Nic Bellamy wrote: >On Mon, 2003-01-06 at 16:50, Mark Foster wrote: > >>At 16:45 6/01/2003 +1300, you wrote: >> >>>This is bloody dangerous. You would be shocked if you measured the >>>potential difference between your cat5 conductor and your PCs chassis.. >>> >>And for those not familiar, potential difference is another name for voltage :P >>And its something id definately want to be checking on a long run.. >> yes Mark, but the term Potential Difference is often used when implying a differential. > >This reminds me of a flat (well, ok, "shed") I used to live in - I >rewired it after discovering over 120V difference between sockets on >opposite ends of the living area. > even the Great Nic B had to start somewhere.. ;-) I have two wall sockets in my lounge that have some PD. I can't put the PC on one and the stereo on the other if I want PC audio through the stereo system.. (good for Q3A - particularly with 400W into a pair of Infinity Rock Speakers.. uh nah.. makes the neighbours wonder a bit..) > >Providing the difference is not major, the isolating transformers in the >network cards should handle it - they're tested to around 1KV if I >remember correctly, and there's often a 500-1KV spark gap too. Lighting >is considered "major" though ;-) > That isolating transformer is the size of your little finger nail.. think about it.. /me shakes head.. It is /designed/ to work around normal current-loops that are always present in the 230VAC M-E-N Wiring system. These voltages are well under 20 V, and mostly well under 1V. Lightning is so all-encompassing that it is irrelevant. If you get a direct strike, you're screwed no matter what. Anything plugged in will be fscked - guaranteed. A /nearby/ strike is different story.. This will 10's of KV over 100M of dry ground. I used to work in a the Protection Lab at a thermal powerstation, and we saw numbers that will make your hair stand on end, particularly around the phone exchange gear. It's all fibre these days - an ideal solution, and one that would solve this little dilemma as well. Long wires are dangerous, and grounding the far end and plugging-in the near end under your feet is mindless, so don't do it. lecture ends. /steve ------------------------------------------------------------------- To remove yourself from this list, email nzlug-request@linux.net.nz with "unsubscribe" in the body of the message.
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