Formula and Method
Three-phase motor FLC = output power / (sqrt(3) x voltage x power factor x efficiency). Horsepower is converted to watts before calculation.
Assumptions
- Three-phase motor
- Nameplate data is not available
- Overload setting is a starting reference only
Important Warnings
- Motor protection settings must follow the motor nameplate, starter type, duty, and applicable standard.
- Starting current, utilization category, and coordination are not selected here.
FAQ
Can this select a contactor size?
It provides a current estimate. Contactor selection also needs utilization category, voltage, duty, and coordination requirements.
Should overload relay setting equal breaker size?
No. Overload protection and short-circuit protection have different jobs and are selected differently.