when it comes to noise and signals getting coupled to another wire remember these two rules
1) current running thru a wire produces a magnetic field
2) a magnetic that CROSSES a wire will produce current
NOW
The size of the field is determined by the amount of current. The amount of the current produced in a wire is determined by the the amount of magnetic field (which is stronger if closer to the source). Sooooooo to get create this noise you most vary the current in the power cable next to the signal cable. The signal cable most be close to the source of the swtching power cable. Cables can also be shielded. This shield will tend to trap the magnetic fields and force them to run thru the shield itself. there is a lot to this and a lot more then I just brought up. The idea here is it you switch a lot current you produce a lot of noise (and most cat 5 cables are not shielded). So for those that really work the A/C they should avoid running signal cables with pwoer cables. Keep in mind it most be changing A/C current for noise to be produced.
Hope this helped.
Joe
Just a couple of side notes. Since we are talking AC here, under any load the current is constantly changing so these wires are always producing some noise. The amount of which depends on the load. The greater the load, the more noise the power line will produce. Fortunantly for us, this is not all bad. The advantage of twisted pair is that it for the most part exposes both wires to the same level of noise which should induce the same voltages on both wires in the pair. The hardware is comparing the voltage of the signal wire of the twisted pair to the ground wire of the twisted pair. Since any induced voltage due to noise should be equal on both wires, the voltage difference between the two should be unchanged and the noise will be ignored.
I do agree with RJ that strapping low voltage wires to high voltage ones does produce some risk. It is not as much of a big deal when the wires are new provided the method of securing them does not damage the insulation but the sun and outdoor elements do take their toll on the insulation of both types of wire which increases the risk of shock or worse. I do run my high and low voltage wires along the same paths but I personally don't strap them together.
