INDUCTION MOTORS

Three-phase induction motors run near synchronous speed N_s = 120·f / P where f is line frequency and P is the pole count. Actual rotor speed N is below N_s by slip s = (N_s - N) / N_s, typically 1-5% at full load. Full-load amps (FLA) follow I_FL = P_out / (sqrt(3)·V_LL·η·PF) for three-phase. Starting current (locked-rotor) is 5-7× FLA; voltage dip during start is a common system constraint. Service factor (SF) allows brief overload (1.0 standard, 1.15 typical for premium-efficiency).

• N_s = 120 · f / P
• s = (N_s - N) / N_s
• I_FL = P_out / (sqrt(3) · V_LL · η · PF) (3φ)
• T = (P_out · 9.55) / N_rpm (N·m)
• I_LR ≈ 6 · I_FL (typical)

References & StandardsNEMA MG 1, NFPA 70 Article 430, IEEE 841

Size feeders, starters, and overload protection per NEC Article 430. Verify branch conductor ampacity at 125% of FLA, short-circuit and ground-fault protection at the appropriate multiple. For VFD-driven motors, derate for harmonic heating. Reduced-voltage starters or soft-starts limit inrush when supply impedance is constrained. Always check name-plate FLA, not table values, for the actual motor.