On Saturday 25 September 2004 19:52, Erylon Hines wrote: > On Saturday 25 September 2004 03:37 pm, Richard Urwin wrote: > | I think "Which" was told off and had to publish a retraction not so > | long ago for publicly giving that bit of advice. > | > | Some things to bear in mind: > | 1. If there's an earth fault the live wire is connected to you. > | 2. The switch is in the live wire. If, like I did, you have an > | extension cable with the live and neutral swapped, then the live > | parts are still live. It may still be a problem with a properly > | wired connection if your neutral is at a different potential to > | your earth. OK, not such a problem with a PC because the PSU is > | enclosed. This is true! > > This in itself is a code violation. Why would anyone swap the hot > and neutral--or the neutral and case ground? Anyone that would do > this shouldn't be doing anything electrical at all (no offense meant, The average homeowner does not understand electricy and has no concept of energy observe the number of people who connect a 15amp tool to a 100 foot #16 extension cord. It takes no imagiation to believe that such a person will replace an electrical outlet with no idea which wire goes where even if they are color coded. You can never be sure that the outlet was installed by a non electrician. How do you hook up three black wires or 3 white wires or even three green wires. Have you inspected your electrical system for proper code. > but everyone should test their equipment before they use it--your > life depends on it). And remember, Never--Ever--switch a neutral. > The neutral and ground go to the very same place. The difference > between them is that the ground wire is bonded directly to the > grounding means--the service ground, the neutral may have connections > interposed between itself and the service ground. (I don't mean to > be condescending about this, but it is an important distinction). True but it isnt according to code. > > | 3. Anti-static straps have 1MegOhm resistors in them. Without such > | they are considered serious health and safety violations. Since > | every piece of anti-static equipment has that, the actual > | resistance to earth of professional gear is usually several meg > | ohms. Thats to keep you alive. > > For the anti-static devices, power supplies, etc.--yes. Electrical > codes (at least in the U.S.) require that the case be bonded directly > to ground. Yes but I live in a house that is pre current code. It does not have grounded connectors just two slots. There are a lot of them in the world. > > | Personally, If I have my wrist strap with me I leave the box > | plugged in and use it. If I don't then I still leave it plugged in, > | but just touch the case frequently to keep myself at the same > | potential. I think very long and hard before I decide to connect > | myself to the case with a piece of wire. You are setting up a condition where you can kill yourself. Always disconnect from power before working on the box. > | > | Another word of warning: some PSUs do not have an off switch. The > | button on the front of an ATX case leaves power to some parts of > | the motherboard. If there isn't a rocker switch on the PSU, you can > | not leave it plugged in without having an external switch > | somewhere. And you cannot usually be sure that the outlet has not been changed by a previos tennant. I once moved into a new house that had the hot water connected to the toilet. > > In such a case, an external jumper from a known good ground would > need to be applied to the metal frame of the case when the unit is > unplugged. Otherwise, the box is floating with potential for static > discharge, unless the repairman is floating also. This probably > won't be the way it is outside of the lab. True. You must always remember that a good ground has 1 ohm or less to earth any more and it cannot do its job. Be Safe and Disconnect from Power before working on the Box.
-- Regards; Hoyt Registered Linux User #363264 http://counter.li.org
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