Editors of Cool Springs Press - The Complete Guide to Wiring

Outdoor emergency disconnects are required for home services in new construction, homes undergoing renovation, and all service replacements. An exterior disconnect is an important safety feature that allows emergency crews to shut off the power safely before entering the home. Disconnects can include main circuit breakers within outdoor-accessible service panels, or they may be disconnect switches in their own outdoor enclosures (typically installed near the utility meter). Disconnects must be clearly labeled with wording that is specific to the disconnect type.

T he only way you can possibly manage home wiring projects safely is to understand how electricity works and how it is delivered from the street to the outlets in your home. The most essential quality to appreciate about electricity is that the typical amount that flows through the wires in your home can be fatal if you contact it directly. Sources estimate that there are about 45,000 electrical fires each year causing 440 deaths, 1,250 injuries, and 1.3 billion dollars in property damage. Home wiring can be a very satisfying task for do-it-yourselfers, but if you dont know what youre doing or are in any way uncomfortable with the idea of working around electricity, do not attempt it. This chapter explains the fundamental principles behind the electrical circuits that run through our homes. It also includes some basic tips for working safely with wiring, and it introduces you to the essential tools youll need for the job. The beginner should consider it mandatory reading. Even if you have a good grasp of electrical principles, take some time to review the material. A refresher course is always useful.

In this chapter:

A household electrical system can be compared with a homes plumbing system. Electrical current flows in wires in much the same way that water flows inside pipes. Both electricity and water enter the home, are distributed throughout the house, do their work, and exit.

In plumbing, water first flows through the pressurized water supply system. In electricity, current first flows along hot wires. Current flowing along hot wires also is pressurized. Electrical pressure is called voltage.

Large supply pipes can carry a greater volume of water than small pipes. Likewise, large electrical wires carry more current than small wires. This electrical current-carrying capacity of wires is called ampacity.

Water is made available for use through the faucets, spigots, and showerheads in a home. Electricity is made available through receptacles, switches, and fixtures.

Water finally leaves the home through a drain system, which is not pressurized. Similarly, electrical current flows back through neutral wires. The current in neutral wires is not pressurized and is at zero volts, when everything is functioning as intended. Do not assume, however, that the neutral is at zero volts. Several defects can put voltage on the neutral, so treat the neutral as a hot wire until demonstrated otherwise.

Water and electricity both flow. The main difference is that you can see water (and touching water isnt likely to kill you). Like electricity, water enters a fixture under high pressure and exits under no pressure.

The Delivery System

Electricity that enters the home is produced by large power plants. Power plants are located in all parts of the country and generate electricity with generators that are turned by water, wind, or steam. From these plants electricity enters large step-up transformers that increase voltage to half a million volts or more.