There are two primary types of wiring in a house: high voltage and low voltage. Electrical contractors almost exclusively install the high-voltage systems that provide electricity for lighting and appliances. Another specialty contractor usually installs low-voltage systems, which serve security, entertainment, communications, environmental control and other functions. High and low voltage wiring systems operate from separate central or service panels, the hubs at the service drop that contain the connection from the utilities and control the distribution of electricity in the house.

Electricity like gas and water enters a house at a service drop, the first point of attachment from the utility to the house. This is the starting point for the contractor's run of wires to each area of the home. Ideally, the service drop is centrally located in the basement or garage of the house and easily accessed by the contractors and homeowners. It should be located to avoid unsightly meters or utility conduits along an exterior elevation. Sometimes a builder will disguise the meter or point of entry, or run an extra length of conduit to shift its location away from view.

High Voltage

High-voltage service is first run through a meter mounted on the outside of the house before entering the structure and the service box inside; low-voltage systems rarely, if ever, involve a meter. Most low-voltage systems are serviced by cable, phone, or data lines, which are monitored by remote service providers. The National Electrical Code or NEC is a national set of rules that govern safe wiring methods. These rules and the design of the high-voltage service panel dictate which wires control what areas of the house, as well as specific appliances that require dedicated power, such as the washer and dryer, furnace, and water heater. For all high-voltage electrical wiring, the NEC dictates the amp (or ampere, the amount of the electrical current at the circuit) and the voltage (the actual power delivered from one point to another) for a given demand. For general lighting and electrical services, a 15-amp circuit and 110-volt wire can service about 600 square feet of space or about a dozen receptacles (switches, outlets and ceiling fixtures).

Large appliances are required to be serviced by a dedicated circuit of at least 20 amps and a single run of wire up to 240 volts to provide adequate electrical power for their separate operation.

Code regulations not only dictate amps and voltage, but also some minimum standards to enhance the safety and security of homeowners. For instance, the NEC requires hard-wired lighting fixtures (as opposed to plug-in lamps) in the kitchen, bathrooms and entry. Similarly, a hard-wired switch must control light fixtures in halls, stairways, attached garages and all livable spaces.

What codes don't dictate is the precise placement of receptacles, except beyond a certain height or distance from water sources, such as the kitchen sink, or the number of receptacles along a length of wall. In housing construction, the builder and electrician decide where to place the outlets and switches. Typically, this decision is based on experience and feel: Switches are placed on the edges of a wall or just inside a door; outlets are centered on a short wall or evenly spaced on a longer section. Some homebuilders, however, prefer to specify the placement of the electrical receptacles for convenience and access. When planning placement, imagine what furniture and functions you'll have along each wall in the house, as well as any physical limitations that might hinder reaching a switch or outlet. While the decision may have to be made on the building plans, you might have time during the framing stage to walk through the house and get a better perspective on where you want outlets, switches and overhead lighting receptacles. In fact, many builders schedule a "walk-through" of the framed house before the mechanical subcontractors arrive to make any minor adjustments.

Low Voltage and Closed-Loop Systems

Smart home wiring systems have been introduced in recent years to combat the inherent dangers of traditional high-voltage house wiring. Some of these systems work on a closed-loop design where each receptacle has a dedicated wire that originates from and terminates back at the service box or electrical panel. Such designs also are designed to deliver electricity only when it is demanded such as when a switch is turned on, or a small appliance operated. Just plugging in a given fixture won't activate the circuit.

The computer-controlled hub recognizes overloads before they happen, denying electricity to an offending appliance or fixture. Closed-loop systems are rare in high-voltage house wiring because they buck traditional methods, require new tools and materials, and necessitate that the appliances themselves contain complex microchips that relay messages to the computer-controlled panel. Still, the closed-loop concept has found a foothold in low-voltage schemes. Closed-loop design for telephone, data, security, communications and environmental control features are becoming increasingly popular in today's new homes. The benefits of a, low-voltage telephone and data wiring scheme are different than for high-voltage wiring. Shock is not the major concern; rather, the ability to offer high-speed access to voice, data, fax and other lines and a dedicated outside line for each is the true advantage.

Finishing

With strands of loose wires and bare outlets and switches sticking out from the walls and ceilings, the bulk of an electrician's job at the finish stage is simply covering up the initial work with ceiling and wall fixtures, light bulbs and faceplates. Even the installation of products with more complicated controls, such as dimmer switches and ceiling fans, are done easily because actual control mechanisms are already in place, tested and inspected during the rough stage. Every outlet and switch needs a faceplate; most every room has a ceiling fixture. Some areas have more complicated or complex schemes. The kitchen for instance, might call for a series of cylindrical recessed light fixtures for general lighting, task lighting under the wall cabinets to illuminate the counters and work surfaces, a hanging ceiling fixture over the breakfast nook table, and perhaps some additional accent lighting. An electrician's crew can be in a house for a day or more just focusing on those items. An electrician working alone might need a week to complete the job. Often, the electrician and HVAC contractor are scheduled in tandem. Not only are they often able to work in the same house without getting in each other's way, the two trades might need to coordinate portions of their work. Ventilation fans in the bathrooms and kitchen, for instance, are electrically controlled, but require attachment to ducts. HVAC contractors, therefore, might tie a bath fan to its vent, but let the electrician strap on the wires to make it run. More commonly, the mechanical subcontractor will be proficient and skilled enough to install the fan completely, with the electrician perhaps checking the work later.