Motor FLA & Protection Calculator (NEC Art. 430)
Size conductors, breakers, and overload protection for safe motor operation.
1Motor Specs
Assumptions
- Motor Type: Induction / Squirrel Cage
- Wire Type: Copper, THHN (75°C Terminations)
- Duty: Continuous
- Protection: 250% of Table FLC
Full Load Current (FLC)
Breaker
Short Circuit Protection
Max 250% of FLC (NEC 430.52). Rounded up to next standard size.
Wire Size
Branch Circuit
Min 125% of FLC (20.0A). Based on 75°C column.
NEMA Starter
Motor Controller
Standard NEMA size for 1 HP @ 115V.
Overload
Heater Setting
115% of Table FLC.
Popular motor control Configurations
Motor Sizing Formula
Ioverload = Inameplate × Service Factor
NEC Article 430
Article 430 covers motors. Table 430.248 (1-phase) and 430.250 (3-phase) provide FLC currents. 430.52 dictates maximum short-circuit and ground-fault protection settings.
Frequently Asked Questions
Do I use nameplate amps or NEC table amps?
For sizing conductors and short-circuit protection (breakers/fuses), you MUST use NEC Table values. For sizing Overload protection (heaters), you use the Nameplate current.
What size breaker do I need for a motor?
Inverse time breakers are typically allowed up to 250% of the motor's FLC per Table 430.52 to handle inrush current without nuisance tripping.
What size wire do I need for a motor?
Conductors supplying a single motor must have an ampacity of at least 125% of the motor's FLC Rating (NEC 430.22).