wiring length

I suspect that 220 is a typo, but just in case it's not ... Let's see how ASCII graphics will work - standard residential wiring is like this. L1 ---------- N ---------- L2 120v ------- 0v ------- 120v |________240v_____| Between Line 1 and Neutral you'll get 120V, between Line 2 and Neutral you also get 120V, and between Line 1 & Line 2, you'll get 240V - Line 1 & Line 2 are two separate circuits, and although they are usually fed from different windings on a single distribution transformer, they can also be fed from completely separate transformers. The extent to which the powerline signal couples from one side to the other can vary depending on the mix of 240v appliances on the circuits and can change as these appliances go on & off - imagine loosing the connection every time an air conditioner or water heater cycles on or off - now imagine that when the appliance is half a block up the street in someone else's home.