Can an unused cable break in?

@jea48 -  That you were able to even hint at things, such as wave-particle duality, dielectric permittivity and a, "conductor" actually being a wave-guide, without being assailed (thus far) by the resident pseudoscientists, is fascinating.                                                                                        KUDOS!

@millercarbon- Were those (perhaps) rhetorical questions, regarding neutral/ground and voltages?                                                                                                                                                                          If so: no condescension intended!

"Normally voltage is measured across the black and white. But there is in principle no reason it cannot be measured across black and ground. Same 120V either way. But what about white/neutral to ground? Where is your 120V? Not there! So where is the voltage? Not there"                                                                                                                   Because they're both attached to the same neutral bus bar, in the breaker box (zero voltage potential).       ie: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/hsehld.html

@jea48 -   "You don’t need a closed circuit to have a difference of potential, voltage.
If you connect a pair of wires to a source at the end or anywhere along the pair of wires the difference of potential exists."                                                                                                                         Isn't that why these work?       https://www.fluke.com/en-us/product/electrical-testing/basic-testers/fluke-2ac 

"When you hold the tester in your hand your body is ground."                                               Been using those for decades and always believed that was the case.       Thanks for the confirmation/insight/link (filling in the blanks)!

@rvpiano- Sorry for the derailment (old fart, reminiscing)!

@jea48 -   " I would never use it to verify the circuit is de-energized if you are going to work on the circuit."  

     Never have.  Always figured: that's what my Fluke DMM was for.   My first DMM was an 8020B, if you remember those.     Bought that for my speaker/electronics shoppe, in the early Eighties.
 
     Most of what I've done in electrical (on and off/here and there/during a hard times) was industrial, 480-600V, Three Phase, in industrial machine (wire pulling) and plating environment (a fall-back, for me).    Lots of electronics, in the control systems, too (my primary forte).  

       Of course: If you've ever been around industrial plating equipment, you know about those rather large, 5mW, SCR Rectifiers.
 
                                    Some of that stuff can bite ya, pretty good!