# Why do most AC motors run at 1725 RPM?

**URL:** <https://boards.straightdope.com/t/why-do-most-ac-motors-run-at-1725-rpm/285596>\
**Category:** Factual Questions\
**Created:** [January 19, 2005, 7:13pm UTC](https://boards.straightdope.com/t/why-do-most-ac-motors-run-at-1725-rpm/285596 "2005-01-19T19:13:55Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Emilio\_Lizardo](https://avatars.discourse-cdn.com/v4/letter/e/898d66/32.png) [@Emilio\_Lizardo](https://boards.straightdope.com/u/Emilio_Lizardo)\
**Post date:** [January 19, 2005, 7:13pm UTC](https://boards.straightdope.com/t/why-do-most-ac-motors-run-at-1725-rpm/285596/1 "2005-01-19T19:13:55Z")

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I would have thought the standard would be some multiple of 60Hz; why 1725 instead?

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**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\
**Post date:** [January 19, 2005, 7:24pm UTC](https://boards.straightdope.com/t/why-do-most-ac-motors-run-at-1725-rpm/285596/2 "2005-01-19T19:24:12Z")

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> [@Emilio Lizardo](#):
>
> I would have thought the standard would be some multiple of 60Hz; why 1725 instead?

See [http://www.aosmithmotors.com/html/motorDoctor/Determiningspeed.htm](http://www.aosmithmotors.com/html/motorDoctor/Determiningspeed.htm)

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**Author:** ![daffyduck](https://avatars.discourse-cdn.com/v4/letter/d/ec9cab/32.png) [@daffyduck](https://boards.straightdope.com/u/daffyduck)\
**Post date:** [January 19, 2005, 9:01pm UTC](https://boards.straightdope.com/t/why-do-most-ac-motors-run-at-1725-rpm/285596/3 "2005-01-19T21:01:44Z")

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You’re right. The theoretical speed is 1800 rpm. However, due to friction and other factors, the actual speed ends up being anywhere from 1775 to 1725 RPM.

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**Author:** ![Stan\_Doubt](https://avatars.discourse-cdn.com/v4/letter/s/53a042/32.png) [@Stan\_Doubt](https://boards.straightdope.com/u/Stan_Doubt)\
**Post date:** [January 19, 2005, 10:34pm UTC](https://boards.straightdope.com/t/why-do-most-ac-motors-run-at-1725-rpm/285596/4 "2005-01-19T22:34:04Z")

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I have nothing to add to the OP, but I wanted to jump in and thank **mks57** for that excellent link.