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©
2009 Magnum Energy Inc
.
Installation
2.6.5
Neutral to Safety Ground Bonding
The standards for safely wiring residential, commercial, RV/truck and marine installations in the
United States require the neutral and safety ground be connected at the AC source; whether it is
the utility feed in your home, 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 hot-wire-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., utility power 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:
In most electrical systems, the neutral-to-ground “bond” is located in the
main utility service entrance panel. Remove any “bond” downstream from the inverter
to prevent multiple bonds. If there is an inverter subpanel - separate from a “main”
electrical panel - it should have a removable wire that allows the neutral buss to be
unbonded from the ground buss bar.
All MS Series Inverter/Chargers have automatic neutral-to-ground switching to speci
fi
cally work
in multiple source applications. The MS Series inverters use 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
fi
gure 2-20. However, when an external
AC source (i.e. shore power or a generator) is quali
fi
ed, another neutral-to-ground connection is
introduced in the system. When the MS Series 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
fi
gure 2-21. 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.
N eutral-to-Ground connection
(inside AC com partm ent)
GR OU N D
N eu-Gnd R elay (K 1)
N EU T IN
In s id e M S S e rie s In v e rte r /C h a rg e r
(In v e rte r M o d e)
N EU T OU T
N eutral-to-Ground connection
(inside AC com partm ent)
GR OU N D
N eu-Gnd R elay (K 1)
N EU T IN
In s id e M S S e rie s In v e rte r/C h a rg e r
(S ta n d b y M o d e)
N EU T OU T
Figure 2-20, Neutral-to-Ground
Connection (Inverter Mode)
Figure 2-21, Neutral-to-Ground
Connection (Standby Mode)
