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©
2020 Sensata Technologies
Installation
2.6.4
Neutral to Safety Ground Bonding
The standards for safely wiring RV installations in the United States require the neutral and safety
ground to be connected at the AC source; whether it is a shorepower feed, an inverter, or a
generator. This is to establish a speci
fi
cation that maximizes the possibility that a circuit breaker
will activate if a hotwire-to-ground fault occurs. These standards also require that the AC neutral
be connected to safety ground (often called a “bond”) in one, and only one, place at any time. The
single bond is established in order to make the electrical panel’s neutral line safe, by connecting
it to ground. Without this bond, the neutral can have up to 60 VAC with respect to ground. On
the other hand, if more than one bond is established, currents can circulate between neutral and
ground and cause “ground-loop” currents. These ground-loops can trip GFCIs, cause an electric
shock hazard, and may be the reason for other annoying side effects.
In applications where you are using an inverter as one of your AC sources along with another
AC source (i.e., shorepower or generator), there is the potential of having multiple connections
(bonds) between neutral and ground. Therefore, you must ensure that the inverter does not also
connect the neutral-to-ground while the other AC source is actively powering the inverter loads.
This can be prevented if your inverter is equipped with automatic neutral-to-ground switching,
similar to what is included in the MSH3012RV.
WARNING:
Whether the AC input source to the inverter is an external AC hook-up
(i.e., shorepower) or an onboard AC generator, the inverter’s automatic neutral-to-
ground bonding system requires the input source to have the neutral-to-ground bond.
Also, any bond downstream from the inverter must be removed to prevent multiple
bonds. If there is an inverter sub-panel—separate from a main electrical panel—it
should have a removable wire that allows the neutral bus to be unbonded from the
ground busbar.
The automatic neutral-to-ground switching in the MSH3012RV is designed to speci
fi
cally work in
RV applications, and requires the AC source connected to the inverter’s input to have a bonded
neutral. The MSH3012RV uses an internal relay that automatically connects the AC neutral output
terminal to the vehicle’s ground while inverting (Inverter mode) to provide the neutral-to-ground
bond; as shown in Figure 2-13. However, when an external AC source (i.e., shorepower or a
generator) is connected, another neutral-to-ground connection is introduced in the system. When
the MSH3012RV is connected to this external AC source and goes into Standby mode, the internal
relay automatically opens the neutral-to-ground connection as shown in Figure 2-14. This design
keeps two neutral-to-ground connections from occurring at the same time, thereby preventing an
electrical shock hazard between the RV’s neutral and the external AC source’s neutral.
GROUND
NEUT IN
Inside MSH3012RV Series
Inverter
/Charger (Inverter Mode)
NEUT OUT
Neu-Gnd Relay (K1)
GROUND
NEUT IN
Inside MSH3012RV Series
Inverter
/Charger (Standby Mode)
NEUT OUT
Neu-Gnd Relay (K1)
Figure 2-13, Neutral-to-Ground
Connection (Inverter Mode)
Figure 2-14, Neutral-to-Ground
Connection (Standby Mode)
