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Old 08-05-2012, 14:09   #1
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Earth Leak to Steel Hull

BOTH HOUSE AND STARTER BATTIERS HAVE POSITIVE AND NEGATIVE ISOLATING SWITCHERS.IF I ISOLATE THE EARTH ON THE HOUSE BATTERIES THE DB PANEL STILL STAYS POWERED UP.WITH BOTH MOTOR SWITCHERS OFF.I CAN CHECK THE VOLTAGE BETWEEN POSITIVE TURMINAL AND THE STEEL HULL AROUND 12VOLTS.I NEED TO LAUNCH AS SOON AS I CAN , HOW DANGEROUS IS THISAND HOW DO I FIND THE LEAK TO EARTH I HAVE ALREADY ISOLATED THE MAST,SSB SOLAR AND WIND CHARGER WITH NO LUCK.PLEASE I NEED HELP THANKS.
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Old 08-05-2012, 20:33   #2
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Quote:
Originally Posted by G.LUKE
BOTH HOUSE AND STARTER BATTIERS HAVE POSITIVE AND NEGATIVE ISOLATING SWITCHERS.IF I ISOLATE THE EARTH ON THE HOUSE BATTERIES THE DB PANEL STILL STAYS POWERED UP.WITH BOTH MOTOR SWITCHERS OFF.I CAN CHECK THE VOLTAGE BETWEEN POSITIVE TURMINAL AND THE STEEL HULL AROUND 12VOLTS.I NEED TO LAUNCH AS SOON AS I CAN , HOW DANGEROUS IS THISAND HOW DO I FIND THE LEAK TO EARTH I HAVE ALREADY ISOLATED THE MAST,SSB SOLAR AND WIND CHARGER WITH NO LUCK.PLEASE I NEED HELP THANKS.
Hi Luke and welcome to CF. FYI typing in all caps on the internet is the equivalent of shouting and also makes reading the post more difficult for most people. Might want to turn off the caps lock.

Let me see if I can interoret what you are saying

- House bank is isolated - disonnected ground cable?
- Start bank switched off but cables still connected
- DB? (Do you mean DC) panel still shows power
- Also a meter between start bank positive and steel hull (ground) shows 12v potential

Off the top of my head is one of the charging sources, perhaps alternator sense or feed, is wired directly to the positive terminal of the start bank rather than through the isolating switch. Which makes the DC bus powered at all times.

Is this a new installation? A new problem? A new to you boat?

Sometimes knowing when the problem started can be helpful.

Good luck...
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Old 09-05-2012, 04:20   #3
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Re: EARTH LEAK TO STEEL HULL

Quote:
Originally Posted by G.LUKE View Post
BOTH HOUSE AND STARTER BATTIERS HAVE POSITIVE AND NEGATIVE ISOLATING SWITCHERS.IF I ISOLATE THE EARTH ON THE HOUSE BATTERIES THE DB PANEL STILL STAYS POWERED UP.WITH BOTH MOTOR SWITCHERS OFF.
Is this with all the house circuit breakers off?
Are the house breakers single pole or double pole?


Quote:
Originally Posted by G.LUKE View Post
.I CAN CHECK THE VOLTAGE BETWEEN POSITIVE TURMINAL AND THE STEEL HULL AROUND 12VOLTS.I NEED TO LAUNCH AS SOON AS I CAN , HOW DANGEROUS IS THISAND HOW DO I FIND THE LEAK TO EARTH I HAVE ALREADY ISOLATED THE MAST,SSB SOLAR AND WIND CHARGER WITH NO LUCK.PLEASE I NEED HELP THANKS.
Is your boat designed with an isolated earth system or has it got a single earth grounding point? Both systems are used on a steel boat.

Sorry for the questions rather than solutions, but it's hard to diagnose otherwise.

Always have a look at the bilge pump, autopilot and anchor winch these are the most common sources of problems.
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Old 09-05-2012, 05:07   #4
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Re: EARTH LEAK TO STEEL HULL

I would add to the above posts that it is not a good idea to have a leak. May I suggest you fix it before launching. Even if it didn't do anything to your boat, it is not healthy on others'.

Keep us posted on your findings if you can.
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Old 09-05-2012, 05:26   #5
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Re: EARTH LEAK TO STEEL HULL

most likely is the engine is grounded to the hull,and to the neg post on the battery.
your battery switch on the neg side only isolate the domestic supply.

if there is an ammeter and voltmeter on the dc panel,the shunt is between the engine and battery on the neg side,and direct to your house batteries on the pos side,hence the presence of voltage all the time.
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Old 09-05-2012, 10:26   #6
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Re: EARTH LEAK TO STEEL HULL

It is very difficult to isolate the battery negative from a metal hull, there are numerous places where this can get bypassed. For this reason it is unusual to provide a negative disconnect. For the disconnect to work it has to be right on the battery terminal, not in a control panel where other connections are going to the battery negative and by-passing it.

Another problem with a negative disconnect switch that obviously has other things bypassing it, is that if you leave the negative switch off but turn the positive on and then try to start an engine, the by-passing object (instrument, pump, whatever) will try to carry the full starter motor current which will destroy the wiring and/or the equipment and could even cause a fire.

On our steel boat, the battery negative was solidly connected to the hull directly and through the engines and we had no electrolysis problems.

So I can only see negative results from having a disconnect on the negative side of the batteries. Unless you can find some compelling reason to need it I would just eliminate it.
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Old 09-05-2012, 10:54   #7
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Re: EARTH LEAK TO STEEL HULL

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It is very difficult to isolate the battery negative from a metal hull, there are numerous places where this can get bypassed. For this reason it is unusual to provide a negative disconnect. For the disconnect to work it has to be right on the battery terminal, not in a control panel where other connections are going to the battery negative and by-passing it.

Another problem with a negative disconnect switch that obviously has other things bypassing it, is that if you leave the negative switch off but turn the positive on and then try to start an engine, the by-passing object (instrument, pump, whatever) will try to carry the full starter motor current which will destroy the wiring and/or the equipment and could even cause a fire.

On our steel boat, the battery negative was solidly connected to the hull directly and through the engines and we had no electrolysis problems.

So I can only see negative results from having a disconnect on the negative side of the batteries. Unless you can find some compelling reason to need it I would just eliminate it.
I have to disagree its not difficult to do. If you have negative wires contacting the hull it can cause major problems and you need to know there is a problem. Some boats ground the negative at one point, this is acceptable but less good IMHO.
It is important with this system that there is only one ground point. You still have to be very diligent about other ground wires connecting the hull. Multiple grounds can cause serious and rapid problems, in some cases.
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Old 09-05-2012, 11:32   #8
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Re: EARTH LEAK TO STEEL HULL

I hear this (mis?) quoted quite often, that there should only be one grounding point on a steel boat, but so far I've not heard any explanation of why this is preferable. The whole hull is at the same potential it makes no difference where ground connections are made.

How does a negative wire touching the hull cause "major problems"? They are at exactly the same voltage so no current can flow. It is true that if there is bare copper in contact at a wet location there may be some local surface electrolysis but battery cables should all be insulated.

Our boat had multiple ground connections to the hull from both DC and AC equipment and in 40 years they had caused no problems.
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Old 09-05-2012, 12:20   #9
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Re: EARTH LEAK TO STEEL HULL

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Originally Posted by Andina View Post
I hear this (mis?) quoted quite often, that there should only be one grounding point on a steel boat, but so far I've not heard any explanation of why this is preferable. The whole hull is at the same potential it makes no difference where ground connections are made.

How does a negative wire touching the hull cause "major problems"? They are at exactly the same voltage so no current can flow.
The explanation is quite simple
If two negative wires contact the hull they will never be at the same voltage. All wires have voltage drop with current flowing.
Once you have two different voltages suspended in an electrolyte ( seawater) you will get corrosion. This stray current corrosion can sometimes be very rapid.
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Old 09-05-2012, 15:14   #10
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Re: EARTH LEAK TO STEEL HULL

Ja broer, I don't think you have big problems, but it would be nice to find where the problem is ne?
Whatever you do, do NOT run anything with the negative disconnected, this could make a groot boggerop!
You should set about finding where "it" is, by dividing and conquering. You have to isolate every circuit. There was already some good advice, in the thread. SO, disconnect the neg switch and the neg is finding a way to the hull and the neg side of another item. It could be the alternator.
One by one disconnect and reconnect cables until the lights on your DB go out. It is a very good thing to do and will teach you everything about your boats electrical side which you MUST know if you are going cruising. Make copious notes and if you dont know how to do an elect schematic, then learn "Ladder diagrams" its the best way to troubleshoot.
You could always call the electrician who installed it and give him a snotklap.
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Old 09-05-2012, 15:34   #11
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Re: EARTH LEAK TO STEEL HULL

Quote:
Originally Posted by noelex 77 View Post
The explanation is quite simple
If two negative wires contact the hull they will never be at the same voltage. All wires have voltage drop with current flowing.
Once you have two different voltages suspended in an electrolyte ( seawater) you will get corrosion. This stray current corrosion can sometimes be very rapid.
This issue can be eliminated by 1. copper bonding straps between any two plates, 2. Insure there are no 12v Positive lines touching either the hull, or liquid of any kind. 3. Clean and secure all grounding points....Ground everything on boat to one grounding buss, that is grounded to hull at only one point.

I think you are on the right path, you should be able to disconnect the one DC ground and have an isolated hull. If you don't, you have a leak somewhere, worn insulation or device left on, and you need to find it. Good luck
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Old 09-05-2012, 16:13   #12
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Re: EARTH LEAK TO STEEL HULL

Quote:
Originally Posted by noelex 77 View Post
The explanation is quite simple
If two negative wires contact the hull they will never be at the same voltage. All wires have voltage drop with current flowing.
Once you have two different voltages suspended in an electrolyte ( seawater) you will get corrosion. This stray current corrosion can sometimes be very rapid.
HUH? We are talking about wiring inside the boat, they are not "suspended in an electrolyte", they are insulated and all connected to the HULL. There is no "stray" current, any current is going straight into (or from) the hull at the hull connections. Any voltage difference between an accidental contact and a metal hull that close to the point of attachment would be less than 1/1000 volt.

It is still a mis-quoted and unsubstantiated assumption.
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Old 09-05-2012, 16:25   #13
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Re: EARTH LEAK TO STEEL HULL

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Originally Posted by capn_billl View Post
This issue can be eliminated by 1. copper bonding straps between any two plates, 2. Insure there are no 12v Positive lines touching either the hull, or liquid of any kind. 3. Clean and secure all grounding points....Ground everything on boat to one grounding buss, that is grounded to hull at only one point.
<SNIP>
This is a STEEL boat, not a fiberglass. Copper bonding is never done on a steel hull, all the underwater objects are already bonded by the HULL. There is no need to bond everything to one point and connect to the hull there, the items are ALREADY bonded to the hull, it is STEEL.

Give me one logical reason why you should isolate through hull items on a steel boat, go to the trouble of bonding them all together and then connecting them to the hull at one point?

You guys are being confused with fiberglass and wooden boat techniques. I have worked on dozens, of steel boats installing and repairing equipment. I have never seen bonding yet.

TM(mis)I

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Old 09-05-2012, 19:44   #14
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Re: EARTH LEAK TO STEEL HULL

Bonding is not an issue to the OP's original post and no you do not bond the thru hulls in a metallic boat. But here is where your confusion is. The dozens of boats you have worked on and installed and repaired equipment on are throwing voltage into the water. That is just a fact. A hull potential will back it up. Have you done one? When you have installed new equipment how did you figure voltage drop and ampacity when you are grounding to the hull close to the equipment? The grounding conductor, the grounded conductor, the DC negative and a single bond to the hull should all terminate at the ship's ground. A single point. If the OP's boat were wired correctly he would not be having this problem and a negative disconnect between the battery and the ships ground would turn off all DC power then with a TDR or a ringer he could find his short.
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Old 09-05-2012, 23:29   #15
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Re: EARTH LEAK TO STEEL HULL

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<SNIP>
The dozens of boats you have worked on and installed and repaired equipment on are throwing voltage into the water. That is just a fact. A hull potential will back it up. Have you done one? When you have installed new equipment how did you figure voltage drop and ampacity when you are grounding to the hull close to the equipment? The grounding conductor, the grounded conductor, the DC negative and a single bond to the hull should all terminate at the ship's ground. A single point. If the OP's boat were wired correctly he would not be having this problem and a negative disconnect between the battery and the ships ground would turn off all DC power then with a TDR or a ringer he could find his short.
No.

Certainly starter motor currents "might" cause local differential voltages for a few seconds but they ALWAYS use heavy copper cables for negative return to minimal voltage drop when starting. Only non-commercial automobiles rely on the "hull" for starter motor return cables.

The other grounds on the hull are things like the hardware on a pump, safety ground on instruments, lightning ground for antennas etc. EVEN if the negative cables to these were to fail and ALL the DC current returned to the battery through the hull we are talking about differential surface voltages in the microvolt range spread out over long distances back to the battery connection. A few microvolts between remote locations on the hull are insignificant compared to electrolysis potentials.

Your assumption that these "internal" currents will alter "hull potential" is ludicrous. To develop a voltage relative to the water as you suggest would require an isolated electrode at a different voltage like they use in Kapac systems but on this example we are talking about the "bonded" items which are all at hull potential.

His problem is anode deterioration and that is totally independent how the negative connections are made to the hull. Current will flow, and is intended to flow, from sacrificial anodes to exposed metal to maintain a voltage larger than existing metal to metal potentials so the current direction protects equipment. Since there is no shore power connection here to be concerned about, it appears that the anodes are in the vicinity of areas of exposed metal so the protective anode currents are large enough to show on the surface of them.

On our boat and most steel vessels we apply an insulating coat over the hull like Coal Tar Epoxy. This doesn't remove but considerably diminishes the electrical conductivity and preserves your anodes. It sounds like this boat did not get an insulating barrier coat so the anodes are working overtime protecting the large surface.
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