You're on the right track! Here's a breakdown of how to calculate the required circuit sizes for your fan motors, along with the relevant NEC sections

Understanding the Key Concepts
Continuous Duty

This means the motors will operate for 3 hours or more at a time. This is crucial for sizing the overcurrent protection (circuit breakers or fuses).

Full-Load Current (FLC)

This is the current a motor draws when operating at its rated voltage and horsepower. You're given 3.2A for each motor.

Electronically Protected

This means the motors have built-in overload protection, which simplifies the overcurrent protection calculation somewhat.

NEC Calculations for Motor Circuits (Simplified)

The primary NEC articles you'll need are Article 430 (Motors, Motor Circuits, and Controllers) and Article 210 (Branch Circuits)Here's the general process, based on your description

1. Determine the Largest Motor:

All your motors are the same (3.2A, 1/3 hp). Therefore, any motor is the largest.2. Calculate the Ampacity of Each Branch Circuit

NEC 430.24. You will be running multiple motors on one branch circuit.

Calculate the overload protection (overcurrent)

Largest motor: 3.2A 125% = 4A The remaining motors are added at 100%: 125% + (X-1)

3. Sizing Branch-Circuit Overcurrent Protection (Circuit Breakers or Fuses)



Individual Short-Circuit and Ground-Fault Protective Device

Largest Motor: The electronically protected motor allows for much higher breakers. For electronically protected motors, you can use up to 250% of the motor’s FLC (NEC 430.52(C)(1) Exception No. 2). Branch circuit with the largest motor (3 motors + 1 at 125%): 3.2A x 3 x 1 = 9.6A + 4A = 13.6A. You would use a 15A breaker for this circuit. Branch circuit with all remaining motors (6 motors): 3.2A x 6 = 19.2A. You would use a 20A breaker for this circuit.

Important Considerations for Overcurrent Protection



Standard Breaker Sizes

You'll need to choose the next standard breaker size up from your calculated value, but ONLY if the calculated value does not match a standard size. Common sizes are 15A, 20A, 25A, 30A, etc. (See NEC 240.6 for standard ampere ratings).

Non-Time Delay Fuses

A non-time delay fuse may trip nuisance because of the starting current of the motors.

4. Determine the Minimum Conductor Ampacity



NEC 430.22

The conductors supplying a single motor used for continuous duty shall have an ampacity not less than 125% of the motor’s full-load current.

Largest motor circuit

3.2 x 125% = 4A 3.2A x 3 = 9.6A + 4A = 13.6A.

All other motors

3.2 x 125% = 4A 3.2A x 6 = 19.2A

NEC 310.15

Look at table 310.16 to determine proper wire size. 14 AWG would suffice for the smallest circuit at 15amps. 12 AWG would suffice for the larger circuit at 20 amps.

5. Grounding

Ensure proper grounding according to NEC Article 250. Since these are cord-and-plug connected, grounding is usually handled through the equipment grounding conductor in the cord.

Why Not Just Use FLC?

You are using the FLC. The NEC requires you to increase the FLC by 125% in many cases to account for continuous duty and potential overload conditions.

Important Considerations and Cautions



Local Codes and AHJ

Always check with your local electrical inspector (AHJ - Authority Having Jurisdiction) for any specific requirements or interpretations of the NEC. Local codes may be more stringent.

Voltage Drop

Consider voltage drop, especially if the distances from the panel to the motors are significant. Excessive voltage drop can damage motors. Use voltage drop calculators to ensure your conductor size is adequate.

Motor Nameplate

Verify the information on the motor nameplates matches what you've been given.

Professional Assistance

If you are not completely comfortable with electrical calculations and NEC requirements, it's always best to consult a qualified electrician. Improperly sized electrical circuits can be dangerous and lead to fire hazards.

Overload Protection vs. Short-Circuit/Ground-Fault Protection

Remember that the electronic protection within the motor is designed to protect against overloads. The circuit breaker (or fuses) provides protection against short circuits and ground faults*.

In summary, your approach is good, but make sure you carefully review the NEC sections mentioned and consider all the important factors before making any changes to your electrical system.Disclaimer: This information is for general guidance only. It's essential to consult with a qualified electrician and refer to the latest edition of the National Electrical Code (NEC) for accurate and code-compliant installations. Incorrect electrical work can be dangerous. Flag for review