How dangerous is induction in my wires?
If the wire is not connected to anything, it is a floating wire and the voltage measured on such wire would depend on parasitics.

More specifically, there is some parasitic capacitance, $C_{fh}$, between the floating wire and the hot wire, as well as some parasitic capacitance, $C_{fn}$, between the floating wire and the neutral wire. 

When you connect one probe of the voltmeter to the floating wire and the other probe to the ground, a voltage divider is formed between the hot wire and the ground and this voltage will be divided between $C_{fh}$ and $C_{fn}$ in parallel with the input impedance of the voltmeter.

The outcome will depend on the type and length of the cable and on the input impedance of the voltmeter, but you can easily measure some significant voltage there.

It is also possible that the cable is faulty ($140$V seems rather high), so don't make any assumptions without careful testing. 

You can find some more details on the topic in this post on the home improvement forum.