Motor Overcurrent Protection Calculator
Determine the correct OCPD size for motor circuits based on NEC guidelines
Motor OCPD Calculator
Compliant with NEC® 2023 Standards
Results:
Calculated OCPD (A): 0.00
Standard OCPD Size (A): 0
How to Use the Calculator
Input Motor FLA
- Enter the Full Load Amps (FLA) of the motor. This can usually be found on the motor's nameplate.
- Ensure the value is accurate for precise calculations.
Select OCPD Type
- Choose the type of Overcurrent Protection Device (OCPD) you plan to use.
- Options include Non-Time Delay Fuse, Time-Delay Fuse, Inverse Time Breaker, and Instantaneous Trip Breaker.
View Results
- Click "Calculate" to see the calculated OCPD size.
- The calculator will also provide the nearest standard OCPD size, which is crucial for selection.
Motor Overcurrent Protection Fundamentals
Purpose of OCPD
Overcurrent Protection Devices (OCPDs) protect motor branch-circuit conductors, motor control apparatus, and motors from overcurrents due to short circuits or ground faults.
- Prevents equipment damage
- Ensures electrical system safety
- Complies with electrical codes
NEC Guidelines
- NEC Article 430 provides specific requirements for motor circuits.
- The maximum OCPD size is based on a percentage of the motor's Full Load Amps (FLA).
- Different OCPD types have different maximum percentages.
Key Multipliers (NEC 430.52(C)(1)):
Non-Time Delay Fuse: 300% of FLA
Time-Delay Fuse: 175% of FLA
Inverse Time Breaker: 250% of FLA
Instantaneous Trip Breaker: 800% of FLA
Calculation Formulas
OCPD Size = Motor FLA × Multiplier
Where Multiplier depends on OCPD type:
Non-Time Delay Fuse: 3.00
Time-Delay Fuse: 1.75
Inverse Time Breaker: 2.50
Instantaneous Trip Breaker: 8.00
Example Calculation
Motor FLA: 50A
OCPD Type: Inverse Time Breaker
Multiplier for Inverse Time Breaker = 2.50
Calculated OCPD = 50A × 2.50 = 125A
Nearest Standard OCPD Size = 125A