Which type of structures do PV system dc circuits installed in metal raceways not require AFCI protection when located on?

In the context of photovoltaic (PV) systems, the requirement for Arc-Fault Circuit Interrupter (AFCI) protection is influenced by the type of structure in which the DC circuits are installed. According to the National Electrical Code (NEC), AFCI protection is intended primarily to reduce the risk of electrical fires caused by arcing faults.

When it comes to detached structures, NEC allows for certain exceptions regarding AFCI protection. Specifically, DC circuits associated with solar photovoltaic systems that are installed in metal raceways do not require AFCI protection when they are located on detached structures. This exception is based on the understanding that detached structures are generally not occupied in the same way as residential homes or multi-family units, which have higher occupancy and associated fire risks.

In contrast, residential homes, commercial buildings, and multi-family units typically have higher occupancy levels and corresponding risks of arcing faults, making AFCI protection necessary in those cases. Therefore, the exemption for detached structures reflects a balance between safety considerations and the nature of the electrical installation in less frequently occupied or used buildings.