©
2009 Magnum Energy Inc
Page 34
Installation
2.6.4 Grounding on Boats
When installing the MS Series inverter/charger on a boat, there are several considerations that
must be followed when grounding to ensure a safe installation, prevent galvanic corrosion and
adhere to ABYC (American Boat and Yacht Council) standards.
Ensure a Safe Ground Connection
When AC on the boat is being supplied by shore power, the onboard neutral should be connected
to safety ground on the dock. Consequently, neutral and safety ground should not be connected
anywhere on the boat when shore power is present. When AC on the boat is being supplied by the
MS Series inverter, the inverter’s output neutral is connected to safety ground through an internal
relay using its neutral to ground connection (shown in
fi
gure 2-20).
The DC ground terminal on the MS Series must also be connected to the boats safety ground
bus. This ensures that both the inverters AC and DC ground terminals are connected to the boats
safety ground bus as a safety measure to provide protection against faults and provide a path for
AC fault currents while the boat is connected to shore power.
Preventing the Risk of Corrosion
The inverter’s AC and DC ground terminals must be connected to the boats safety ground to
provide an important safety feature. However, this ground connection introduces the risk of galvanic
corrosion and/or electrolysis of the boat’s underwater metallic hardware.
Two possible solutions are typically used to maintain the correct on-board grounding requirements
while greatly reducing (if not eliminating) the risk of galvanic corrosion. These solutions would be
either using a galvanic isolator or an on-board isolation transformer.
Galvanic Isolators allow high AC voltage faults to pass, but block low voltage corrosion/electrolysis
currents from conducting.
Marine isolation transformers allow the shorepower to be connected to one side of the transformer
and boat’s AC wiring system is connected to the other side. Since transformers do not allow DC
currents to pass, the problem with galvanic corrosion is eliminated.
ABYC Inverter/Charger Grounding Requirements
1
DC Grounding Connections:
1) The DC grounding conductor (equipment ground) shall be:
a) connected from the metallic case or chassis of the inverter/charger to the engine negative
terminal or its bus;
b) an ampacity equal to that of the DC positive conductor (under certain conditions, there is
an exception to allow this conductor to be one size smaller - refer to the ABYC standard).
2) The inverter/charger’s negative battery terminal and DC grounded conductor (negative cable)
shall not be connected to the inverter case or chassis at the inverter/charger itself.
AC Grounding Connections:
1) The AC grounding conductor (green) shall be connected to the inverter/charger in a manner so
that the AC ground connection will not be disconnected in servicing. This conductor is in addition
to and independent of the DC grounding conductor.
2) The neutral for AC power sources shall be grounded only at the following points:
a) the shore power neutral is grounded only through the shore power cable and not grounded
on board the boat;
b) the inverter neutral shall be grounded at the inverter; and the output neutral shall be
disconnected from ground when the inverter is operating in the charger/pass-through mode.
c) on systems using an isolation transformer or a polarization transformer, the inverter neutral
(and the transformer secondary neutral) may be grounded at the AC main grounding bus instead
of at the inverter.
Note 1: See the ABYC Standard for complete AC/DC grounding requirements.
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