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Generator Size Calculator
Running watts, motor starting surge, and recommended generator kW with transfer switch guidance
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NEC / Sizing Reference
Running WattsContinuous power draw during steady-state operation
Starting WattsInrush / locked-rotor current on motor start; only the single highest surge applies
×1.25 FactorPer NEC 445.12, generator nameplate rating must not be exceeded by connected load
NEC 702Optional Standby Systems — governs generator installation, transfer switches, and wiring
NEC 250.35Grounding of portable generators; bonding of equipment grounding conductor required
NEC 702.6Transfer equipment must prevent parallel operation with utility unless rated for it
Professional disclaimer: Generator sizing involves safety-critical decisions including fuel, ventilation, bonding, and transfer switch installation. This calculator provides estimates only. Always consult a licensed electrician and verify with the Authority Having Jurisdiction (AHJ) before installation.
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