©
2015 Sensata Technologies
17
2.0 Installation
2.5.3 AC Neutral to Safety Ground Bonding
Electrical safety standards for 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 the utility feed in the RV Park/Marina, an inverter, or
a generator. This is to establish a specification 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 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.
CAUTION:
The AC input neutral terminal is electrically isolated
from the AC output neutrals terminals (N1/N2) while inverting. This
is related to the neutral-ground bonding requirement and helps
prevent ground-loops. The input neutral and output neutrals must
not an any time be connected together or damage to the inverter
may occur.
The CSW2012-X
inverter has
automatic neutral-to-ground switching to
specifically work in multiple source or mobile (i.e., truck/RV/boat) applications.
The
CSW2012-X inverter
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. 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
CSW2012-X inverter
is connected to this external AC source and goes into
By-Pass mode, the internal relay automatically opens the neutral-to-ground
connection. 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.