1. What is NEC Motor Load Calculation?

The NEC (National Electrical Code) motor load calculation determines the total current required for multiple motors on a circuit. It accounts for the largest motor's starting current and combines it with the running currents of other motors.

2. How Does the Calculation Work?

The calculation uses the NEC formula:

Where:

• 1.25 — Factor for largest motor (accounts for starting current)
• Largest Motor — Full load amps (FLA) of the largest motor
• Sum of Other Motors — Combined FLA of all other motors

Explanation: The 125% factor for the largest motor accommodates starting current, while other motors are calculated at 100% of their full load current.

3. Importance of Proper Load Calculation

Details: Accurate motor load calculation ensures proper sizing of conductors, overcurrent protection, and other circuit components to prevent overheating and ensure safe operation.

4. Using the Calculator

Tips: Enter the full load current (in amps) of your largest motor and the sum of all other motors' full load currents. Values must be zero or positive.

5. Frequently Asked Questions (FAQ)

Q1: Why 125% for the largest motor?
A: The 125% factor accounts for the higher starting current (inrush current) that motors draw when they first start.

Q2: How do I find motor full load amps?
A: FLA is typically listed on the motor nameplate or can be found in motor performance tables based on horsepower and voltage.

Q3: Does this apply to all motor types?
A: This is a general calculation. Certain motor types (like hermetic refrigerant motors) may have different requirements.

Q4: What about continuous vs non-continuous loads?
A: Motor loads are generally considered continuous (operating 3+ hours), hence the conservative calculation.

Q5: Are there exceptions to this rule?
A: Yes, specific applications may have different requirements. Always consult the latest NEC code for exceptions.