©
2013 Magnum Energy, Inc.
Page 25
Installation
2.6.4
Grounding on Boats
When installing the MSH-M 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 to adhere to ABYC (American Boat and Yacht Council) standards.
Ensure a Safe Ground Connection
When AC on the boat is being supplied by shorepower, 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 shorepower is present. When AC on the boat is being supplied by
the MSH-M Series inverter, the inverter’s output neutral is connected to safety ground through an
internal relay, using its neutral-to-ground connection (shown in Figure 2-11).
The DC ground terminal on the MSH-M Series must also be connected to the boat’s safety ground
bus. This ensures that both the inverter’s AC and DC ground terminals are connected to the boat’s
safety ground bus as a safety measure to provide protection against faults, and to provide a path
for AC fault currents while the boat is connected to shorepower.
Preventing the Risk of Corrosion
The inverter’s AC and DC ground terminals must be connected to the boat’s 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 onboard grounding requirements
while greatly reducing (if not eliminating) the risk of galvanic corrosion. These solutions would be
either using a galvanic isolator or an onboard isolation transformer.
Connecting a galvanic isolator between the shorepower inlet and the AC breaker/panel 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 the 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) of 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 shorepower neutral is grounded only through the shorepower 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.
