The Complete Guide to Electrical Wiring

Electricity delivery

Large power plants generate the electricity that homes use. Electricity is produced by power plants across the nation using generators that are powered by steam, water, or wind. This power goes into massive “step-up” transformers that boost the voltage to half a million volts or higher.

Communities as far as hundreds of miles away from power plants can still receive electricity thanks to high-voltage transmission lines. The power is subsequently reduced for distribution down the street lines by “step-down” transformers installed at distribution substations. A series of smaller transformers mounted on utility power poles further lower the voltage to the standard 120 volts needed by most homes.

There are two common ways that electricity might reach a home: either underground or overhead from a pole known as a service mast. Two 120-volt power cables plus a grounded neutral wire typically connected to the service head in houses constructed after 1950.

Electric water heaters and laundry dryers, which operate on 240 volts, can be powered by connecting two 120 volt wires at the service panel.

A meter is used to measure the amount of electricity that is consumed as it goes through. The power then travels to the service panel, from whence it is sent to the various circuits installed throughout the home. Fuse or circuit breakers located in the service panel can cut power to specific circuits in case of an overload or short circuit.

It is common practice to use separate circuits for high-wattage appliances like microwave ovens in order to avoid overloads.

Power companies and manufacturers have made changes to voltage ratings over the years. New devices linked to older wire will continue to function normally after these upgrades. When doing electrical calculations, it is recommended to utilize circuit ratings of 120 or 240 volts.

Understanding Electrical Circuits

An electrical circuit is a continuous loop. Household circuits carry electricity from the main service panel, throughout the house, and back to the main service panel. Several switches, receptacles, light fixtures, or appliances may be connected to a single circuit.

Current enters a circuit loop on hot wires and returns along neutral wires. These wires are color coded for easy identification.

The service panel also has a bonding wire connected to a metal water pipe and a grounding wire connected to a metal grounding rod, buried underground, or to another type of grounding electrode.

If a circuit carries too much current, it can overload. A fuse or a circuit breaker protects each circuit in case of overloads. Current returns to the service panel along a neutral circuit wire. Current then leaves the house on a large neutral service wire that returns it to the utility transformer.

Grounding and Polarization

Electricity always seeks to return to its source and complete a continuous circuit. Contrary to popular belief, electricity will take all available return paths to its source, not just the path of lowest resistance.

In a household wiring system, this return path is provided by white neutral wires that return current to the main service panel. From the service panel, current returns along the uninsulated neutral service wire to a power pole transformer.

You will see the terms grounding and bonding used in this and other books about electricity. These terms are often misunderstood. You should understand the difference to safely work on electrical circuits.

Bonding connects the non-current-carrying metal parts of the electrical system, such as metal boxes and metal conduit, in a continuous low-resistance path back to the main service panel. If this metal becomes energized (a ground fault), current travels on the bonded metal and quickly increases to an amount that trips the circuit breaker or blows the fuse.

The dead circuit alerts people to a problem.