Xantrex Technology 120 VAC/60 Neutral-To-Ground Bond Switching Rv And Marine Applications, Page

INSTALLATION

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 used.

NEUTRAL-TO-GROUND BOND SWITCHING (RV AND MARINE APPLICATIONS)

As required by NEC code and UL specification 458, inverter/charger installations in the U.S. that are used in RV or Marine applications employ ground-to-neutral switching. The purpose for this requirement is to ensure that all the neutral conductors are connected (“bonded”) to a single ground point in a three-wire (hot, neutral and ground) AC system. This prevents a voltage difference from developing between the vehicle/boat’s AC neutral and the external AC source’s (generator or shore power) neutral, which may cause an electric shock or cause nuisance tripping of GFI’s. The SW Series Inverter/Charger does not include Neutral-to-Ground switching and must be provided in the AC installation.

When the unit is operating as an inverter, the AC output neutral should be connected or “bonded” to the frame/hull (chassis ground). When an external AC source (AC shore cord) is provided, the inverter’s AC output neutral should be disconnected from the frame/hull (chassis ground) and allow the “bond” to be provided by the external AC source. The requirement to switch the neutral can be met by your inverter internally or can be easily met by using an external relay to connect and disconnect the external AC source’s neutral. If another AC source (on-board generator) is included in the RV or boat, this AC source neutral is required to be connected to ground when it is being used, and to disconnect all other neutrals from ground. An AC transfer switch can be used if it switches both the shore cords and generators neutral.

In some marine applications, neutral-to-ground switching is not required or acceptable. The potential for galvanic corrosion caused by small leakage currents between boats with dissimilar metals is present. The proper and safe ways to prevent this is by using galvanic isolators or include an isolation transformer for the AC input. Disconnecting the common ground between the AC and DC system could contribute to a hazardous and potentially fatal situation.

The figures below graphically describes the neutral-to-ground switching system for the two cases in question: the unit operating as an inverter feeding the AC subpanel, and the unit connected to an external AC source (generator, shore power, etc.).

No external AC

source is present

NEUTRAL-TO-GROUND

“BOND” is provided by this relay

for the entire AC system

INVERTER

NEUTRAL-TO-GROUND SWITCHING RELAY (provided in the AC installation): Connects the output neutral to chassis or vehicle ground when AC is not present at inverter input. This assures all equipment in the vehicle is referenced to the same

(AC Terminal Block)

AC HOT IN

AC NEUTRAL IN

EARTH GROUND

CHASSIS GROUND

RY1

AC HOT OUT

AC NEUTRAL OUT

ground.

AC PANEL
(RV/Marine)
HOT	NEUTRAL
GROUND

The neutral conductor should not be connected to the

equipment grounding

conductors or enclosures.

Figure 12, Neutral-To-Ground Bond Switching: No External AC Source Connected

 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

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