Do I have to plug off psu cable while handling a mobo ?

[Mukachaka]

If I'm gonna open a PC case and add a hard disk to it, do I have to plug off psu ? Flipping a psu switch off is enough for motherboard ?

 

[geofelt]

There is still residual current even with the psu switch off.
Why take a chance? Just unplug the psu.

 

[omegadoom13]

unplug

 

[jankerson]

It's good practice to unplug the PSU.

 

[drea.drechsler]

If I'm gonna open a PC case and add a hard disk to it, do I have to plug off psu ? Flipping a psu switch off is enough for motherboard ?

Assuming that 'residual current' comes from charged capacitors, it won't go away simply by removing the power cord. Before starting to work inside, and after removing the power cord, you should press and hold the power-on button just to help discharge those capacitors. It may be unnecessary, but maybe not.

But that 'residual current' could also be from some power supplies that don't disable all voltages when the system is turned off. That power is what enables you to charge your cell phone from USB ports on some systems even when the system is turned off, among other things.

 

[Peter Martin]

yes, do as the above posts says. drain all currents first, then unplug, and ground yourself on the case if you can while handling sensitive stuff