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In 2014, the National Electrical Code included a new requirement. 690.12(1) through (5) A short requirement, only six sentences.
PV system circuits installed on or in buildings shall include a rapid shutdown function that controls specific conductors in accordance with 690.12(1) through (5) as follows.
- More than 5’ inside a building, or more than 10’ from a PV array
- Controlled conductors shall be limited to not more than 30V and 240 volt-amperes within 10 seconds of rapid shutdown initiation.
- Voltage and power shall be measured between any two conductors and between any conductor and ground.
- The rapid shutdown initiation methods shall be labeled in accordance with 690.56(B).
- Equipment that performs the rapid shutdown shall be listed and identified.
But those six short sentences had a big change on PV system design. Gone were the days of simply wiring the solar panels, or modules, to the grid tied inverter or charge controller through a simple pass-thru or combiner box. Rapid ShutDown (RSD) has a noble cause. It is to protect the firefighters trying to put out a fire in your home or business. Even when they turned off the grid power to your house, and the inverter automatically shut itself off (in accordance with UL1741), the wires from the solar array all the way down into the inverter or controller were still live. In grid tied systems, they could have as much as 600VDC. Combine that voltage with a firefighter’s ax to vent the roof, and you have a disaster on your hands.
Rapid Shutdown gives the firefighters a way to also shut down the DC power from the solar array to the inverter. In 2014, it could shut it down to the area up to 10’ from the solar array, and more than 5’ of entering a building.
