To
@CoolWill : The issue with pulldown resistors is not the heating when removing the 'phantom', it is the heating when the circuit is supposed to be on. The 'phantom' coupling here has an impedance of about 46K. Place this in series with a 500 ohm resistor and the heating on the resistor is negligible. The problem comes when the control switch is toggled and now you have 120V across that 500 ohm resistor.
To
@Shuntme : You say "The actuator says 19V will interfere with the electronics controls but did not specify if it's a actual or a phantom voltage specification." This suggests a conceptual error on your part. "Phantom voltage"
is actual voltage, not some different beast. The reason it is called 'phantom' is because the source of the voltage is very high impedance, so a low impedance load will make this voltage go away. But this voltage is every bit as real as the output of any voltage divider. Instead of thinking of 'phantom voltage', think 'real voltage in series with a high impedance' and you will have a better understanding of what you need to deal with.
IMHO there are several open questions:
1) Is the source of this 'phantom voltage' capacitive coupling between energized wires and the control wire, or is it coupling from the grounded conduit to an _ungrounded_ control wire. I think that the grounding of this system hasn't been nailed down.
2) Is the source of this 'phantom voltage' capacitive coupling between wires or something else. The current (2.6 mA) is high enough that I suspected something like an LED indicator built into the switch (sort of like the residential lighted switches that function by passing a tiny amount of current through the load when off), but the 3000 foot long run is enough to make 2.6mA of capacitive coupled current quite plausible.
As to solutions:
You describe this system as "seven wires per actuator controls(3-open/off/close + power(L/N) + 2 indicators(position)" I read this that you have 3 switches that can energize (connect to L power) one of 3 wires to make your system do something.
Can you change the control switches to be double pole, so that they either connect to power or connect to neutral? In this way the wire will either be actively powered at 120V, or actively attached to your 0V reference. I think right now the control wire is left floating, which is the key problem.
A shielded pair as
@herding_cats describes is an elegant approach but expensive at 3000 feet.
A pull down resistor is simple but as you've noted will have problems with heat dissipation. Some sort of active circuit that has a fixed current draw would be better; some circuit that draws say 2.6mA over the range of 5V to 120V AC would pull down the phantom voltage nicely, but dissipate 0.3W when energized.
-Jonathan
Got it. Thank you for clarifying that. Would running 230V 3-phase + Neutral + Gnd in same conduit 2500ft cause an induced voltage in the wires?. Thinking out loud about my 44V phantom source.