Okay, let's break down your situation and address your questions and concerns regarding your residential electrical setup. Your goal is to simplify the installation, remove unnecessary components, and ensure code compliance.

Here's a step-by-step analysis


Understanding Your Setup



200A Utility Service

You have a 200A service entrance, which is good.

200A Meter Main

The Square D meter main with the 100A breaker feeding the interior panel is a bit unusual but not necessarily wrong.

22kW Generac Standby Generator

This is a substantial generator, designed to power most, if not all, of your essential loads.

200A Service-Rated ATS

This is critical. Its primary purpose is to seamlessly switch between utility power and generator power, and to provide a service disconnect for the entire house.

Siemens Distribution Panel (Questionable)

This is where your primary concern lies, and rightfully so.

Ancient MLO Square D Panel

A "Main Lug Only" (MLO) panel, meaning it doesn't have a main breaker.2.

Is the Siemens Distribution Panel Necessary? Likely Not

You are likely correct that the Siemens panel is redundant. Since your ATS is service-rated, it acts as the main service disconnect for your home. The ATS protects the downstream panel, and the panel's breakers protect individual circuits.

NEC 230.71(A) - Maximum Number of Disconnects

The NEC limits the number of service disconnects to six. Your ATS is your single service disconnect.

MLO Panel within 3' of ATS

Since your MLO panel is close to the ATS, it meets the requirement for readily accessible overcurrent protection downstream of the main service disconnect.

Conclusion: You can likely remove the Siemens panel. This simplifies the installation, reduces potential points of failure, and removes the odd wiring practices you mentioned.3. Addressing the Existing Wiring Practices #2 Copper to 2/0 Copper Splice

This is odd and likely not done correctly. The electrician likely upsized the conductors because they thought they needed to achieve the 200A rating of the ATS. However, the 100A breaker in the meter main panel limits the current, making the upsized conductors unnecessary and potentially creating a point of failure (poorly made splices).

#2 Copper from ATS to MLO Panel

As long as the 100A breaker in the meter main panel remains, and the calculated load of the MLO panel is below 100A, #2 Copper is likely sufficient. This is based on the 75C ampacity column in NEC table 310.16.
4.

Your Proposed Solution (Removing Siemens Panel)



Yes, it's likely acceptable, but with these considerations



Replace 100A breaker in meter main panel with 200A breaker This will now provide 200A protection to the feeder conductors leading to your interior panel. Replace #2 copper feeders from ATS to MLO panel with 2/0 copper. Now that the entire setup from the meter to interior panel is rated at 200A, you can remove the 100A restriction.5. Key Considerations & Steps Load Calculation

Before making any changes, perform a thorough load calculation for your entire house, including the workshop if it's built. Verify that your calculated load is below the 200A capacity of your service. This is crucial.

Conductor Sizing

Refer to NEC Table 310.16 for proper conductor sizing based on your calculated load and the termination temperature rating of the breakers and lugs.

Short-Circuit Current Rating (SCCR)

Ensure that all components (ATS, interior panel) have adequate SCCR for the available fault current at your service. Your inspector will likely check this.

Bonding and Grounding

Verify that your grounding and bonding are correct, including the grounding electrode conductor size, bonding jumpers, etc. This is crucial for safety.

Permits and Inspections

Obtain all necessary permits and schedule inspections with your local electrical inspector. Do not skip this step. They will have the final say on whether your installation meets code.

Professional Consultation

Seriously consider consulting with a different, qualified electrician to review your plan and ensure it meets code and safety requirements. Pay them for an hour or two of their time to review your plans.

ATS Load Management

Verify the ATS's load management settings. A 22kW generator has limitations.

Specific Recommendations


Load Calculation (Mandatory)

This is the foundation for everything.2.

Consult with a Qualified Electrician

Get a second opinion, especially considering the original installation's questionable practices.3.

Obtain Permits and Schedule Inspections

Absolutely necessary.4.

Document Everything

Keep detailed records of all changes, including load calculations, conductor sizes, breaker ratings, and inspection approvals.

Important Notes



NEC is a Minimum Standard

Following the NEC ensures safety but may not always be the best solution.

Local Codes Vary

Your local municipality may have amendments or requirements that differ from the national NEC.

Safety First: Electricity is dangerous. If you are not completely comfortable working with electrical systems, hire a qualified electrician.By carefully considering these factors and following the recommendations, you can likely simplify your electrical system, improve its safety, and ensure code compliance. Good luck! Flag for review