1. What is the Breaker Size Calculation?

The breaker size calculation determines the appropriate circuit breaker size for electric motors based on the full load amperage (FLA). The National Electrical Code (NEC) typically recommends sizing breakers at 250% of the motor's full load current.

2. How Does the Calculator Work?

The calculator uses the standard breaker sizing formula:

Where:

• \( I_{\text{fla}} \) — Full Load Amperage of the motor
• 2.5 — Standard multiplier for motor circuit protection

Explanation: The 250% multiplier accounts for motor starting current which can be 6-8 times the running current.

3. Importance of Proper Breaker Sizing

Details: Correct breaker sizing prevents nuisance tripping during motor startup while providing adequate protection against overloads and short circuits.

4. Using the Calculator

Tips: Enter the motor's full load amperage (FLA) as specified on the motor nameplate. The value must be greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: Why is the multiplier 2.5?
A: NEC Article 430.52 typically requires motor branch circuit protection to be no more than 250% of the motor's full load current for standard applications.

Q2: Are there exceptions to this rule?
A: Yes, some motor types or applications may require different multipliers. Always consult the NEC and local codes.

Q3: What about motor starter sizing?
A: Motor starters are sized differently from breakers, typically based on motor horsepower and voltage.

Q4: Should I round up the breaker size?
A: Yes, you should round up to the next standard breaker size after calculation.

Q5: Does this apply to three-phase motors?
A: Yes, the same multiplier applies to both single-phase and three-phase motors.