Motor Pole Count from Nameplate RPM

From the nameplate full-load rpm and line frequency, the pole count is the nearest even integer to 120 x f / rpm - pole-pairs = round(60 x f / rpm), poles = 2 x pole-pairs, then Ns = 120 x f / poles and the slip. A 1750 rpm 60 Hz motor is 4-pole (Ns 1800, 2.78% slip); 1150 rpm is 6-pole, 3450 rpm is 2-pole. A speed at/above the identified Ns (zero or negative slip) never appears on an induction nameplate - recheck the rpm. The nameplate governs.

pole-pairs = round(60 x f / rpm); poles = 2 x pole-pairs; Ns = 120 x f / poles; slip = (Ns - rpm) / Ns.

First-principles AC-machine speed relation Ns = 120 x f / P inverted to identify the poles; classical induction-machine theory.

First-principles physics; no licensed source required.

Estimate. AHJ and licensed professional govern.

Field names used by the API: rated_rpm, line_freq_hz, poles, sync_rpm, slip_pct

• Nearest even poles poles = 2 x round(60 x f / rpm); the synchronous speed sits just above the running speedAC-machine theory
• Induction machine the nameplate speed is below synchronous; a zero/negative slip flags a bad rpm or frequencyAC-machine construction