Electrical & Controls
Motor synchronous speed and slip
Synchronous speed from poles and frequency, and slip from actual speed.
Calculating…
How it's calculated
Ns = 120 × f ÷ p
Slip = (Ns − N) ÷ Ns × 100%
An induction motor always runs slightly below synchronous speed; the difference is slip, typically 1–5% at full load. A 4-pole motor on 50 Hz has a synchronous speed of 1500 rpm and usually runs at about 1440–1480 rpm. On 60 Hz it is 1800 rpm.
If you know the nameplate speed, the nearest synchronous speed above it tells you the pole count.