The easiest way to test for
line voltage is with a non-contact
voltage detector. They cost about $10-$15, and are really handy.
All you do is hold it up to
insulation of the wires, and it'll beep and flash if there's
line voltage. This works without having to actually touch the conductive material, so it is much safer than other testing methods. I use mine a lot if a light isn't turning on to see if there's even
current from the
dimmer, because more often than not a problem in the patch is why a light won't come on, as opposed to a problem with the lamp. The only thing you need to do is put it next to the
cord.
Beyond pulling out a multimeter or a
voltage detector though, you should have an electrician come in, especially if you're to the
point where you want to open branch
circuit panels and use
circuit tracers. I'm also a student, and our district electrician always has time for my little projects and questions, especially when it comes to tracing wires and finding out where conduits run. Next week he's coming in to do an electrical analysis of one of our venues, so he'll hook up his logging analysis equipment, a we'll put on a rehearsal that night, and then the next day eight shows, and then process the data for how much
power we sucked up, and examine all of the amperage and
voltage data. The primary reason is to find out which lamps will last the longest for us with the
voltage differences on the local
grid, be it
HPL/120's or
HPL/115's. His impression of the
grid is that we tend to get our
voltage a little
bit on the high end, which if that's the case, then we'd stop buying 115's and get more bang for our buck out of our lamps.