Okay, let's break this down to determine the correct breaker size according to the NEC 2017 for your 240V, 8000VA oven.

Understanding the Calculations VA to Amps

You correctly calculated the current draw of the oven: 8000 VA / 240 V = 33.33 Amps

125% Rule (Continuous Load)

The NEC requires you to size the overcurrent protection (breaker) for 125% of the continuous load. A continuous load is defined as a load that operates at its maximum current for 3 hours or more. Ovens are generally considered continuous loads because they can run for extended periods at or near their maximum heating power. 33.33A 1.25 = 41.67 Amps.

NEC 2017 Considerations Article 422.11(F)(1)(3)

Household Cooking Appliances. Branch circuit conductors supplying one or more household cooking appliances shall be sized in accordance with 210.19(A)(3), 210.20(A).

Article 210.19(A)(3)

Household Cooking Appliances. Branch-circuit conductors supplying household cooking appliances shall have a rating not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8 3/4 kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

Article 240.4(B)

Protection of Conductors. Where the overcurrent device ratings do not correspond to the conductor ampacity, the next higher overcurrent device rating shall be permitted to be used.

Analysis1. Your calculation indicates a minimum ampacity of 41.67 amps required for the conductors after applying the 125% rule for continuous loads.
2. NEC 210.19(A)(3) calls for a minimum branch circuit rating of 40A.
3. Standard breaker sizes don't typically include a 45A breaker.

Conclusion and Recommendation

Based on NEC 2017, you should use a 50A breaker. Here's the reasoning: Your calculated minimum conductor ampacity is 41.67A. A 40A breaker is too small, because it doesn't meet the 125% rule. NEC 240.4(B) allows you to use the next higher standard overcurrent device rating if your calculated ampacity doesn't match a standard size. The next standard size above 41.67A is 50A. A 50A breaker will protect your conductors and the oven in the event of an overcurrent or short circuit, while still allowing the oven to operate normally.

Important Considerations and Recommendations Wire Size

Ensure the wire gauge you use is rated for at least 50 amps. Consult the NEC ampacity tables (Table 310.16 in NEC 2017) based on your wire type (e.g., THHN, NM-B) and installation method (e.g., in conduit, free air, cable type) to determine the correct gauge. Copper wire of #6 AWG will be needed at a minimum.

Local Codes

Always check with your local electrical inspector or authority having jurisdiction (AHJ). They may have specific interpretations or amendments to the NEC that apply to your area.

Manufacturer's Instructions

Always follow the oven manufacturer's installation instructions. If they specify a specific breaker size, that should be followed (unless it conflicts with the NEC or local codes).

Qualified Electrician

It is highly recommended that you hire a licensed and qualified electrician to perform the installation. Electrical work can be dangerous, and proper installation is critical for safety and code compliance.

Disclaimer: I am an AI chatbot and cannot provide professional electrical advice. This information is for general guidance only. Always consult with a qualified electrician for specific advice regarding your situation. Flag for review