pdccs@unix.cis.pittsburgh.edu (Patrick Champion) (05/26/89)
Hi. I have a hardware related question but did not know where to post it, so here it is. 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??? A paranoid software developer getting his first home computer, Patrick Champion
santol@cbnewsc.ATT.COM (shawn.r.antol) (06/01/89)
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.
pdccs@unix.cis.pittsburgh.edu (Patrick Champion) (06/03/89)
To clear a few things up... The "surge supressor" is an Inland ProGuard 3. It has 3 mode protection. It uses cascaded diodes, gas discharge tubes (probably one), and their own multi function ceramics which are supposed to have a better life-time and response than varistors. The response time is under 5 pico seconds. The voltage clamps at 205 volts. The thing will take up to 2.5 million watts of power. Each mode absorbs 60 joules, resulting in 180 joules being absorbed. Oh yes, and it of course has a circuit breaker for surges. The thing has a 25 year warranty. They will even pay the cost of fixing dammaged equipment if it can be shown to have been damaged static, etc. going through the protector. ************************************************************************** Please do not construe the above to be an advertisement for Inland. I am in no way related to them. I am only buying the product via a mail order house. I just think that the product seems to be a good product. With a near irresistable warrantee. ************************************************************************** Yes. I did a bit of research before I bought the thing. So it does protect against EMI/RF, surge, and spikes. Yes. My environment is staticy. During winter I can get a nice long half inch visible ZAP when I run my shoes across the carpet and touch the radiator. Also, if I take off an acrylic sweater and turn off the lights I can watch a light show of static with dim arcs over a foot in length. The rug covers most of the floor. How's that for static! My worry was: When I ground my self to the desk, that the static would cross over into the keyboard or monitor and conduct down into the computer off the side of the desk. My second worry was whether a 10,000 ohm resistor was too high or too low in resistence to effectively ground out the desk. If it was too low of a resistance then I might get mild electorcution during summer storms when I had the computer off but was working at the desk. If I had the resistance to low, then the static might not be able to bleed off the resistor before it jumped overcame the resistance of the plastic insulating the keyboard and cables and jumped into the computer. I guess WHAT I really want is to find out a reasonably "idea" resistance value. And if I should use static mats, and where. Patrick Champion