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Unplugging & Shutting off at PSU, why?

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  • Switch
  • Components
Last response: in Components
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June 21, 2013 9:39:06 AM

I have always been taught then when working on your PC you need to first shut if off, then shut off the switch at the PSU then unplug the PSU, then turn the computer back on to use the extra juice.

Well my friend shut his pc off and then he shut the switch off as the psu but did not unplug it. He asked me why do we need to still unplug it, I am not too sure why it must still be unplugged. I think it might be just in case type of a thing..but is there an actual technical reason? Can minor amounts of juice still come into the pc even with the PSU off?

I don't know much about electricity, but it seems like it might have something to do with grounding? Anyways, any thoughts? Thanks guys.

More about : unplugging shutting psu

June 21, 2013 11:40:49 PM

power is always going through the cable as long as its plugged into a electrical socket, turning the switch off on the back of the psu is just like turning a light in your room on and off from the switch, electricity is still going through it, but you haven't completed the circuit.
June 22, 2013 11:54:41 AM

In the wire in the wall and running to the PC there are 3 wires, a hot, a neutral and a ground, the switch on the back of the PSU, just like a light switch, disconnects the hot line, there is no power from the point the switch broke the circuit(just after the plug into the PSU), there is electricity flowing in the PSU if the switch has been flipped. The switch does leave the ground and the neutral wires connected, neither of these have a voltage on them.


Leaving the system plugged in allows the chassis to remain at earth ground through the power cable which helps to further reduce ESD risks.

I think the reasoning for unplugging it is that there are some PSUs out there that do not have the switch on the back, i have encountered several units that just have the plug going into them, and a glowing LED to let you know if they are still charged up, the only way to truely remove power from the system is to unplug them.
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