Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

Galvanic Isolators

As mentioned above, each boat plugged in at a
dock is helping to protect all the other boats at
the dock. They are all married to one another
via the green wire. For this reason, I strongly
recommend a galvanic isolator for any boat
that spends its time plugged in at a dock.
The proper location for the galvanic isola-
tor is in series with the green grounding conduc-
tor, and as close to the AC inlet on the boat as
possible. Install it so that it can’t be bypassed
electrically, as shown in the illustration opposite.
You may need to test the galvanic isolator
to ensure that it is functioning properly. An
ABYC-compliant isolator is made up of two
sets of opposed diodes and a parallel-
connected capacitor (exclusive of any status-
monitoring circuitry that may be associated
with the device), as shown in the detail in the
illustration. You must confirm continuity for
current flow in both directions to rule out a case
short to ground of one or more of the diodes
and to ensure the capacitor is functional.

Testing a Galvanic Isolator

In most cases, this test is a three-part process,
as outlined below.
Step 1. Check the continuity of the
diode set in one direction:

1 Connect your DVOM leads to the termi-
nals where the boat’s green wires attach.
It doesn’t matter which lead connects to
which terminal; you will be checking cont-
inuity in two directions through the device.

2 Set the DVOM to the “diode” test
function.

3 With the leads connected, watch as the
meter’s reading gradually increases, showing
that the battery in your DVOM is charging
the capacitor inside the galvanic isolator.

4 If you get an immediate continuity
reading through the isolator and no

a basic corrosion survey 115

gradual increase in your reading, then the

isolator is not equipped with a capacitor

and is not compliant with current ABYC

standards.

5 Assuming the isolator has a capacitor, wait

until the numbers on the DVOM stop

increasing (this may take a few minutes).

Make a note of the number.

Step 2. Check the continuity of the

diode set in the opposite direction:

1 Disconnect the meter leads and “flash” the

two terminals on the isolator to discharge

the capacitor.

2 Reverse the meter’s leads from the previous

connection and repeat the Step 1 test above.

3 If the capacitor is in good condition, the

meter reading should stop within 10% to

15% of the value from Step 1.

If you get a no-continuity reading from

either test, the isolator diode sets have failed to

Checking the continuity of the diode set in one direction. A grad-

ual rise in the reading indicates the charging of the capacitor

from the battery of the DVOM. Once charged, the meter reading

will stabilize. The reading is essentially the amount of voltage

drop across the isolator——typically around 0.9 volt.

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