BleepingComputer.com: Using a Anti Static Wrist Band?

A friend gave me a anti static wrist band to use since I work on the inside of PC's pretty often. I have read that a good way to use it is by clipping the metal clip on the end of the band to the pc chassis with the pc being unplugged. I have two questions from those who use a anti static band: 1. Is clipping the band to the unplugged pc chassis good for grounding and decreasing electro static discharge? 2. After strapping on the wrist band to my wrist does this allow me to touch components with both hands or just the hand with the wrist band? Thanks for any advice.

1. Yes.
2. Both hands.

Read this : http://www.pcworld.com/article/82184/avoid_static_damage_to_your_pc.html

Thanks!

If you unplug it it's not earthed. I use an old wrist watch with a metal band, a length of electric wire connected to it on one end and the other end to the box and I keep it plugged to the power point so its earthed.

John

bigjohn, on 08 December 2011 - 08:56 PM, said:

Both ways are okay.
1. You plug it to wall socket. So now the electric potential of box and your wrist arm becomes equal to the the electric ground. Everything is at same voltage so no flow of charge - no damage.
2. You just connect wrist band to box without plugging it to wall socket. Now electric potential of box and your wrist is same. So no charge flows - no damage.

Important point is to keep your body's electric potential same as the box or motherboard. Earthing is not required.

Edit: changed now to no.

This post has been edited by Romeo29: 11 December 2011 - 08:01 PM

Romeo, I would like to offer one proviso to your comment if I may?

It's true that the requirement for prevention of ESD is maintaining you and the equipment at (approximately) the same potential. This doesn't require the equipment to be earthed.

The potential (pun intended) risk of having the equipment not earthed is that the common potential is indeterminate with respect to earth, and this common potential is only maintained by the safety series resistance (at least 1 Meg Ohm, can be up to 10M). If your body potential suddenly changes greatly, it's possible you could touch an ESD sensitive component before the bleed current has time to equalize the potential. The most likely thing to suddenly change your body potential is touching something that is earthed, such as another device, lamp or whatever. So in the absence of a complete ESD workstation, having the equipment you're working on earthed neutralizes this scenario, and removes an unknown quantity from the equation.

John, have you considered that having yourself connected to earth in a way that will conduct lethal current and you cannot detach from yourself by falling, could prove fatal if you contact live mains? As I mentioned above, an ESD wristband has a safety series resistance included for this reason.

bigjohn, on 08 December 2011 - 08:56 PM, said:

Please Do Not do this. Unplug it from the wall, and if you feel the need to "Ground" the PC, just use some Alligator clips and section of wire to clip the PC Case to a metal work table.

One thing that needs to be understood is that the Power Supply is a Step Down Transformer and in some instances will maintain a slight charge after being disconnected from the power outlet. (Cycling the power button a few times will relieve the slight charge)

Again:
Always disconnect the PC from the wall outlet before working on it!

FWIW: Ground = Earth

i suppose they are a safety item,better safe than sorry ,but i have never used one and have been inside hundreds of tower and never has a issue

Over the span of 35 years in the electronics industry it has been rare for me or other technicians I've worked with to use anti-static straps. Keeping yourself at substantially the same potential as what you're working on by frequently touching metal chassis surfaces is effective in practice, but can let you down. I can recall only one occasion where I know an ESD occurred. Years ago I "zapped" a 486 CPU whilst working on a system at my parent's house, not being particularly attentive to how I was handling some stuff I'd picked up at a market. The system halted but suffered no other obvious effect, only time would have told whether the CPU actually sustained any damage.

Using a strap is a safe practice, as you've commented, since it works to help exclude an unknown from the environment - in this case whether you've acquired a relative static potential since you last contacted the equipment you're working on.

Technically, what we're referring to is equipotential bonding, rather than earthing or grounding, which is a related but different matter.

BlackSpyder, on 10 December 2011 - 06:53 PM, said:

On the other hand in a desktop PC the highest voltage coming out of the power supply is the 12 volt line. even going from that to the -5 is only 16 volts.

Inside the power supply you do need to drain the two big capacitors as they filter the rectified line voltage which could mean approx 160 volts on a 120 volt line supply as I remember it. I did get a nasty shock off of them one time when I got in a hurry.

Not as bad as I got of th HV lead on a CRT. I had discharged it and it seems it built itself back up and Zap and loud cursing!

This post has been edited by rotor123: 25 January 2012 - 05:01 PM