Article 705 of the 2011 National Electrical Code (NEC), “Interconnected Power Production Sources,” provides requirements for any system producing electricity and operating in parallel with the utility grid. That means Article 705 applies to more than just utility-interactive PV systems (Article 690)—it’s also applicable to small wind electric systems (Article 694, new in the 2011 NEC), fuel cell systems (Article 692), and generators (Article 445).
Sections of 705 cover disconnecting means, overcurrent protection, requirements for when the primary (utility) power source goes down, conductor sizing for inverter output circuits, and more. Some of these sections, such as Section 705.100, “Unbalanced Interconnections,” were duplicated in the 2008 NEC in Articles 690 and 705. In 2011 several of these duplicative sections have been removed from 690, as they apply to any type of parallel power production system, not only PV.
A major change in the 2011 NEC was the removal of Section 690.64 which, in the 2008 NEC, was essentially duplicated in Section 705.12. Harmonizing the requirements for grid-connected systems makes sense, and allows the articles that cover the specific types (PV, wind, etc.) to be more streamlined. Expect more of this in future revisions—for example utility-interactive inverter output conductor sizing requirements are still duplicated in 690 and 705, and may end up residing only in Section 705 with a note indicating such in 690.
This “Code Corner” (and part 2 on load side connections in the next issue) will primarily focus on Section 705.12, “Point of Connection.” This section governs how the output of grid-tied with battery backup, batteryless grid-tied, or other types of systems operating in parallel with the grid.
The differences in how systems are interconnected are primarily dictated by system size (based on AC output current), the requirements of the local utility and authority having jurisdiction (AHJ), and rebate and incentive program requirements. Many residential and small commercial systems are net-metered, and connected on the load side (typically a back-fed circuit breaker in an AC panel) of existing service equipment. Larger systems, and systems that receive feed-in-tariff payments, may be interconnected directly to the utility through a meter or on the utility side of a building’s main service disconnect (the supply side).
Section 705.12(A) permits connection on the supply side of the AC service disconnecting means, and refers to Section 230.82(6), which covers the various types of equipment that can be connected on the supply side. There are essentially two types of supply side connections. In areas with net metering and where system size does not allow it to be connected on the load side, they occur between the existing utility meter and main AC service disconnecting means.
On the other hand, “buy-all sell-all” type systems are connected directly to the utility through what is essentially a new AC service and a second meter—this is common in areas where feed-in-tariffs are offered, and all energy generated by the system is “sold” to the utility, while all energy used at the site is “bought.” Large, multi-megawatt systems are connected in a similar manner, since there typically is no building or existing electrical service, and the size of the interconnection is beyond what would have existed.
There are numerous ways to make a supply side connection. In order to comply with OSHA requirements and NFPA 70E Standard for Electrical Safety in the Workplace, work should not be performed on energized conductors and proper personal protective equipment must be used. Careful coordination with the local utility and the AHJ is required, as power will have to be shut off from the existing service so that the new equipment can be installed and to ensure that the disruption to electrical service is minimized. Typically this involves the utility dropping the power, the work being performed, the AHJ inspecting the new work, and then the utility reconnecting power.