CODE CORNER: Simpler NEC Disconnection Rules

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One of the biggest changes in the National Electrical Code (NEC)’s Article 690 from 2014 to 2017 came in Part III, Disconnecting Means. Several sections have been deleted, the entire part is now only two sections, 690.13 and 690.15. The two sections deal with system disconnecting means and the disconnection of the equipment. The changes have simplified the rules and should be a big help for installers.

To fully understand NEC PV system disconnecting means requirements, look at definitions (found in Article 100) and refer to new diagrams included in 690.1. Article 100 defines a PV system as “the total components and subsystem that, in combination, convert solar energy into electric energy for connection to a utilization load. (CMP-4).” This definition is one that will come up for proper application of several NEC rules, so it is always worth rereading when in doubt.

In conjunction with the definition, the new figures located in 690.1(b) are a huge step forward in helping determine where PV systems “end” relative to other electrical systems that may be present. The diagrams in 690.1(b), show the location of the PV system disconnect, which can be on the DC or AC side of the system.

For proper application of Part III’s PV system disconnecting means, make sure you are applying the rules to the correct disconnect. This is how the combination of the definition and figures comes into play. When trying to determine if you are at the PV system disconnect, it can be easiest to look downstream (electrically speaking) from the disconnect. Does any of the equipment downstream require the PV array to operate? If the answer is yes, then you are not yet at the PV system disconnect. If none of the pieces of electrical equipment after that disconnect require the PV array to operate, then you are at the disconnect.

Let’s look at relatively simple example, a PV array connected to a DC disconnect, which is connected to an inverter with the inverter connected to a circuit breaker in the main distribution panel, such as the diagram labeled “Interactive system” in 690.1(b). There are two options for the PV system disconnect—the DC disconnect and the circuit breaker connected to the inverter. Since the inverter is downstream of the DC disconnect and requires the PV array to operate, that would not be the PV system disconnect. The circuit breaker would be considered the PV system disconnect, since none of the equipment downstream (the loads connected to the main distribution panel) requires the PV array to operate.

A more complex system including additional equipment (especially energy storage) is the “DC-coupled multimode system.” In this case, the PV system disconnect is on the DC side of the inverter, directly after the PV array. Again, looking downstream of the PV system disconnect, none of the equipment requires the PV array to operate. The energy storage system and multimode inverter require each other, but the PV array is not an absolute requirement for operation. Note that in this diagram, a DC charge controller is not shown; it would typically be located between the array and PV system disconnect.

Having an effective means to define the PV system disconnect location makes it easier apply the Part III rules. Back to 690.13, Photovoltaic System Disconnecting Means, which says, “means shall be provided to disconnect the PV system from all wiring systems, including power systems, energy storage systems, and utilization equipment and its associated premises wiring.” This impacts rapid shutdown requirements and the controlled conductors (Section 690.12).

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