In 2017, Article 690 of the National Electric Code (NEC) was updated, which tells solar designers, engineers, and installers how to ensure that a PV (solar energy) system will operate safely. Specifically, changes were made to how the NEC applies to system disconnects, which is what we’ll look at in this article.
How Does the Code Define a PV System?
As with all technical code, it’s important to read all definitions to ensure that you are interpreting the rules properly as they apply to your exact situation. So, let’s review the NEC’s definition of a PV system. As per Article 100 of the NEC, a PV system is defined as “the total components and subsystem that, in combination, convert solar energy into electric energy for connection to a utilization load.” In order to properly install a PV system disconnect, it must isolate the components referred to in the official definition. This might seem simple, but there are so many different possible PV system configurations that in practice it can be difficult to place the system disconnect.
How To Determine the Appropriate Disconnect Location
In order to determine the correct disconnect location, it’s best to refer to the single-line diagram of the system. Then ask yourself if where you plan to place the disconnect will in fact disconnect all of the equipment that converts solar energy into electricity, while still allowing the remainder of the connected system to function properly.
To fully demonstrate this, let’s look at three different examples of PV systems:
Interactive PV System
The easiest scenario in which to determine the correct disconnect location is a grid-direct PV system with an inverter as shown in the graphic. In this system, the solar panels (the power source) are connected to an interactive inverter, which is in turn connected to a distribution network system (a grid-tied electrical panel).
There are two potentially acceptable disconnect locations for such a system, and the right one for your specific system will be determined by your local authority having jurisdiction (AHJ).
In the diagram, we show an external disconnect switch between the inverter and the electrical panel. This is one possible way to meet the disconnect requirement, although some AHJs may allow the breaker in the electrical panel to fulfill the need.
Again, ask yourself the question from above: Will this disconnect the equipment required to turn solar energy into electricity without affecting downstream equipment? In either case here (whether you’ve installed an external switch or flipped off the breaker), the answer will be yes and you will know that the disconnect is properly placed.
It’s important to note that the integrated DC disconnect on the inverter does not count as a PV system disconnect, since it does not isolate all of the equipment as per the NEC definition – the AC side of the inverter is still connected to the utility load even the DC side of the inverter and the solar panels are disconnected.
DC-Coupled Multimode System
Here we have the special case of a DC-coupled multimode system, which presents an exception to the NEC. Since there is an energy storage system that requires the multimode inverter to remain connected in order to function, the correct placement of the disconnect is between the solar panels and the inverter. This type of system also necessitates an interactive system disconnect between the inverter and the utility grid connection, so that the energy storage system can continue providing power to the standalone system while not impacting the utility grid or creating a dangerous situation.
So, as you can see, it’s impossible to make a single ruling about where in the system the disconnect should be placed in relation to the inverter since it depends on the configuration of the overall system.
AC-Coupled Multimode System
Finally, let’s look at an example of an AC-coupled multimode system. This system functions similarly to the DC-coupled system but it uses different equipment and therefore requires a different disconnect configuration. In this case, the disconnect can be placed between the interactive inverter and the standalone load in order to disconnect as much of the system as possible while still allowing the energy storage system to power the stand-alone system load.
An energy storage disconnect between the multimode inverter and the storage system and an interactive system disconnect between the multimode inverter and the grid connection complete the safety requirements for disconnects that are up to code.
2017 Changes to Article 690
Let’s look at some of the specific changes to the code that were made in 2017. First, the scope of the article was changed to remove large-scale PV systems entirely – they now have their own article. The figures section was revised to clarify the exact endpoint of a PV system, and several definitions were added or revised for greater clarity. Other sections have been moved, reorganized, and/or revised to offer guidance on more system types.
Article 690.10 regarding stand-alone systems was actually moved to the new Article 710. Article 690.11, which details arc-fault detection, was revised and now exempts PV output circuits on ground-mounted systems if they use certain methods of wiring. Many more details and marking requirements were added to Article 690.12 in reference to the rapid shutdown of a PV system.
In Article 690.13 about PV system disconnecting means, the language is now clarified to show that there are only two types of disconnects in PV systems. Finally, 690.16, 690.17, and 690.17 have been removed and the information within was consolidated into 690.13 and 690.15. Isolating devices were added to the article as well.
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