Rapid shutdown for PV systems on habitable buildings was introduced to protect firefighters and allow for the DC side of a system to be de-energized. This was first introduced in the 2014 NEC and was built upon in the 2017 NEC.
During an emergency, first responders will activate the rapid shutdown system and safely access the roof, knowing that all DC conductors will be de-energized if they are more than 1 foot from the array.
Rapid Shutdown Overview
The National Electric Code can be a very intimidating and confusing “rule book” when it comes to solar.
690.12 covers the rapid shutdown of PV systems on buildings. Microinverters easily comply with rule 690.12 as long as the microinverter is mounted within 1 foot of the array’s edge. The common practice is to mount the microinverters to the rail and therefore are within the array boundary and would comply with this rule.
String inverters are a different story when it comes to rapid shutdown. Each string must be limited to 80VDC within 30 seconds of initiation of rapid shutdown. For these applications, Module Level Power Electronics are used (MLPE). Optimizers and RSD (rapid shutdown device) are the most common. RSD are cheaper than optimizers and can be utilized on arrays that do not see any shading.
Rapid Shutdown section directly from the NEC 2017:
690.12(A) and (B)(1):
690.12 Rapid Shutdown of PV Systems on Buildings.
PV system circuits installed on or in buildings shall include a rapid shutdown function to reduce shock hazard for emergency responders in accordance with 690.12(A) through (D).
(A) Controlled Conductors. Requirements for controlled conductors shall apply to PV circuits supplied by the PV system.
(B) Controlled Limits. The use of the term, array boundary, in this section is defined as 305 mm (1 ft) from the array in all directions. Controlled conductors outside the array boundary shall comply with 690.12(B)(1) and inside the array boundary shall comply with 690.12(B)(2).
(1) Outside the Array Boundary. Controlled conductors located outside the boundary or more than 1 m (3 ft) from the point of entry inside a building shall be limited to not more than 30 volts within 30 seconds of rapid shutdown initiation. Voltage shall be measured between any two conductors and between any conductor and ground.
(2) Inside the Array Boundary. The PV system shall comply with one of the following:
(1) The PV array shall be listed or field labeled as a rapid shutdown PV array. Such a PV array shall be installed and used in accordance with the instructions included with the rapid shutdown PV array listing and labeling or field labeling.
(2) Controlled conductors located inside the boundary or not more than 1 m (3 ft) from the point of penetration of the surface of the building shall be limited to not more than 80 volts within 30 seconds of rapid shutdown initiation. Voltage shall be measured between any two conductors and between any conductor and ground.
(3) PV arrays with no exposed wiring methods, no exposed conductive parts, and installed more than 2.5 m (8 ft) from exposed grounded conductive parts or ground shall not be required to comply with 690.12(B)(2).
The requirement of 690.12(B)(2) shall become effective January 1, 2019.
(C) Initiation Device. The initiation device(s) shall initiate the rapid shutdown function of the PV system. The device “off” position shall indicate that the rapid shutdown function has been initiated for all PV systems connected to that device. For one-family and two-family dwellings, an initiation device(s) shall be located at a readily accessible location outside the building. The rapid shutdown initiation device(s) shall consist of at least one of the following:
(1) Service disconnecting means
(2) PV system disconnecting means
(3) Readily accessible switch that plainly indicates whether it is in the “off” or “on” position.
Where multiple PV systems are installed with rapid shutdown functions on a single service, the initiation device(s) shall consist of not more than six switches or six sets of circuit breakers, or a combination of not more than six switches and sets of circuit breakers, mounted in a single enclosure, or in a group of separate enclosures. These initiation device(s) shall initiate the rapid shutdown of all PV systems with rapid shutdown functions on that service. Where auxiliary initiation devices are installed, these auxiliary devices shall control all PV systems with rapid shutdown functions on that service.
(D) Equipment. Equipment that performs the rapid shutdown functions, other than initiation devices such as listed disconnect switches, circuit breakers, or control switches, shall be listed for providing rapid shutdown protection.
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