Maximum Number of Disconnects: Page 2 of 2
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New service. Another option is to have the utility supply another service to the building and separately meter PV production. While Section 230.2 generally allows only one service per building, more services are permitted in accordance with Sections 230.2(A) through (D). According to Section 230.2(A)(5), the existence of parallel power production systems is one of the special conditions under which additional services to a building are allowed. While this approach is not commonly used, it is allowed according to Code.
Supply-side interconnection. A final option is to interconnect the PV system between the service equipment and utility meter associated with the house loads, as shown in Figure 2. In this scenario, the 120% rule does not apply. Instead, the rating of the service limits PV system capacity, according to Section 705.12(A). Therefore, the benefit of a supply-side interconnection is that in most situations it allows for the installation of more PV capacity as compared to a load-side interconnection.
PV Disconnect Interpretation
If you propose to interconnect a PV system like the one shown in Figure 2, then you need to be prepared to have a conversation with the AHJ. You must be able to explain to an inquisitive plan checker or inspector precisely why the proposed equipment configuration does not violate the six-handle rule. This is a situation in which the high degree of specificity found in the Code is helpful.
To justify the addition of the PV disconnect as shown, you must first refer to Section 230.40 Exception No. 5, which reads, “One set of serviceentrance conductors connected to the supply side of the normal service disconnecting means shall be permitted to supply each or several systems covered by 230.82(5) or 230.82(6).” If you then refer to Section 230.82 in general and to Section 230.82(6) in particular, you can show that “solar photovoltaic systems” or “interconnected power production sources” are “permitted to be connected to the supply side of a service disconnecting means.”
Following this logic, Exception No. 5 to Section 230.40 allows for the installation of an additional set of serviceentrance conductors, shown in brown in Figure 2, on the supply side of the service equipment associated with the house loads. You now have one set of service-entrance conductors supplying five occupancies and one house loads panel. In addition, you have a second set of service entrance conductors supplying the PV system.
Note that from the Code perspective— see Section 230.71(A)—there are two sets of service-entrance conductors in Figure 2. This is a key distinction to make in your conversations with plan checkers and inspectors. Not only is the configuration of equipment in Figure 2 Code-compliant, but Section 230.71(A) also allows for up to six “service disconnecting means … for each set of service-entrance conductors permitted by 230.40, Exception No. 1, 3, 4 or 5.” Therefore, the interconnected PV system could have as many as six disconnects supplied from the new service-entrance conductors and still comply with the NEC.
PV disconnect grouping. If you propose installing multiple PV system disconnects, Section 230.72 requires that you group these together since they are associated with the same set of service-entrance conductors. Best practice is to locate the new group of PV disconnects in the same general area as the existing group of service disconnects. (In an emergency situation, it is important that all first responders can locate and open the service disconnects quickly.) However, it is not always possible or practical to group both sets of disconnects, and the Code requires only that the disconnects associated with each set of service-entrance conductors be grouped together.
Unless the AHJ says otherwise, the PV disconnects can be grouped together and located away from the service disconnects. If the PV system disconnects are not grouped with existing service equipment, Section 705.10 requires that “a permanent plaque or directory, denoting all electric power sources on or in the premises, shall be installed at each service equipment location and at locations of all electric power production sources capable of being interconnected.”
It is very important to keep in mind that local requirements may exceed those found in the Code. Utility requirements often dictate where the PV system disconnect has to be located and what kind of disconnect can be used. If the AHJ requires that the PV system disconnect be located at an interior location with the existing service disconnect and the utility requires a visible and lockable disconnect at an exterior location, then the integrator will have to provide two disconnects in series to satisfy all the requirements. To reduce the possibility of last-minute surprises, always check with the AHJ and the utility in advance to verify their PV disconnect location and equipment requirements.
Editor’s note: For additional recommendations about making supply-side PV connections, please refer to NEC Section 705.12 and “Utility Interconnections” (December/January 2012, SolarPro magazine) by nationally recognized Code expert Mike Holt.
—Marvin Hamon, PE / Hamon Engineering / Alameda, CA / hamonengineering.com