Fan Motors Demand Calculator

Understanding Fan Motors Demand Calculation at Continuous Duty

Accurately determining electrical demand for industrial fan motors operating under continuous duty cycles is critical for designing safe, compliant electrical distribution systems. Continuous loads, by standard definition in electrical codes such as the NEC, are loads where the maximum current is expected to continue for three hours or more. Because fan motors run continuously in HVAC, ventilation, and industrial exhaust systems, sizing conductors, transformers, and protective devices requires factoring in a safety multiplier—typically 125% of the full-load motor rating.

Formula Used

The total electrical demand for continuous duty fan motors is calculated using mechanical power conversion combined with electrical efficiency and continuous multipliers:

• Total Horsepower (HP): Sum of all active motor ratings $\sum (Qty \times HP)$
• Power Conversion: $KW = Total HP \times 0.746$
• Continuous Demand Load: $Demand (kW) = KW \times \left(\frac{Duty Factor}{100}\right)$
• Total Current (Amps): $I = \frac{KW \times 1000}{V \times \sqrt{3} \times PF \times Eff} \times \left(\frac{Duty Factor}{100}\right)$ (for 3-phase systems)

How to Use This Calculator

1. Input your facility's system voltage, phase type, power factor, and motor efficiency percentages in the first column.
2. Enter the exact quantity and horsepower ratings of your deployed small, medium, large, and heavy-duty fan motors into the second column.
3. Adjust the continuous duty factor multiplier (default is 125%) and click the Calculate Demand button to instantly view aggregated results above.

Frequently Asked Questions (FAQs)