Magnum Energy MSH-M Series - Manual (Page 35)

Page 26
©
2013 Magnum Energy, Inc.
Installation
2.6.5 Neutral to Safety Ground Bonding
The standards for safely wiring RV, truck, and marine 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 specifi 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.
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 AC 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 MSH-M is designed to specifi cally work in multiple
source or mobile (i.e., truck/RV/boat) applications, and requires the AC source connected to the
inverter’s input to have a bonded neutral. The MSH-M uses an internal relay that automatically
connects the AC neutral output terminal to the vehicle/boat’s ground while inverting (Inverter
mode) to provide the neutral-to-ground bond; as shown in Figure 2-11. 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 MSH-M 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 2-12. This design keeps two neutral-to-ground connections from occurring at the
same time, thereby preventing an electrical shock hazard between the vehicle/boat’s neutral and
the external AC source’s neutral.
GROUND
NEUT IN
Inside MSH-M Series
Inverter /Charger (Inverter Mode)
NEUT OUT
Neu-Gnd Relay (K1)
GROUND
NEUT IN
Inside MSH-M Series
Inverter /Charger (Standby Mode)
NEUT OUT
Neu-Gnd Relay (K1)
Figure 2-11, Neutral-to-Ground
Connection (Inverter Mode)
Figure 2-12, Neutral-to-Ground
Connection (Standby Mode)