Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!tut.cis.ohio-state.edu!att!cbnewsc!santol
From: santol@cbnewsc.ATT.COM (shawn.r.antol)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: Help: Grounding against static
Keywords: static
Message-ID: <1082@cbnewsc.ATT.COM>
Date: 31 May 89 18:07:18 GMT
References: <2320@mit-caf.MIT.EDU> <18182@unix.cis.pittsburgh.edu>
Distribution: usa
Organization: AT&T Bell Laboratories
Lines: 91

Patrick Champion writes:
  ...
>	I am getting a pc clone.  I have already ordered a surge suppressor
>that protects against EMI, surges, and whatnot.  My question is, I am
>going to have this PC in a tower case on the side of the desk, but the
>keyboard and monitor will be on the desk.  The desk is all metal.  Do I need
>a static mat under the keyboard or can I just connect the desk to the 
>radiator in the room with a wire.  Also, if I wire the desk to the radiator
>I heard that I should connect it through a 10,000 or so ohm resistor. Is 
>this true???

       Congrats on the clone.  

   A surge suppressor does not protect "against" EMI (electro magnetic 
   radiation) but it does help prevent your machine from "creating" it.
   The majority of the surge suppressors on the market today are really
   nothing more than an extension cord with multiple tap-offs on the end.
   Not much protection...
   "It is my opinion" that anything under $30 isn't worth the money.
   Check the specification sheets (spec. sheets) for response time and
   power dissipation of "your" surge suppressor.

   If you are trying to prevent damage due to everyday lightning strikes on
   the AC power line, one of the most effective AND CHEAPEST methods is as
   follows:   ( but it takes some time/work on your part and may void your 
   warranty 8-( )

   Basic Info:
   A varistor is a device that changes it reactance (think of it as resistance
   for now) as the voltage across it changes. Varistors are the primary
   component in any surge supressor. The better the varistor, the better the 
   protection.  The two main parameters in choosing a varistor is the response
   time and power dissipation.

   You will need three of them (total)
		   	1 General Electric (GE) V130LA10A
			2    "       "          V130LA2
Connect the one V130LA10A device between the "hot" prong and "neutral" prong
Connect the two V130LA2 devices:  One between the "hot" prong and "gnd" prong
		          and One between the "neutral" prong and "gnd" prong
The word "prong" above refers to the three prongs on your power cord. Attach
the varistors inside the power supply casing where they will be enclosed for
your safety.
The parts should cost you no more than $5.00 and are very effecient. 
If you are even the slightest bit sqeemish about soldering stuff to your new
PC, get some experienced help. It is quite easy and can save you lots of $$$.

Now on to the static mat...

You didn't state in your letter what material your floor was made out of...
Carpeting and tile floors are the worst. Also your shoes have a lot to do 
with it... in one sentence STATIC is dependant on the environment...
							
However, you do not need static pads, floor mats, grounding cables, etc if you
do not have a static problem.  Static is most prevalent in the winter months of
the year when it is dry. If you reach out to touch the door knob and any kind 
of a spark is there to greet you, your environment does have a static problem.
If there is not spark, then you have no static "problem".  

The LAW is you can NEVER completely GET RID OF STATIC. 
								
As for grounding the metal desk to the radiator, you don't need to do it.
Give who-ever recommended that you use a 10K ohm resistor an applause. The
resistor is there to protect you from electrocution.

                                 Voltage (V)
Using Ohm's Law, Current (I) =  --------------     or I = V/R
                                Resistance (R)

With the 10K Ohm resistor, the current would be limited to 

                          120 Volts
                          ---------      or   12 milli amps
                          10,000 Ohms

You get more current out of a nine volt battery (look out kids!).

In conclusion, I feel that you do not need any static protective devices to 
protect your PC (because it is on the metal desk AND you didn't indicate that
you HAD a static problem), in addition you should have some form of surge
suppression which you already purchased.  Good luck and happy hacking!
								
Shawn Antol
AT&T Bell Laboratories
Naperville, IL.
312-979-5622
Email address:    att!ihlpb!santol

My employer and I are in no way responsible for damage and/or losses due to
the use and/or misuse of the above information.  In addition, the opinions
stated above are mine solely, and in no way reflect those of my employer.