> possible), you can use the 2 pairs for just the positive voltage and the 
> shield as the ground.  O, and don't forget to use a nice filter 

Be careful of ground loops.  If you have two grounds tied to
earth at two different places, the actual potentials at each
spot can be different, resulting in a small current flow across
your ground conductor... and a resulting voltage drop at one end
across your ground connector.  This can driver you nuts trying to
find problems in your signaling.  

Ethernet uses differential pairs which *should* be immune to
this, but there may be logic circuits inside the device that are
affected.  

The current flow can result in galvanic corrosion too, resulting
in ground connections that get eaten through.  :(

Be careful, think it through.  You may want to "float" the far
end powered device and ground it only through the ground
conductor you've definded in the CAT5 cable.  If you do that,
remember that a long wire run has appreciable resistance and
factor that into your fuse plan... you may want to go with a
smaller fuse, since a short inside your remore unit may result in
less current than you would get if there was not a whole long run
of wire involved.  Don't skip fusing it though!

Greg

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