What is a galvanic isolator and why should my shore power system have one?
A galvanic isolator is a device used to block low voltage DC currents coming on board your boat on the shore power ground wire. These currents could cause corrosion to your underwater metals; through hulls, propeller, shaft etc.
Boats in a marina plugged into shore power
all act as a giant battery. They are all connected together by the
green shore power ground wire, which is (or should be) connected to their
DC grounds, engine block, and bonded underwater metals. If the boats
are in salt water then that forms an electrolyte and the dissimilar metals
connected together act as a battery, causing corrosion.
As the galvanic isolator fulfills such a key function in the AC circuit it is only prudent to use the best quality unit available.
How to test a galvanic isolator that doesn't have a monitoring system..
Galvanic isolators are a bit difficult to test. Current ABYC standards require that galvanic isolators be self testing. For testing older isolators without this feature there are a number of methods that can be used, the one that follows is one that I found most useful.
Unplug the boat from shore power
before starting the test.
As the capacitor starts to conduct current the reading should rise to approximately 0.9 volts. Remove the test leads, short the two wires of the isolator together to discharge the capacitor and repeat the test with the test leads reversed. You should get the same answer.
Interpreting the readings:
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