Rapid Shutdown of Photovoltaic Systems
Posted in: July 2014
This was a concept that caused a lot of anguish and pain throughout the PV industry. Many comments and proposals regarding this topic were presented to Code Making Panel 4 regarding this issue. Questions arose such as: What does it do? How will we implement this? Is it technically possible? All needed to be addressed by the panel.
Article 690.12 is new for the 2014 National Electrical Code. This article requires any PV system circuits that are installed on or in buildings to have a rapid shutdown feature. As the language contains the word “building,” this requirement does not apply to a ground-mounted array or pole-mounted system.
This code change addresses a concern championed by firefighting officials that there is no practical way to de-energize a PV system. Even at night, a PV system can potentially have voltage across the array. Firefighting officials were looking to safeguard fire fighters and other emergency personnel when a PV system was encountered in an emergency. To address their concern, the code limits the uncontrolled conductor length from a PV system to 10 feet (3m) from the array or 5 feet (1.5m) inside of a building. The Code Panel justified the length limitations by modeling after a requirement to label conduit at 10 feet (3m) intervals as well as a 5 feet (1.5m) limit to battery conductors before a disconnect. This essentially creates a “safe zone” around the array where an emergency responder can reasonably expect not to encounter energized conductors from a PV system. Labeling requirements are also a part of this article to notify emergency personnel of the presence of a rapid shutdown system.
So, what’s the solution? As of this writing, I am not aware of any listed product solely for rapid shutdown as there is no rapid shutdown listing. The Code Panel wanted to make sure that industry implementation could occur as quickly as possible without having to wait for new listing requirements or special testing procedures. They did this by merely requiring the products used for rapid shutdown to be listed and identified. Listed components on the market are available that can perform the required function, such as a listed PV combiner boxes with shunt trip. Another solution to implement rapid shutdown is to use micro inverters. Micro inverters inherently comply as the AC wiring connecting modules is a branch circuit that will de-energize upon the loss of utility power. The PV system conductors are only at the module which satisfies the length limitation found in paragraph 1 of 690.12. System layout can also be a solution if the design calls for string inverters to be located within 10 feet (3m) of the array. Although, locating string inverters near the array may not always be practical, especially in residential applications.
The code does not address the means and methods of how to accomplish the requirement as not to stymie innovation. The code also does not address where to locate a disconnecting means or any controlling equipment. The idea is simple, some means of disconnect must be used. As usual, the Authority Having Jurisdiction (AHJ) will have their input. When in doubt, consulting with the AHJ prior to install is always recommended. Changes are always cheaper when they are made on paper.
Adam Corbin is Vice-President of Corbin Electrical Services, Inc. and Vice-President of Corbin Solar Solutions, LLC. He is a licensed Master Electrician and NABCEP Certified PV Installation Professional. Corbin has served on Code Making Panel 3 since 2003.