Twisted Pairs [RE-wrenches]

[Mark Byington]

I twisted some wires together for a distance of 150 feet and it was 
not easy! I could have divided it into sections and twisted it in 
opposing directions in each section, which would have made it very 
easy, but since I don't understand the principle, I couldn't assure 
that it would be effective.

Can anyone induce some understanding into my twisted mind?


The principle of twisting a pair of conductors (for example, a hot and a  neutral) to reduce pickup is that each wire in the pair will experience the same interfering electromagntic field, if there is one, and the differential between the two wires in the pair will be approx. zero, cancelling each other out.  If the wires were not twisted, one wire might be closer to the source of interference than the other one, and therefore the pair would pick up a differential mode signal.

Note that even twisted pairs will pick up a common mode signal, which means each conductor picks up the same signal relative to ground.  Common mode is easily removed by an isolation transformer, up to the isolation voltage rating of the transformer.

An easy way to twist pairs is to put a J-hook or eye bolt in your electric drill, stretch out the wires on the ground, and twist away.  By the way, it's perfectly OK to twist clockwise for 50 feet, then counterclockwise for 50 feet, etc.  Same effect as if you twisted only one way.  Although I guess the wires could have more of a tendency to untwist themselves this way.

_______________
Mark Byington
President
Cobalt Power Systems, Inc.
Tel 650-948-9574   Fax 650-948-9573   Cell 415-298-1947
markb at cobaltpower.com   www.cobaltpower.com


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