Okay, let's break down your options and the pros/cons of each, and then I'll give you my recommendation. This is for informational purposes only and not a substitute for a professional electrician consultation. Consult with a qualified electrician and follow all applicable codes and regulations.

Understanding the Situation

You have a service entrance that feeds a 200A Automatic Transfer Switch (ATS). From the ATS, you split the power: Option 1

100A to the house panel (using Polaris connectors).

Option 2

200A to the garage. The house panel has a 60A feed to a barn sub-panel. You need to add a sub-panel for an addition.

Option A: Tapping Off the Existing 100A House Panel Pros

Potentially simpler installation if you have physical space and breaker space in the existing 100A panel. Keeps the new addition electrically tied to the house.

Cons



Load Calculation is Critical

This is the BIGGEST concern. Can your existing 100A panel actually handle the additional load of the addition? You MUST perform a thorough load calculation according to the NEC (National Electrical Code). This means adding up all existing loads (lights, appliances, outlets) PLUS the anticipated loads from the addition (lighting, appliances, HVAC, etc.). If the total exceeds 100A (or even comes close, you're setting yourself up for problems). You're limited to a 100A breaker maximum, even if you wanted to future-proof for higher power needs later. Adding a 100A breaker will likely require moving/consolidating existing circuits, making the existing panel even more cramped. The 60A barn sub panel is also counting towards the 100amps total.

Option B: Tapping Off the 200A Feed Directly Pros



More Capacity

You're tapping directly off the main service feed before it's limited to 100A. This gives you more headroom and reduces the risk of overloading the 100A house panel.

Flexibility

You can choose a breaker size appropriate for the addition's actual load requirements, rather than being limited by what's left over on the 100A panel. Potentially better for future expansion.

Cons

Potentially more complex physical installation, especially if space is tight in the junction box. Requires careful wire management. Requires larger gauge wire from the tap to the new sub-panel. More expensive as requires new connectors

Recommendation

I strongly recommend Option B: Tapping Off the 200A Feed Directly, provided your service and equipment can handle it.

Here's why:1. Load Calculation

Even if the existing 100A panel seems to have room, the addition will add significant load. Tapping off the 200A main service provides more capacity and reduces the risk of overloading the 100A panel. Overloading a panel is a fire hazard.2.

Future-Proofing

Even if the addition doesn't require a full 100A sub-panel now, having the extra capacity available is beneficial for future expansion or changes in appliance usage.3.

Safety

Minimizing the load on the 100A panel is a safety factor.4.

Code Compliance

A proper load calculation is essential for code compliance, and tapping off the 200A feed makes it more likely that you'll meet code requirements.

Important Considerations (Regardless of Option)



Professional Electrician

This is not a DIY project. Hire a qualified, licensed electrician to perform the work. Electrical work is dangerous and requires expertise in code compliance, safety, and proper wiring techniques.

Permits and Inspections

Obtain the necessary permits from your local building department before starting any electrical work. This ensures that the work is inspected and meets code requirements.

Load Calculation

Your electrician must perform a thorough load calculation to determine the appropriate breaker size and wiring for the new sub-panel.

Wiring and Conduit

Use the correct gauge wiring for the amperage of the breaker and the distance to the sub-panel. Use appropriate conduit to protect the wiring.

Grounding

Proper grounding is essential for safety. Ensure that the sub-panel is properly grounded to the main service.

AFCI/GFCI Protection

Install AFCI (Arc Fault Circuit Interrupter) and GFCI (Ground Fault Circuit Interrupter) breakers as required by code.

Polaris Connectors

Polaris connectors are fine if sized correctly and torqued to spec.

ATS Capacity

Ensure your ATS is rated to handle the total potential load. This is often overlooked. A 200A ATS doesn't necessarily mean you can draw 200A from each leg. The total capacity might be limited. This is something your electrician MUST verify.



Short Circuit Current Rating (SCCR)

Your new panel must have an SCCR at least as high as the available fault current at the point of connection. Your electrician should calculate this.

Steps to Take


Consult with a Licensed Electrician

Discuss your project with a qualified electrician. They can assess your existing service, perform a load calculation, and recommend the best solution for your needs.2.

Obtain Permits

Apply for the necessary permits from your local building department.3.

Have the Work Done by a Professional

Let the electrician handle the installation.4.

Schedule an Inspection: After the work is completed, schedule an inspection with the building department to ensure that the work meets code requirements.In conclusion, while Option B may be slightly more involved initially, it's generally the safer, more flexible, and future-proof solution, provided your service and equipment can handle the increased load*. However, a thorough assessment by a qualified electrician is crucial before making any decisions. Prioritize safety and code compliance. Flag for review