Touching a PSU can kill you?
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Touching a PSU can kill you?
When yesterday my uncle and I were fixing a problem with an undetected HDD inside a PC, I put it temporarily on the PSU and my uncle warned me I should never do such a thing since touching a PSU is very dangerous and can kill you (it was unplugged).
Since he has a background in electronics as a hobbyist I wouldn't want to ignore his advice. But if he's right then touching my case may kill me since it's all metal, I would have to be surprised I'm still living.
He warned me about the electrolytes, and I know that the inside can be very dangerous..but surely there must be some safety in place concerning the PSU casing?
Or in other words, is it safe to touch the PSU on the outside (even with the PC running)?
Since he has a background in electronics as a hobbyist I wouldn't want to ignore his advice. But if he's right then touching my case may kill me since it's all metal, I would have to be surprised I'm still living.
He warned me about the electrolytes, and I know that the inside can be very dangerous..but surely there must be some safety in place concerning the PSU casing?
Or in other words, is it safe to touch the PSU on the outside (even with the PC running)?
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Touching the outside of a PSU is not dangerous. If you have a fairly open fan grill or something, it's possible you could accidentally stick something inside which could be dangerous even if the PSU is unplugged. PSUs have capacitors inside that hold a charge even when unplugged. Usually, pressing the power button on the PC after unplugging the PSU will discharge any stored electricity. Although you still should be careful any time you open one.
I think your uncle was just being cautious. Maybe a little over cautious.
I think your uncle was just being cautious. Maybe a little over cautious.
Re: Touching a PSU can kill you?
Yes.TomMe wrote:Or in other words, is it safe to touch the PSU on the outside (even with the PC running)?
Not quite. IIRC, PSU, when system is power off, sends a 720mA at 5V (pin 9 from ATX connector). In practice this is the current for WOL. With this current when you press power button MB "tell" PSU to go on full power (more on less). This current is from separate circuit than the circuit which power other components.BillyBuerger wrote:Usually, pressing the power button on the PC after unplugging the PSU will discharge any stored electricity.
So if the PSU is unplugged, even if you press Power button, you only discharge capacitors that are on stand-by rail. But you don't want to discharge those capacitors.
My barbarian method is to unplug the power cord from computer while it's in POST (if you have some concerns about HDD, disconnect it before this maneuver). Never fail until now.
There's some useful info in this sticky....TomMe wrote:Thanks guys! This confirms what I suspected.
I agree your uncle was probably just being extra cautious (understandably so given the... ahem... "potential" consequences). I suppose if there were a fault with the PSU's earthing (grounding), even the outer casing might in some circumstances give you a nasty jolt.
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I always said this forum was full of zombies!Amourek wrote:Yes, this is true. I got zapped twice while fiddling inside a power supply and i died both times.
On a more serious note, you can get a serious or even fatal shock if you touch the live parts inside a PSU while it is connected to the mains. Generally the outside is safe to touch even when the PS is on, because the live PCB is grounded.
Could be that the PSU is venting hot air into the inside of your case, as it was with me. I solved it by lowering the pressure inside the case (venting hot air out the back with an additional fan) allowing cool air to be drawn in from the front.wolfboy wrote:Kind of Off-Topic, but is it normal if the PSU is really hot if you touch the top of your PC case in normal room temperature?
Yeah, it must be this hot weather.TomMe wrote:Could be that the PSU is venting hot air into the inside of your case, as it was with me. I solved it by lowering the pressure inside the case (venting hot air out the back with an additional fan) allowing cool air to be drawn in from the front.wolfboy wrote:Kind of Off-Topic, but is it normal if the PSU is really hot if you touch the top of your PC case in normal room temperature?
That reminds me... it's probably not a bad idea for all of us to check to make sure their house wiring doesn't have a bad ground. (I wonder if that's what some UPS devices check for?) The point of the third electrode is to make sure that any voltage that may reach the outer metal casing can be bled off to ground instead of zapping you. There's still the possibility that the PSU is grounded fine, but your home wiring isn't.nick705 wrote: I agree your uncle was probably just being extra cautious (understandably so given the... ahem... "potential" consequences). I suppose if there were a fault with the PSU's earthing (grounding), even the outer casing might in some circumstances give you a nasty jolt.
BrianE, it would take a shockingly bad ground in your house wiring to make the ground fail. After all, if the third wire simply touches the frame in the wall of your house it is a better ground than the current going from the PSU to you to the house frame. But don't play with plumbing and electronics at once.
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A big-time misconception is that the ground wire is used to discharge live current on the case to the ground; what it can do is discharge static, even a minute current through the ground will switch the house's electrical circuit off (the more important part in ensuring safety).
But I can only say this for areas that have this protection, other areas... heh heh. And if your wires are not even fused, congrats.
If there is an undetected (and unstopped) short circuit from live to ground, your casing would be glowing and a fire will start. Well, it won't be undetected for long.
But I can only say this for areas that have this protection, other areas... heh heh. And if your wires are not even fused, congrats.
If there is an undetected (and unstopped) short circuit from live to ground, your casing would be glowing and a fire will start. Well, it won't be undetected for long.
Oh... I don't know very much about home construction/wiring. What is the ground wire connected to again? I always thought it was connected to the hydro ground outside the house or a ground rod somewhere....darthan wrote:BrianE, it would take a shockingly bad ground in your house wiring to make the ground fail. After all, if the third wire simply touches the frame in the wall of your house it is a better ground than the current going from the PSU to you to the house frame. But don't play with plumbing and electronics at once.
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Wrong. Ground wire is used forwwenze wrote:A big-time misconception is that the ground wire is used to discharge live current on the case to the ground; what it can do is discharge static
a) supress common-mode noise currents; ground wire is connected to power wires (L and N) with two Y2-class ceramic capacitors (see here, pages 3-4); current flows through capacitors is about 1 mA;
b) protect users from electric shock if PSU fails in the way that high voltage will be connected to the PSUs' case.
Wrong again. There is no protection against current through the ground wire.even a minute current through the ground will switch the house's electrical circuit off (the more important part in ensuring safety)