Induction Motor Slip

An induction motor's rotor must lag the rotating field — if it ever caught up, the field would stop sweeping past the rotor bars, no voltage would be induced, and no torque would exist. That lag is slip. A 4-pole motor on 60 Hz has a synchronous speed of 1800 rpm; a nameplate reading of 1750 rpm means s = 100 × 50/1800 ≈ 2.8%, entirely typical for a healthy machine at full load.

Slip is a free load indicator: it is very nearly proportional to torque, so a tachometer reading tells you how hard the motor is working without a single meter lead. At no load slip falls under 1%; at breakdown torque it may hit 20%. Rising slip on a familiar machine means added mechanical load, low voltage, or a broken rotor bar. Note that this solver treats rpm as a frequency, so answers appear in hertz unless you pick rpm from the table.