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Starting Amps Formula:
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Motor Starting Amps (also known as Locked Rotor Amps) is the current drawn by an electric motor when it first starts up. This initial current surge is significantly higher than the normal running current and is a critical factor in motor protection and circuit design.
The calculator uses the NEMA standard formula:
Where:
Explanation: The starting current is typically 6 to 8 times the full load current for standard induction motors, depending on motor design and application.
Details: Accurate starting current calculation is essential for proper circuit breaker sizing, motor starter selection, voltage drop calculations, and ensuring reliable motor operation without nuisance tripping.
Tips: Enter the motor's full load current in amps and select the appropriate code factor (6, 7, or 8) based on motor type and application requirements.
Q1: What is the difference between starting amps and running amps?
A: Starting amps are the initial surge current when the motor starts (6-8 times FLC), while running amps are the current drawn during normal operation (equal to FLC).
Q2: When should I use factor 6 vs 7 vs 8?
A: Use factor 6 for high-efficiency motors, factor 7 for standard motors, and factor 8 for motors with high starting torque requirements or older designs.
Q3: How does starting current affect circuit protection?
A: Circuit breakers and overload relays must be sized to handle the starting current surge without tripping, while still providing protection against actual faults.
Q4: Can starting current be reduced?
A: Yes, through soft starters, variable frequency drives (VFDs), or reduced voltage starting methods like star-delta starting.
Q5: What factors affect starting current?
A: Motor design, load characteristics, supply voltage, and starting method all influence the actual starting current drawn.