AC AFCI for PV systems with microinverters or AC PV Modules

PV systems that utilize microinverters or AC PV Modules provide an alternate source of AC power within the wiring of a residential building structure, and AC Arc Fault Circuit Interrupters (AFCI) should therefore be present on these exterior branch circuits to also protect from potential AC arc faults. New and remodeled residential structures and interior wiring have been protected by NEC required AC AFCI since 2002. The branch circuits with microinverters or AC PV Modules are exposed to weather, aging, and the environment – all things that can contribute over many years to the potential for AC arcing.

The 2011 NEC now requires PV DC AFCI to provide enhanced protection from DC arcing events for rooftop, grid tied PV systems that have DC voltages above 80V. Although microinverters and AC PV modules limit the DC voltage present to what is produced by a single module (vs. a string), the potential for an AC arc fault is still present on the 240VAC, 15-20A branch circuit and associated AC PV wiring. The AC PV wiring harness that daisy chains 1-16 AC PV modules or microinverters together on a branch circuit also introduces more connections and increased the probability for an arcing condition.

We will discuss the risk of arc fault events and the consequences for rooftop PV systems; proposed 2014 National Electric Code (NEC) and UL1699 requirements for PV AC arc fault circuit interrupters on AC PV branch circuits; types of arc faults; means of detection; and arc fault protection solutions.