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Understanding Rapid Shutdown Requirements for Your DIY Solar Project

If you are installing your own solar, you will have to make sure your system meets the “Rapid Shutdown” requirements. 

These requirements first appeared in NEC 2014 and were modified in NEC 2017. The purpose of these requirements is to make things safer for emergency responders. The basic premise is that the DC conductors of a PV system are typically live any time the sun is out. Without a rapid shutdown system, firefighters that need to shut off all electrical sources may have no safe way to turn off the DC wiring on the roof, in the attic and running down the side of your house. Generally, if firefighters are at your house, there is a big enough problem happening that there isn’t time to mess around with trying to figure out what to do about these live solar conductors so the wonderful people who write the electrical code came up with this solution.

Rapid shutdown systems improve fire fighter safety

Rapid shutdown requirements apply to any PV circuits installed in or on a building. In NEC 2017, they added an exception for ground mounted systems when the sole purpose of the building is to house the PV equipment. 

Exactly where and how the conductors need to be controlled changed between NEC 2014 and NEC 2017 so it depends on which code version your city or county is following. NEC 2014 says that you have to control any PV conductors that are more than 10’ from the array or more than 5’ in length inside the building and the rapid shutdown system has to bring these conductors down to 30 volts or less within 10 seconds of rapid shutdown initiation. NEC 2017 gets a little more difficult. They want any conductor more than 1’ from the array or more than 3’ in length inside a building brought down to 30 volts and conductors within the array brought down to 80 volts within 30 seconds. 

NEC 2014 made no mention of the location of the device that starts this rapid shutdown process but NEC 2017 makes it clear that it needs to be in a readily accessible location outside the building. Finally, it is required that your system be very specifically labeled that it is equipped with rapid shutdown so those firefighters know for sure what they are dealing with.

So how do you accomplish this? Well, the simplest method is to install a system that is inherently equipped with rapid shutdown like the SolarEdge system that incorporates DC optimizers at every solar panel or Enphase microinverters that are installed at every solar panel. These devices easily shut off the power around and within the array on the roof when you flip the switch installed at ground level. Then all you have to do is get the appropriate rapid shutdown labeling from your solar kit distributor and it is easy peasy done.

Rapid Shutdown Label

If you wanted to install a more traditional central inverter, you still have options. For NEC 2014 compliance you simply need to install a rapid shutdown device on the roof at the edge of the array and link it to the switch at ground level. If you are dealing with NEC 2017 requirements, then you have to install module-level equipment that can manage the rapid shutdown at each solar panel. It is not too big of a deal provided you know ahead of time, order the right equipment and install it at the same time as the solar panels. But, if you weren’t lucky enough to read this article and have to install these after you already have the array done, it will be a major pain.       

Now you are equipped with the knowledge to equip your PV system with a rapid shutdown system that meets your local building department’s requirements.  

Author: Harold Tan

I believe clean, renewable energy is key to the evolution of society as a whole. Solar powers our planet, why not harness it to power humanity? Let's power our homes, our work, and our vehicles with solar energy. It begins with raising awareness and encouraging those around us to go green.

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1 Comment

  1. If some thought is put into the design of the system, you will naturally build a system that complies with these codes. My first phase of soalr used string inverters because micros had not yet been invented. Unlike most, I placed the inverters on the roof to minimize line loss with big DC runs. When either main or QF disconnect is pulled at the boxes on the wall next to the meters, the only remaining energized wires are from the panels to the inverters located under the shade of the panels. On phase two, I used micros, accomplishing the same results. Inverters under panels in the shade, DC to AC as quickly as possible, pull the disconnect, the only electricity left on is 36dc on the micros, 300vdc on the strings. Might wake you up, but won’t kill you.

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