Bad bilge pump connections are the most common as those wires are often in water, but it could be any wet connection the way some boats are wired. With the AC green connected to DC negative it shouldn't be hard to imagine happening. The majority of corrosion issues are caused by the boat with the problem. The green wire carries current from the stray current to nearby boats. That is the purpose of a galvanic isolator - it blocks 1.2 volts of current on the green wire but will let an AC fault pass. The so-called "hot marina" is really a problem with another boat causing DC voltage to travel to others connected.
AC Power Onboard and Dockside
- Thread starter Chenega
- Start date
you said that the majority of corrosion issues are caused by the boat with the corrosion problem, ie the boat itself (but didn't show any numbers again to back this up).
And.. we agree that a galvanic isolator gets rid of the issue with the green ground not being at ground potential voltage (caused by some other boat somehow putting current on the green wire - up to 1.2 volts caused by the current).
So if the majority of corrosion issues are caused by the boat itself with the problems, this means that it was NOT caused by a different boat and the common green wire not being at ground. This imply's that galvanic isolators don't solve the majority of corrosion issues - since as you said, the corrosion is caused by a condition on the boat itself.
Is this really true? Not exactly what I thought. If the galvanic isolatator does solve the majority of corrosion issues, it is a voltage potential on the green wire that is causing the corrosion (and ELCI used everywhere in the marina would get rid of the problem).
Something that might make the ELCI issue and corrosion a little more clear. ELCI wont protect an individual boat from corrosion caused by the green earth wire not being at earth potential. However, ELCI used every where at a marina does get rid of the boats that cause the problem with the green earth wire by not allowing a boat with faulty AC wiring to even connect to the grid.
An ELCI will not protect any boat from corrosion caused by stray DC current, nor is that what it is supposed to do. DC current is the main cause of stray current corrosion of underwater metals. An ELCI will protect lives from leaks in the AC system, its design intention. An ELCI (30 millivolt whole boat GFCI) doesn't care about DC current on the green wire, just an imbalance between hot and neutral and will not reduce any corrosion caused by this.
A galvanic isolator will minimize current from entering a boat with the shore power ground (green) wire. An isolation transformer will reduce this current to zero as it means that there is no hard wired connection between shore power and the boat. This only leaves stray current on the boat itself as the cause of any problems and eliminates your neighbor's wiring problems from becoming yours - the often named "hot marina".
If you don't believe stray DC current can cause problems on a boat to that boat leave an exposed DC wire in bilge water and check back in a month or so. Many boats have bad wiring exposed to moisture. The boat that eats zincs rapidly while on a mooring is surely a victim of their wiring.
A galvanic isolator will minimize current from entering a boat with the shore power ground (green) wire. An isolation transformer will reduce this current to zero as it means that there is no hard wired connection between shore power and the boat. This only leaves stray current on the boat itself as the cause of any problems and eliminates your neighbor's wiring problems from becoming yours - the often named "hot marina".
If you don't believe stray DC current can cause problems on a boat to that boat leave an exposed DC wire in bilge water and check back in a month or so. Many boats have bad wiring exposed to moisture. The boat that eats zincs rapidly while on a mooring is surely a victim of their wiring.
Please read my email again for a question I had. I will repeat it.. What you said imply's that a galvanic isolater doesn't solve a majority of the corrosion issues in a marina with AC? Im still curious. If the galvanic isolator does solve a majority if the corrosion issues, then it would imply that ELCI used every where in a marina would reduce corrosion. Your experience on this (or Maine Sail) really is key to this question.
Regarding your question about leaving a 12 volt wire exposed in the bilge water.. Im am also curious..
If I leave an exposed 12 volt hot wire in the bilge water and come back in a month, what would you expect? The wire would likely be all corroded. What about the zinc. What about all the metal structures that are at DC ground but in the water. Does that 12 volt hot wire in the bilge affect any of these? What is the real world experience..
Regarding your question about leaving a 12 volt wire exposed in the bilge water.. Im am also curious..
If I leave an exposed 12 volt hot wire in the bilge water and come back in a month, what would you expect? The wire would likely be all corroded. What about the zinc. What about all the metal structures that are at DC ground but in the water. Does that 12 volt hot wire in the bilge affect any of these? What is the real world experience..
A galvanic isolator solves the majority of stray current issues caused by current entering a boat through the green wire - up to 1.2 volts. It will pass a larger voltage. An isolation transformer will not pass any current to the boat through the green wire as there is not a hard wired connection. Neither will solve any problems caused by wiring practices on the boat itself.
If a 12 volt wire is exposed to the bilge water any underwater metal the water comes in contact with will be at a different potential from any other underwater metal that the bilge water is not in contact with. All underwater metal is in the same electrolyte - the water outside the boat. With different potential between these items - seacocks, shaft, or the propeller (the most vulnerable) as well as any zincs - a battery is created with metal leaving the anode and moving to the cathode. Propellers make good anodes if there is a lack of zincs.
ELCI's have nothing to do with DC corrosion. They will work - as will a GFCI - without a ground wire which is there passively until there is an AC fault. They only care about any imbalance between hot and neutral.
ELCI's (as well as ABYC's requirement for AC green to be connected to DC negative) are concerned with safety, not corrosion.
Just a little summary regarding the ELCI and corrosion..
A GFCI or ELCI socket will trip if the AC to a load is improperly wired such that a portion of the current uses the green wire for the return. The green wire is safety only and should have no current.
A marina that has all ELCI or GFCI sockets (and working) will insure that no boats are putting current on the green safety wire by faulty AC wiring. Any boat that has an AC wiring fault would be prevented from connecting to the power grid by the ELCI tripping. A marina that has a “hot green wire” that is caused by improper AC wiring would have the problem eliminated if every socket were ELCI.
There is an additional method that current can be put on a green safety wire and that is though the boats DC voltage being in contact with the water (not just bilge water but the water body itself). If a 12 volt source is connected to a green wire by its ground, a circuit can form where the 12 volt current travels through the water itself and then returns to the earth ground. ELCI will not trip for this. This type of “DC” leakage current is dependent on the water itself so will be proportional to the area of the electrode in contact with the water (higher area = higher current) plus the conductivity of the water itself. In fresh water, this leakage current may be 100 to 1000 times smaller than in salt water generally meaning that in a fresh water marina, if there is an issue with current on the green wire, it is likely to be caused by faulty AC wiring and not DC leakage (which must use the water itself for the circuit).
In salt water, the water is much more conductive and therefore leakage currents are higher. We don’t have any numbers on this leakage (probably wont find any either) but assume that in salt water for one example, 110 VAC produced a current of 2 amps. We don’t know the size of the electrode in the water that created this much current (maybe a prop and shaft?) but at 12 volts, the current for the same configuration would be 1/10 or around .2 amps. If the size of the electrode is reduced (example, it’s only the exposed end of a wire and connector for a bilge pump), the leakage current would be further reduced.
So it is certainly possible for a 12 volt leakage to put current on the green wire in salt water (not likely at all in fresh water). And, if the green wire to the marina were for example 300 foot of 14 gauge, the 0.2 amps could create a parasitic voltage of 0.14 volts - which could be significant.
If we look at the current caused by faulty AC wiring, let’s consider two cases for 110 VAC in the US. In once case, the green wire is used instead of the white wire and all the load current returns on the green wire (which of course will trip the heck out of ELCI). 110VAC currents can be up near 15 amps. Compare this to the number we had for DC leakage of .2 amps. The AC fault current is a factor of 75 times higher (i.e., WAY higher). If the AC fault happens from the return current being shared by the green and white wires, the current put on the green wire would be somewhere on the other of ½ of using the green wire only. Note that this could still be on the order of 35 times higher than currents caused by 12 volt DC leaking. In fresh water, DC leakage is just not likely an issue at all.
DC leakage from a 12 volt source that puts current on the green wire will not trip the boats ELCI.
The issue of any of these current leakages onto the green wire are solved by a galvanic isolator. And, a galvanic isolator or eliminating AC wiring problems in a marina by using all ELCI AC sockets won’t affect corrosion from DC leakages on the boat itself.
A GFCI or ELCI socket will trip if the AC to a load is improperly wired such that a portion of the current uses the green wire for the return. The green wire is safety only and should have no current.
A marina that has all ELCI or GFCI sockets (and working) will insure that no boats are putting current on the green safety wire by faulty AC wiring. Any boat that has an AC wiring fault would be prevented from connecting to the power grid by the ELCI tripping. A marina that has a “hot green wire” that is caused by improper AC wiring would have the problem eliminated if every socket were ELCI.
There is an additional method that current can be put on a green safety wire and that is though the boats DC voltage being in contact with the water (not just bilge water but the water body itself). If a 12 volt source is connected to a green wire by its ground, a circuit can form where the 12 volt current travels through the water itself and then returns to the earth ground. ELCI will not trip for this. This type of “DC” leakage current is dependent on the water itself so will be proportional to the area of the electrode in contact with the water (higher area = higher current) plus the conductivity of the water itself. In fresh water, this leakage current may be 100 to 1000 times smaller than in salt water generally meaning that in a fresh water marina, if there is an issue with current on the green wire, it is likely to be caused by faulty AC wiring and not DC leakage (which must use the water itself for the circuit).
In salt water, the water is much more conductive and therefore leakage currents are higher. We don’t have any numbers on this leakage (probably wont find any either) but assume that in salt water for one example, 110 VAC produced a current of 2 amps. We don’t know the size of the electrode in the water that created this much current (maybe a prop and shaft?) but at 12 volts, the current for the same configuration would be 1/10 or around .2 amps. If the size of the electrode is reduced (example, it’s only the exposed end of a wire and connector for a bilge pump), the leakage current would be further reduced.
So it is certainly possible for a 12 volt leakage to put current on the green wire in salt water (not likely at all in fresh water). And, if the green wire to the marina were for example 300 foot of 14 gauge, the 0.2 amps could create a parasitic voltage of 0.14 volts - which could be significant.
If we look at the current caused by faulty AC wiring, let’s consider two cases for 110 VAC in the US. In once case, the green wire is used instead of the white wire and all the load current returns on the green wire (which of course will trip the heck out of ELCI). 110VAC currents can be up near 15 amps. Compare this to the number we had for DC leakage of .2 amps. The AC fault current is a factor of 75 times higher (i.e., WAY higher). If the AC fault happens from the return current being shared by the green and white wires, the current put on the green wire would be somewhere on the other of ½ of using the green wire only. Note that this could still be on the order of 35 times higher than currents caused by 12 volt DC leaking. In fresh water, DC leakage is just not likely an issue at all.
DC leakage from a 12 volt source that puts current on the green wire will not trip the boats ELCI.
The issue of any of these current leakages onto the green wire are solved by a galvanic isolator. And, a galvanic isolator or eliminating AC wiring problems in a marina by using all ELCI AC sockets won’t affect corrosion from DC leakages on the boat itself.
The issue of leakage is solved by a galvanic isolator only up to 1.2 volts. Above that passes.
Most, but not all corrosion is caused by voltages under 1.2.
AC current is rarely responsible for corrosion, DC is.
Ergo an ELCI doesn't reduce corrosion as the problem it is designed for isn't corrosion causing to start with.
Most, but not all corrosion is caused by voltages under 1.2.
AC current is rarely responsible for corrosion, DC is.
Ergo an ELCI doesn't reduce corrosion as the problem it is designed for isn't corrosion causing to start with.