The plans, as usual, guide the work. For the electrician, there'll be a separate drawing that will map out the location of every switch, plug receptacle, and light fixture. Special-purpose circuits like those for an electric range in a kitchen, a room-size air conditioner in a bedroom, a clothes dryer, or other appliances will also be indicated.
The size of the lines required will be specified. For light fixtures, 15 amperes is usually adequate; for plugs, 20 amps is preferable. (In simple terms, amperes or amps are a measure of the power or flow of electricity; the number of volts identifies the rate; and watts are the power actually used.) An air conditioner might require 30 amperes at 240 volts (rather than the 120 volts needed for powering your toaster or bedside lamp). An electric wall oven might need 50 amps at a voltage of 240. Most major devices (like a water pump, hot water heater, furnace, range, or refrigerator) have separate lines (dedicated circuits) with separate breakers.
The anticipated electrical load on a given circuit will dictate the size of the wire required. But the plans and specifications will determine for the electrician the wire size and the number of fixtures or receptacles on each line. It's the job of the electrician-and the electrical inspector-to ensure the wires are correctly sized and properly located.
The wires will extend from the existing electrical panel unless the building project requires that the power of your service entrance be increased. The entrance is the combination of the electrical meter outside and the service panel, typically inside your cellar or garage, where the feed lines enter from the power lines on the street. There'll be a main circuit breaker (or, in older installations, a fuse) that is the switch that controls all power entering the house. Smaller breakers or fuses then control individual circuits.
When the electrical rough-in is completed, there'll be a new nest of wires that extend from the panel to new boxes attached to the framing where plugs, switches, and fixtures will later be mounted. The boxes for plugs will be at a consistent height near the floor, the switches at a level of 3 or 4 feet. Wall and ceiling boxes will be located for lights. All these boxes will be set carefully so that when finished wall surfaces are later put in place, each box will sit neatly behind the plane of the wall.
Your Communication and Entertainment Needs
During the rough-in, wires should also be run for phone and cable TV. If you are planning on a built-in sound system or intercom, this is the time for the rough wiring for those systems as well. The alarm installers, too, will do their preliminary work, should you be installing a security system. Your job isn't to check wire sizes or to look for code violations. Your concern is with what's there and, perhaps just as important, what isn't there. If you want a phone in a particular location, running the line and installing a box at this stage is a matter of a few dollars. Later on, with finished surfaces in place, the price goes up by about a factor of ten. You need to think through one last time all your electrical, cable, phone, speaker, and other needs and communicate your wants to the crew on hand.