You're asking some good, insightful questions about how to integrate Enphase equipment into a 400A service, and how their design choices might be limiting wider adoption. Let's break it down, keeping in mind that this is for theoretical discussion and understanding the challenges, not for implementing anything that violates codes or manufacturer instructions.Why the Meter Collar Limitation?

First, it's important to understand why the meter collar is limited to 200A services: Current Carrying Capacity

The physical meter collar itself is likely not rated to safely handle 400A continuous current. Overheating and failure are real risks.

Utility Approval

Utilities are very particular about anything connected to their meter. They own the meter and the socket, and unauthorized modifications (like a non-approved meter collar) are a big no-no. They also have to ensure the meter can accurately record consumption and production.

Safety

Incorrectly installed or overloaded connections at the meter base can lead to dangerous conditions.

The Hypothetical Dual Meter Collar Approach

Your idea of using two 200A meter collars, one on each 200A panel's feed, raises several complex issues:1. Parallel Operation of Control Signals

The biggest challenge is how the control signals from the two meter collars would interact. The Enphase system uses the meter collar to detect grid outages and control the transfer switch, preventing backfeed to the grid during an outage. Paralleling the control signals could create unpredictable behavior:

Conflicting Signals

If one collar detects an outage and the other doesn't (due to a localized problem), the system could get confused, potentially leading to improper grid isolation or even backfeeding.

Unknown Logic

Enphase's control logic is proprietary. We don't know how the system would interpret two sets of conflicting or even slightly different signals.2.

CT Summation and Accuracy

While theoretically, you could add the CT readings, the practical challenges are significant:

Synchronization

The CTs need to be perfectly synchronized. Even slight timing differences could skew the readings, leading to inaccurate grid import/export data and potentially incorrect operation of the battery system.

Calibration and Offset

You'd need to meticulously calibrate both CTs to ensure they have the same output for the same current. Any offset in the CTs would be amplified when summed.

Wire length and impedance: Wire length needs to be perfectly equal for both CTs.3. Legality and Compliance

This is the most important point. Using the meter collars in this manner would almost certainly violate:

National Electrical Code (NEC)

It's unlikely the installation would meet the NEC's requirements for overcurrent protection and proper connection methods.

Manufacturer's Instructions

You would be operating the meter collars outside of their intended use and specifications, voiding any warranty and potentially creating a safety hazard.

Utility Regulations

The utility would likely consider this an unauthorized modification of their equipment and could disconnect the service.4.

Transparency to the IQ Combiner 6C

The IQ Combiner 6C is designed to work with a single set of grid current readings from a single meter collar or a current sensor. The system isn't designed to handle two different sets of data. It would likely misinterpret the combined data, leading to incorrect battery management and grid interaction.

Why Enphase Doesn't Have a Simpler 400A Solution (Yet)

You're right to question why Enphase hasn't addressed the 400A service issue more directly. There are likely several reasons: Cost

A 400A-rated meter collar and associated control circuitry would be more expensive than the 200A version.

Market Demand

While 400A services are common, they might not represent a large enough portion of the residential market to justify the development effort.

Complexity

Designing a 400A solution that meets all safety and regulatory requirements is more complex than a 200A system.

Existing Solutions

There are existing solutions for 400A services, even though they might not be as "clean" as a meter collar. Enphase may feel that those solutions are adequate for now. For example:

External CTs

Using a larger set of external CT's and a transfer switch panel, the Enphase system can already control battery backup.

Potential Future Solutions

It's likely that Enphase will eventually offer a more integrated 400A solution. Here are a few possibilities: 400A Meter Collar

The most obvious solution is a true 400A-rated meter collar with integrated grid control.

Split-Core CTs

Enphase could develop a system that uses large split-core CTs to measure the total current at the service entrance, combined with a more sophisticated control system.*

Partnerships

Enphase could partner with manufacturers of transfer switches or service entrance equipment to create integrated solutions for 400A services.

In Conclusion

While your idea of using two 200A meter collars is creative, it's not a viable solution due to technical challenges, safety concerns, and code compliance issues. It highlights the need for Enphase to develop a more robust and integrated solution for 400A services.Remember, any electrical work should be performed by a qualified electrician who is familiar with local codes and regulations. Flag for review