In 2014, section 690.12 “Rapid Shutdown of PV Systems on Buildings,” was included in the National Electrical Code to safely allow firefighters and emergency responders to easily and quickly shut down energized PV system circuits on buildings. Here, we’ll explain what needs to happen and which PV circuits are subject to this Code requirement, and discuss the methods and equipment available to achieve compliance. Additionally, we look forward to the upcoming 2017 NEC and how changes to the Code will impact rapid shutdown requirements.
Why is Rapid Shutdown (RSD) Needed?
Residential PV arrays are commonly installed with series string voltages up to 600 VDC (non-residential systems up to 1,000 VDC). A simple rooftop DC disconnect cannot protect emergency responders from these high voltages—during the day, full array voltage is produced on the conductors up to the input side of that disconnect. And on the output side of the DC disconnect, capacitors in the inverter can create high voltage between the DC disconnect and the inverter. Article 690.12 proposes solutions to rapidly reduce voltage to an acceptable level.
2014 NEC 690.12 Requirements
This NEC section is broken into five subsections. In 690.12(1), the NEC specifies which conductors must be controlled by a RSD method—PV system conductors of more than 5 feet in length inside a building, or more than 10 feet from a PV array. The 2014 NEC permits having a 10-foot zone around the PV array within which PV circuits on a building can still be at high voltage after shutdown is activated. This area will be reduced in the 2017 NEC as RSD requirements become more restrictive.
Sections 690.12 (2) and (3) specify that when RSD is activated, controlled conductors must be no more than 30 V (with a maximum power of 240 volt-amps) within 10 seconds. 30 V is considered the “touch-safe” voltage limit in wet environments. This voltage still allows for 24 V control circuits to be used, to allow RSD methods using contactors. Limited voltage and power is measured between any two current-carrying conductors and also between any conductor and ground.
Part 4 of 690.12 requires labels be provided, informing responders that the system is equipped with RSD, with instructions on how to initiate shutdown. Lastly, 690.12(5) specifies that equipment must be listed and identified, but not specifically for PV systems—off-the-shelf contactors, motorized switches, and shunt trip breakers can be used. This is another subsection that will be changing in the 2017 NEC. Under the 2014 NEC, installers can use any listed equipment to provide RSD, as long as it’s not installed in a way that could violate the product’s listing.