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Friday, June 10, 2011

Anti-Static Wrist straps

As the humidity in the air drops during the winter months, you can collect huge levels of static electricity from moving across carpeted floors, shifting around on a plastic or fabric chair or even from friction between the layers of fabric in your clothes. When the static builds to a level higher than your surroundings, it may arc from you to a conductive surface like a door knob, a file cabinet, the person you were about to shake hands with, your computer case or other electrical appliance.

Electro-Static Discharge (ESD)
The problem is that static electricity is being generated throughout the year, not just during the cooler seasons. Increased humidity can reduce the levels of static build-up that can occur, but it does not totally eliminate the problem.

Static electricity can be an unseen threat to electronics and especially to computer components during an upgrade or build. What you can't see (or feel) is that even a tiny amount of static build up can easily be in the range of hundreds of volts. Considering that computers are designed to run on 3.3 volts, +-5 volts, or +-12 volts; running several hundred volts through them is not a good idea. Anti-Static wrist straps are one way to prevent damage to your components from handling or during installation.


[caption id="attachment_75" align="alignnone" width="300" caption="A typical Anti-Static Wrist Strap has a flexible band to slip over your wrist, a snap-attached wire that has a clip or plug-type connector that must be attached to a good electrical ground to work."]ESD strap[/caption]


Anti-Static or ESD (Electro-Static Discharge) straps are designed to conduct any static electricity from the wearer to the electrical ground. This assumes a couple of things - one, that you are wearing one of the conductive bands, and two, that it is actually connected to something grounded.

A secondary feature of Anti-Static straps is that they also protect you from severe electrical shocks. The way the straps can do this is by placing a resistor between you and the ground. There is a 1 meg-ohm resister between the wire and ground clip to prevent electrical shocks if you touch something you shouldn't. The resistor allows electricity to flow, but limits how much, or how fast it can get there; in technical terms, a resistor limits the current, but not the voltage.


[caption id="attachment_76" align="alignnone" width="300" caption="A closer look at the wrist strap shows the metal back plate that conducts to the snap and ground wire. The black weave you see in the elastic band is electrically conductive to increase the amount of contact between you and the ground."]Wrist strap details[/caption]


Electrical ground is required
The important activity is to conduct static charge harmlessly away from you to an electrical ground before it can reach levels harmful to electronics. This means you must have a physical connection through the strap to an electrical ground.

The solution recommended by many people is to connect the clip to exposed metal on the computer case. But is that an electrical ground? The answer to that is "maybe"; if your computer is plugged into the wall outlet, then it is probably yes. The trick is to have the power turned off on the computer but leave the plug connected for the ground.


[caption id="attachment_77" align="alignnone" width="300" caption="To keep the case grounded, plug it in and turn off the power switch on the back."]Power Supply[/caption]


Use the rocker switch on the back of the power supply to turn off power to the supply. The ground is still there even when no power is flowing. If there is not a rocker switch on the power supply, you can always connect the system to a surge strip and turn the power off on the strip instead. The same thing happens - no line power to the system to damage components during installation or removal, but a good electrical ground should be maintained.


[caption id="attachment_78" align="alignnone" width="300" caption="A Wireless Anti Static Strap - No ground required - it says so right on the package!"]Wireless ESD strap[/caption]


Wireless Straps - Do they really work?
I found that the elastic band on the Wireless strap is conductive just like the wired strap, and there is a 1 meg-ohm resister between the metal back plate and the screw that is located on the top surface. But that screw is the only thing that is exposed to discharge static. Without a connection to an electrical ground, you risk damaging any electronic components you might handle.

So, how does a wireless Anti-Static strap work? The short answer is that they don't. If there is no connection between you and the electrical ground, you cannot be eliminating a potentially damaging static charge. Wearing a metal watch does not prevent you from getting shocked when you touch a door knob, so wearing a conductive strap that is not electrically connected to anything is not going to discharge any better.


[caption id="attachment_79" align="alignnone" width="180" caption="A Gothic wireless ESD collar?"]graphic[/caption]


What might work? How about some of that "Goth" spiked jewelry - Sharp pointy bits will discharge more static charge then smooth metal. Static charge will dissipate evenly across a conductive surface (like skin or metal), however, at a sharp edge or point, electrical energy can discharge into the air more readily. You won't bleed off all of the accumulated charge, but maybe just enough to avoid the big spark to your next doorknob.

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