Starting differs from running
A motor may briefly draw high current during starting, causing generator voltage and frequency dips. Successful starting depends on transient response, alternator capability, mechanical load, acceleration time and loads already running. Adding motor kW alone is insufficient.
Starting method changes the demand
Direct-on-line, star-delta, soft starters and variable-frequency drives have different current and torque characteristics. A universal “three times motor power” rule is not reliable. Soft starters and drives still require manufacturer input-current data, settings and compatibility checks.
An illustrative calculation only
Assume a balanced three-phase load at 400 V line voltage with a specified 300 A starting line current. Starting apparent power is approximately √3 × 400 × 300 ÷ 1000 = 208 kVA. This is not a recommended generator rating. Allowable voltage and frequency dips, starting duration and existing loads still need evaluation.
Prepare a useful starting-load inquiry
Send motor nameplates, starting or locked-rotor current, starting method and sequence, whether starting is loaded, and equipment voltage/frequency tolerances. Staggered starts may reduce simultaneous demand, subject to equipment supplier confirmation. If data is missing, begin with equipment photos and a load list.
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Technical reference: Cummins