INSTALLATION
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Copyright Trace Engineering Company, Inc.
5916 - 195th Street N.E.
Arlington, WA 98223
Telephone: 360/435-8826
Fax: 360/435-2229
www.traceengineering.com
PS Series Inverter/Charger
Part No. 3597
Rev. D: November 23, 1999
SYSTEM GROUNDING
Even system designers and electricians often misunderstand system grounding. The subject is more
easily discussed if it is divided into three separate subjects. The grounding requirements vary by country
and application. Consult local codes and the NEC for specific requirements. Refer to Table 18, Safety
Ground Wire Size Table on page 132 for safety ground wire sizes.
EQUIPMENT OR CHASSIS GROUNDS
This is the simplest part of grounding. The idea is to connect the metallic chassis of the various
enclosures together to have them at the same voltage potential, which reduces the possibility for electric
shock. It also provides a path for fault currents to flow through to blow fuses or trip circuit breakers. The
size of the connecting conductors should be coordinated with the size of the overcurrent devices involved.
Under some circumstances, the conduit and enclosures themselves will provide the current paths.
GROUNDING ELECTRODES/GROUND RODS
The purpose of the grounding electrode (often called a ground rod) is to “bleed” off any electrical charge
that may accumulate in the electrical system and to provide a path for “induced electromagnetic energy”
or lightning to be dissipated. The size for the conductor to the grounding electrode or grounding system is
usually based on the size of the largest conductor in the system. Most systems use a 5/8” (16 mm)
copper plated rod 6 feet (2 meters) long driven into the earth as grounding electrode. It is also common to
use copper wire placed in the concrete foundation of the building as a grounding system. Either method
may be acceptable, but the local code will prevail. Connection to the ground electrode should be done
with special clamps located above ground where they can be periodically inspected.
It is often desirable to use multiple ground rods in larger system. The most common example is providing
a direct path from the solar array to earth near the location of the solar array. Most electrical codes want
to see the multiple ground rods connected by a separate wire with its own set of clamps. If this is done, it
is a good idea to make the connection with a bare wire located outside of the conduit (if used) in a trench,
the run of buried wire may be a better grounding electrode than the ground rods!
Well casings and water pipes can also be used as grounding electrodes. Under no circumstance should a
gas pipe or line be used. Consult local codes and the NEC for more information.
BONDING THE GROUNDING SYSTEM
This is the most confusing part of grounding. The idea is to connect one of the current carrying
conductors (usually the AC neutral and DC negative) to the grounding system. This connection is why we
call one of the wires “neutral” in the North American type electrical systems. You can touch this wire and
the grounding system and not be shocked. When the other ungrounded conductor (the hot or positive)
touches the grounding system, current will flow through it to the point of connection to the grounded
conductor and back to the source. This will cause the overcurrent protection to stop the flow of current,
protecting the system. This point of connection between the grounding system (ground rod, vehicle frame,
boat hull, etc.), the current carrying grounded conductor (AC neutral and DC negative), and the
equipment grounding conductor (green ground wire, equipment ground) is often called a “bond”. It is
usually located in the overcurrent protection device enclosure. Although it can be done at the inverter,
codes do not generally allow it since the inverter is considered a “serviceable” item that may be removed
from the system. In residential systems, it is located at the service entrance panel, after the power has
gone through the kilowatt-hour meter of the utility. In mobile applications (RV and marine), this “bond” is
provided by the different AC sources on board.
Bonding must be done at only one point in an electrical system. Our systems inherently have two
separate electric systems - a DC system and an AC system. This means that two bonding points will
occur in all inverter applications. The bonding point will also be connected to the equipment (chassis)
grounding conductors. It is common to have two separate conductors connect the ground electrode and
the two bonding points. Each conductor should use a separate clamp.
In some countries, the neutral is not bonded to the grounding system. This means you may not know
when a fault has occurred since the overcurrent device will not trip unless a “double” fault occurs. In some
marine electrical codes, this type of system is also used.
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