Maximum Number of Disconnects
Inside this Article
Most people in the industry have heard of the “six-handle rule.” The source of this rule is found in Section 230.71(A) of the NEC, which indicates that in general “each service” or “set of service entrance conductors” shall have “not more than six switches and sets of circuit breakers.” The requirement to group these service disconnects is found in Section 230.72.
What many individuals, including plan checkers and inspectors, have not fully considered is how this rule applies to PV system disconnecting means. For example, what if you want to add a supply-side–connected PV system at a facility that already has six service disconnects? You might encounter this scenario at a multifamily dwelling unit or a commercial building with multiple tenants. If the AHJ treats the PV system disconnecting means as a service disconnect in addition to the existing six disconnects, then the PV system cannot be added without violating the six-handle rule. However, a careful reading of the Code does not support this interpretation.
Typical Multiunit Service
A representative multiunit service is shown in Figure 1. This is the type of service you might find supplying a five-unit multifamily dwelling or a five-tenant office building, where each occupant has its own service disconnect and meter. The sixth meter and service disconnect is dedicated to house loads, which are loads associated with public or common areas, like landscape or stairway lighting. Most of the time, tenants are responsible for paying for their own electricity usage, whereas the facility owner pays for the energy used by the house loads. Therefore, when you are installing PV on a building with multiple units or tenants, your goal will typically be to interconnect the system in a manner that offsets these house loads on behalf of the facility owner.
While Article 230 of the NEC covers installation and equipment requirements for services, many of the terms used in Article 230 are defined in Article 100. For example, a service is defined as “the conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.” There are at least ten additional definitions in Article 100 related to services. Several of these terms are identified in Figure 1, which is an example of a service for a five-tenant office building with house loads.
Looking at Figure 1, you can see that the service drop conductors, shown in blue, terminate at the service point, which is located overhead and outside the building. The overhead system service-entrance conductors run between the service point and the service equipment, which consists of six individual disconnects that are grouped together. Each disconnect is supplied by a set of service-entrance conductors tapped off the serviceentrance conductors in the auxiliary gutter box.
We can show that the service in Figure 1 is Code-compliant. A single service serves the building, which the NEC generally requires (see Section 230.2). The Code also generally requires that each service drop “supply only one set of service-entrance conductors” (see Section 230.40). However, Exception No. 2 to Section 230.40 states, “Where two to six service disconnecting means in separate enclosures are grouped at one location and supply separate loads from one service drop … one set of service entrance conductors shall be permitted to supply each or several such service equipment enclosures.” This exception applies to our example, since each disconnect is dedicated either to a different tenant or to the house loads. As shown, the service also complies with the six-handle rule in Section 230.71 and the service equipment grouping requirements in Section 230.72.
PV System Interconnection
There are several ways to interconnect a PV system that will offset the house loads in Figure 1 or will provide a net financial benefit to the facility owner. While I focus on the Code implications of making a supply-side interconnection, other options include making a load-side interconnection or adding a new service.
Load-side interconnection. Code Section 705.12(D) allows for a load-side interconnection, provided that certain requirements are met. One benefit of a load-side connection is that there is no need to add a seventh disconnect for the PV system. However, the load-side connection is subject to the 120% rule found in Section 705.12(D)(2).