I just had the face plate of my boat A/C panel off to check if a P/O had installed any type of galvanic protection. I found a 'Professional Mariner' Zinc Saver. It is wired with one green wire run from the A/C panel green bus bar and the other wire run to connect with the DC bonding system. The main A/C green supply/return wire is unbroken to shore power plugin. Is this setup giving me proper protection? Should I upgrade to something cut into main green wire? On the 'Zinc Saver' it reads "install between AC green wire and DC bonding system - ABYC recommended ". How would I check to see if this unit is still doing its job? Seeing as how this unit may not be a fail-safe type device, it probably should not be used on the main green grounding wire? Researching GI's, I found that DEI are highly rated and the patent holder of fail-safe technology, do you know of a West Coast, Canadian supplier?
Your hunch is right; the Galvanic Isolator is improperly installed on your boat. A Galvanic Isolator should be installed as close as possible to the AC shoreside receptacle and intercepting the grounding wire from the receptacle before it goes into the boat. With this approach, it is a sure thing for the GI to intercept all stray low amperage DC current on the AC grounding wire.
A good way to test a Galvanic Isolator is to have a multi-meter in a diode setting and test both sides of the AC grounding wire, one on the boat and the other on the AC receptacle of the boat. Please note that there is no need to have AC present while testing a GI.
You are right, DEI invented the fail safe GI. They are other fail safe GIs available on the market as well. We use the Newmar GIs on all our installs since they are a reputable marine company and their products are readily available.