Code Corner: Article 705: Interconnected Electric Power Production Sources


Inside this Article

Back-fed breaker
This back-fed breaker has been secured with an additional fastener, providing another level of protection against shock hazards.
Back-fed breaker

Article 705 of the National Electrical Code (NEC), “Interconnected Electric Power Production Sources,” has expanded and contains some significant changes. This Code Article applies to any power-production system connected to the utility through an inverter, regardless of the energy source—examples include generators, PV systems, wind turbines, and fuel cells. Some general requirements are that interactive systems must:

  • Use interactive and/or multimode inverters “listed and identified for interconnection service” (705.4)
  • Be compatible with the electrical characteristics (voltage, wave shape, and frequency) of the primary power source, meaning the utility (705.14)
  • Address all potential fault currents (705.16)
  • nterconnect on the supply (line) side of ground-fault protection equipment (705.32)
  • Disconnect upon loss of the primary power supply (705.40). This includes disconnecting all ungrounded conductors when one phase in a three-phase system is lost (705.42).

Article 705 also stipulates that all power sources on the premises need to be marked per the requirements of Sections 705.10 and 705.12(D)(3):

  • At the service equipment (in the case of the utility); 
  • At any interconnected power production sources (the “point of connection”)
  • When equipment contains multiple sources of supply (such as utility-supplied breakers and a back-fed breaker from a PV system).

Article 705 applies to any interconnected source, but its evolution has paralleled the development of Article 690 from the tremendous growth in PV installations—so some content is duplicated. These include equipment disconnecting means (690.15 and 705.21), circuit sizing (690.8 and 705.60), overcurrent protection (690.9 and 705.65), and grid-tied inverters in non-readily accessible locations­ [690.15(A) and 705.70].

New in Section 705.2 is the inclusion of “multimode inverters,” which can operate as both stand-alone and grid-tied inverters (examples include OutBack Power’s Radian series and Schneider Electric’s Conext XW inverters). PV systems with multimode inverters are subject to the requirements of Articles 705 and 690, including Section 690.10, “Stand-Alone Systems” (see “Additional Fasteners,” below). Section 705.80 pertains to interactive systems with energy storage, and dictates that the maximum operating voltage (including any equalization voltage) and the polarity of the grounded conductor be marked.

Load-Side Connections

The 2014 NEC now addresses feeders, taps, and busbars in systems that are interconnected on the load side of the main AC service. Also new is the requirement to use 125% of the inverter output circuit current, rather than the size of the overcurrent protection device (OCPD) in the circuit, for determining the required busbar and conductor ampacity ratings.

Dedicated OCPD & Disconnect

The language in 705.12(D)(1) referring to “one or more inverters installed in one system” means that the interconnection circuit be dedicated to the PV system up to the disconnecting means and OCPD required by 705.20 and 705.65.

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