You can start by:
1. Have you added any AC devices since last year?
A) Unplug ALL your ac devices on board. (Do not forget the battery charger.) Now plug in the shore power with all breakers off as well.
B) Check your readings. Does the needle deflect below .9 reading? If things are clean and they should be it should be stable.
C) Turn on AC devices one at a time. (Start with your battery charger). It is not uncommon for a battery charger to be "dirty", Hopefully you will find the offending DC leaker.
D) Make sure it is has a safety green ground and it is connected to your galvanic isolator.
E) If it is, and the readings are deflecting then the isolator is no longer protecting.
I have seen cases where a neighbor's boat was leaking DC to green ground which was flowing to other boats on the dock. Your readings would be normal if you were a couple of slips away but as soon as you plug your shore power in then the DC on green runs into your cirucits. That is what isolators are suppose to prevent.
Also check to see if your galvanic isolator is warm when your system is energized. If it is cold then it is not working.
It is a place to start. There are others that may be able to provide more pinpoint diagnosis and possible corrections.
safe boating,
dave
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