The basic house wiring in homes built in recent decades have copper wire in them. Houses built in the 1970's may have aluminum wire in them. Aluminum wire has been linked to fires and is no longer allowed in most places. If you encounter aluminum wire in your home you may want to have an licensed electrician check it out.

Got an electrical project that you need to do? See the articles 'Home Electrical Repair', 'Residential Wiring Projects' and 'Basic House Wiring' for a listing of do it yourself projects that a homeowner can accomplish.

Wire or Cable?

Sometimes we use these terms interchangebly and there is nothing wrong with that. Technically speaking 'Wire' is the individual strands that are used for various purposes in an electrical installation. Wire can have insulation or be bare. It can also be made of different materials. However, most wire used in residences that is available for purchase is copper.


Wire comes in several gauges. The gauge of the wire is simply the diameter or a way of specifying how much current it can carry. Wire gauges that you are likely to encounter in your home are sized from 24 to 6. Guage sizes are counterintuitive since the larger the number the smaller the wire is. A wire rated 24 AWG is a very thin wire that you would use on a doorbell or garage door opener. Wire that is rated 6 AWG would be used for an electric range or an central airconditioning condenser.

Common Wire Sizes In Your Home

Amperage for Wire Sizes

16 - 24 gauge low voltage

14 gauge 15 amps 1440 watts (120) volt

12 gauge 20 amps 1920 watts (120) volt | 3840 watts (240) volts

10 gauge 30 amps 2880 watts (120) volt | 5760 watts (240) volts

8 gauge 40 amps 7680 watts (240) volts

6 gauge 55 amps 10560 watts (240) volts

Wire Colors


Not really a color, but worth mentioning. The bare wire if there is one, is always the ground wire. Inside of 'Romex' or NM-B cable, the ground is bare and it is wrapped with kraft paper.


Black, Red, Blue, Orange, Yellow, etc....

Wire Insulation



Wire Types




Cable generally refers to a group of wires. The wires are not necessarily all the same size and are usually different colors. Cable is shielded with either abmetal or plastic casing. This serves to protect the wires. Inside the cable the individual wires will also have a plastic insulation. Sometimes the ground wire inside of a cable will not have any insulation.

Cables can have different quantities of wires. They can also have different gauges in them. Most of the time when you are talking about wire, you mean a cable that has all the conductors that you need for a particular application.

Shielded cable is usually three or four wires. A designation such as 12-2 w/Ground or 10-3 w/Ground refers to the wire gauge and number of conductors. The first number is the gauge. Standard gauges are #14, #12, #10, #8 and #6. The second number indicates the number of insulated conductors. A "2" would mean a black and white wire. A "3" will likely mean a black, red and white wire. The w/Ground would mean that it has a bare ground wire inside also. Almost all shielded cable, that is sold today, comes with a ground wire in it.

Cable Designations

There are certain designations for cables that tell you what it is used for in general. For residential applications, you will likely run into three different types. The desinations are listed below:


NM = Non Metallic, B = Temperature Class (194 deg farenheight). This is probably the most common wire you will find in your home. It is often called 'Romex' and is fairly easy to work with. If you don't have this type already, it is still the type you will most likely use for any upgrades. Originally, NM-B cable was all white, no matter what gauge of wire was inside of it. Now the jacket for the cable is color coded for the conductors that are inside of it, see 'Cable Colors' below.

Installing NM-B Cable

There are some restrictions for installing this type of cable. It is a flexible cable so it needs to be attached to something that provides support. It needs to have approved fasteners within a foot or less of a termination box and every four feet along an otherwise unsupported suface. Running a non metallic sheathed cable through the holes in wood studs counts as support.

NM cable is generally used for wood frame buildings. It cannot be used for metal studs without additonal protection. For wood studs the cable should be kept a minimum of 1 1/4" back from the edge of the stud. If this cannot be done, a metal protection plate needs to be installed.


UF = Underground Feeder, B = Temperature Class (194 deg farenheight). This type of cable is a direct burial cable that can be used for outdoor and underground applications. The plastic jacketing is bonded to the wires, creating a tough cable that resists moiture and damage. You would normally use this wire in a wet environment and buried in the ground.

Installing UF-B Cable


MC Cable

MC = Metal Clad Cable, Temperature Class (194 Degrees farenheight). Similar to 'romex' or NM cable, this type can have multiple conductors of various gauges. It can also include a ground wire

AC Cable

NM-B Cable Color

White = 14 ga wire; Yellow = 




Using Wire & Cable

The wire you need to use will depend on the situation. For outlets and lights you will use 14-2 or 12-2 w/Ground in most situations. Exceptionally long runs or high amperage devices may require heavier wire. Examples of this might be a sump pump, furnace or refrigerator.


Some 240 volt devices such as a hot water tank or electric base board heaters might use 12-2 or 10-2 w/Ground. Local codes, amps and distance will govern the correct wire size. Ranges and electric ovens require a lot more amps and are usually wired with 8-3 or 6-3 w/Ground. Appliances that are 240 volt but do not use as much amperage, like a dryer can be wired with 10-3 w/ground.

Remember, local codes govern and some areas require installations that are more stringent than national codes. Check with your local building inspector before beginning a project.

Purchasing Wire