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 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.
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.