All GT inverters must be listed by a nationally recognized testing laboratory, such as Underwriters Laboratories (UL), Intertek (ETL), or Canadian Standards Association (CSA). Each of these organizations tests inverters to the same standard, UL1741. Within this standard, the exact requirements for the inverters are outlined to allow tests to be replicated among the various organizations. These safety tests give both consumers and utilities assurance that the inverters will operate safely when installed correctly.
One of the UL1741 tests is “anti-islanding.” Islanding is when an inverter remains connected to the grid and sends power into the lines during a utility outage. This poses a hazard to workers, who may be repairing the lines—an unexpected source of power feeding those lines puts them at risk for injury. To prevent this, GT inverters have built-in safety switches, isolating them from the grid as soon as grid voltage or frequency goes off-specification. The inverter continues to monitor the grid; and once the grid has returned to normal operating conditions for five continuous minutes, the inverter resumes sending energy from the PV array to the grid.
The UL1741 testing also checks inverter equipment for components that reduce shock hazards, verifies that cabinet space is large enough for the wires that will be installed, and establishes safety labeling requirements, along with other safety requirements.