UL ALERT: Xantrex SW-series PV Inverters May Pose Hazard

source: UL website 2001.11.16

Underwriters Laboratories Inc. (UL) is notifying electric utility companies,
installers and authorities having jurisdiction (AHJs) that Xantrex Technology or Trace Engineering
photovoltaic inverter models SW3512, SW4024, SW4048 and SW5548 may: 1) support an unintentional
island in the presence of a balanced load, when utility power is interrupted; and, 2) exceed the output
current total harmonic distortion limit.

Results of operational tests recently conducted by UL during field investigations revealed that SW series
inverters may not cease to export power to the utility grid when power from the grid is interrupted in the
presence of a balanced load. The SW series inverters may continuously sustain an unintentional island
condition under multiple balanced test load conditions while exporting power at the tested 25%, 50% and
100% power levels.

Unintentional islanding occurs when a utility interactive inverter energizes a portion of the utility grid system
when power from the grid is interrupted. Unintentional islanding may create a risk of electric shock for utility
line personnel by causing a utility line to remain energized when it is assumed to be disconnected from all
energy sources. This islanding condition may also cause damage to utility equipment, interfering with the
operation and or restoration of normal utility service.

In addition, the SW series inverters'output current total harmonic distortion may exceed the 5% limit
required by UL 1741, the Standard for Inverters, Converters and Controllers for Use in Independent Power
Systems and IEEE929, the Recommended Practice for Utility Interface of Photovoltaic (PV) Systems when
the inverter is exporting power onto the utility grid. This problem is most apparent when the SW inverters
are connected to low impedance utility lines.

Installed in both the U.S. and Canada, these devices are not authorized to bear the UL Mark.

For additional information from UL, contact Tim Zgonena at 847-664-3051 or via e-mail at
Timothy.P.Zgonena@us.ul.com.

Additional information on this subject is available from Xantrex at www.traceengineering.com.