The word on the street in my inverter beat at Intersolar North America mainly revolved around NEC 2014. The new national electric code will guide installation and design while making solar systems safer for owners, technicians and first responders like firefighters. This code is updated every three years, and two major focuses of this year’s edition for inverter manufacturers concern arc fault protection and rapid shut-down.
Arc Fault Circuit Protection (DC)
NEC 2011 established arc-fault protection requirements for DC PV circuits, but only for systems with a maximum voltage more than or equal to 80 VDC and with DC circuits on or entering a building. But NEC 2014 expands these requirements to all systems at this voltage no matter where they are. The intention is to help protect people and property from damage due to fires, which can of course occur on ground-mounted arrays as well as on the roof. Arc fault protection can help prevent these risks.
Many string inverter manufacturers at the show say they already integrate arc-fault protection. But designers using central inverters may need to include it at the combiner box–level. Microinverters and power optimizers could provide arc-fault detection at the module-level.
Rapid Shutdown On Buildings
Also, to improve fire and electrical safety, NEC 2014 requires that PV system conductors (wires) have to be able to be “de-energized” (or powered down) at any given time. The idea is to be able to shut down any electricity flowing through wires that run more than 10 feet from the array, or more than 5 feet within a building. These wires are limited to maxing out at 30V and 240VA within 10 seconds of shutdown. As one inverter manufacturer at the show explains, firefighters and other professionals expect voltage to be flowing close to the PV array, but they don’t always realize it may be flowing at a separate location, such as when string inverters are not placed directly near the array on the roof.
The requirement may also be met using combiner boxes as long as they are placed within 10 feet of the array and the control switch or button is in an accessible location. Some manufacturers have also specified DC to DC inverters that meet rapid shutdown requirements for systems on buildings.
Again, most inverter manufacturers at the show don’t seem concerned or phased by these requirements. Their models are NEC 2014 ready, as they support meeting the the code that continues to ensure a safe and successful solar industry for all.
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