Supply-Side Connections
Section 705.12(A) allows for the interconnection of power production sources to the supply side of the servicedisconnecting means, often referred to as line-side connections. For consistency with the Code, I refer to them as supply-side connections. For the purposes of this article, ?power production sources? are classified as PV systems.
A sentence added to this subsection in 2011 helps clarify how much current PV systems can impose on the service conductors. The sum of the overcurrent protection devices (OCPDs) from the PV system connected to the service conductors cannot exceed the service conductors? rating.
Beyond 705.12(A), the NEC does not provide rules for the methods required to make supply-side connections. Consequently, PV system integrators have had to improvise and work with their inspectors to install systems that everyone thinks are safe. In most cases, this has resulted in treating supply-side connections as service connections and following the direction of Article 230 exclusively, even though this approach is not completely accurate because of the differences between utility services and other electrical power production sources such as PV. Unfortunately, the lack of direct guidance pertaining to the methods required to make supply-side connections leads to multiple interpretations and Code applications among installers and inspectors. In this article I present what I consider to be the best options under the circumstances.
One example where the lack of Code guidance can cause confusion is in determining how to apply Section 230.71(A), ?Maximum Number of Disconnects,? to supply-side PV connections. Section 230.71(A), which electricians often refer to as the ?six-handle rule,? requires that the service disconnecting means contain no more than six sets of service disconnects per service. Technically, the disconnecting means for a PV system is not a service disconnect. Article 100 defines a service as ?the conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.? Because a PV system is outside that definition, the PV disconnecting means is not governed by the six-handle rule. Section 690.14(C) (4) requires that PV system disconnecting means must have no more than six switches or six circuit breakers. Given the Code definitions and requirements, a supply-side connection could have up to six PV-specific disconnects in addition to the utility service disconnects.
This conclusion contradicts solar integrators? traditional line of thinking, as well as information presented in the article ?Can We Land?? (see June/July 2009, SolarPro magazine). My position is that a PV system disconnecting means is not a service disconnect because the inverter?s output circuit is not a utility service, and the utility service is not affected when the disconnect is in the Off position. PV system disconnects are service rated, contain overcurrent protection and must be installed in a similar fashion to service disconnects, but PV system disconnects are not service disconnects. This interpretation of the Code will likely require a conversation with your AHJ, one I suggest having before the final inspection if you feel there will be any questions or objections.
The NEC also lacks specific guidelines for supply-side connections in the bonding of grounded PV conductors, bonding raceways and wiring methods for the inverter output circuit. The methods I recommend below result in the PV disconnecting means being installed under the same rules as service disconnects. These methods are not direct Code requirements, but rather what I consider best practices using existing rules from Code that result in a safe installation utilizing supply-side connections, and they will satisfy most AHJs.
Grounded conductor bonding. The grounded current-carrying conductor on the supply side of service equipment for PV systems should be bonded to the PV disconnect in accordance with Section 250.24. This is to make sure that the grounded service conductor provides the effective groundfault current path from the power supply to ensure that dangerous voltages from a ground fault are quickly removed by opening the OCPD.
Raceway bonding. Raceways containing the supply side of service equipment conductors for PV systems should be bonded in accordance with Section 250.92(B). This helps ensure the electrical continuity at the service equipment, as intended by Code.
Wiring methods. The conductors and methods used for supply-side connected PV systems should be limited to those identified in Section 230.43. Using these methods keeps the inverter output circuit consistent with the wiring methods used for the service conductors. This imposes a higher standard on the wiring methods, as compared to treating them as branch circuits, and results in a robust installation.
