While PV related fires are rare, additional connection points and components are a potential hazard and can therefore increase the risk of fire (see studies). With the implementation of Module Level Shutdown, current certified devices increase component and connection count by a very large multiple under both the UL1741 and UL3741 standards. Arc Fault Circuit Interruption (AFCI) adds an additional layer of safety in preventing PV related fires by interrupting and extinguishing DC PV arcs. However, the AFCI requirement is currently not applied to PV systems with microinverters, which ironically have a much higher component and connection count than other systems with AFCI detection (such as string inverter systems). Therefore, the code is not applied consistently.
Because AFCI is a good safety feature to prevent fires in PV systems, we think that the code should be corrected. Today’s code does not require any arc fault detection below 80V, where microinverters typically operate. Studies have shown that you only need as low as 25V to create a stable serial arc that can lead to a fire. This is well below the 80V threshold. Thus, we believe that this loophole in the code needs to be closed, to provide this safety feature to all systems, regardless of the applied inverter technology. The concern of nuisance tripping will be mitigated via our request to require low electrical noise levels as a standard, since these noise levels are often the root cause of nuisance tripping, as explained here.
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