When I put an o-scope probe into my (120VAC) wall socket, with no ground (reference) attached, just a single wire, I get a perfect 60 Hz sine wave, with about 35Vrms magnitude. When I plug the o-scope probe into the socket with the ground attached appropriately to the return of the same socket, I get the 120V 60Hz sine wave as expected. Why do I get the perfect sine wave (with the smaller magnitude) with no reference attached? Is it capacitive coupling? The reason I ask this is because I was chasing down a signal today at work on some equipment and was receiving this signal (unexpectedly) off of a circuit with a known open conductor... This got me to thinking about why. Hope that made sense.