The shore power ground wire connects the boat's underwater metal, through the dock, to every other boat plugged in. A galvanic isolator in that wire blocks the small galvanic currents that eat anodes and fittings, and still lets fault current through to trip a breaker. A-28 is the standard for the isolator itself.
What it covers
ABYC lists A-28 as Galvanic Isolators. In our words: how isolators fitted in the shore power safety ground must perform. Under its revised version, a fail-safe isolator, one an independent laboratory has confirmed will keep working or leave a permanent ground path if it fails, needs no monitor. Units come rated 30 A, 50/60 A, 100 A and 200 A to match the supply.
What surveyors check against it
Whether a boat on shore power has an isolator or an isolation transformer at all. If it has an isolator, whether it's fail-safe or monitored, rated for the shore supply, and fitted in the ground conductor near the inlet. Then the evidence: anode wastage and corrosion on fittings. See no galvanic isolator and stray current corrosion.
Citing it in a finding
"Fit a fail-safe galvanic isolator, ABYC A-28, rated for the 30 A shore supply, in the ground conductor near the inlet." Record the shore supply rating and the anode condition that backs it up.