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 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, 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). | 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. 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. | | 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. | | 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. 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.
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