Rapid Shutdown is a concept of assuring PV system safety introduced by US National Electrical Code (NEC). The main purpose is to protect firefighters, PV system installers and maintenance personnel. Back in 2014, NEC issued the standard “Component Level self-shutdown Solution” (NEC2014 690.12), which explicitly required that all PV systems in buildings should be equipped with rapid-shutdown switches, and the DC voltage of PV system needs to drop below 30V within 10 seconds. In the 2017 edition of NEC690.12, there was more specific requirement for this rapid shutdown – with a distance of 305mm from the PV array set as a limit, within 30 seconds after initial the rapid-shutdown switch, the DC voltage should drop below 30V outside the limit range and below 80V within the limit range.
PNNL’s Paiss recently retired from his post as captain for the San Jose Fire Department after 23 years. He never dealt with a structure fire involving solar PV during his tenure, but he knows the importance of protecting first responders and homes as solar becomes more common — and systems installed in the past show signs of aging. These issues were front of mind when he worked on developing rapid shutdown requirements in the NEC.
“Our concern was multi-pronged. It wasn’t just the safety of the responders. When you reduce the voltage, you reduce the energy available to start fires. You don’t eliminate it, but you reduce it. So, we were concerned about the number of fires being started by faulty wire management, arc faults not being detected, and as these systems age and installation breaks down, there’s going to be a higher likelihood of additional faults,” Paiss said. “If the system had rapid shutdown [ability], if there was a fault that is detected, one of the requirements of the NEC is that it initiate and put itself into a safe state.”
The solar installers and owners need a reliable and durable Rapid Shutdown Solution which would be effective during the whole PV panels life cycle. TSUN Rapid Shutdown Control Unit is a cost-effective rapid shundown device. Through one-button operation, the DC high voltage will be limited to the roof or near the modules. In emergency situations such as fire, the personal safety of firefighter is protected to a certain extent to avoid electric shock accidents.