I work on power lines, im trying to create something that would sense touch of overhead wire.
The wire is isolated from ground and has no voltage. Is there a way to use capacitive touch for this or would it be to unreliable?

 

My preference would be something like this:
https://www.keyence.com/ss/products/sensor/sensorbasics/proximity/feature/index.jsp

https://www.keyence.com/ss/products/sensor/sensorbasics/proximity/info/

Detection based on “Changes in Eddy Current”

 

If you work on power-lines then you know that the only safe way to touch a power-line is if you are at the same potential as the line. If line is unpowered, by definition, to do capacitive sensing, you have to charge the line as the other side of the capacitor. As a conductor, it does not have the necessary diameter to do what you need. The entire purpose of the way a capacitor is designed is to effectively increase the diameter of the wire to several feet square, even though the capacitor leads are miniscule.

 

The floating line could have significant capacitance to ground if the line is long.

You could detect this capacitance with a probe energized with a high-frequency AC signal, but you would need to reference earth ground to accomplish this, creating a closed capacitive circuit.
A floating circuit will not work.

It may seem counterintuitive, but capacitive sensing always needs a closed circuit, even if it's entirely capacitive.