Okay, let's break down your electrical load calculations and discuss your proposed wiring strategy. It's crucial to be accurate to avoid overloading your system and potentially causing hazards.1. Cabin Load Calculation



Baseboard Heaters

1500W x 3 = 4500W 1000W x 1 = 1000W 500W x 1 = 500W Total Heating Load: 6000W

Hot Water Heater

3800W

Refrigerator (20 cu ft)

A standard refrigerator consumes approximately 150-200 watts running and can surge significantly higher during compressor start-up (up to 600-800W). We'll use 200W as a running average.

Lighting and Receptacles

This is the trickiest part. We need to estimate a general lighting and receptacle load. Per NEC (National Electrical Code), you must account for at least 3 VA per square foot. You have 860 sq ft + 300 sq ft (loft) = 1160 sq ft. 1160 sq ft x 3VA/sq ft = 3480 VA. However, since you mention 20-amp receptacles, you should also consider the potential for heavier loads. Realistically, you won't likely use all those receptacles at once at their full 20-amp capacity. But we need to consider this. For example, if you had 10 20-amp receptacles, we would need to include 2000VA for each set of two or fewer receptacles per NEC 220.14(I), so 10000VA for the receptacle load.

Since it is a cabin in Idaho, it is unlikely that you will be using the 20 amp receptacles to their full capacity. A more realistic approach would be to assume that a combination of lighting and receptacle load would amount to approximately 3000VA. Cabin Total Estimated Load (VA)

Heating: 6000W (VA) Hot Water: 3800W (VA) Refrigerator: 200W (VA) Lighting & Receptacles: 3000VA

Total: 13000 VA2. Garage/Living Space Addition Load Calculation



Baseboard Heaters

1500W x 2 = 3000W 1000W x 1 = 1000W 500W x 2 = 1000W Total Heating Load: 5000W

Hot Water Heater

3800W

Refrigerator (20 cu ft)

200W

Lighting and Receptacles

630 sq ft x 3 VA/sq ft = 1890VA

Since it is a cabin in Idaho, it is unlikely that you will be using the 20 amp receptacles to their full capacity. A more realistic approach would be to assume that a combination of lighting and receptacle load would amount to approximately 2000VA. Garage/Living Space Addition Total Estimated Load (VA)

Heating: 5000W (VA) Hot Water: 3800W (VA) Refrigerator: 200W (VA) Lighting & Receptacles: 2000 VA

Total: 11000 VA3. Total Combined Load (Cabin + Addition)

Cabin: 13000 VA Addition: 11000 VA

Combined Total: 24000 VA4. Converting VA to Amps (using 240V)

Total VA / Voltage = Amps 24000 VA / 240V = 100 Amps

Analysis of Your Proposed Wiring



Existing 200A Service Panel

This is where the power enters your property.

Existing 200A Sub-Panel

Currently fed from the 200A service panel.

Proposed Change

Replacing the 200A breaker in the sub-panel with a 100A breaker is a move in the right direction for load management. However, it is only a limiter and doesn't solve the underlying issue.

Addition Feed Options



Option 1: 70A Breaker from Service Panel to Garage Sub-Panel

The total combined load is right at 100 amps, but the total load calculation may be increased. If the cabin is on a 100 amp breaker at the sub-panel, then the garage would be as well. This leaves no room for the refrigerator start-up. It is not enough to use only 70 amps for the addition.

Option 2: Sub-Feed Lugs to 100A Sub-Panel in Garage

This is a viable option, but it is also cutting it close.

Recommendations


NEC Load Calculation

Conduct a thorough load calculation per the National Electrical Code (NEC). This will account for all circuits, appliances, and future expansion. While our estimates are a good starting point, the NEC provides specific guidelines for different types of loads (heating, cooking, motors, etc.).2.

Demand Factors

You might be able to apply demand factors based on NEC guidelines. Demand factors allow you to reduce the calculated load based on the likelihood of everything running at full capacity simultaneously. This is especially applicable to the heating load. Consult a qualified electrician on whether these can be applied in your case.3.

Electrician Consultation


Crucially, hire a licensed and experienced electrician to perform the final load calculation, determine the appropriate wiring method, and install the new circuits. This is not a DIY project. Electrical work can be dangerous and must comply with local codes.4. Consider a Load Management System

If you're very close to your capacity, consider installing a load management system. These systems monitor the current draw and can automatically shed loads (e.g., temporarily turn off a water heater or a non-critical heater) if the total load exceeds the capacity.5.

Assess the Main Service

Double-check the rating of your main service panel (the one where the power enters your property). Make sure it's genuinely a 200-amp service and that the utility company is providing adequate service to handle the increased load.

Key Considerations



Future Expansion

Plan for future electrical needs. Will you want to add a workshop in the garage, an electric vehicle charger, or other appliances later? It's always better to have some extra capacity.

Safety

Electrical safety is paramount. Always follow the NEC and local codes, and hire a qualified electrician.*

Local Codes

Local codes may be more stringent than the NEC, so be sure to check with your local building department.

In summary, your total estimated electrical load is pushing the limits of your existing 200-amp service. I strongly advise consulting with a qualified electrician to perform a comprehensive load calculation and ensure your wiring system is safe and compliant. Do not proceed without professional guidance. They can help you explore options like demand factors, load management, and service upgrades if necessary. Flag for review