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What is Rapid Shutdown and why was it implemented in the United States?

RAPID SHUTDOWN WAS INTRODUCED IN THE UNITED STATES TO REDUCE FIRES AND IMPROVE FIRE FIGHTER SAFETY ON SOLAR SYSTEMS

Rapid shutdown was first introduced in the 2014 National Electrical Code (NEC) with the intent of providing a simple method for fire fighters to de-energize solar system DC conductors easily to ensure a safe condition on the roof of a building during a fire.   This is because on a standard string inverter solar system, when the inverter is switched off, the DC wiring from the solar system remains live when the sun is shining.

In the 2017 NEC, rapid shutdown was expanded with different requirements based on how close the PV system conductors are to the PV array boundary, which is now defined as the area 1 foot (305mm) from the array in all directions.

PV circuits located outside the boundary or more than 3 feet (1m) from the point of entry inside a building shall be limited to not more than 30 volts within 30 seconds of rapid shutdown initiation.

For PV circuits located inside the array boundary, one of the following three options must be used beginning with an effective date of 1 January 2019:

  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 or field labeling.
  2. PV conductors located inside the boundary or not more than 3 feet (1m) 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.
  3. PV arrays with no exposed wiring methods, no exposed conductive parts, and installed more than 8 feet from exposed grounded conductive parts or ground shall not be required to comply with rule 2 above.

2017 CODE LANGUAGE (FOR THE TECHNICALLY MINDED)

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).

Exception: Ground mounted PV system circuits that enter buildings, of which the sole purpose is to house PV system equipment, shall not be required to comply with 690.12.

N(A) Controlled Conductors. Requirements for controlled conductors shall apply to PV circuits supplied by the PV system.

N(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 morethan 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 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.

WHERE IS THE NATIONAL ELECTRICAL CODE (NEC) IN EFFECT?

As of 1 May 2019, the 2017 NEC is in effect in 29 states, the 2014 NEC is in effect in 14 states, the 2011 NEC is in effect in one state, and the 2008 NEC is in effect in three states.

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