The History of Supply-Side Interconnections and the National Electrical Code

Supply-side interconnections have long been permitted by the National Electrical Code (NEC) as a method of interconnecting a power production system with the electrical system of a building. Common power production systems in modern times include solar photovoltaic (PV), generators, fuel cells, energy storage systems, and wind generation systems. To clarify, per the definition of “power production systems” found in Art. 100 of the 2020 NEC, services for electric utilities are not considered as power production equipment.

Requirements for supply-side interconnections?

Even though NEC editions prior to the 2020 NEC allowed for supply-side interconnections for power production sources, there was not a lot of clarity on the requirements that needed to be followed when performing such a method of interconnection. From the 1999 edition of the NEC to the 2005 edition, the language for supply-side interconnections was: “A photovoltaic power source shall be permitted to be connected to the supply side of the service disconnecting means as permitted in 230.82…” This language was found under NEC Sec. 690.64(A).

In the 2008 NEC, the same language was moved from Sec. 690.64(A) to Sec. 705.12(A), but only the words “photovoltaic power source” were replaced with “electric power production source.” In the 2011 edition of the NEC, additional language was added to Sec. 705.12(A) to clarify that the sum of the ratings of overcurrent devices for power production sources are not permitted to exceed the rating of the service that such system is connecting to [paraphrased].

Such language continued to be unchanged through the 2017 NEC. As far as NEC Sec. 230.82 was concerned (prior to the 2020 edition), such language was also not specific on what was required for supply-side interconnections. Rather, it only noted that other types of systems, such as solar photovoltaic, fuel cell, wind electric, or other electric power production sources, are permitted to be connected on the supply-side of the service disconnecting means.

So, essentially it was clear that the NEC allowed for supply-side interconnections of power production systems, but it wasn’t very clear how such interconnections needed to be installed.

Service equipment or not?

There was another issue causing confusion — the definition of “service” found in Art. 100 of the NEC appears to indicate that a service is only for delivering or connecting a serving utility to the electrical system for the premises. This definition was leading some individuals to believe that the first point of disconnecting equipment used for the power production system to connect to the supply-side of the premises electrical system was not required to be considered as “service equipment,” primarily because a power production source is not considered as an electric utility as explained at the beginning of this article.

However, by not treating the first point of disconnect for the power production system as service equipment, it created issues such as improper bonding and grounding of the disconnect equipment. For example, there were installers that were not providing a neutral-to-ground main bonding jumper and grounding electrode conductor (GEC) for the power production disconnect equipment. This was a concerning trend for some in the industry, and many felt that changes were necessary.

Changes made

In the 2020 NEC, a change was made to Sec. 230.82(6) that clarified when making a supply-side interconnection, the disconnecting means for the power production source must be listed as “suitable for use as service equipment,” and the disconnect must meet the overcurrent protection requirements of Part VII of Art. 230 (see Fig. 1).

Fig. 1. The disconnect must meet the overcurrent protection requirements of Part VII of Art. 230 — **Fig. 1.** The disconnect must meet the overcurrent protection requirements of Part VII of Art. 230

In addition, Sec. 250.25 was added to the 2020 NEC to clarify that the disconnecting means for the power production source must meet the grounding and bonding provisions of Sec. 250.24(A) through (D). This essentially clarifies that a neutral-to-ground main bonding jumper and GEC are required for the power production source disconnect.

Although it is important to understand that this requirement only applies when the disconnecting means for the power production source is located in a separate enclosure from the premises service equipment, there are sometimes situations and service equipment where a breaker for the power production source can be connected in an available service breaker slot in the premises service equipment, which is also considered as a supply-side connection if the service equipment busbars that the power production breaker connects to is not protected by an overall main breaker. But in such a scenario — since the power production breaker is in the same enclosure as the service equipment — the provisions of Sec. 250.25 of the 2020 NEC do not apply to any downstream disconnects for the power production system (see Fig. 2).

Fig. 2. Since the power production breaker is in the same enclosure as the service equipment, the provisions of Sec. 250.25 do not apply to any downstream disconnects for the power production system. — **Fig. 2.** Since the power production breaker is in the same enclosure as the service equipment, the provisions of Sec. 250.25 do not apply to any downstream disconnects for the power production system.

The future

The changes made to the 2020 NEC help provide guidance on what is required for the disconnecting means when making a supply-side interconnection. Additional changes will occur in the 2023 NEC to help provide further clarity for such methods of interconnections.

Supply-side interconnection requirements found in the NEC continue to evolve and provide more clarity for installers, AHJs, and the industry. The NEC is on the right path. Such methods of interconnection will continue to be an important option for connecting power production sources to premises electrical systems, but doing so safely (and in an appropriate manner) is essential.

Inspector Intel articles are provided by the International Association of Electrical Inspectors (IAEI), www.iaei.org, a membership-driven, non-profit association headquartered in Richardson, Texas, that promotes electrical safety throughout the industry by providing education, certification of inspectors, advocacy, partnerships, and expert leadership in electrical codes and standards.

Doug Smith is the energy division manager for West Coast Code Consultants (WC3) and has been an inspector/plan reviewer for more than 17 years. He currently serves on NEC Code Making Panel 10 representing IAEI and serves as an STP Member for UL 9540, UL 1741, UL 1703/61730, UL 2703, and UL 6703. He has been teaching solar PV, energy storage, and general electrical classes for over 10 years. He can be reached at [email protected].