Short answer: Galvanic isolator vs isolation transformer comes down to boat size, budget and how much isolation you want. A galvanic isolator blocks low-voltage galvanic current in the shore-power ground and suits most boats; a fail-safe unit lists around $605. An isolation transformer breaks the direct shore connection entirely, removes the onboard ELCI requirement when near the inlet, and suits larger yachts.
Long Beach Marine Electric gets asked about galvanic isolator vs isolation transformer by owners whose zincs are disappearing in a crowded marina. Both devices solve the same core problem: on shore power, your boat’s underwater metal is connected to every other boat’s through the marina’s green safety ground, which turns the whole dock into one galvanic circuit.
How each one works
A galvanic isolator sits in series with the green ground wire from the shore cord. Galvanic currents between boats are driven by small voltages, typically well under a volt. The isolator’s diodes block current below a threshold while letting a real fault current pass, so the safety ground still works when it’s needed.
An isolation transformer takes the shore power in on one winding and delivers it to the boat on another, with no direct electrical connection between the two. The boat’s ground isn’t tied to the shore ground at all, so there is no galvanic path to other boats, and a marina-side ground fault can’t reach the boat’s systems.
Side by side
| Galvanic isolator | Isolation transformer | |
|---|---|---|
| Blocks galvanic current through shore ground | Yes | Yes |
| Full electrical isolation from shore | No | Yes |
| Typical size and weight | Small, a few pounds | Large and heavy |
| Typical price | A fail-safe unit lists ~$605 | Considerably more |
| ABYC standard | A-28 | E-11 |
| Replaces onboard ELCI | No | Yes, within 10 ft of the inlet (ABYC E-11) |
| Common on | Most boats | Larger yachts, 50–100 A service |
Which one fits your boat
Choose a galvanic isolator when you have a 30 A or 50 A boat, galvanic loss through shore power is the problem, and budget and space matter. It’s the standard fix for most boats in Long Beach-area marinas. Choose a fail-safe unit that meets ABYC A-28 and has monitoring if possible.
Choose an isolation transformer when you have a larger yacht with 50 A or 100 A service, you want full protection from marina wiring faults as well as galvanic current, or you want to cover the ELCI requirement at the same time. Under ABYC E-11, an isolation transformer within 10 feet of the inlet removes the need for a separate onboard ELCI.
Measure before you buy
Neither device fixes stray current from a wiring fault on your own boat. That has to be found and repaired. A reference-electrode test with shore power on and off shows whether the problem actually comes through the shore ground, which is the problem these devices solve. See zincs wearing out fast.
Bottom line
For most boats, a fail-safe galvanic isolator is the right, affordable fix. For larger yachts, an isolation transformer gives full isolation and covers the ELCI requirement. Measure first. See galvanic corrosion testing or call (562) 374-7233.
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