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Weird question, I hope it has its place here: is it true that electric devices like washing machines, computer and so on, should be (1) plugged in, and then (2) turned on, rather than the contrary?

In other words, is it OK to have an electric device on, and then you plug it in the wall plug so it starts, or should you first plug it on and then turn it on?

Michael Karas
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drake035
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1 Answers1

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It doesn't matter from an electronics perspective, assuming you're talking about switches that directly switch the main voltage. For other switches, like the power button of your computer, you have to plug the device in first, and then turn it on.

You can see this as an AND. In order for the device to work, both requirements must be met: the device has to be plugged in and switched on. When either of the two isn't met, the device doesn't do anything. The two situations of one met requirement aren't distinguishable for the device.

There might be mechanical issues, as PeterJ and Michael Karas point out in the comments.

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    Although one possible issue is arcing as you plug in the appliance (if the current is high). The switch will normally be designed to try and switch in a more positive / faster way. – PeterJ Jun 17 '13 at 10:03
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    +1 for PeterJ's comment. A plugging action also may result in a number of connect / disconnects occurring as you try to engage the plug into the power receptacle. In some cases this may result in increased device component stress due to extra inrush current repetitions. – Michael Karas Jun 17 '13 at 10:39
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    @CamilStaps - Your "AND" scenario may be correct in a large number of cases - but not always. Many devices these days do not even have direct AC power switches and instead use a logical low voltage switch that turns the equipment on and off between an a standby state and an active state. My cloths washer and dryer work like that! There can be a difference in how a device acts when the AC is plugged in versus when the logical control switch is activated. The common case is often one where when AC is plugged in you still need to press the logical ON button to activate the device. – Michael Karas Jun 17 '13 at 10:45
  • @MichaelKaras hm, good point, not every device has a direct AC power switch –  Jun 17 '13 at 10:49
  • So you can see that your answer "It doesn't matter" may not be entirely accurate. – Michael Karas Jun 17 '13 at 10:51
  • @PeterJ and Michael Your comments together are the correct answer IMO; the main reason one shouldn't plug a device in when its switch is "on" (assuming it is a simple device with no standby state), is the potential for arcing and intermittent connection. – JYelton Jun 17 '13 at 17:49