Vessel Electrical Safety Committee - Message #1

There’s been a fair amount of activity with the advent of the Vessel Electrical Safety Committee and improvements to club rules regarding vessel electrical compliance. One of the more frequent topics that pops up deals with galvanic isolators. Following is some insight on the issue.

A boat wired according to the prevailing standards of the American Boat and Yacht Council and plugged into a dock wired according to the National Electrical Code is subject to increased galvanic corrosion as small DC electric currents move between boat and shore through the safety ground wire in the shore cord.

Changes in electrical standards now specify the onboard DC NEGATIVE bus be hardwired to the AC GROUND (green wire) bus. This ensures a specified pathway back to ground for any stray AC current encountered by onboard machinery or running gear. The downside to this connection is that it allows stray DC current from a nearby mooring vessel to leach onto the marina power grid’s “green wire” system and onto neighboring vessels. This stray DC current is a primary cause of galvanic corrosion, or known in more technically accurate terms as stray current corrosion.

How does this happen? It all starts with old or improperly wired equipment that spills DC current onto the vessel’s machinery and that current is looking for ground. On a vessel with inadequate anode protection, that current “backs up” and finds it way off the boat via the AC (green wire) safety circuit. Once off the boat, it continues to look for ground and the neighbor’s vessel that has proper anode protection is the place to go. Thus, we hear stories of one owner having to replace anodes yearly, while the guy next door comment’s that his are “going on year three”.

As vessel owners, we combat this problem in two ways. The first is to ensure we have properly attached and serviceable anodes (aka zincs). For those moored at the main station, the anode material of choice is made of aluminum alloy. The alloys used are blended to provide optimal protection in freshwater, while still allowing for transitional saltwater use. For vessels moored in saltwater, the traditional zinc alloy is still the anode of choice.

The second preventative measure is to install a galvanic isolator on the AC green wire circuit between the vessel’s shore power receptacle and the AC ground bus on the vessel master panel. These devices effectively isolate your vessel from your neighbors by breaking the DC current pathway, WITHOUT compromising the necessary AC grounding safety.

Galvanic Isolators have been widely used since 1988 to interrupt the flow of harmful, low voltage currents that may cause galvanic corrosion. Today, most U.S. built boats with factory installed 110 or 240 volt shore power systems are equipped with Galvanic Isolators.

How do you know if you have one? A simple visual inspection will probably tell. Using a flashlight, visually follow your AC green wire from the hull AC power receptacle to the vessel’s electrical panel. Somewhere along that route, you should encounter a device about the size of a butter tub, where the green wire goes in and comes out. It should be labeled, “Galvanic Isolator”. If you don’t see such an item, then you probably don’t have one.

Although a galvanic isolator will run you around $200 - $300, consider the alternative. A set of good replacement anodes for a boat will run about $150 - $200. Add to that the cost of a haul out ($500+) or a diver’s services ($200). It’s quick math to realize that if it gives you just one more season on your anodes, you’re cash ahead to install the device.  That’s not to mention the protection it provides to your engines, transmissions and running gear.

These are a routinely stocked product at both Fisheries Supply, West Marine and other chandleries. They are certainly within the realm of a DIY project and come with step by step installation instructions.

Members of the VESC will continue to post information articles to the QCYC website Member’s Forum as more questions arise. Thanks for reading and happy boating.