Let's break down the NEC requirements and whether your setup is compliant.

Understanding the Requirements Transformer Primary Overcurrent Protection

NEC 450.3 governs transformer overcurrent protection. The primary protection should generally not exceed 125% of the transformer's primary current rating.

Disconnecting Means (Local Disconnect Switch)

NEC 450.14 and other articles (like 430 for motors) require a disconnecting means that is readily accessible and capable of interrupting the transformer's primary current. The disconnect must have an ampere rating not less than 115% of the transformer's primary current rating.

Calculations1. Transformer Primary Current (FLA)

KVA = 45 Voltage (Assuming a common 480V primary): We'll assume a 480V primary for this example. You need to use the actual primary voltage of your transformer for accuracy. FLA = KVA 1000 / (Voltage √3) FLA = 45 1000 / (480 1.732) FLA ≈ 54 Amps2.

NEC 450.14 Disconnect Sizing

Minimum Disconnect Ampacity: 54 Amps 1.15 = 62.1 Amps

Analysis Overcurrent Protection (70A C/B)

54 amps 125% = 67.5 amps. The 70A breaker is permitted for primary protection.

Disconnect Switch (60A rated)

The calculated required disconnect ampacity is 62.1 Amps. Your 60A switch does not meet this requirement.

Conclusion

The 60A-rated non-fused disconnect switch is NOT acceptable according to NEC requirements. You need a disconnect switch rated for at least 62.1 Amps. A 70A or higher rated disconnect is necessary.

Important Considerations and Recommendations



Actual Primary Voltage

The calculations highly depend on the actual primary voltage of your transformer (e.g., 208V, 240V, 480V, 600V). Use the correct voltage to get accurate FLA and disconnect sizing.

Nameplate Data

Always refer to the transformer's nameplate for the FLA and recommended overcurrent protection.

Local Amendments

Always check for local electrical code amendments or interpretations that might affect these requirements. The AHJ (Authority Having Jurisdiction) has the final say.

Fused vs. Non-Fused Disconnect

A fused disconnect can sometimes provide both the disconnecting means and the overcurrent protection. If using a fused disconnect, ensure the fuses are sized appropriately to meet both the overcurrent protection requirements (125% or less) and the disconnect ampacity requirements (115% or more). If you used a fused disconnect you would need to ensure the fuses are sized between 54A115%=62.1A and 54A125%=67.5A, so 65A fuses would be permitted.

Disclaimer: I am an AI Chatbot and not a qualified electrical engineer or electrician. This information is for general guidance only. Consult with a licensed electrical professional to ensure your installation complies with all applicable codes and regulations and is safe for your specific application. They can perform a thorough assessment and provide tailored advice. Incorrect sizing or installation can create a significant fire and safety hazard. Flag for review