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A 3‑phase electric motor is a sizable piece of equipment that operates on a polyphase circuit, enabling it to handle heavy power loads at lower voltages. This setup improves line efficiency and delivers the steady power flow required by many industrial machines. While the cost of running a 3‑phase motor is ultimately based on kilowatt‑hours, determining its consumption involves a slightly modified power equation.
Consult the motor’s manufacturer specification sheet for the line voltage. Most motors display the operating amperage on a built‑in meter. If not, use a 3‑phase ammeter that can safely handle the motor’s current. Follow the ammeter’s wiring instructions to obtain an accurate reading.
For a 3‑phase motor, the active power (W) is calculated with:
W = A × V × √3
Where √3 ≈ 1.73. For example, a motor drawing 50 A at 240 V consumes:
W = 50 × 240 × 1.73 ≈ 20,760 W (20.76 kW).
Document the motor’s daily operating time. In a typical manufacturing setting, a 3‑phase motor might run 8 hours per day, 5 days a week. That averages to roughly 173.3 hours per month.
Multiply the power (kW) by the monthly hours:
kWh = 20.76 kW × 173.3 h ≈ 3,771.7 kWh per month.
Apply your local electricity rate. If the tariff is $0.10 per kWh, the monthly cost is:
Cost = 3,771.7 kWh × $0.10/kWh ≈ $377.17.
Even small errors in voltage, amperage, or operating time can lead to significant cost miscalculations, especially for facilities with multiple motors. Regularly verify readings and adjust for power factor losses to maintain precise budgeting.
For detailed rate tables or advanced calculations, consult your utility’s website or a qualified electrical engineer.
