Xantrex Technology Inc. (Arlington, WA) released special instructions for its dealers to address questions surrounding its Trace SW inverter. Last month, Underwriters Laboratories Inc. (UL) said models SW4024, SW4048 and SW5548 do not comply with certain requirements of the UL 1741 standard, and may pose a hazard under specific circumstances.
The standards organization said some grid-tie installations with the “sell” mode enabled may support an unintentional island, and may continuously generate and feed power into the transmission line at the tested power levels of 25, 50 and 100 percent. In addition, the total harmonic distortion may exceed the limit of five percent when the inverter is exporting power, and the problem is most apparent when the SW inverters are connected to low-impedance utility lines.
UL noted that the SW inverters manufactured before November 2000 or installed in off-grid or in backup applications comply fully with all UL requirements and retain a full listing. The alert did not require grid-interactive units to be removed from service, and left each utility to make its own decision.
Xantrex recommends that utilities accept or “grandfather” the pre-November anti-island protection levels for existing SW installations. If utilities require additional information, Xantrex recommends that system owners disable the “sell” feature to prevent the export of power.
