Is it a code violation to use seal tight to cross an expansion joint in a parking garage instead of using expansion couplings

I'm trying to install 3 new wall lights. There were lights there previously. When I check to make sure the wires are live before installing the fixture, they are live. Once the fixture is installed and I check again, the wires are no longer live. Any help would be greatly appreciated.

Why we connect inductor in series & capacitor in parallel across the resistor in mxwells inductance bridge

want to buy a swag plug-in chandelier but it only comes in a pendant lamp to be hung from the electric box in the ceiling. Can I change the electric cord with one that has a plug on the end to plug into the wall? I will need more chain and a long cord with a plug. Can I do this and how difficult...