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Breaker Calculation Formula:
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Motor breaker calculation determines the appropriate circuit breaker size for protecting three-phase motors. The standard calculation multiplies the motor's Full Load Amps (FLA) by 2.5 to determine the breaker size needed for proper motor protection and safe operation.
The calculator uses the standard breaker calculation formula:
Where:
Explanation: The 2.5 multiplier accounts for motor starting currents which are typically 6-8 times the running current, while providing adequate overload protection.
Details: Correct breaker sizing is crucial for motor protection, preventing damage from overloads and short circuits while allowing for normal starting currents. Undersized breakers may trip unnecessarily, while oversized breakers may not provide adequate protection.
Tips: Enter the motor's Full Load Amperage (FLA) value as specified on the motor nameplate. Ensure the value is in amperes (A) and is greater than zero.
Q1: Why use a 2.5 multiplier for motor breakers?
A: The 2.5 multiplier accommodates high starting currents while providing overload protection, following NEC guidelines for motor circuit protection.
Q2: When might this calculation need adjustment?
A: Special applications like high-inertia loads, frequent starts, or specific motor types may require different multipliers per manufacturer recommendations.
Q3: Is this calculation suitable for all motor types?
A: This calculation is standard for most three-phase AC induction motors. Always consult manufacturer specifications for specialized motors.
Q4: What about wire sizing for motor circuits?
A: Wire sizing should be based on 125% of motor FLA per NEC requirements, which is separate from breaker sizing calculations.
Q5: Should this calculation be used for motor starter selection?
A: No, motor starter selection follows different criteria. This calculation is specifically for circuit breaker sizing.