Do I measure voltage, you mean from one system to another when I need to send audio and/or video to it for the first time? Absolutely. I think I mentioned working at a stereo store and hearing a loud snapping sound from the Pioneer A30 Class A power amp when the whole rack was connected to power, but not when the Soundcraftsman power amp was gone, which was powered by a different receptacle that turned out to be on a different circuit and phase. I have seen sparks when connecting the cable box that I had and felt a decent jolt when I unplugged the coax while my arm was laying on the cover. I have seen equipment smoke as soon as it was connected to cabling from another area of the building, even though the other equipment worked as expected.

If I have installed equipment and it's working, I don't measure but if I'm coming into a system that I didn't work on, I don't assume it was installed correctly because I have seen really shoddy work in my almost 40 years of doing this.

I have been working at a house that was wired by a company which advertised themselves as the premier AV contractor and their website had many photos of interesting jobs. I did the initial walk-through with the client and saw the structured wiring enclosure, opened it and found that the network switch, cable splitter and most of the cables were just hanging and only the phone and data punchdown modules were fastened. Above this enclosure, were speaker cables and coax that were looped and wire tied to a conduit, unused. In the adjacent laundry room is a drop of bundle (2 coax, 2 Cat5e in a blue jacket) and extra Cat5e & coax, hanging down to the floor behind the door. I also saw a 12' x 16' area removed from the ceiling (wood lath & plaster) and a couple of extra small holes in the ceiling, which I assume are from their attempt to feed cabling to the equipment at the top of the pantry cabinet in the kitchen, directly above the holes. They tried to go from the bottom, I went in from the top and I think it took me less than 15 minutes to take my cables (which didn't come from the same place as theirs) and pass them into the cabinet. They missed by 8"- if they had drilled a hole in the next joist space, they would have been able to finish, but they chose to feed the cables between the TV cabinet through the wall to the hole they cut into the cabinet and abandon the others, rather than remove them. Then, they ran bundle to a few places on the 2nd floor, but I don't measure continuity on many of them. In addition, they labeled far too many cables 'Playroom'- it uses only four and I think I counted 7 or 8 with that name. I know where one bundle goes and it's being used for the modem and router, but the blue Cat5e may be cut, pinched or they may have dead-ended them in the attic, to be assigned later. One of the coax in the bundle to the wall plate at the 2nd floor desk shows continuity, but when I connect a TV to it, the TV doesn't pick up a channel. Neither of the Cat5e shows continuity. The two Cat5e to the AV cabinet in the Sun room don't work for network, either.