If there is 3 connections on the primary. Then the dock cable ground attaches to the center tap. Taps should be labeled 1/120,2/n,3/120-1/220,3/220. Other than that there is no physical ground attaching to shore. The output should be marked the same. Depending on your transformer design. There is NO physical connection between the input side and the output side of the transformer.


BILL

[67hat34c]

Maynard, we had the same problem for a while. we hung a guppy overboard and that helped, finaly installed a galvonic isolator and i believe we have it licked. we no longer use the guppy

[Maynard Rupp]

Maynard, we had the same problem for a while. we hung a guppy overboard and that helped, finaly installed a galvonic isolator and i believe we have it licked. we no longer use the guppy

We have a guppy and he is getting eaten pretty badly. When I check for continuity between the green wire on either shore receptacle and ships bond, it has that continuity. Seems like everyone agrees that this is bad, but I can't figure how to unhook it. My boat is wired to the factory prints and that connection shows clearly at the iso. transformer.

[Maynard Rupp]

Ok, here is how an isolation transformer SHOULD be wired:

1. Shore cord hot and neutral (black/white) (or hots/black for 240V service) are wired to isolation transformer inlet lugs.
2. Shore ground is connected to isolation transformer SHIELD. NOT to the case - that risks KILLING someone. The transformer should have a shield lug that is NOT connected to the transformer case.
3. Shore cord NEUTRAL (white) on a 240V cord is NOT CONNECTED AT ALL.

1. OUTLET of isolation transformer has either two or three lugs, depending on whether the transformer is for 120 or 240V. If 240V, then it has two "hots" and one "neutral" (more correctly, "grounded conductor.") If 120V then it has two "hots".
4. The center tap on the 240V or one of the "Hots" on a 120V transformer outlet is BOLTED to ship's ground at the outlet of the transformer on board. This is NOT connected to the transformer shield and is not connected to the shore inlet ground wire! It IS connected to the physical transformer CASE, which MUST NOT be shorted to the shield referenced in #2.

An isolation transformer secondary is wired EXACTLY as is a generator. Both are "power sources" and as such "neutral" and "protective ground" must be connected together at their case and nowhere else.

A shore cord is a "power source" ON SHORE; as such you NEVER connect neutral and ground together on board. That power source ENDS at the isolation transformer inlet (if you have one.)

For a diagram of this see Calder's book on page 103. This is in conformance with ABYC standards; the diagram shows both 120 and 240V transformer setups.

If your boat is not wired like this, its wired wrong and is the source of your problem. Fix it and as long as the leakage is not on board your vessel the problem will go away.

It sounds like your SHORE ground is tied to the SHIP'S ground, even though you have an isolation transformer. This is wrong and defeats the purpose of the isolation transformer - you're hauling around all that iron for nothing!

Thanks Karl, you really put in in clear terms. I just checked and there is no connection between the ground pins and neutral pins on either shoreline connector. My problem is that there is a connection between the ground pins on both connectors and the bonding system. Is that OK?

[TedZ]

I understand you folks see isolation x-formers this way. I continue to disagree and if i had a nickle for every guy who has said to me "I've been doing it this way for thirty years" i'd have a lot of money.

As far as catagorizing 120 VAC systems as "two hots" and either one can be connected to "the ships ground" all i can say is you ought to know better. One of the 120 VAC "hots" may be 30 VAC above the real earth and the other maybe 150 VAC above. At least the one that is closest to earth should be connected to the ships ground, and even 30 VAC will light you up in the pouring rain when there is 30 VAC potential between ground and ground.

Of course you dont bond up the grounds. When the x-former is wired wrong, bonding causes meltdowns...that should be a clue. With the right x-former wired right all grounds can be bonded.

When the x-former manufacturer bonds the x-former shield to the case it means that they have balanced the windings to avoid voltage from ground to ground. That is a true isolation x-former. Am i to believe because it is a boat we are supposed to undo ground continuity??

Let me put it this way. IF in a perfect world, all metal could be the potential of the earth, mother earth, i.e. sticking one end of the meter in the dirt and the other on any piece of metal in the marina including metal anywhere on the boat and have no voltage differences, that would be the safest of all situations. You can't disagree with that.

That is what should be the goal. Purposely wiring things that have a built in potential between earth and earth because some book says that the way to do it is not smart IMHO. I can, and have shown literature from many x-former manufacturers that say don't wire modern iso x-formers that way and, as the one making the equipment, they are 10 times more valid, again IMHO.

Ted

[TedZ]

And by the way if i had a nickle for every ABYC standard that should have been changes or modernized for 20 years or so...you know the rest.

Also in the original post i'm having trouble following where there is undesired continuity, but if you are chasing strays, get a meter that measures conductance, unit is mho's. At least 10 times more sensitive than trying to find small resistances that the meter is incapable of reading.

Ted

[Maynard Rupp]

Ted, are you saying that it is OK to have those ground pins on the shore connectors connected to our bonding system? They sure are connected at this time.