every electric (non-ceiling) fan I have ever used is operated with a dial with settings off, high, mid, and low in that order. Why does it go from off straight to high? Why not do the more intuitive “get higher the more you turn away from off”?
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ELI5: The “High” first is needed to ensure the fan begins rotating (does not stall) and also turns in the correct direction.
ELI’mOlder: Unlike DC, there really is no “positive” and “negative” with single phase AC. (If you don’t understand what single phase means, don’t worry, you don’t need to worry about it. Single phase is what you have in your homes.) It doesn’t matter HOW you connect the fan to the hot and neutral wires, the fan will SEE the same waveform. (Because the 120V, 60 Hz waveform is symmetrical about the X axis). If you have a multimeter, try this (safely) yourself. Go measure the outlet in your home. Put red in the hot side and black in the neutral side, then switch them. They both measure +120V (or whatever your local voltage is.)
Because of this, we actually need to do some electrical trickery to ENSURE that the fan turns on and spins in the correct direction. Unlike a DC motor or fan, we can’t just “switch the leads” and get the fan to turn in the opposite direction. Because switching the leads does nothing. If you just took a normal AC electric motor, without any of this trickery, there are three things that could happen when you plugged it in.
1. The motor would turn clockwise.
2. The motor would turn counterclockwise.
3. The motor would stall (the “poles” of the “spinny part” of the motor can get magnetically “caught” between the “poles” of the “non spinny part” of the motor.)
If the motor stalls (which honestly is pretty common on a motor without a starting capacitor), it does not matter how much voltage you apply, it will REMAIN stalled (because more voltage would just hold it in place “harder.”) (This is why on some old sewing machines, you gotta “help” it get started in the correct direction.)
Because we always want fans to turn on and run in the same direction (well, MOST fans), we do some electrical trickery. Mainly it’s a capacitor. From what I understand, they use this capacitor to inject an additional phase into the motor to ensure it turns on in the correct direction.
The reason “High” is first is because it requires a lot of current to start an electric motor, and if low was first there’d be a higher chance that it could get stalled. Think about it like trying to start a lawnmower. What’s more likely to start it, a shorter, very hard pull, or a long, very slow pull?
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