Every electric fan that I’ve ever had with a speed knob goes “Off-High-Med-Low.” Our current and previous gas stoves, along with my friend’s electric one, goes the same way “Off-6-5-4-3-2-1.”
Why doesnt it go from “Off-Low-Med-High”? The odd way its arranged isnt on every appliance, but a lot of it. It just seems weird that they would do it this way. 
My gut reaction is that it’s because of how those kinds of rotary knobs work. IIRC, they are often connected to a metal strip which is coiled into a spring that resembles a rolled-up tape measure. As you turn the knob, the tension in that spring changes, and that controls the appliance.
I’m not entirely sure how adjusting the spring relates to output of the device but I think it has something to do with an increase in the tension of the spring causing a decrease in the flow of electricity to the device’s motor/heating element/whatever. When there’s only a little tension, as when you’ve only turned the knob one click to “High”, the not-very-tense spring allows a lot of current through, possibly by completing a circuit; as you continue to turn the knob, the spring is placed under additional tension, reducing the current flow and thus the output; continuing with my circuit explanation from last sentence, I would guess the tension causes the spring to no longer complete the circuit as completely as it did before, thereby reducing current flow.
Of course, this is all based upon an incident in which I accidentally pulled the controller knob off the clothes dryer and got to see what was underneath, so I’m pretty much just guessing…
If anyone else has, y’know, a REAL answer, I too would love to hear it, as I’ve often wondered this same thing.
When you are starting up a motor you want it to give it high current to get it up to speed quickly. Then you can “tone it down” so to speak.
It’s even more important with the gas stove that it gives out a lot of gas so it ignites easily. Then you can back it off. It’s easier and safer to do it that way then to have to turn the knob all the way around to get ignition, then have to return it.
There’s been many previous threads on this and they all have zillions of examples of fans that go Off-Low-Med-High. I own one myserlf.
My gas stove requires a full turn, past HIGH, to LIGHT when you turn it on. Just to the left of LIGHT is HIGH, and then left of that is MED and LOW is just before OFF. Very intuitive, once you grok that you have to turn it past high to light it.
But I do have several OFF-HIGH-MED-LOW fans, as well as some OFF-LOW-MED-HIGH ones, so I think it’s more designer’s preference than a rule of wiring. I can tell you that I prefer the OFF-HIGH-MED-LOW kind because then I never leave it on LOW thinking I turned it OFF. If it’s one notch away from OFF, it’s very obvious if that notch is for HIGH. If it gets slower towards OFF, then I sometimes think it’s OFF when it’s really just slowing down.
It has to do with the type of controls used to start the fan motor. As a motor turns it generates a voltage within the motor called the counter EMF (cemf); a motor turning slowly doesn’t generate as much counter emf because it is not cutting as many lines of force over a given time period. At the same time the total impedance goes down because the inductive reactance is proportional to the frequency (the total impedance of an ac circuit is made up of resistance, inductive and capacitive reactance). Basically, at low starting speeds, more voltage and less impedance results in higher rotor current and the motor heats up. A fan can be started at high speed and then slowed down because it has built up some cemf, low-speed start will cause it to overheat in getting to speed. Some fans can start on low speed because electronic controls can use a wide variety of methods to compensate for these effects and allow the machine to start on low speed.
So…designer preference, then. They can choose which type of compensatory methods, if any, to use so they can start it high or low.
YogSosoth asked why start off-high-low; that’s kind of the ‘natural’ way which the designer works around. Absolutely it’s the designer’s preference but I didn’t feel it addressed the OP’s question entirely.
>they are often connected to a metal strip which is coiled into a spring that resembles a rolled-up tape measure. As you turn the knob, the tension in that spring changes, and that controls the appliance.
What in the world are you talking about?
I have heard specifically that motorized appliances are wired like this so that the motor is started with a larger current, guaranteeing that it will start spinning. If the bearings are old and sticky or given other poor conditions, turning the motor on with a weak current might leave it sitting still and overheating. I think this is reasonable, but also think there are plenty of cases where this isn’t necessary, and wonder if it might have become a bit of a convention.
In general, starting larger motors often involves applying more power at first. For example, motors of perhaps a half horsepower to five or ten horsepower often run on single phase power and generate a second phase with a series capacitor. At startup the capacitor has a larger value - or more accurately there is a smallish capacitor always connected and a larger one that is paralleled in when the motor is spinning at lower than some cutoff speed, using a centrifugal switch. This would be called a capacitor start capacitor run motor. Motors much bigger than this are usually 3 phase and don’t have any of that.
Older gas stoves that have a pilot light sometimes go off low med high.
I’ve got a slow cooker that goes “High - Low - Medium”. I think this is the order of most common usage for a slow cooker.
I think you might ave been looking at some sort of thermostat or timing spring. Springs have nothing to do with the physics of controlling electricity flow. Fascinating interpretation though!
You’re right. They’re heated by passing current through nichrome wires wrapped around the crock. Purely resisitive heating.
A motor on the other hand is an inductive load. At start-up it will look like a resistive load to the power source and as it starts to turn it develops a counter emf which brings the starting current back down, but it needs to rotate to do this unless there are semi-conductor controls keeping the volts/hertz down. The start capacitor doesn’t cause the high starting current although it does affect it. It causes a phase imbalance so that the rotor can start turning, essentially turning the motor into a two-phase machine at start-up. The more the capacitor winding is out of phase with the run winding the stronger the starting torque is.
Without electronic controls if you start a motor on low speed it won’t be able to develop a counter emf and the start current will stay high and cause it to overheat. It’s also a big part of the reason why a motor with bad bearings overheats, if you could get it to speed and then slow it down it would still draw extra current but not nearly as much.