Home Electrical Wiring

Use The Right Wire Size

Introduction: Electrical wire has been in use in home construction for over 100 years. Electrical wiring refers to insulated conductors used to carry electric current to electrical devices in your home. Modern homes and the high use of electrical appliances can typically have several miles of electrical wiring strung throughout the home. If you are a DIY handyman that has the skill to do your own wiring you should be familiar with the different types of home electrical wiring and the code that applies to standard household wiring.

Your home wiring can deteriorate overtime and increase the risk of fire due to electrical shorts or current overloads. For safety purposes electrical wire safety codes were developed in the 1880s as electrical power companies and distribution systems were developed to bring electric power to nearly every home. The codes for electrical wire are set locally and by a national standard electric code.

Residential electrical wiring safety codes are intended to allow the most effective transfer of electrical energy while at the same time preventing damage or injury due to electrical shock or fire. The code provides for technical standards for materials and installation standards.

Electrical Wire Types:

Most circuits in the modern homes are wired with non-metallic sheathed cable, often referred to by the brand name Romex. This type of cable is the least expensive for a given size and is used for dry indoor applications. The designation NM XX-Y indicates, respectively, the type of sheathing (NM means non-metallic), the size of the conductors (XX), and (Y) the total number of wire conductors less the ground conductor. For example: A NM 14-2 cable Romex cable is a 14 gauge cable that contains three conductors (two plus one ground). The14 gauge cable is used for most of the electrical circuits in the home that are less the 15 amps.

Circuits with larger currents such as furnaces, boilers, heat pumps, water heaters, air conditioners, and electric heat circuits use a dedicated 12 gauge cable. The 12 gauge cable is limited to 20 amps by the code. Dedicated means there is only one electrical device on the circuit.

The NM cable conductor insulation is color-coded for identification. There is one black, one white, and a bare (sometimes green) grounding conductor. The code specifies that the black conductor as the hot conductor, the white conductor is the neutral, and the bare or green is the grounding conductor.

For 240 volt applications not requiring a neutral conductor, the white wire is used as the second hot conductor, but must be re-colored with tape or by some other method. For four-wire equipment there is a red conductor. For example, a light circuit that has more than one on/off switch uses a NM 14-3 cable that has a black, white, red, and a bare/green ground conductor.

Aluminum electrical wiring:

It is worth mentioning that aluminum wiring was used in the 1970s. Aluminum wiring became implicated in numerous house fires because of the improper installation technique. Most local codes no longer allow the use of aluminum wire for new home construction. If for some reason your local code does not limit its use, I recommend that you avoid the use of any aluminum electrical wire in your home.

Electrical wire sizes and current limits:

Wire size is expressed by gauge, inversely. For example, a 12 gauge wire is larger than a14 gauge wire. The wire diameter approximately doubles in size for every increase in six gauge sizes. Use 14 gauge wires on 15 amp circuits, 12 gauge on 20 amp circuits, and 10 gauge on 30 amp circuits.

These are the basic home wiring codes that a DIY homeowner should be familiar with before attempting a home electrical wiring job. Consult your building code officer or the national building electric code for more information.

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