On Thu, 2003-07-31 at 01:02, Wayne Rooney wrote: > >> Under normal conditions, stringing cat5 a short distance between 2 houses > on the same distribution transformer would be fine. Under abnormal > conditions expect trouble. Plan for the abnormal conditions. > > > >How much of your work was "normal conditions" ? > > That's a bit of a moot question - if you're working 'faults' then abnormal > conditions is what you see all the time. > A better question may be "out of a hundred houses, how many will have a > serious problem regarding electricial supply in a one year period?" Not > many. What I'm getting at is - these homes who have 300 meters of CAT5 strung around the place - under these abnormal fault conditions you describe, can you generally say that the cat5 cable will not present a risk _during_ the fault conditions ? This is the clincher. Sure it will be safe 99.999% of the time - almost anything is. What about one day when a fault or a strike pushes the grounds' PD gradient above a safe level for a 300 metre cable ? How regularly is *that* going to happen, IYO ? > >How many of the abnormal conditions could not have been foreseen ? > > I would say 99% of abnormal conditions can be foreseen, and the way they can > be foreseen would be to figure out all the things that can go wrong: cars > running into poles, trees falling through power lines, snow snapping lines, > high wind banging lines together* etc, etc. The problem is that such > conditions are statistically unlikely and so are not really taken into > consideration. And then they happen. okay, the risk for the supply authority, and for consumers is not economically worth lowering any further. perfectly reasonable. But what happens when someone strings a 300m wire and takes it into their living room? These faults that spot-crank the earth potential around could (and will) present quite a large voltage in someones' lounge - enough to break down a tiny 2kv isolator that was not designed to do that job. comments ? /steve > > Wayne > > * I remember one time when it was a bit windy and the power to the whole > town on Amberley kept going out - got sent up to check it out - had a look > at the Amberley end, looked ok, drove up to Waipara, looked ok. So I say to > the guy I'm with, "Shall we follow the lines across country?" He says, > "Nup, we'll sit here for a bit," and pulls out the paper and starts reading > it. > > Couple of minutes later there's this enormous ZAAAP! and the sky to the > right lights up. "There it is," he says. The wind was blowing the 33kv > line up into the earthing conductor that was strung along the top to attract > lightning away from the lines. > > ------------------------------------------------------------------- > To remove yourself from this list, email nzlug-request@linux.net.nz > with "unsubscribe" in the body of the message. ------------------------------------------------------------------- To remove yourself from this list, email nzlug-request@linux.net.nz with "unsubscribe" in the body of the message.
|
If you have any questions or comments about this page, email the
Webmaster Copyright © 1998-2002 Linux.net.nz |