Re: pole pig question (fwd)

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Original poster: List moderator <mod1@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Mon, 21 May 2007 15:47:43 -0400 (EDT)
From: M G <gt4awd@xxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: pole pig question (fwd)

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This is correct, I do remember seeing a photograph that showed the ground
connection is also connected directly to the "neutral" return path of the
transformer. Just thought I would verify, although most of us on the list
probably know this already. I believe it was Terry who posted the article
that included this image.

Matt G.


      ---------[ Received Mail Content ]----------

      Subject : Re: pole pig question (fwd)

      Date : Mon, 21 May 2007 09:59:19 -0600 (MDT)

      From : "Tesla list" <tesla@xxxxxxxxxx>

      To : tesla@xxxxxxxxxx



      Original poster: List moderator







      -----! ----- Forwarded message ----------

      Date: Mon, 21 May 2007 11:34:35 -0400

      From: Jonathon Reinhart

      To: Tesla list

      Subject: Re: pole pig question (fwd)



      How is that possible? There is a neutral/grounded wire that
      runs along with

      the three phase wires from pole to pole. It is the neutral
      conductor that

      carries the return current back to the substation
      transformer. That wire

      running down the pole is one of many hundreds of similar
      wires that run down

      (just about) every other pole that the wires travel along. It
      simply keeps

      the grounded neutral conductor at ground potential (~0V). If
      it were to

      break, there shouldn't be much problem, as the current is
      still traveling

      down that neutral conductor back to the substation.



      Grounded circuits, such as the 120/240V in your house, and
      the 7.2/14.4kV

      systems in your neighborh! ood do not use the earth as a
      return path. In a

      fault conditio n in the wiring in your home (say a hot
      conductor comes lose

      and touches a grounded metal box in the wall), that current
      is NOT seeking

      to return to "ground", meaning the earth. This is a common
      misconception

      due to the fact that the third wire ground system is connect
      to an earth

      grounding rod. However, the third wire ground is bonded to
      the neutral

      conductor in your panel box (in many installations, they
      simply use the same

      terminal bar). Thus, the fault current returns to the
      transformer then via

      the grounded neutral conductor. The reason this point on the
      system is

      grounded is again, to keep the whole system's "ground"
      voltage level at the

      same voltage level we are in constant contact with ( ~0V, the
      earth). If

      your house's ground/neutral were allowed to float at any 0V
      (relative) it

      wishes, the fault system would still work. However, a
      "grounded" metal box,

      could be considerably high! er potential than the earth, and
      a human could

      receive a shock.



      Imagine if there were no neutral conductor running along the
      poles. How

      would you ever get electricity? The current would have to
      travel

      tens/hundreds of miles along the utility lines to your
      transformer. Then how

      would the current return to the substation? Through the
      earth? Imagine the

      voltage drop over miles and miles of earth! Does anyone have
      any rough

      guesses to the ohms/foot of earth at 8' depth? It would not
      work.



      It is a terrible thing that happened to that poor kid, but
      something else

      had to have gone wrong. Perhaps the connection to the neutral
      line up on the

      pole was weak at some point, and there was fault current
      traveling to earth.



      Jonathon Reinhart









      > That innocuous looking wire that runs down the pole into
      the ground (it

      > often ends in a spira! l coil stapled to the bottom end of
      the utility

      > pole) play s a critical function. A teenager around here
      was killed a

      > few years ago when he scraped a utility pole with a lawn
      mower, breaking

      > the down wire, and essentially running 14.4 KV into the
      mower deck.

      >

      >

      >










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