Rapid shutdown requirements were first introduced in the 2014 Edition of the National Electrical Code (NEC). The rule, as outlined in Sec. 690.12, calls for the string voltage on roof top solar photovoltaic (PV) array conductors to be reduced to less than 30VDC within 30 sec from system shutdown. Only conductors more than 5 ft in length inside a building or located more than 10 ft from an array are affected. It also requires that equipment performing the rapid shutdown must be listed and labeled.
In this technical session, Allen Austin, market development manager, ABB/Thomas & Betts, offered an overview of these Code requirements and presented a number of different types of rapid shutdown devices that are currently available in the market to meet these Code rules.
The goal of this Code rule is to decrease the risk to emergency responders, particularly fire fighters when they work on a fire at a building with a PV system. Austin noted there are a variety of products that can address this problem. They include:
• Micro inverters with integrated rapid shutdown
• AC modules
• DC to DC optimizers with integrated rapid shut down
• Exterior string inverters located within 10 ft of the array.
• Rapid shut down DC boxes located within 10 ft of the PV array with remote activation of shunt trip or contactor device.
Austin also outlined the electrical arrangement associated with each of these product solutions and discussed how they operate to protect first responders during fire fighting activities.
One thing to be aware of on this front is that additional changes have been adopted in the 2017 Edition of the NEC. EC&M will present an overview of the new 2017 NEC requirements in a series of future articles.
