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Nominal Size Breaker for Motor

  1. This expert calculator provides the nominal and maximum size breaker for motor or feeder circuit given electrical load requirements.
  2. Although the expert calculator provides the maximum size breaker and overload protection allowed by code a smaller size breaker or overload protection is generally used.
  1. NEC Code Compliant
  2. Motor /Feeder is less than 700 Amps
  3. Motor / Feeder is less than 2000 Volts
  1. NEC 2005 Sections 430 and 316
Step 1: NEC® Motor Table Data
1.1 Type of Motor Power Supply (used to determine Full Load Current)
1.2 Horse Power
1.3 Motor Voltage
Step 2: Motor Name Plate
2.1 Service Factor
2.2 Temperature Rise Rating (in degrees Celsius)
2.3 Full Load Amps (FLA) (leave blank if not known)
2.4 Type of Motor
Step 3: Short Circuit and Ground Fault Protection
3.1 Short Circuit and Ground Fault Protection
Step 4: Conductor Data
4.1 Conductor Type
4.2 Conductor Insulation
4.3 Temperature Rating of Conductor (in degrees Celsius)
Step 5: Installation Data
5.1 Min. Equipment Terminal Rating (in degrees Celsius)
5.2 Equipment Terminal Rating
5.3 Highest Ambient Temperature
5.4 Conductor Length
5.5 Number of Current Carrying Conductors
Step 6: Solve
6.1 Proof steps
6.2 Solve for Nominal Sized Breaker