Use a drywall saw and knife to cut drywall and gypsum board plaster, use a reciprocating or keyhole saw to cut wood lath plaster. With the framing exposed, use a small saw to cut two vertical kerfs in the plate about an inch apart and then use a wood chisel to chip out a notch about ½inch or so deep, between the cuts.
At the floor the wallboard is cut to allow for boring a hole in the soleplate. Then the run can be made from an upper floor to the room below or vice versa.
Pry the molding off the wall working at each stud. Drive a broad chisel-type joint knife between the baseboard and wall. Pull out on the handle several times to loosen the molding enough to wedge a crowbar behind it.
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.
Unintended flow of electricity from a circuit to a non-circuit conductor. A short can occur when a hot circuit wire touches anything other than its intended contact. A short will cause a circuit breaker, fuse or gfci to instantly shutoff electrical flow to prevent injury or fire.
An easier alternative to repairing the damage is to use one coat of mud and then cover the rough repair with a preformed medallion. A plastic medallion can be installed using caulk to stick it to the surface or using the fixture cover plate to hold it in place. You can also get a plaster medallion, these should be installed using setting joint compound or plaster of Paris to attach it to the ceiling. Keep pressure on the medallion to hold it in place until the mud has set.
Where no means exists within the snap switch enclosure for connecting to the equipment grounding conductor or where the wiring method does not include or provide an equipment grounding conductor, a snap switch without a connection to an equipment grounding conductor shall be permitted for replacement purposes only.
In a room with old plaster of at least ¾inch thickness, an armored cable or greenfield can usually be run under the baseboard by chiseling a channel along the floor wide enough to bury the metal casing flush with the wall surface. The metal will protect the wires from nail punctures with this method, but care should be used when nailing baseboards to miss the cable.