Development of Arc-Fault Circuit-Interrupter requirements for Photovoltaic systems

Photovoltaic systems, which typically consist of an array of PV modules, are often associated with buildings, where the PV system components can either be mounted to the building, such as on the roof, or integrated into the building structure. The 2011 edition of the National Electrical Code® (NEC®) will require all PV systems with DC circuits operating at 80 volts or greater on a building to be protected by a listed Arc-Fault Circuit Interrupter (AFCI), PV type, or other system components listed to provide equivalent protection. In response to this new NEC requirement, Underwriters Laboratories Inc. (UL) has developed the 1st Issue of the Outline of Investigation for Photovoltaic DC Arc-Fault Circuit Protection, designated Subject 1699B. This new Outline includes requirements for listing PV arc-fault circuit interrupters (PV AFCIs), arc-fault detectors (AFDs), and associated interrupting devices (IDs). These requirements will also address inverters, converters, and charge controllers with integral AFCI protection. In addition to using existing requirements from the UL1699 Standard for Arc-Fault Circuit-Interrupters for residential (AC) arc-fault protection developed in the 1990s, this new Outline includes special DC arc fault detection tests that were developed from more recent research. This paper presents the feasibility of DC arc fault protection in PV systems, and the development of the safety requirements for this protection. It will also address the various types of arcing faults in PV systems, and the challenges for arc fault detection schemes in being able to respond to this arcing and mitigate the risk of fire ignition.