1. What is Breaker Size Calculation?

The breaker size calculation determines the appropriate circuit breaker rating for an electric motor based on its full load current (FLA). The standard multiplier of 2.5 accounts for startup current surges while providing overload protection.

2. How Does the Calculator Work?

The calculator uses the standard formula:

Where:

• FLA — Full Load Amps (motor nameplate rating)
• 2.5 — Standard multiplier for motor circuits

Explanation: The calculator provides both the calculated value and the next standard breaker size for practical application.

3. Importance of Proper Breaker Sizing

Details: Correct breaker sizing prevents nuisance tripping during motor startup while ensuring protection against overloads and short circuits. Undersized breakers trip unnecessarily, while oversized breakers may not provide adequate protection.

4. Using the Calculator

Tips: Enter the motor's full load amps (FLA) from the nameplate. The calculator will provide the calculated breaker size and recommend the nearest standard breaker size.

5. Frequently Asked Questions (FAQ)

Q1: Why use 2.5 as the multiplier?
A: The 2.5 multiplier accounts for motor starting current (typically 6x FLA) while allowing normal operation without nuisance tripping.

Q2: What if my calculated size isn't standard?
A: Always round up to the next standard breaker size (15, 20, 25, 30, etc.). Never round down.

Q3: Are there exceptions to this rule?
A: Some motors with special starting characteristics or high inertia loads may require different calculations. Consult NEC Article 430.

Q4: Does this account for ambient temperature?
A: No, for high temperature environments or unusual conditions, additional derating may be necessary.

Q5: What about wire sizing?
A: Wire size must be appropriate for both the breaker size and motor requirements (125% of FLA minimum).