The uninterrupted path of electricity. A wire from one end to another has continuity, install a switch between the two end and turn it off to break the path and interrupt the continuity.
Grasp the top and bottom brackets and pull the device straight out from the outlet box so you can reach the sides and back. If you will be disposing of the old device, completely remove the terminal screws. This will make it much easier to free the hooked ends of the wires.
Press a small board against the bottom of the outlet box to hold it flush with the ceiling while attaching the support assembly to the joists. Working through the channel, drive deck screws or nails through the holes in the metal hangers and into the joist. Use four screws on both ends of the support, two on each side of the hangers.
Also called an old-work box, these are electrical boxes with built-in clamps to fasten them into finished walls. All that is needed to install one is to cut a hole the proper size in the hollow part of a wall and insert the box. These can be used in drywall, plaster or paneling. They are best suited for adding wall receptacles and switches. Because they don’t offer much support, old work boxes are not a good choice for installing a new ceiling fixture.