Electrical Motors - Speed at Operating vs. Synchronous Load

Speed of an operating electrical motor with load is lower than the synchronous speed (no load) of the motor. This tool provides synchronous and approximate speed (rpm) at rated load for small and medium motors operating at 60 Hz and 50 Hz.

No. Poles	Speed with Rated Load (60 Hz)	Speed with Rated Load (50 Hz)	Synchronous Speed (60 Hz)	Synchronous Speed (50 Hz)
2	3450	2850	3600	3000
4	1725	1425	1800	1500
6	1140	950	1200	1000
8	850	700	900	750

Reference Information

Synchronous Speed Formula:

Synchronous Speed (rpm) = (120 × Frequency (Hz)) / Number of Poles

Speed Slip:

Slip = (Synchronous Speed - Operating Speed) / Synchronous Speed × 100%

The operating speed is always lower than the synchronous speed due to mechanical load and slip in the motor.