Why Is the US Standard 60 Hz?

February 01, 2016 by PatrickM

The choice of 60 Hz for the AC line frequency is a win for Tesla’s engineering, but 110 V is an example of compromise for Edison’s business interests,

Our history determines our standards.

It’s one of those things I never actually recall stopping to think about as I flew through college and then into the working world, but when I picked up Tesla: Man Out of Time by Margaret Cheney, I found why our US grid is 60 Hz (AC at 110 V). It turns out it’s a combination of great genius and horrible compromise for the sake of business. As is so often the case.

Where did 60 Hz AC Come From?

The origin of 60 Hz AC, as many of you probably know, goes all the way back to Nikola Tesla, our favorite engineer. He first worked for, and then later was forced to compete viciously with, Thomas Edison. That competition is a whole story unto itself and one that has left me very cold toward Edison.

It’s funny how history leaves little things out, like how Edison hired kids to kidnap neighborhood cats and dogs so he could electrify them to show how dangerous Tesla’s AC distribution system was compared to his own DC system. Or how he electrified an elephant and recorded it, or invented the execution chair using AC and marketed the act as being “Westinghoused” because of George Westinghouse’s support of Tesla.

What does all this have to do with 60 Hz? Well, when Westinghouse wanted to build an electrical supply grid using the kinetic power of Niagara Falls circa 1888, he turned to Tesla, as Tesla had earlier demonstrated the benefits of AC and knew a few things about electric motors and power distribution. He had already done the analysis and already figured out that 60 Hz at 220 Vac was the most efficient means of doing so.

Thomas Edison

Edison--a genius, but a genius at any cost.

However, Westinghouse’s engineers had already committed to 133 Hz. In her book, Cheney said it best:

“When he so informed the engineers, he succeeded in rubbing them the wrong way and only after months of futile and costly experiments doing it their way, did they finally accept his word. Once they had done so, the motor worked exactly as it had been designed to. Sixty cycles has ever since been the standard for alternating current.”

Now, this paragraph is absolutely loaded with stereotypical engineer psychology: for instance, Tesla’s unerring precision and exactitude combined with a disassociation from the “feelings” of the other engineers. On the other side, the 133-Hz advocates were stubbornly typical in their disdain of this “outsider” (aka: “not invented here,” syndrome) and were determined to prove out their own work. 

Tesla's induction motor

Tesla's induction motor

Still, given the time, proving the efficiency of 60 Hz with respect to driving Tesla’s induction motor was critical, as motors were the heart of the industrial revolution, which was then in full throttle.

As to how we ended up with 110 Vac vs Tesla’s preference for 220 Vac, we can thank Edison, who already had an installed base of 110 Vdc, so there was a compromise to accommodate business. “A most un-American mental attitude,” said Tesla’s fellow Serb, Michael Pupin, who worked for Edison but had a hard time understanding why business would ignore the engineering experts.

Some things never change.

So, do you know why Europe is 50 Hz AC (15 to 20 percent less efficient)?

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    SamCummins February 02, 2016

    I don’t know why Europe is 50 hz.  I don’t know why that would be less efficient.  The power factor would increase, but that may not correlate to efficiency. 

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    • tonyr1084 February 12, 2016
      I was hoping to learn more about why 60 Hz is most efficient. So all I can offer is a guess: I think it has to do with the rate of change in the magnetic flux. Motors seem to work better on 60 Hz. Maybe 70 Hz is too fast for the motor to convert the magnetic force into torque, same as 50 Hz may be too slow to take full advantage of it. Remember, this is just a guess.
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  • Shae Abraham February 03, 2016

    Good story however I would like to see the more technical side as to why 60 Hz is the most efficient frequency.

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