I used to run 2-3 wires with the reasoning that I needed one high enough that the cows wouldn't step over it and at least one low enough that the calves wouldn't go under, and one in the middle to keep calves from jumping through the middle. Here's what I now think (with regard to pulsed fences anyway)
1) The more wires you have the more chance there is that one of them is going to get knocked off and ground against the post which will short out the whole fence.
2) You will spend twice as much time fixing problems with a 2 wire fence as you will a one wire fence mainly because it shorts out twice as often
3) You will spend three times as much time fixing a 3 wire fence as you will a one wire fence for the same reason
4) Calves don't seem to care much about electric fences and so low wires don't seem to stop them.
5) Low wires (under 24 inches or so) are more susceptible to vegetation shorts in the spring and summer.
6) Low wires don't seem to deter hogs much either (inspite of what the local extension agents say)
7) Cows typically (mine anyway) test a wire they see with their nose first before trying to step over it. Wet noses make good electrical conductors and will persuade the cow not to cross it whether its knee high, or over their head.
8) One wire at about 30 inches is high enough to avoid most hog damage and vegetation shorts, is about nose high on a calf when it starts venturing away from mama and hopefully will encourage the calf to test it like mama (though I really haven't seen much proof of that yet).
In short, I think I am becoming a one wire man, one wire at a time.
