Okay, let's break down this scenario. You're looking at replacing a 200A meter with a 400A meter, while keeping the existing panels, and you're concerned about compliance and best practices. Here's a summary of the key considerations

Understanding the Existing Setup:
200A Meter

Current service entrance rating.

Parallel 2/0 AL Conductors

Feeds the load side of the meter to the panels inside.

Two 150A Main Panels

These are the service disconnects.

4/0 AL Underground Feed (Utility Owned)

Important because the utility determines the service entrance rating and what you're allowed to have connected.

Key Questions and Concerns


Like-for-Like? No. You are not doing a like-for-like replacement; you're significantly increasing the service amperage at the meter.2.

Load Calculation

Your customer's belief that they won't exceed 200A is insufficient. You MUST perform a proper load calculation according to the NEC to determine the actual service requirements.3.

Utility Approval (Critical)



You MUST contact FPL before doing anything. They own the underground feed and determine the service capacity they will provide. Increasing the meter size without their approval is a major code violation and could lead to serious problems (e.g., refusal to energize, fines, red-tagging).4.

NEC Compliance

NEC is a minimum standard. Local jurisdictions might have stricter requirements.

Why a 400A Meter Is Problematic (in this scenario without upgrades)



Over-metering

Installing a 400A meter when the service is not upgraded to support 400A (including the service entrance conductors and the utility feed) is generally not compliant. The meter rating should match the service capacity. A larger meter does not increase the available power if the rest of the system can't handle it.

Increased Fault Current

A larger service capacity (implied by a 400A meter) can potentially increase the available fault current. The existing panels and breakers are rated for a specific available fault current, if there is an increased fault current available than the equipment is listed to handle it will cause a greater risk of malfunction.

Existing Panels and Conductors

Your two 150A panels, in total, would have 300A of main breaker protection. This could be seen as insufficient for a 400A meter. Your existing 2/0 AL conductors are not likely rated for 200 amps each (400A total). They are likely rated for around 175A each (350A total).

What You Must Do


Contact FPL

This is the first step. Explain what you're planning and ask if they will allow a 400A meter on the existing 4/0 AL underground feed. They may require an upgrade of the underground feed to support a 400A service. Get it in writing! Ask specifically for the permissible ampacity of the service. Ask if they have any specific requirements for metering.2.

Perform a NEC Load Calculation

This is mandatory. Article 220 of the NEC details how to calculate the service load. Document this calculation thoroughly. If the load calculation is significantly less than 200A, the 200A service should be sufficient.3.

Upgrade or Modify as Needed (Based on FPL and Load Calculation)



Service Entrance Conductors

If FPL allows a 400A service, you'll absolutely need to upgrade the conductors from the meter to the panels. This likely means replacing the parallel 2/0 AL with appropriately sized conductors. Consider copper for easier installation in many cases.

Panels

You might need to replace the two 150A panels with a single 400A panel or two 200A panels to properly accommodate the increased service capacity.

Grounding and Bonding

Ensure the grounding and bonding system is adequate for the new service size.

Why the Bypass Handle Matters

The bypass handle on the 400A meter can is there to allow the meter to be removed and the service to continue to be supplied with power. This is needed for a variety of reasons, such as testing, repairs or replacement of the meter.

Bottom Line

Do not install a 400A meter without: FPL's approval for a 400A service on the existing underground feed or upgrading the service to 400A. A NEC-compliant load calculation. Upgrading the service entrance conductors and potentially the panels to match the 400A service capacity.Going ahead without these steps could lead to serious safety issues, code violations, fines, and the utility refusing to energize the system.

Recommendation: Start with FPL. They dictate the terms of service. Once you have their requirements, perform the load calculation and determine the necessary upgrades. Provide the customer with a detailed proposal outlining the entire scope of work, including all required upgrades and costs.Good luck, and stay safe! Flag for review