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ESD: Using the antistatic band to case, or with PSU plugged but off?

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December 10, 2011 4:55:17 AM

When avoiding or taking proper ESD (electrostatic discharge) precautions, is it proper to simply attach the antistatic wrist band to the case from your body?

Or must you have the PSU plugged in but turned off?

I keep hearing people say plugging in the PSU but even OFF still has a charge running through it, while others say it's necessary to ground yourself properly.

I've always just used the static band and then attached that to my case. And then put the case on top of my antistatic mat, which then ALSO attaches to my metal case, when installing all my components for a fresh build (psu, cpu, mobo,e tc..) . Is this SUFFICIENT?

THANK YOU, please help; all the contradictory ESD information confuses me :(  :heink:  :bounce: 
December 10, 2011 12:56:42 PM

I always unplug the power cord before working inside the case. When I use the antistatic wrist band, I attach it to the case.
December 10, 2011 1:54:24 PM

^agree
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December 10, 2011 2:51:53 PM

The PSU is a large chunk of metal and electronics capable of absorbing quite a bit of charge, if its in the case that you are grounded to it will dissipate all of the charge from you easily, having it plugged in but turned off is unnecessary. Even the case alone is generally sufficient, you just need something that is capable of holding more charge than you easily so you don't have a significant voltage differential.
December 10, 2011 3:24:12 PM

1) With a antistatic mat. I also have a antistatic mat. When used, I have the mat attached to earth ground. I use a 3 prong ac plug with a single ground wire. I attach my wrist strap to the ground on the mat. This would negate the question of the PSU being plugged in and PSU rocker switch OFF.

2) When I do not use the mat. I plug the PSU in to AC outlet and turn the rocker switch Off and connect the wrist strap to an UNPAINTED point on the Case.

Comments:
"I keep hearing people say plugging in the PSU but even OFF still has a charge running through it" Answer - If PSU is plugged in and Rocker switch is OFF, then NO as long as House wiring is per code. IF Computer is OFF, PSU rocker Switch is on, then Yes it is posible for voltage to still be on in a standby state (Note, grond is still 0 volts.)

Is case a suitable ground when not connected to earth ground- Debatable. In most cases probably OK. When the case is ungrounded you will simply transfer the charge from your body to the case until the case and you have an equal potential. In normal conditions (ie relative humidity above 30 % this charge can be disipated quict quickly do to surrounding air. In cases where the relative humidity is low, the dissipation can be slow - hense the "debatable". When the case is connected to earth ground there is no question - there is a path for electrons to create a "zero" potential. Might bring this up to our ESD Instructor, to see what happens when an Individual is charged and touchs a ungrounded computer case and the resulting charge on the case.

Bottom Line: when RH is Low (winter time), I recommend playing safe and have wrist strap (and mat) connected to an earth ground.
December 10, 2011 3:41:10 PM

hunter315
Large mass is a relative term. An automobile is considered a ground, but that is a ton, or more metal, alittle bit more than a computer case. If the case is ungrounded and your body has say a Positive 1000 Volts and you touch the case then you will simply suck off electrons so that body = case, both now at 500 Volts charge. Unless the electrons can be replaced the case will remain charged. Normally with RH >30% the electrons will quickly be "sucked" out of the surrounding air nuetralizing both you and the case. With RH below 30 %, the nuetralization takes longer. Case in point At work when working on systems when the RH is =< 30 % a ionoizer is required in addition to ground strap.
December 10, 2011 3:48:51 PM

How many of you fiddle around without an ESD? I just did my first build without one
December 10, 2011 4:25:20 PM

^ mrtesseract -5
How about doing a little "googling" on ESD and then say that is a wise choice.

ESD does not always result in immeadiate fauilure, it sometimes results in reduced performance, and or downstream fauilures refered to as "walking wounded"

Recently a poster here grabbed a HDD (in an enclouser) set it on a Glass surface and you quessed it drew an static arc - HDD no longer workeeee.

A while back there were a number of cases where indivuduals plugged in a USB device, discharged themselfs into the USB port wiping out their USB, seem to remember one whoes computer would no longer post.

You might be surprised at how many computer components are returned as being defective (did not work, or failed a month later) due to ESD damage. Most companies do not track this as it is not cost effecive and just jack up the price to compensate.
To evaluated a device for ESD damage cost about 10 grand - just not worth it for "cheap" $200 components (ie memory modules, Gpus, and CPUs).

PS I know I catch Flack on my ESD stand from "knowledgable" ET techs. But facts are facts.
December 11, 2011 3:36:01 AM

Whoa thanks for the plethora of info.

RetiredChief man, thanks.

But what do you mean that you plug your "antistatic mat into the earth ground"??

I keep hearing terms like "earth ground" and "ground yourself" what the heck does that mean?

Did you just mean you plug your antistatic mat alligator clip to your case??

Can't you just plug the alligator clip from the wrist strap to your case and your perfect?
December 11, 2011 5:07:54 AM

I'm a tech, and while there is truth to ESD, one of the easiest things I can say is honestly, use common sense. Maybe I should, but most times, I don't bother with an ESD strap. Typically, if you ground yourself by grabbing an unpainted metal part of the case, you will be grounded. Once you do that however, do not move much, touch an unpainted metal part of the case before touching any parts, and NEVER handle parts by the connectors, chips, etc. Keep parts in their casing until use, if working with a motherboard, ground yourself before touching it, keep it sitting on top of an antistatic bag until you install it, etc. Wrist straps help, but mainly use common sense.
December 11, 2011 3:06:34 PM

1) House wiring (US). 3 prongs 1 Hot Has a 120 V sinewave), 1 Neutral (also may be referred to as Return), and the round prong is earth ground (normally just called ground).
The earth ground/ground is connected to the earth, normally by connecting it to the water pipes buried in the "ground” In some cases a ground rod is used. If you live in Florida this may or may not be a suitable earth ground – In some cases they have taken a car (from junk yard) and buried it and tied the earth ground to the Car. - This is primarily for lightning protection. A simple ground rod will cause the sand to turn to glass when lightning sticks it. But also the sand is a poor ground material. The "neutral" is also a "ground" It’s just a question of where it ties to the earth ground.

You quest on the ESD Mat. An ESD mat is made of a static dissapative4 material that has a very high resistance between any two points on the mat (order of 10 Megs per square). There is a metal point (mine uses a “snap” type connection (similar to the snap fasteners found on Jeans and coats). What I did (as I lost the connecting wire) is to take a three prong AC plug. Attracted ONLY one wire to the Round prong and run it to the mat. This I then plug into either the AC wall out let, or normally in to a switched outlet strip. This then becomes my “single” point earth ground.
If the mat is not tied to earth ground and you touch the mat you are simply transferring the charge to the mat – The electrons have to go somewhere and if the mat is not tied to earth ground they will remain as a charge, normally will slowly dissipate into the air.

Just a comment on wrist straps. They contain a 1 megohm resistor. These do go bad (not common, but been known to happen). This is to protect you so that you are not “shorted” to ground. If this resistance becomes an open, the wrist strap is useless. At work, we are required to verify the wrist strap is good prior to use on a daily basis (overkill). But do recommend that a wrist strap be periodically checked. Easily checked with an ohm meter, should be 1 Meg ± 20%.
!