Philip Charles wrote: > >[....] As the current builds up in the primary coil a >voltage builds up in the secondary caused by the growing magnetic field. >When the current drops the magnetic field collapses causing a reverse >voltage in the secondary. A car ignition coil work this way. The points >open, the current stops, the magnetic field collapses and ~10,000v produced >in the secondary. With AC the voltage/current is always changing. > This is all talk-on-a-cereal-box when the energy levels in question are in the "outrageous" category, and the isolation device is the size of your little fingernail. The rules of motion of electrons give way to the "get the fsck out of the way" rule, which in general will take precedence. Why aren't people getting this ? You CANNOT isolate spikes in the "outrageous" category. The only thing you can do is "bond" everything local - keep everything at the same potential. This is not feasible over long cable runs unless you are going to lay a substantial ground mat, or /seriously/ isolate one end. Running any long wire breaks all the protection systems.. We really need someone from the heavy electrical industry to comment. Regarding the questions of underground protection - this will help greatly with lightning strikes, but not with substantial electrical faults. Lightning tries to get to "ground" by the best possible path. Once it has done so, it will proceed to drill a hole at said point on the ground. HOWEVER, the point on the ground that has suffered the strike will rise *substantially* in potential, causing both ends of the cabling to do so as well. If I had to run a length of cat5 underground I would be looking for the following ; Both ends of the cabling were roughly equidistant from any substatial mains electrical apparatus, particularly large pole/roadside transformers, and also not passing within 5 meters of the same. A lightning shunt is created by burying the cable to 100mm depth minimum, at least at the points where it entered any building (one meter buried), or near any termination. Cabling to be kept WELL clear of any substantial metal structure - distance to be at least 0.5M (buried) or 4M<wince> for exposed cabling. Tin sheds, buildings with lots of metal (cowsheds), buildings with substantial mains electrical installations, and the like, to be avoided completely. Use wireless. or you will die. Structures with substantial vertical height must be lightning shunted. 100mm depth, 1 meter length, minimum. Cables that enter a residence must be kept short, and preferably terminated at a hub/switch well away from any possible contact. Be aware that the switch may destroy itself in flames during a substantial fault. Will it burn your house down ? Will you know about it? Are you insured for this? Metal cases of machines connected to outdoor cabling must be positioned so that humans or pets do not come into contact with the metal frame. Heavier wiring MUST NOT BE USED, or you will die. The very fine wiring of Cat5 will vaporise and protect you and your property. 2.5mm wiring WILL NOT. disclaimer: I don't like the idea of running long lengths of cabling. I don't do it, and I suggest you don't do it. If you really want to, then you probably will - but don't quote me on any the above. If you do it, and kill someone you love - even while following the above instructions/warnings, then be it on your head - and don't tell me about it either, I don't wanna know. /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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