manually resume exporting power to the utility once the primary source is restored.
FPN No. 1: Risks to personnel and equipment associated with the primary source could occur if an utility interactive electric power production source can operate as an intentional island. Special detection methods are required to determine that a primary source supply system outage has occurred and whether there should be automatic disconnection. When the primary source supply system is restored, special detection methods can be required to limit exposure of power production sources to out-of- phase reconnection.
FPN No. 2: Induction-generating equipment on systems with significant capacitance can become self-
excited upon loss of the primary source and experience severe overvolt-age as a result.
A utility-interactive inverter shall be permitted to operate as a stand-alone system to supply loads that have been disconnected from electrical production and distribution network sources.
705.42 Loss of 3-Phase Primary Source. A 3-phase electric power production source shall be automatically disconnected from all ungrounded conductors of the interconnected systems when one of the phases of that source opens. This requirement shall not be applicable to an electric power production source providing power for an emergency or legally required standby system.
Exception: A listed utility-interactive inverter shall be permitted to automatically cease exporting power when one of the phases of the source opens and shall not be required to automatically disconnect all ungrounded conductors from the primary source. A listed utility-interactive inverter shall be permitted to automatically or manually resume exporting power to the utility once all phases of the source are restored.
705.50 Grounding. Interconnected electric power production sources shall be grounded in accordance with Article 250.
Exception: For direct-current systems connected through an inverter directly to a grounded service, other methods that accomplish equivalent system protection and that utilize equipment listed and identified for the use shall be permitted.
II. Utility-Interactive Inverters 705.60
Circuit Sizing and Current.
(A) Calculation of Maximum Circuit Current. The maximum current for the specific circuit shall be calculated in accordance with 705.60 (A)(1) and (A)(2).
(1) Inverter Source Circuit Currents. The maximum cur- rent shall be the maximum rated input current of the inverter.
(2) Inverter Output Circuit Current. The maximum cur- rent shall be the inverter continuous output current rating.
(B) Ampacity and Overcurrent Device Ratings. Inverter system currents shall be considered to be continuous.
(1) Sizing of Conductors and Overcurrent Devices. The circuit conductors and overcurrent devices shall be sized to carry not less than 125 percent of the maximum
currents as calculated in 705.60(A). The rating or setting of overcurrent devices shall be permitted in accordance with 240.4(B) and (C).
Exception: Circuits containing an assembly together with its overcurrent device(s) that is listed for continuous operation at 100 percent of its rating shall be permitted to be utilized at J 00 percent of its rating.