I recently dropped my digital volt-ohm leads across the neutral-to-ground GFI plug on the dock where my boat resides... When I found around .55 volts I checked a couple of others to find as much as 1.5 volts. This doesn't seem like much, but I understand that it only takes a couple of mili-volts to eat up the zincs.... It was also rumored that the boat next to mine was replacing his every 3-months... Am I at risk of damage if I don't plug in? I don't seem to need to keep a 'float' charger going if I use it regularly....and only plug-in when on board and consuming lighting, stereo, etc.... any thoughts? Don't these GFI's trip-out with this kind of discrepancy?
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Debra B
AC versus DC ground currents
I'm no expert, but the galvonic isolators control current between AC and DC ground. Not AC ground and neutral. Neutral is not ground, so there will be some potential between them. I don't think this is really the issue. The issue seems to be when AC ground has a potential versus DC ground (which should be grounded to the engine which is grounded via the shaft to the water). This potential - if the 2 grounds connect - is what induces the currents that destroy metal. This is the current that galvonic isolators control. But zincs are cheap after all. Replacing them can be a pain, so get one of the fish zincs (They weigh a couple of pounds) and use it when you are away from the boat.
I'm no expert, but the galvonic isolators control current between AC and DC ground. Not AC ground and neutral. Neutral is not ground, so there will be some potential between them. I don't think this is really the issue. The issue seems to be when AC ground has a potential versus DC ground (which should be grounded to the engine which is grounded via the shaft to the water). This potential - if the 2 grounds connect - is what induces the currents that destroy metal. This is the current that galvonic isolators control. But zincs are cheap after all. Replacing them can be a pain, so get one of the fish zincs (They weigh a couple of pounds) and use it when you are away from the boat.
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Dave
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Dale I
More @ fish zincs...
Connection would be to any grounded metal onboard, i.e. engine block, prop shaft, negative battery terminal, etc.....they should all be interconnected. A search of the archives had little beyond the mere purpose and connection of zincs.... Per my original question then, if I don't plug in to the dockside A.C., I won't be affected by another boats faulty grounding or the leakage of current elsewhere on the dock....correct? ....
Connection would be to any grounded metal onboard, i.e. engine block, prop shaft, negative battery terminal, etc.....they should all be interconnected. A search of the archives had little beyond the mere purpose and connection of zincs.... Per my original question then, if I don't plug in to the dockside A.C., I won't be affected by another boats faulty grounding or the leakage of current elsewhere on the dock....correct? ....
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Tim
You are correct Dale
Dale, Yes, unplugging from the dock will break the grounding wire connection, and will minimize or eliminate galvanic corrosion. This is from Don Casey's "Sailboat Electrics Simplified". A galvanic isolator in the system will block current flow up to about 1.2 volts, so if you have neighbors who show 1.5 volts leakage, there would be G.C. even if you had a galvanic isolator. Cheers, Tim
Dale, Yes, unplugging from the dock will break the grounding wire connection, and will minimize or eliminate galvanic corrosion. This is from Don Casey's "Sailboat Electrics Simplified". A galvanic isolator in the system will block current flow up to about 1.2 volts, so if you have neighbors who show 1.5 volts leakage, there would be G.C. even if you had a galvanic isolator. Cheers, Tim
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Dale I
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Greg Estep
isolating transformer
Your other option is to install an isolating transformer, and you are seperated from the dock ground all together. The cost is about $400, but well worth it.
Your other option is to install an isolating transformer, and you are seperated from the dock ground all together. The cost is about $400, but well worth it.
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Jack Tyler
Better alternative than iso transformer is...
...to install a galvanic isolator, which is exactly intended for this kind of problem (neighbor with a hot boat, poor dock wiring, etc.) Newmar makes an excellent one that weighs 20 times less than an iso transformer and costs 1/4 the amount. OTOH an iso transformer offers add'l benefits. FWIW I just installed an isolation transformer made by Olsun that handles 250V/220V/110V input power, came with an input voltage selector switch, and is serious gear. Rated for 2.5 kVA. It was custom built and cost me $300 plus $70 to ship, since it weighed 120# (!) and is roughly 18" x 10" x 10". All these numbers are worth considering if there's interest in doing something similar - an iso transformer is a serious piece of gear to handle and install. Jack
...to install a galvanic isolator, which is exactly intended for this kind of problem (neighbor with a hot boat, poor dock wiring, etc.) Newmar makes an excellent one that weighs 20 times less than an iso transformer and costs 1/4 the amount. OTOH an iso transformer offers add'l benefits. FWIW I just installed an isolation transformer made by Olsun that handles 250V/220V/110V input power, came with an input voltage selector switch, and is serious gear. Rated for 2.5 kVA. It was custom built and cost me $300 plus $70 to ship, since it weighed 120# (!) and is roughly 18" x 10" x 10". All these numbers are worth considering if there's interest in doing something similar - an iso transformer is a serious piece of gear to handle and install. Jack
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