ok, now I understand. Closest we came to that situation was a bad compression connection to one of the 220 volt wires coming from our transformer.
Made a resistive connection rather than tight metal to metal. Must have been done at the time of original installation in 1982. When the resistance dropped the voltage too low for the house appliances to work, my called in a panic. I measured the voltages and saw how low one 120 volt side was and called the power company. Quite a struggle to trace the problem down and replace the connection.
I agree with the post about the capacitive coupling. You do not even need a neon bulb, just a capacitive AC voltage to a sensor that will detect the voltage on an open wire. Remember how an Arduino pin works when it is left floating? In this case, we want it floating and connected to a diode and capacitor to ground giving pulsed DC. Any Arduino connected will show a high because the voltage on the cap will hold the voltage through the negative half of the cycle.
So, one wire capacitor on each leg of the 220 feed should do it. Don't need much wire.