Chandlery October 2009 Issue

Shorepower Cop

Marinco’s heavy-duty GalvanAlert offers a visual check for AC problems.

Billed as “the world’s only shorepower corrosion detector with reverse polarity indicator” by West Marine, Marinco’s new Galvan-Alert attaches to your existing 30-amp shorepower inlet and power cord and monitors galvanic and stray current corrosion flowing through the green ground wire ground of your shorepower system.


Appearance-wise, the GalvanAlert is similar to a miniature Marinco power cord. It is well constructed and utilizes the same plugs, connectors, and locking rings that are familiar to most every boater with an AC shorepower cord. The GalvanAlert has four LED indicators—a green LED to indicate power, a red LED indicating reverse polarity, and two other LEDs to show “medium” (green) and “high” (red) galvanic corrosion activity.

The GalvanAlert’s four lights warn of problems in the shorepower system.

The GalvanAlert can be used in a couple of ways. Plug it into the marina shorepower pedestal for a quick reverse polarity check. (Most vessels with 30-amp service already have a polarity indicator, however it’s typically located belowdecks.) You can also get a plug-in polarity checker for about $10 at most home-improvement stores. As the name implies however, the GalvanAlert’s primary function is to alert boat owners to the potential for galvanic corrosion of underwater metals. Galvanic corrosion occurs when two dissimilar and electrically connected metals are immersed in electrolyte, forming a galvanic cell. In such cases, the least noble metal gives up electrons and corrodes. While stray DC current is the most insidious destroyer of underwater metal, AC current can also cause problems.

When inserted in line with the power cord (either at the pedestal or vessel power inlet), the GalvanAlert will indicate when there are corrosion-causing faults in the shore-power supply. Product literature states that the GalvanAlert “fends off corrosion caused by stray currents that occur when boats come in contact with poorly insulated shorepower supplies or faulty wiring;” however, it’s important to note that this “fending” is in the form of a visual indication only. The GalvanAlert indicates a potential problem exists, it doesn’t correct it or provide any protection.

Galvanic isolators (which also attach to the green grounding wire) can actually limit galvanic current flow up to about 1.2 volts. However, galvanic isolators don’t block corrosion currents driven by higher voltages, a situation the GalvanAlert could at least warn you about.

West Marine (the exclusive distributor) states that once in place, the GalvanAlert allows you to “constantly monitor unsafe corrosion activity.” That may be true, but we’d be pretty leery of leaving a $150-plus piece of test equipment within easy reach of the dock, particularly if no one’s around to constantly monitor the unit anyway. If moored at a public marina or facility, a better approach may be to simply plug the unit in, check the readings, then remove and stow the unit aboard in a safe place until ready to check again.

If you are serious about protecting your boat from AC power problems, isolation transformers offer a very good solution. These, although they’re still expensive, have come down in price in recent years.


While the GalvanAlert tells you something is wrong, you’ll still have to determine where the problem lies. The West Marine video ( states that a green light indicates a “healthy” shorepower system. That’s not totally correct, as a system with an “open ground” wire will give the same indication, a situation that is not healthy for equipment and is potentially lethal to nearby swimmers.

Although it isn’t cheap, the Galvan-Alert should serve well as a simple, easy to use tool for basic checking and monitoring of a vessel’s AC power system—as long as buyers understand exactly what the unit is (and isn’t) telling them. For more serious protection from the problems associated with AC power supplies, consider an isolation transformer. 

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