The 2014 National Electrical Code’s (NEC) new Section 690.12—Rapid Shutdown of PV Systems on Buildings—is creating buzz in the PV industry. And sometimes it is leading to confusion and controversy, as authorities having jurisdiction (AHJs) and PV professionals attempt to interpret and implement the new requirements. (A subsequent “Code Corner” covers possible ways of implementing rapid shutdown using currently available equipment. (See "Part 2" here.)
Section 690.12 only applies to PV system circuits “on or in buildings.” For example, a ground-mounted array with the inverter and utility interconnection not on a building is not required to have rapid shutdown capability. “On” buildings also means you cannot get around this requirement by just running all the PV system circuits on a building’s surface.
The goal is to decrease the risk emergency responders—particularly firefighters—face when they work on a fire at a building with a PV system. Ideally, they should be able to shut off the PV system along with the utility service (if present), preferably with a single switch or disconnect; next best is a readily accessible, clearly labeled switch dedicated to this purpose. The risks are due to:
A power source—the PV array—that continues to be energized when the sun is shining on it. The array is often wired for high-voltage DC which increases arcing hazards, and could become re-energized after fire damage occurs, possibly reigniting a fire.
Batteries—New battery chemistries are being used, which may require new firefighting training and techniques if involved in a fire—or even if they are just in a building that catches on fire, since the batteries will be energized.
Circuits that may be energized by a PV system even if the AC utility service or meter is pulled, or main disconnect is shut off. And components with “terminals on both the line and load sides” may still be energized in the open position.
Inconsistent labeling—In an emergency, how might a firefighter pick out the most important red label to read when there’s a bunch of equipment with red labels? The 2014 NEC refers to the National Electrical Manufacturers Association (NEMA) ANSI Standard Z535.4-2011 (Product Safety Signs and Labels), which governs appropriate signage colors, but this is only an Informational Note—and not necessarily being enforced by AHJs.
The complexity of different system types and configurations—stand-alone, grid-tied, supply-side connections, and different architectures even among systems that are the same “type.”
A rooftop disconnect may not be enough depending on its location in the circuit. Though now required for rooftop combiners per Section 690.15(C), this switch stops current in the circuit, but the box the switch sits in will still have voltage present on one side of the switch and all the way back to the modules, whenever the sun is shining.