Why 60Hz?

I was recently posed a question that I didn't know the answer to. Maybe I just forgot. Now I know.

POP QUIZ - Question of the day: Why 60Hz? Why not 220? Or 221? Or 440? Or 880?

Why not 400Hz? (This is where you military types can jump in and explain where you DO use 400).

Didja know?

Doesn't it have something to do with the fact that time is based on 60ths of things. i.e. 60 cycles per second, 60 seconds per minute, 60 minutes per hour. I heard a story one time about a clockmaker being the major push for the choice of 60 hz, so that he could use line voltage easily, but I don't know if its true.

correct me if I'm wrong but doesn't the rest of the world (Europe and Japan anyway) run on 50Hz?

MA_PE said:

correct me if I'm wrong but doesn't the rest of the world (Europe and Japan anyway) run on 50Hz?

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Yep, thats right. And in europe, most residential voltage is 230 V instead of 115.

Check out this entry on Wikipedia.

So what would it take to convert the U.S. (which is certainly in the minority) to 220V 50hz? I'd think the frequency is only a problem for big motors (I'm thinking refrigerators and other appliances with compressors would be the biggest issues). To go to 220V we could get by with the same diameter wire? If 220V were going to 110V wouldn't it require larger diameter wire?

It seem like most electronics these days are dual voltage and 50/60hz. What say we make the change the same day we go to metric? Yeah, right.

That Wiki-entry was more than I ever wanted to know!

A EE prof I was chatting with recently told me the reason we use 60Hz and not higher (50Hz if you're a euroweenie) is that the higher frequencies are audible - to the human ear, 60Hz is not. I asked what about power transformer hum and he says that's a mechanical vibration.

That Wiki-entry gives some great detail on why lower frequencies fell out of favor.

Wolverine said:

That Wiki-entry was more than I ever wanted to know!
A EE prof I was chatting with recently told me the reason we use 60Hz and not higher (50Hz if you're a euroweenie) is that the higher frequencies are audible - to the human ear, 60Hz is not. I asked what about power transformer hum and he says that's a mechanical vibration.

That Wiki-entry gives some great detail on why lower frequencies fell out of favor.

Click to expand...

Actually the audible frequency range is from about 20 Hz to 20,000 Hz. A pure 60 Hz tone would be audible.

However you have to move the air for it to be audible. I suspect the "hum" from large electrical cabinets is related to physical movement (although very slight) of components driven by the alternating current. If you pick up a sheathed lamp cord with the light on, you can't "feel" the electric power going through the cord. However, you can feel the "buzz" if you hold some larger energized cords/cables (even without touching the live bare wires).

Wolverine said:

A EE prof I was chatting with recently told me the reason we use 60Hz and not higher (50Hz if you're a euroweenie) is that the higher frequencies are audible - to the human ear, 60Hz is not. I asked what about power transformer hum and he says that's a mechanical vibration.

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Isn't ALL sound due to a mechanical vibration? <_< It isn't like you can hear electric current flowing through a wire at 200hz if there is no mechanical vibration. I think he needs to re-think his theory.

I was always under the impression that 60 hz was used for three reasons:

1) Consistent units of time, as mentioned before. 60 minutes in an hour/60 seconds in a minute/60 cycles in a second

2) Optical clarity - A fluorescent light bulb flashes on and off at the frequency of the line voltage, as do CRT screens. And most humans can detect around 30-40 flashes a second; some people who have not polluted their eyes reading "Fudgey" stories can detect close to 50 flashes per second. (Strobe lights were fun at high school dances, but I’d hate to live my life under one.)

3) Higher frequencies allow for smaller transformers; less iron and copper.

SteveR said:

Isn't ALL sound due to a mechanical vibration? <_< It isn't like you can hear electric current flowing through a wire at 200hz if there is no mechanical vibration. I think he needs to re-think his theory.

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To get technical (and this is an engineering forum) sound is due to fluctations in air pressure sensed by the ear drum. The mechanical vibrations force air movements which cause changes in pressure.

to quote a movie trailer ...."In space no one can hear you scream."

Freon said:

2) Optical clarity - A fluorescent light bulb flashes on and off at the frequency of the line voltage, as do CRT screens. And most humans can detect around 30-40 flashes a second; some people who have not polluted their eyes reading "Fudgey" stories can detect close to 50 flashes per second. (Strobe lights were fun at high school dances, but I’d hate to live my life under one.)

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Actually I believe fluorescent lamps typically operate at 20kHZ to 120kHZ. The ballast increases the frequency to the lamp. Incandescant lamps however do pulse at 60hz. And the refresh rate of a CRT can be varied...it is not set by the frequency of the supply voltage.

#3 makes sense though.

My first answer was the 60 base for time, but the prof rejected that.

The argument that higher frequency allows for less transformer core iron came up, but that was cited as a reason military (and other self contained installations, like ships) might use 400Hz systems.

His postulation I think was that, while 60Hz may be audible, it's not easily audible by the human ear, say like a 440hZ signal. The more I think about it though, the more I think I'd like to hear an amplified 60Hz signal to see if I can hear it or not. I might call BS.

The Wiki entry seems to point towards 60 as the Goldilocks number, found after years of iteration - not too hot, not too cold, but just right. I'm not sure there's a pure answer to the question but it's interesting discussion.

60 Hz is sort of a low "mid bass" tone. Anyone with normal hearing would be able to hear a 60 Hz tone. Below 20 Hz, bass is "felt" but not truly "heard". You can "hear" 60 Hz electrical current as a "hum" sometimes in a stereo system if you have grounding problems, or if you get an unsheilded interconnect wire to near a power supply line. Or at least, that's how it has seemd to me, playing around with stereo gear.

Audio pure tone - test files

Check out this link to hear some pure tones (based on the site, I haven't checked them on a scope).

The files are set up to play quick bursts at descending amplitudes. It took some fudging with the speaker settings on my computer to hear the 60Hz through my cheap ear bud speakers (It's one of the freebie headsets from Jet Blue). But I could distinctly hear the first 3-4 bursts. It is a bass tone.

Higher frequencies are heard much more easily. You can also enable the visualization feature on the *.wav player to confirm that there is indeed a signal playing.

Have fun.