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RE: [K12OSN] Networking a new school for K12LTSP?

A simple way to think about it is that a ground wire running between
buildings is no longer a ground wire - it becomes a second nutral wire, but
without that big fuse that protects your building.  A ground wire is suposed
to be the shortest path to ground.  When you go between buildings, it no
longer is the shortest path.

With any line running between two ground circuts (same building or different
buildings, low voltage or high), you need to make sure that your grounds are
isolated - that is the box where the wire enters each building is properly
grounded to the buildings ground.  You also need something that will break
the circut (such as a nice breaker...).  For low-voltage stuff (like the
telephone or cable wires) this is done on the pole outside, or in the box
they put on the side of your building.  If you run your own, you need a
device to do the same thing.  They makes boxes to do this for ethernet, but
they are not cheep (and they have to be properly grounded).

The other tricky thing is sheilding.  Data often requiers sheilding for the
cables, which makes the whole thing a LOT harder.  Consult the NEC.

Steven Santos
Director, Simply Circus, Inc.
Email: Steven SimplyCircus com
 Mail: 14 Pierrepont Road
       Newton, MA 02462
Phone: 617-527-0667
  Web: www.SimplyCircus.com

> -----Original Message-----
> From: k12osn-bounces redhat com [mailto:k12osn-bounces redhat com]On
> Behalf Of John Lucas
> Sent: Tuesday, January 30, 2007 10:19 PM
> To: k12osn redhat com
> Subject: Re: [K12OSN] Networking a new school for K12LTSP?
> On Tuesday 30 January 2007 21:31, Rob Owens wrote:
> > To eliminate the ground plane problem, couldn't you
> > just run a grounding cable from one building to the
> > other (in the
> > same conduit as your network wire).  This seems to me
> > like it would solve the problem, but I'm not 100% sure
> > -- and I
> > don't know if it is allowed by the electrical code
> > (but I don't see why it wouldn't be).
> >
> > -Rob
> >
> Nope. Unless the two locations already share a common ground
> plane, you need
> to optically isolate them. Connecting two separate grounds will
> only ensure
> that any electrical potential will travel between locations. I have seen
> problems *within the same building* where there has been an addition that
> wasn't properly grounded.
> --
>         "History doesn't repeat itself; at best it rhymes."
>                         - Mark Twain
> | John Lucas                          MrJohnLucas gmail com
>         |
> | St. Thomas, VI 00802
http://mrjohnlucas.googlepages.com/ |
| 18.3°N, 65°W                        AST (UTC-4)                         |

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