Short for ampere, a unit of measure for current or the volume of electricity running through a circuit. The amp rating for a device or cable determines the amount of current it can safely handle. Typical household circuits begin at 15 amps and go up to 50 or 60 amps.
By code the junction box must remain accessible, so look for a spot where the cover plate will blend. Use a 3x2½ inch device box like the ones use for wall outlets and set it at the same level as the existing wall receptacles to minimize visual impact.
A wall receptacles with two outlets. These are available rated for 15 and 20 amps, as well as special ground fault circuit interrupters (gfci) and isolated ground receptacles.
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.
Hold the fixture up to splice the wires. Usually the first wire splice will aid in supporting a small light, but have a helper assist with supporting a large, heavy fixture while making the connections. While still supporting the weight, attach the base to the mounting strap with the screws and tighten the base to the ceiling.
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.
Electrical cable is available with 3 or 4 wires running through the sheathing. Cable with 3 wires is referred to with labels like 14/2 and 12/2, where the two represents the black and white, current carrying wires in the cable. The other wire, the ground wire, is ignored in this labeling. Cable with 4 wires is referred to as 14/3 or 12/3 cable. Here 3 wires carry electricity, the black, red and white. All household cable is available with 2 or 3 current carrying wires and one ground.
Often a wall receptacle from an upper floor can be used as a source for a new ceiling fixture below, but a switch loop must be run to a wall switch in addition to fishing the cable from the source.