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Static discharge query

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December 26, 2012 12:55:55 PM

I will be working on my desktop PC again later this week to modify a few components and give it a general tidy-up. As far as I'm aware, attaching an anti-static wristband from my wrist to the case chassis is sufficient to allow static to discharge into the case. I've heard others insist that you leave the PSU plugged in to get sufficient ground, although many electrical experts disagree with this strongly.

Anyway, I will be working with the case on an Ikea coffee table. Just to clarify, static will be discharged into the case when using the strap, allowing me to touch all components safely?

Another viewpoint I read is that touching the case will equalise the charge potential between the user and the case, so that no current can flow. Is this the same thing? So what would happen if I then touched a graphics card with a different potential?

Thanks.

More about : static discharge query

a b ) Power supply
December 26, 2012 1:26:04 PM

Yes, touching the case does exactly the same thing as a wristband does. All the wristband does is allow you to forget about doing so.

If you leave your PC without electrical ground connected, it becomes a floating or "isolated" ground and this means the PC itself will get charged to the same electrostatic voltage you are. This means that while you aren't going to be able to discharge into components already inside your PC, you + PC can discharge into components you pick up if your environment is prone to generating electrostatic charge.

Leaving the PSU plugged in with the hard-switch in the OFF position has the benefit of providing real ground that you can rely on. The only disadvantage is the risk of accidentally turning the PSU on in mid-build but the likelihood of any damage from that is relatively low since you would need to fail to notice the lit 5VSB LED reminding you to cut power (hard-OFF) and hit the motherboard's power button for the PSU to power up. By the time you are plugging the ATX power connector into the motherboard, you shouldn't have any need to mess around the back of the PC (at least not anywhere near the PSU) and any risk of shorting out the 5VSB are should already be long gone so the risk of anything happening is very low if you are the least bit careful.
December 26, 2012 2:08:46 PM

Wearing a wrist band wont hurt. If you think you are prone to forget to
A. Not touch ant electrical connectors, anything golden in colour.
B. Touch the case every now and then.

A. is the main one as long as you don't do this you will be fine. I have build plenty of PC'a and never had one plugged in and don't even own a wrist strap.

Mactronix :) 
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December 29, 2012 4:54:10 PM

InvalidError said:
Yes, touching the case does exactly the same thing as a wristband does. All the wristband does is allow you to forget about doing so.

If you leave your PC without electrical ground connected, it becomes a floating or "isolated" ground and this means the PC itself will get charged to the same electrostatic voltage you are. This means that while you aren't going to be able to discharge into components already inside your PC, you + PC can discharge into components you pick up if your environment is prone to generating electrostatic charge.

Leaving the PSU plugged in with the hard-switch in the OFF position has the benefit of providing real ground that you can rely on. The only disadvantage is the risk of accidentally turning the PSU on in mid-build but the likelihood of any damage from that is relatively low since you would need to fail to notice the lit 5VSB LED reminding you to cut power (hard-OFF) and hit the motherboard's power button for the PSU to power up. By the time you are plugging the ATX power connector into the motherboard, you shouldn't have any need to mess around the back of the PC (at least not anywhere near the PSU) and any risk of shorting out the 5VSB are should already be long gone so the risk of anything happening is very low if you are the least bit careful.



The main issue is that I don't want to be working with my PC connected to the mains in any way what so ever. Say for instance I was very statically charged, and then I touched the case. Now the case and I are at the same potential. If I was then to touch an external graphics card, I would discharge into it and possibly damage it (presumably)

Can anyone else justify leaving the case plugged in during assembly?


Thanks again.
a b ) Power supply
December 29, 2012 5:36:58 PM

narga191 said:
Can anyone else justify leaving the case plugged in during assembly?

As I said above, whether or not real ground is absolutely necessary depends on how much your environment is static-prone.

In my case, I usually pick rooms with hardwood or ceramic floors to work in and wooden surfaces to work on. Wood has very low potential for building up electrostatic charges so I do not need to worry about ESD unless air is exceptionally dry.
December 29, 2012 6:24:39 PM

I would never work on a plugged in PC

Mactronix :) 
December 29, 2012 6:41:12 PM

InvalidError said:
As I said above, whether or not real ground is absolutely necessary depends on how much your environment is static-prone.

In my case, I usually pick rooms with hardwood or ceramic floors to work in and wooden surfaces to work on. Wood has very low potential for building up electrostatic charges so I do not need to worry about ESD unless air is exceptionally dry.



Ok, so generally I'll be fine. Lastly, if I am at the same potential as the case and then I touch a piece of RAM outside the case (by its sides) then the RAM is now at equal potential?
a b ) Power supply
December 29, 2012 6:53:45 PM

narga191 said:
Ok, so generally I'll be fine. Lastly, if I am at the same potential as the case and then I touch a piece of RAM outside the case (by its sides) then the RAM is now at equal potential?

The copper planes within the RAM's PCB should extend very close to the cut edges and allow ESD to safely discharge from you to the copper planes. This discharge will drop your electrostatic potential by a few volts so you still need to touch the case again to re-equalize with the motherboard/case before putting the DIMM in.

Pick components by edges, IO plates or other grounded surface (so any ESD gets diffused through ground/power planes rather than ICs' IO pins - high speed signals like discharges follow the path of least impedance and it doesn't get any lower than power/ground planes) and remember to touch the case as you bring components in. Those are the two most important things to remember when assembling without actual ground.
a b ) Power supply
December 29, 2012 7:03:30 PM

+1 above...
the best thing to do is turn off the pc. leave it plugged in for about 5 mins to let any residual current fade. if your at home take your shoes off, then touch the case and remove the plug form the wall. this will have grounded you and the carpet (if its nylon) i recommend you work on the floor rather than a desk as your carpet will be earthed by the radiators in the room if they use under floor piping.
wood and plastic flooring will have no bearing.

anyways 1s your earthed you can choose to attach a band to your wrist or just go ahead and start working on the innards...

1 thing to note. if you get an electro static shock when you first touch the case it means your carpet is likely holding a high charge and that room isnt suitable to work on a pc in. 1 stray swipe of your foot on the carpet could create enough current to fry a cpu. so use a different room.

December 29, 2012 7:58:43 PM

Ok great. Finally for peace of mind, would getting a grounding plug and attaching the wrist strap to it be effective? That way there is no risk of shorts and the static is dissipated?
!