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I believe IBM's Token Ring Shielded Twisted Pair (STP) cabling system was the
first wide spread commercial use of twisted pair wiring intended to increase the
cables immunity to electrical noise. It consisted of wire pairs twisted around
each other, with several pairs per "cable", and all the pairs shielded by a
single continuous foil shield that would be grounded. STP was expensive, and
hard to work with. It isn't used much any more.
 
UTP (Unshielded Twisted Pair) wiring is commonly used in the microcomputer
networking business. Any site that runs a typical Ethernet network these days is
using Category 5 UTP cable to move the signals. These UTP cables are intended to
be even more immune to the effects of ambient electrical noise on the signals
they carry than the STP was.  
 
The secret is in the number of twists per inch. Todays UTP has many more twists
than yesterdays STP. Other than that, UTP is basically STP but without the foil
shield.
 
It was discovered that taking 2 wires and tightly twisting them around each
other, so that you have several twists per inch, greatly reduces noise that can
interfere with the intended signal. The reason is that any electrical noise that
makes its way to the UTP gets canceled out due to the twists.
 
Any cables that carry a significant current, like those running motors and
lights, become an antenna that radiate electrical noise especially at start up
and shut down. Using UTP wiring would help eliminate some of it, but STP would
be even better because of the power levels. Here you are trying to eliminate the
generation of electrical noise at relatively high power levels. Since the wire
diameter is also larger, its tough to get the high twist per inch count, and
consequently additional shielding helps.
 
Any cables that carry electrical signals, typically of low power, would benefit
by being twisted. Here you are trying to eliminate the reception of electrical
noise as is the case with the typical Ethernet network cabling. UTP is fine.
Since wire diameter is small, you can get lots of twist per inch.
 
If you intend to run two wires from point A to point B, consider using a drill
to tightly twist them around each other to produce your own twisted pair of
whatever current carrying capacity you need. That would be UTP. Trying to make
your own STP isn't reasonable.  
 
Remember, that you'll end up using more wire and adding weight to span a
distance.



Bill Gradwohl
IV-P Builder


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