You're right to be concerned about the interpretation of "single feeder" in the context of 220.84 (Optional Feeder or Service Load Calculation for Dwelling Units). This is a gray area, and ultimately the Authority Having Jurisdiction (AHJ) will have the final say. However, let's break down the arguments for and against your interpretation.

Arguments for your interpretation (Qualifying as a single feeder)



Totalization

The utility company is treating the two 200A services as a single metered supply to the dwelling unit. They are adding the usage from both meters to determine the total consumption and billing amount. In effect, the utility sees it as one service.

Intent of 220.84

The intent of 220.84 is to provide a simplified calculation method for dwelling units with typical load profiles. Using the standard method for these larger units could be unnecessarily conservative and lead to oversized feeders and equipment. The fact that the utility is totalizing the service suggests they understand the actual load profile will likely be less than the sum of the individual meter capacities.

Practicality

For very large units, two 200A services may be more practical and cost-effective than a single, larger service (e.g., a 400A or larger service). The Code allows for multiple services in certain circumstances (230.2), and this approach can be a reasonable compromise.

Arguments against your interpretation (Not qualifying as a single feeder)



Literal Interpretation of "Feeder"

The NEC defines a feeder as "all circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device." You literally have two sets of conductors originating at the service equipment and terminating at overcurrent protection devices within the dwelling unit.

Potential for Misuse

Allowing multiple services per dwelling unit, even when totalized, could be seen as a loophole to circumvent the standard calculation methods and potentially undersize the overall service.

How to Proceed


Consult the AHJ

This is the most crucial step. Present your reasoning and explain the utility's totalization practice. Get their approval before proceeding with the design. Document their decision in writing.2.

Provide Load Calculations

Be prepared to provide detailed load calculations using both the standard method (Article 220 Parts III and IV) and the optional method (220.84). Show that the optional method provides a reasonable estimate of the load and does not result in an undersized service.
3.

Consider Adding a Note to the Plans

Clearly state on the electrical plans that the dwelling unit is served by two 200A services that are totalized by the utility company and that the load calculation is based on 220.84, as approved by the AHJ.
4.

Explore Alternative Designs

If the AHJ rejects your interpretation, consider alternative designs that would comply with the "single feeder" requirement. This might involve a single larger service with a single meter.

Important Considerations



Diversity Factor

The utility's totalization suggests they are applying a diversity factor. Understand how they calculate the totalized load.

Demand Factors

The standard calculation methods incorporate demand factors that account for the fact that not all loads will be operating simultaneously. The optional method also includes built-in assumptions about load diversity.

Safety

Regardless of the calculation method used, ensure that the service is adequately sized to handle the maximum potential load of the dwelling unit and that all components are properly rated and installed.

In Summary:

While you have a reasonable argument that the totalized service functions as a single feeder in practice, the NEC's wording is open to interpretation. Proactive communication with the AHJ is essential to ensure compliance and avoid costly rework. Be prepared to provide detailed information and justification for your design. Good luck! Flag for review