Latest Release From Enphase regarding micro inverters and why they are the safest system on the market.
"Microinverters Still Safest After 2017 Code Changes"
Rooftop solar will be safer for US homeowners and installers thanks to recent changes in the electrical code used by permit inspectors across the country.
As each state adopts the 2017 edition of the National Electrical Code (NEC), high voltage will be restricted to the solar module array. That’s good news, because Enphase already complies with the 2017 NEC. But it’s important to remember that tighter safety standards don’t mean that all solar technologies will become as safe as Enphase technology.
We’ll talk more about Enphase safety features later in this article. First, let’s go over the code changes that affect rooftop solar safety and the reasons why those code changes were introduced. Next, we will explain how different types of residential solar technology satisfy code requirements limiting where high voltage can go. Lastly, we’ll help you look up the latest version of the NEC that’s been adopted in your state and check where the process of adopting the 2017 code changes has already begun.
What’s new in 2017
The National Fire Protection Association (NFPA), a 120-year-old trade association representing public safety personnel, is tasked with updating the NEC every three years. The 2014 edition introduced a significant change for rooftop solar, requiring energized DC conductors outside of the array area to operate at less than 30 volts within 10 seconds any time the inverter is cut off from utility service, leaving no wires energized more than 5 feet inside a building or 10 feet from the solar module array. The rapid shutdown requirement protects firefighters from unnecessary risks when providing emergency response at a solar-powered home.
In 2017, the NFPA strengthened the rapid shutdown requirement with two additions. High voltage can no longer extend 10 feet outside of the array; it’s restricted to the boundary of the array. And rapid shutdown equipment must be independently tested and recognized as compliant with the 2017 NEC. These changes give firefighters added confidence and may point the way toward further code changes down the road that improve safety even more.
Compliance: Microinverters vs. string inverter systems.
Rapid shutdown compliance comes automatically with Enphase. Here’s why: In the Enphase system, a microinverter beneath each module converts low-voltage direct current (DC) to alternating current (AC). When the sun is shining, each microinverter verifies that its module does not have a ground fault and the grid is operating normally before exporting power. If the grid has a failure or the AC wires are disconnected, the microinverters stop producing power very quickly, in a fraction of a second. Without a connection to the grid, our microinverters cannot export current or voltage, or energize connected wiring.
Systems with string inverters, including those with additional DC power optimizers behind each module, require workarounds to comply with the 2014 NEC. They need a specialized rapid shutdown electrical box installed on the roof, within 10 feet of the array, and a ground-level shutoff switch that’s easily accessible to first responders. These changes can require an additional run of conduit connecting the two extra pieces of equipment. Once the 2017 code changes take effect, a solar system with high voltage running 10 feet from the array boundary will need yet another workaround.
The way Enphase handles rapid shutdown compared to how string inverter technologies do this hints at a larger philosophical difference in the approach to system architecture, one that cannot be resolved by costly and cumbersome workarounds. Enphase achieves industry-leading performance from an all-AC system with inherently low voltage. String inverter systems build up DC voltage from module to module, generating power from dangerously high voltage. They can temporarily bring individual units down to a voltage level allowed by code, but lower voltage is, by nature always, safer.