# Synchronous Speed? **URL:** \ **Category:** Factual Questions\ **Created:** [November 3, 2002, 3:06am UTC](https://boards.straightdope.com/t/synchronous-speed/135056 "2002-11-03T03:06:39Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [November 3, 2002, 3:06am UTC](https://boards.straightdope.com/t/synchronous-speed/135056/1 "2002-11-03T03:06:39Z")
This should be easy enough for the mechanically inclined Sdopers. What is synchronous speed for a motor? If it matters, this question is regarding motors used on industrial pumps, so I WAG they must be three-phase AC motors. Is it 3600 rpm? Does it have something to do with 60 Hz \* 60 s/min = 3600? Thanks, - Jinx ---
**Author:** ![AndrewL](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AndrewL](https://boards.straightdope.com/u/AndrewL)\ **Post date:** [November 3, 2002, 4:57am UTC](https://boards.straightdope.com/t/synchronous-speed/135056/2 "2002-11-03T04:57:04Z")
> [@](#): > > \*Originally posted by Jinx \* > \*\*Does it have something to do with 60 Hz \* 60 s/min = 3600? > \*\* That’s exactly why. A synchronous AC motor has an armature surrounded by non-moving windings. The AC current through the windings creates a rotating magnetic field that spins the armature. With a 60HZ line frequency, the magnetic field, and hence the armature, rotates 60 times per second. 60 HZ times 60 seconds per minute = 3600RPM. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [November 3, 2002, 6:29am UTC](https://boards.straightdope.com/t/synchronous-speed/135056/3 "2002-11-03T06:29:05Z")
Synchronous speed is 3600/N rpm, where N is the number of pairs of poles in the field winding.