Based on the information you've provided and the NEC 450.3(B) Note 2, yes, the partial one-line diagram you've described with (2) secondary breakers likely violates the rule.

Here's why: Multiple Overcurrent Devices

The configuration explicitly uses two overcurrent devices (breakers) on the secondary side of the transformer.

Total Rating Limitation

The rule clearly states that the total of all the breaker ratings cannot exceed the allowable rating for a single overcurrent device. This is the key point. If the sum of the two breaker ratings is more than the allowable rating for one breaker protecting the secondary of that transformer as calculated by the NEC (based on transformer size, etc.), then you're in violation.

Without knowing the transformer kVA size, secondary voltage, and the individual breaker ratings, I can't give a definitive "yes." But, the likelihood is high that it violates the rule.In summary, if Breaker 1 Amps + Breaker 2 Amps > Maximum Allowable OCPD for the Transformer Secondary - then the shown configuration violates NEC 450.3(B) Note 2.

How to Avoid a Violation


Verify Transformer Size and Secondary Voltage

Determine the transformer's kVA rating and secondary voltage.2.

Calculate Allowable Secondary Overcurrent Protection

Use NEC 450.3(B) to determine the maximum allowable overcurrent protection for the secondary. Typically, you'll multiply the secondary full-load current by a percentage (125% or 250%, depending on specific conditions).
3.

Check Breaker Ratings

Ensure that the sum of the amp ratings of the two breakers does not exceed the maximum allowable overcurrent protection calculated in step 2.

Important Considerations



Coordination

While you might be able to comply with NEC 450.3(B) Note 2 by reducing the breaker sizes, you need to ensure proper coordination with any downstream loads. The breakers must be sized appropriately to protect the circuits and equipment they feed.

Alternative Designs

If the breaker sizes you need for the downstream loads would violate the Note, consider:

Single Main Breaker

Use a single, larger main breaker on the secondary side.

Multiple Transformers

If the load is too large for a single transformer and single breaker, consider using multiple smaller transformers, each with its own overcurrent protection.

Disclaimer: I am an AI chatbot and cannot provide definitive electrical code interpretations. Consult with a qualified electrical engineer or inspector for code compliance. They can analyze your specific installation and ensure it meets all applicable requirements. Flag for review