Q. New boats are advertising isolation transformers between shore power and the boat’s electrical system. What are the benefits of adding an isolation transformer to an older boat?

A. Isolation transformers can be used on both new and older vessels that are connected to shore power. When you utilize AC shore power on board the boat, you are electrically connecting your boat to your marina neighbours and the marina docks. The connections are made via the water (through underwater metal parts) and via the shore power safety ground.

In a perfect world, this would not present a problem. Everyone would be equipped with a galvanic protection system that would protect their boat. In the real world, this is unlikely to be the case.

To reduce or eliminate electrical interactions between neighbouring boats and/or the marina itself, you need to have some method of “isolating” your boat. The most common method of isolation is a “galvanic” isolator installed in the shore power safety ground. A galvanic isolator blocks low-voltage (up to approximately 1.2 volts) DC currents from flowing through the shore power safety ground wire. The galvanic isolator does an adequate job for the majority of installations.

A problem the galvanic isolator can’t handle is a DC voltage fault that produces voltages more than approximately 1.2 volts DC. This current will flow and create serious galvanic corrosion damage.

A marine isolation transformer eliminates this problem. The safety ground wire that is incorporated into the boat’s wiring does not connect physically to the shoreside wiring ground. The isolation transformer eliminates all physical electrical connections between the boat’s wiring and the shore wiring. These transformers are typically found on larger vessels with extensive AC systems, whereas “galvanic” isolators are more common and less expensive.