> Seriously, what are the implications of using remaining pairs in an STP
> low-cap cable for carying 24Vdc over fairly long distances (200 feet) ? I
> plan on using something similar to Alpha 5272 or Belden 9842. The low
> impedance rating (120 Ohms) of these cables is my main concern. I presume
> this figure means the cable's impedance per 1000 feet ? Will I be
"choking"
> my power-suplly with such a low impedance ?

The cable impedance rating has nothing to do with its DC resistance.  The
transmission line impedance is what the cable looks like to step voltage
source before the step bounces back from the end of the cable back to the
source.  Note that this is independant of the cable length.  You need to
find resistance per length of cable, then multiply that by your distance.
The cable will look like a resistor at low frequencies, and this resistance
is proportional to length.  Don't forget to consider the resistance of the
return wire too.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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