Code Corner: Rapid Shutdown of PV Systems: Part 1

Because these circuits are within 10 feet of the PV array, they are not subject to rapid shutdown requirements.
Even those these PV output circuits don’t penetrate the building, they are on the building and portions are more than 10 feet from the array­, so a means of rapid shutdown is required.
The inverter and interconnection point in this grid-tied PV system is on an exterior wall. PV circuits that are on the building, but less than 5 feet in length, do not require rapid shutdown.
This rooftop combiner box has a contactor that can be activated either with a dedicated switch or by shutting off the AC service to the building. It is within 5 feet of the connected PV array.
MidNite Solar’s Birdhouse is designed specifically for disconnecting a rooftop PV array—as well as other PV system circuits—at ground level.

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.

Comments (3)

Edward-Dijeau's picture

Micro inverter based Solar panel systems with the micro inverter intigrated into the back of each solar panel meets this reqirment because of the built in electronics that shuts down the output and shunts the panel, but, series wired high voltage inverters would require a remotly fired DPDT Relay(s) that would open all the series conections and Shunt their panels at the same time when it was dropped out , either by utility power loss or fired off switch at the Meter disconect.

kathy swartz's picture

Hi Meredith, as I understand it your inverter is located at the array and not on the building, and this is a grid-direct system without batteries. As such, shutting off power to the building will shut down the inverter and de-energize all circuits related to the PV system that touch the building. Therefore meeting the rapid shutdown requirement is as simple as putting a label on the main utility disconnect. The minimum language in 690.56(C) would suffice, but also amending it to state something to the effect of "the PV system shuts down and all circuits touching the building are de-energized upon shutting off the utility" would be helpful for emergency responders. (Posted by Brian, accidentally using Kathy's login! :)

Meredith Bond's picture

I am installing a grid-tied ground-mount 7500W PV system. The AHJ annotated my permit with a sticker that says: "RAPID SHUT DOWN AND LABEL REQUIRED PER ART. 690.12 AND 690.56(C)." Everything that I can find about the requirements of 690.12 discuss roof-mount systems, PV-related circuits (and primarily DC wiring) within the house, and firefighter safety. My inverter will be at the ground-mount PV array, some 300+ feet of underground buried cable away from the house. The AC disconnect mounted at the house will serve to totally disconnect all solar PV system related supply immediately upon dropping that switch. While there will be about 10 feet of AC cable within the house (between that exterior mounted and labeled AC disconnect and my load center panel in the basement), that can be isolated from the entire solar power supply by dropping the AC disconnect. In my estimation, that meets the requirement of 690.12 - looking for others' thoughts before I call up the AHJ to discuss... I note that my county only adopted the 2014 NEC a few months ago, so I anticipate the plan reviewers and inspectors are learning the ins-and-outs of this new requirement, too.

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