Xantrex Technology SW Series owner manual System Grounding, Equipment or Chassis Grounds

INSTALLATION

SYSTEM GROUNDING

GROUNDING INSTRUCTIONS - This inverter/charger should be connected to a grounded, permanent wiring system. For most installations, the negative battery conductor should be bonded to the grounding system at one (and only one point) in the system. The subject is more easily discussed if it is divided into three separate subjects; Chassis Ground, Ground Rods and Bonding. The grounding requirements vary by country and application. All installations should comply with national and local codes and ordinances. Even system designers and electricians often misunderstand system grounding. Consult local codes and the NEC for specific requirements. Refer to Table 15, page 133 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.

Many large systems use multiple ground rods. 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 enclosures (both AC and DC). 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, see NEUTRAL-TO-GROUND BOND SWITCHING (RV AND MARINE APPLICATIONS) on page 27.

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.

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 2001 Xantrex Technology, Inc.	Telephone: 360/435-8826	SW Series Inverter/Charger
5916 - 195th Street N. E.	Fax: 360/435-2229	Part No. 2031-5
Arlington, WA 98223	www.traceengineering.com	Rev. C: February 2001