Peter_the_Grate
New member
OK guys, what's a Galvanic Isolator? What does it do and why should I fit one?
Galvanic Isolator
- Thread starter Peter_the_Grate
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A "galvanic isolator" is a device containing at least 2 one-way diodes and usually a capacitor that is placed in-line in your
AC power ground wire (earth). Since the AC and DC ground wires (earth) are supposed to be joined, the objective of the
device is to prevent current leakage below a certain amount which prevents "glavanic corrosion".
I have one on my sailboat....which we live aboard here in SW Florida and it has served to protect my zincs (anodes) and
my running gear (prop and shaft). Others in the marina apparently have leakage of AC/DC power and suffer fast anode erosion and other problems.
If your boat is not plugged into shore power constantly and it does not have AC circuits energized..... you would be wasting you money.
If the boat is "isolated" from AC power most of the time.....I wouldn't install one, unless you are in a "hot" marina where there
is alot of galvanic corrosion damage.....and in that event I would install one.
If you have a 30 Amp hoookup - you need 1 isolator, and 50 Amp hookups require 2, especially when the 50 Amp service
"y's" to two 30 Amp cables and has two receptacles on the hull.
AC power ground wire (earth). Since the AC and DC ground wires (earth) are supposed to be joined, the objective of the
device is to prevent current leakage below a certain amount which prevents "glavanic corrosion".
I have one on my sailboat....which we live aboard here in SW Florida and it has served to protect my zincs (anodes) and
my running gear (prop and shaft). Others in the marina apparently have leakage of AC/DC power and suffer fast anode erosion and other problems.
If your boat is not plugged into shore power constantly and it does not have AC circuits energized..... you would be wasting you money.
If the boat is "isolated" from AC power most of the time.....I wouldn't install one, unless you are in a "hot" marina where there
is alot of galvanic corrosion damage.....and in that event I would install one.
If you have a 30 Amp hoookup - you need 1 isolator, and 50 Amp hookups require 2, especially when the 50 Amp service
"y's" to two 30 Amp cables and has two receptacles on the hull.
Peter_the_Grate
New member
Thanks for that. How do I tell if my marina is "hot"?
oldsaltoz
New member
G’day Peter.
If the marina you are in has steel piles or other major steel structures it may well have an impressed cathodic protection systems installed, they pass a small electrical current through the steel and water to anodes to protect the steel. This can affect your anodes if they are less noble than those used by the system.
Soavagoodweekend Old Salt Oz……
If the marina you are in has steel piles or other major steel structures it may well have an impressed cathodic protection systems installed, they pass a small electrical current through the steel and water to anodes to protect the steel. This can affect your anodes if they are less noble than those used by the system.
Soavagoodweekend Old Salt Oz……
G
Guest
Guest
Peter, you would need to take a volt meter, set it to AC volts, insert one probe into the ground (earth) socket on the
dockside shore power outlet....(make SURE it is the ground/earth!!)...and dangle the other into the water and any resulting
voltage reading indicates a "Ground (earth) fault".
After doing the above test, reset the volt meter to the highest DC Amps setting and check for DC current between the
grounding outlet and the water. Any reading above 10mA suggests stray current from nearby boats and you should not
connect to this outlet unless you have a galvanic isolator.
Next, with your shore power cord plugged into the boat but no into the dock (your generaors and inverters must be off
and disconnected), make sure there is no AC voltage between the grounding socket in the dock receptacle and the
grounding blade on the cord plug. Set the meter to the highest DC amp setting, switching down as necessary. Any current
that passes through the meter is leakage. If the current is flowing toward the boat (a + reading with the red proe to the receptacle,
black to the plug) it is damaging your fittings; if it flows the other way, the fittings on your neighbors boats are being
damaged. A galvanic isolator in the ground/earth wire should block all galvanic current and your meter shoul read zero
(although some isolators pass a few milliamps, which zinc anodes should handle). If the meter reads higher than 15mA, then
the isolator is not preventing corrosion.
Note: This is an explanation of how to do the tests by Don Casey, a recognized authority on boats. These tests can be found in his
book "Sailboat Electrics Simplified".
dockside shore power outlet....(make SURE it is the ground/earth!!)...and dangle the other into the water and any resulting
voltage reading indicates a "Ground (earth) fault".
After doing the above test, reset the volt meter to the highest DC Amps setting and check for DC current between the
grounding outlet and the water. Any reading above 10mA suggests stray current from nearby boats and you should not
connect to this outlet unless you have a galvanic isolator.
Next, with your shore power cord plugged into the boat but no into the dock (your generaors and inverters must be off
and disconnected), make sure there is no AC voltage between the grounding socket in the dock receptacle and the
grounding blade on the cord plug. Set the meter to the highest DC amp setting, switching down as necessary. Any current
that passes through the meter is leakage. If the current is flowing toward the boat (a + reading with the red proe to the receptacle,
black to the plug) it is damaging your fittings; if it flows the other way, the fittings on your neighbors boats are being
damaged. A galvanic isolator in the ground/earth wire should block all galvanic current and your meter shoul read zero
(although some isolators pass a few milliamps, which zinc anodes should handle). If the meter reads higher than 15mA, then
the isolator is not preventing corrosion.
Note: This is an explanation of how to do the tests by Don Casey, a recognized authority on boats. These tests can be found in his
book "Sailboat Electrics Simplified".
jfkal
Active member
Disagree. If your shore power plug is in and power is off you still create a "battery" with your underwater hardware and that of neighboring boats. Fit an isolator!!
jfkal
Active member
Take a sensitive voltmeter switch it to DC. Hook it up between the ground pin of your cable and the ground receptable of the shorepower outlet. If you have any voltage there you have galvanic corrosion. If switched to AC and you get a readin g you have hot marina and rapid corrosion. BE CAREFULL NOT TO TOUCH ANY LEADS and test on the right pins. AC kills.