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Old 03-29-2009, 11:26 PM   #1
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Ceiling fan + potentiometer question

Hi all,

I have a ceiling fan in my bedroom, and in the wall it has a potentiometer (to set its speed), and two switches (one for the fan, the other for the light in it).

When the potentiometer is set at any speed other than zero, and I switch the fan on (or off) , a small 'flash' is visible in the switch button (probably a small spark).

Why this happens? In my layman's electric knowledge, I think that when the potentiometer is set at any speed other than zero and I switch the ceiling fan, it draws voltage causing a small voltage drop which explains the flash in the switch button.

My question: is this small flash or spark able to damage the ceiling fan? Or any electronic equipment I have in my bedroom? (PC, DVD, LCD monitor, game console etc).

I have a surge suppressor where I plug these electronic equipment - voltage drops are quite common in my region (I never had damaged equipment due to this). Although I don't know if when I switch on the ceiling fan, what happens is either a voltage drop or a surge.

Regards in advance,


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Old 03-30-2009, 07:47 AM   #2
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When an electric circuit is made or broken using a mechanical switch, the electricity jumps the gap between the switch contacts when the contacts are almost touching. The resulting arc gradually wears out the contacts. (>>> low velocity) The faster the contacts are physically separated the shorter the duration of the arc and the less the damage. The higher the voltage and the higher the humidity, the greater the distance through air the electricity can jump. Breaking a circuit under load produces a larger arc than turning the current on.

The arc can generate minute electromagnetic radiation that travels through the air and can cause interference to radio, etc. reception and communication. The one you saw won't cause damage to nearby electronic equipment or electronic equipment plugged into the same branch circuit.


The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.

Last edited by AllanJ; 03-30-2009 at 07:50 AM.
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Old 04-19-2009, 11:41 PM   #3
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Thank you very much for the answer, AlanJ!
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Old 04-21-2009, 11:23 AM   #4
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I think a new switch would be in order. Since Allan told us why, I thought I would tell you how. New switch.
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Old 04-21-2009, 01:11 PM   #5
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I have nothing of value to add.

I just wanted to see what a potentiometer was.

We call them fan speed controls
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