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Old 05-01-2011, 11:30   #1
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Stray Current

Seems as if I have a stray current on my boat. Two indications, the zinc anode is disappearing too quickly. This I have now noticed two seasons running. The other indication comes from the fact that when I plugged in shore power while the boat is in dry storage the GFI popped. I tried three other plugs before one would not pop. I am assuming that the one that did not pop just has a larger threshold, i.e. it allows for a greater amount potential difference before it trips. I am certain that the plugs that popped are not defective: other boats are plugged into them.
My question is how do I locate the source of this problem?
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Old 05-01-2011, 12:13   #2
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If your zincs are dissapearing rapidy while at the slip, do you stay plugged in to shorepower all of the time? If so a fault in an adjacent boat may be flowing back to yours on your ground wire. Either install a galvanic isolator or (better) install an isolation transformer.

But your zinc dissapearing could come from a fault in your own boat. Check the wiring on your bilge pump. This is a common cause of the problem if it is wired backwards.

On the subject of GFCI's on yard power systems popping, there isn't an easy solution. Boats are wet and slight ground faults occur. I used a separate power cord for tools and stuff while I was on the hard to avoid this problem.

David
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Old 05-01-2011, 12:57   #3
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LOL I love how boaters always blame the boat next to them for a problem when 90% of the time the problem is on their own boat. Guess it is easier to blame someone else than to fix the problem.

Boats on the hard NEED to be grounded. Get a piece of #8 or 10 green wire connect one end to a 120 VAC 15 Amp plug ground pin only the other end attach a big alligator clip and connect that to your underwater metal like shaft. Now you will be safe.

As for tripping the GFIC sounds like you have a problem and it could be causing your wastage or not most likely not but is a safety issue and needs to be fixed. Almost all zinc wastage is from a DC leak as it takes a lot for AC to do this.

Bilges pump wiring is also rarely a problem in excessive anode wastage. I would think you have 2 separate problems.

Hire a pro to look at it or spend a lot of time learning about it. You will get a lot of suggestions from the readers here but most will not help. This is not really the type of problem that can be diagnosed from off the boat. You really need meter in hand to do a bit of detective work, you can guess all day long but it is really good ol in the trenches detective work and testing that will find the problem.

You can read my article here or any of the other good books out there on marine electrical. Project Boat Zen - Checking your shore Power System

Good luck and be careful
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Old 05-01-2011, 14:11   #4
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Originally Posted by sailvayu View Post
LOL I love how boaters always blame the boat next to them for a problem when 90% of the time the problem is on their own boat. Guess it is easier to blame someone else than to fix the problem.

Boats on the hard NEED to be grounded. Get a piece of #8 or 10 green wire connect one end to a 120 VAC 15 Amp plug ground pin only the other end attach a big alligator clip and connect that to your underwater metal like shaft. Now you will be safe.

As for tripping the GFIC sounds like you have a problem and it could be causing your wastage or not most likely not but is a safety issue and needs to be fixed. Almost all zinc wastage is from a DC leak as it takes a lot for AC to do this.

Bilges pump wiring is also rarely a problem in excessive anode wastage. I would think you have 2 separate problems.

Hire a pro to look at it or spend a lot of time learning about it. You will get a lot of suggestions from the readers here but most will not help. This is not really the type of problem that can be diagnosed from off the boat. You really need meter in hand to do a bit of detective work, you can guess all day long but it is really good ol in the trenches detective work and testing that will find the problem.

You can read my article here or any of the other good books out there on marine electrical. Project Boat Zen - Checking your shore Power System

Good luck and be careful

Thanks for the reply. I know it is not the boat next door. I have the problem. AC can do cause this problem, especially if you are plugged into shore power whenever you are not sailing. I am looking for suggestions on how to trace this problem. Experts I don't need at the moment. Before this is all over and fixed, I will be the expert.
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Old 05-01-2011, 14:53   #5
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I beg to differ experts are what you need if you want to solve that problem quickly. Why not learn form them?
Lesson #1 you are wrong about the AC part. The problem with shore power is that DC currant can leak back into the boat thru the ground which is in turn connected to your underwater metal (or should be). A series of boats in neat rows make for a perfect battery if the potentials are off (not that, that ever happens) That is why those AC ground isolators are designed to block DC only, that is they allow current flow in one direction only and of course that is DC as AC flows in both directions. It takes a lot of AC currant to cause loss of metal as it is flowing back and forth. DC however will flow only in one direction taking the metal (zinc) with it.

Like I say read the article it will tell you everything you need to trace the problem if it is from the shore power.

There really is only one way to find the problem and that is to systematically trace the problem one step at a time not just try this then that. You have to know what to look for and how. I have been doing this for 35 years I think I have learned a thing or 2 in that time.

Good luck
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Old 05-01-2011, 16:19   #6
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Martin, is your AC ground connected to your DC negative or bonding in any way that you know if? If it is not, then I would suggest disconnecting the main battery leads, shutting the DC systems, and see if you pop the GFI with just your AC systems connected. That would confirm a problem in the AC system, which on most boats is simple enough thta you can trace (hands and eyes) to look for shorts, miswired sockets, physical problems that might be causing this.

"Divide and conquer" try to break it down to discrete sections or circuits, then attack the one that trips the GFI.
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Old 05-01-2011, 21:16   #7
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a second question...GFIs pop for my boat also. The 120 and 12 volt grounds are the same. I have one of those power panels that indicate if the polarity is correct on the 120. Will this polarity monitoring cause the GFI to pop? I have no other signs of power issues, zincs do not wear.
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Old 06-01-2011, 01:54   #8
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Just to emphasise others sorting the GFI problem isn't difficult just tedious.

Start by isolating the AC sections in big groups. Like does it pop with the boats breakers off ,then feed in each section. Most likely you have a ground fault path.

Ps as to the posters suggestions 're bonding underwater while on the hard well I'm laughing. Never in my life have I seen it. But then I'm in 230vac where we have a safe system. ( there are four RCB devices between my boat and the supply). Anyway I have 14 underwater fittings and as in Europe we don't bond or connect the AC and DC grounds, I'd have a tight rats nest of wires and clips LOL !!

Dave
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Old 06-01-2011, 09:56   #9
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Dave-
"bonding underwater while on the hard well I'm laughing."
One can't bond underwater while on the hard. However, if there is a bonding system, and that system is as usual connected to the engine block or other "DC ground" bus in the boat...that means there are now ay number of opportunities for the bonding system to be connected to a ground common with the AC system, which in turn means the DC systems must now be examined since they may be causing the "fault" in the AC systems they are connected to.

Underwater or on the hard.

If there's no bonding system at all--there are less wires and connections to be suspected.
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Old 06-01-2011, 19:05   #10
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Just to emphasise others sorting the GFI problem isn't difficult just tedious.

in Europe we don't bond or connect the AC and DC grounds, I'd have a tight rats nest of wires and clips LOL !!
GoBoating---

First, I am not picking on your post but I am curious about many of your comments. Would you help me better understand how things are done differently in Europe?

Would you explain how you avoid jointly bonding the AC and DC grounds? Here in the US, our wiring codes, NEC requires a grounding wire for safety. Granted, the NEC rules do not get to boats but the same aspects of safety apply to marine dock wiring. Maybe you mean (and I am guessing) that in Europe your AC is bonded via back to back diodes which would float the grounding wire by about 0.7 v. I would presume that an equipment safety ground is just as important in Europe.

Another question, you have mentioned in several posts that European wiring is inherently safe. Are you aware of any specific wiring guidelines/code we adhere to in the US that is unsafe? Our electrical and safety engineers spend great effort to ensure safe wiring guidelines are enforced by code in all states as detailed in the NEC--National Electrical Code.

Getting close th the end-----can you explain how your RCBs differ other than by name from GFIs used here in the US? Our GFIs trip when a differential current of 30ma happens between the source and return currents.

Finally my last question-- you mention European voltage is 230vac whereas voltage here in the states is distributed primarily at 110vac. Yes, I can understand that higher voltage allows lighter gage wires to deliver higher power to loads. There are trade offs in everything. My guess is that the lower voltages used here in the states was selected because of limitations in wiring insulation years ago

But I don't see how operating at 230vac is better anymore than I see operating at 50Hz better than 60Hz. European transformers and motors require more steel because of the lower frequency. But again, everything is a trade off. For example, 60Hz has higher reactance issues that must be contended with in our distribution systems.


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Old 06-01-2011, 19:25   #11
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Foggy, there was a good article in "Professional Boat Builder" a few years ago that talked about the differences in US and EU boat electrical systems and in how to troubleshoot the system. It also talked about differences in RCBs. Maybe a search of the PBB website would find it. It was an article by Nigel Calder.
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Old 06-01-2011, 19:28   #12
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Thanks DeepFrz!!!

I am curious, will do a Google. I was not picking on Goboat at all. The better informed we are the better off we are.

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Old 07-01-2011, 08:09   #13
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Originally Posted by sailvayu View Post
I beg to differ experts are what you need if you want to solve that problem quickly. Why not learn form them?
Lesson #1 you are wrong about the AC part. The problem with shore power is that DC currant can leak back into the boat thru the ground which is in turn connected to your underwater metal (or should be). A series of boats in neat rows make for a perfect battery if the potentials are off (not that, that ever happens) That is why those AC ground isolators are designed to block DC only, that is they allow current flow in one direction only and of course that is DC as AC flows in both directions. It takes a lot of AC currant to cause loss of metal as it is flowing back and forth. DC however will flow only in one direction taking the metal (zinc) with it.

Like I say read the article it will tell you everything you need to trace the problem if it is from the shore power.

There really is only one way to find the problem and that is to systematically trace the problem one step at a time not just try this then that. You have to know what to look for and how. I have been doing this for 35 years I think I have learned a thing or 2 in that time.

Good luck


Many thanks for your help. I have read the article and it does state that if there is a neutral/ground problem with the AC and DC system, that this can cause galvanic corrosion. It is possible that I have such a problem.

I have to fully digest what the article says before I can fully understand the possible problem but it is the first step in getting to a solution. At least it describes a testing method, and that is what I was looking for.

I respect your 35 years of experience and do not discount it by any means. I am not a simpleton when it comes to these matters. I am a civil engineer and have a some knowledge of electrical and electronic theory. I was for many years, in my younger days, a ham radio operator.

Also, I am in no hurry to solve this problem. Sailing season does not start for me until April and the boat will be out of the water until at least the middle of March.

Again, thanks for your help and if you come with any other ideas on testing for this problem, let me know.

Martin
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Old 07-01-2011, 09:18   #14
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a second question...GFIs pop for my boat also. The 120 and 12 volt grounds are the same. I have one of those power panels that indicate if the polarity is correct on the 120. Will this polarity monitoring cause the GFI to pop? I have no other signs of power issues, zincs do not wear.
Quite possibly.

It’s important to note that the Reverse Polarity Indicator Circuit must have a minimum resistance of 25,000 Ohms.

By applying Ohm's Law, we find that, if the polarity is reversed on a 120-volt circuit, activating the device, the current flow will be 120/25,000 = 4.8 milliamps, which is just below the tripping threshold of U.S. Ground Fault Circuit Interrupters (GFCIs); which trip at 5 milliamps. This way the alarm will alert the operator without tripping the circuit. With such a high resistance in the circuit provided by the 25K-ohm resistor, there is no need to worry about leaks to ground, galvanic corrosion, etc.

AC Reverse Polarity - Resources - Blue Sea Systems

Reverse Polarity Indicators - Resources - Blue Sea Systems
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Old 07-01-2011, 09:41   #15
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Finally my last question-- you mention European voltage is 230vac whereas voltage here in the states is distributed primarily at 110vac. Yes, I can understand that higher voltage allows lighter gage wires to deliver higher power to loads. There are trade offs in everything. My guess is that the lower voltages used here in the states was selected because of limitations in wiring insulation years ago

But I don't see how operating at 230vac is better anymore than I see operating at 50Hz better than 60Hz. European transformers and motors require more steel because of the lower frequency. But again, everything is a trade off. For example, 60Hz has higher reactance issues that must be contended with in our distribution systems.
Foggy
So you do agree that 230V is more efficient (produce less pollution, waste less energy) than 110V. If one system requires less than half the amount of wire for only a small increase in steel I would agree with you that 230V is more efficient than 110V. Now to blame the lack of progress on limitations in wiring insulation years ago is like saying that big car (petrol guzzler) a safer in the case where it involve a collision with a truck so every body should be forced to drive a big car or use an inefficient electrical system. Imagine what would append if suddenly a large country was to require less than half the material it used to purchase for electrical wiring. The industrialists will never tolerate it. So the people of that country are stuck paying more that they need to. In Europe that would start another revolution. “A la guillotine ou aux reverberes” would scream the French.
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