Microinverters Still Safest After 2017 Code Changes

Feb 07, 2017

Microinverters Still Safest After 2017 Code Changes

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 within 305 mm (1 ft.) 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: Enphase 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 over 305 mm (1 ft.) 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.

Speaking of enhanced safety, here’s another way that Enphase is staying ahead of the curve. We’re partnering with leading module manufacturers, such as LG, SolarWorld, and Jinko, to produce factory-integrated AC modules. Because all DC component wiring takes place during production, AC modules improve quality assurance and eliminate one more step from the field installation process. Systems with AC modules therefore remove one more rooftop hazard for firefighters, installers, and all building occupants.

State-by-state adoption

The NFPA and its partners in the Electrical Code Coalition keep tabs on the latest edition of the NEC in effect at the state level and track progress as states advance toward NEC 2017 adoption. As of Jan. 1, 2017, the latest changes had already taken effect in one state, Massachusetts. Another 23 states had begun the process of updating to NEC 2017 while continuing to use older versions of the code.

Visit the Electrical Code Coalition webpage on NEC state adoptions and select your state from the list at the bottom of the page to get more information about the status of NEC changes in your state. For Rapid Shutdown resources from Enphase, click here

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