1. Estimate full-load current
For three-phase output power, I = Pout / (√3 × U × η × cos φ). For 7.5 kW, 400 V, efficiency 0.90 and power factor 0.85, estimated current is 14.15 A.
2. Check the actual motor
Use the motor nameplate and starting method. Starting current, start duration and duty can change the suitable protection. A design multiplier is not an automatic overload or breaker setting.
3. Select the complete combination
Check the overload, contactor, disconnect and short-circuit protective device together. Use the relevant manufacturer coordination data and rating conditions for the intended installation.
4. Review short-circuit capability
Open FaultChain with the site fault current and verified device data. Numerical peak and energy checks alone do not establish UL combination approval.
Source: UL combination motor controller ratings
5. Engineering protection checklist
A complete motor branch is more than a breaker and an overload setting. Treat the motor, conductors, contactor or starter, overload device, disconnect and short-circuit protective device as one coordinated system.
- Running current: start with the applicable code table or nameplate value required by the adopted rules; use the FLC calculator only as an engineering estimate where appropriate.
- Starting duty: verify starting current, acceleration time, starts per hour and the selected starting method so nuisance operation is not mistaken for protection.
- Overload protection: set and select the overload function from the applicable motor data and rules, not from a generic multiplier.
- Short-circuit protection and SCCR: verify the protective device, available fault current, tested combination and manufacturer coordination tables for the exact components and ratings.
Release rule: final device selection requires the adopted code edition, motor nameplate, manufacturer data and the actual installation conditions. A numerical current estimate alone does not establish a compliant or tested motor-control combination.