Vik Olliver wrote: >On Mon, 2003-07-28 at 09:03, Steve Wright wrote: > >>Nope. Just go work for someone in the generation industry for a while >>and find out the hard way, or get your ear burnt off by some senior >>technician wailing on about how dangerous this is. >> > >We're not talking about unisolated signal or power lines here. Such >advice is not relevant. > yes we are, and this is the thing you are not getting. "ground" ceases to become ground when large fault currents are present in the MEN system, or from external sources, viz lightning strikes. Many, many megajoules of energy become apparent between two arbitrary points on the "ground" that you are expecting to be "ground" under such conditions, and it is unreasonable to expect that an isolation device the size of your little fingernail will cope with these. Like I said, this is OT in this forum, and I invite you to troll google if you need to satisfy your quest for information. >A simple web reference would suffice. > no such thing exists unless you find it yourself. >I really want to know why the >isolations standards on Ethernet are not considered sufficient. I used >to *design* these things and I want to sort out the source of this >rumour once and for all. > Because the isolation devices are *physically small* considering the amount of *energy* that has the potential to be dissapated in this case. Remind yourself that the cable would almost certainly be turned into a smoking grey line on the ground before the energy surge actually arrived at your PC, consequently protecting the isolation device on the NIC. If the energy burst DID actually arrive at your PC, it is likely that YOU will be turned into a smoking grey line on the ground. I will not comment further on this thread. /sw ------------------------------------------------------------------- To remove yourself from this list, email nzlug-request@linux.net.nz with "unsubscribe" in the body of the message.
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