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Is it possible to safely use a rheostat as a potentiometer to control an incandescent ceiling light? I have replaced a ceiling fan with a light fixture and would like to use the existing rheostat as a potentiometer.

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  • The short answer to your question is: "It can't be done safely", but the longer answer is "It may be possible, depending on what's in the box." Can you post a photo of the speed controller, preferably showing its innards and wiring to the mains and to the fan?
    – EM Fields
    Oct 10, 2015 at 22:41

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Come on guys the answer is absolutly not! the way both reostats and potentiometers work is they absorb the heat not used on the load so you would be making a wall heater in your box,,, a modern dimmer uses SCR or TRIAC solid state devices that limit the amount of AC making it to the load. Dont use a standard Dimmer for floresent lamps unless the ballest are listed for this. most dimmable Floresent lamps require a special ballest and dimmer combination. I thought I should specify, some old celing fans did use variable resistors to control the field winding (speed control) these can cause a fire if used as a dimmer, if the the device is a modern dimmer it would be ok to use it should have what it is made for listed on the body of the divice and how many watts it can handle.

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This question is confusing. Rheostats and potentiometers are essentially the same thing. Modern household dimmer switches no longer use variable resistance; typically solid-state modulation is used to dim the light. If your switch is truly a potentiometer, I recommend replacing it with a modern dimmer which is vastly more efficient and safer.

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    Strictly, they're not the same since a rheostat is a two-terminal device and a potentiometer is a three-terminal device. Such being the case, a potentiometer can be used as a rheostat but a rheostat can't be used as a potentiometer
    – EM Fields
    Oct 10, 2015 at 22:23
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Additional facts observed: I wired it up just to see the result. The two 60 W bulbs will only lite up (full bright) using the highest setting on the Rheo. No dimming apparent at 2 middle detentes. I will be swapping out the Rheo for a Pot. Thank you to all for responses.

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