YANR-55, Reprinted Oct 1997. Tony Cook, Extension 4-H Program Specialist, Auburn University. Originally prepared by James O. Donald, Extension Agricultural Engineer.

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Which Kind of Wire?

Wires for carrying electricity come in many different types and sizes. Each type is right for a certain use, but it may be very wrong for other uses. Because you will be using electricity all the rest of your life, you should know which kind of wire to use.

What to Do

1. Collect samples of various types of wires, cables and cords.
2. Learn the characteristics, advantages and limitations of each.
3. Learn where and how to use each type.
4. Learn how to determine the proper size of wire, cable or cord.
5. Prepare a demonstration or an exhibit on what you have learned.

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Materials You Will Need

• Samples of as many different types of electric wires, cables and cords as you can get.
• Labels or tags.
• Pencil or pen.
• Piece of hardboard (perforated or plain) or plywood. It should be large enough to hold the samples you collect.

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A Conductor Takes Current From Here To There

Wires, cables and cords are all conductors of electricity. Their main job is to provide a good path for the current.

A conductor must carry the current with the least amount of what electrical engineers call "line loss." For this reason, the metal in wires, cables and cords is always a "good" conductor--usually copper or aluminum.

Big Enough, But Not Too Big

The larger the amount of current to be carried, the larger the conductor must be. Using a conductor that is too small results in wasteful, and sometimes damaging, heating of the conductor and poor operation of the lights or appliances being served. Using too large a conductor wastes money and it may be too bulky and stiff.

On the other hand, it is sometimes wise to use conductors that are larger than needed to allow for increasing needs for electricity.

The length of a conductor affects its size, as well as the load to be placed on it. The greater the distance to the load, the larger the conductors should be. Voltage (115 vs. 230) and the amount of voltage drop permissible also affect wire size.

Conductors come in many sizes. They are designated by American Wire Gauge (AWG) numbers such as 14, 12, 10 and so on. The smaller the number, the larger the wire.

Insulation Protects All electrical conductors are insulated. However, the wires that carry very high voltages on the tops of poles may be insulated only where they are attached to the poles. Of course, the air surrounding such wires serves as effective insulation.

The conductors in your house are insulated with rubber, plastic or some other nonconductive material wrapped around the individual wires. This material prevents electricity from leaving one conductor if it should touch another, such as your body or an appliance frame or the ground.

Insulation also protects the conductor from damage. Sometimes this protection is provided by another material wrapped around the outside.

There are many different types of insulation and protective wrapping and coatings. Most of the insulation on the wires, cables and cords used in a home or on a farm is rated at 600 volts. This provides a good margin of safety because such wire usually carries only 115 or 230 volts.

Stranded or Solid?

In many sizes, conductors may be either stranded (made up of many small wires) or solid (made up of one piece).

The use to which a wire, cable or cord is to be put determines whether it should be stranded or solid. Larger sizes (6 and heavier) are always stranded so that they will be flexible enough to be coiled and handled while being installed.

Cords, of the type used on appliances and in extension cords, may be designated either "Stationary" or "Constant Service." Constant Service cords have many more and smaller strands; therefore, they will be more flexible and less subject to breaking.

Is It Wire, Cable or Cord?

In the classification of conductors which follows, the terms wire, cable and cord are used. You should know what they mean.

A wire is a single conductor. It may be solid or stranded, bare or covered with a wide variety of materials. Generally, wire is permanently installed, either overhead on poles or between buildings, in conduit (electrical tubing), or as a grounding conductor at an electrical service entrance.

A cable is two or more stranded conductors, used primarily for installation in the permanent electrical system of a building. They are coarsely stranded in the larger sizes.

A cord is two or more stranded conductors, used where portability or movement is required. Cords are used on appliances and lamps which are not built in, and on permanently installed equipment which may require electrical service to a part that moves.

Cables and cords may or may not have an uninsulated ground wire in them. This is to connect to the ground the frame of the wiring device or appliance they serve.

Types of Wires

Rubber covered wire, called type R, is used in conduit. If the rubber is moisture resistant, it is called type RW. If it is insulated with rubber that resists heat, it is called type RH. If it is resistant to both moisture and heat, it is type RHW. It has an outer braid covering available in a variety of colors such as black, white, red and green.

Weatherproof wire, type WP, is used outdoors overhead between poles and buildings. It is insulated either with neoprene or an asphalt impregnated braid. It should never be used inside.

Trench wire, type USE, can be buried directly in the earth.

Thermoplastic covered wire, types THW and TW, are also used in conduit. THW is heat resistant and moistureproof. TW is moisture resistant and flame retardant. Plastic insulation is thinner than rubber because of its higher insulating value. It does not support combustion. It comes in many colors.

Ground wire is either bare or armored. It is used to ground the service entrance at each building (or on a pole, if the meter is located there). Armored ground wire is a bare copper wire that has a metal strip wrapped spirally around it to protect it from injury.

Types of Cables Nonmetallic sheathed cable in plastic, type NMW or UF, is resistant to moisture and corrosion. It can be used in livestock buildings and other places where moisture is a problem. It can be "fished" into the hollow cores of block or tile walls. When marked UF it can be buried directly in the earth.

Nonmetallic sheathed cable in neoprene, type NMC, has an outer jacket made of neoprene. It resists rot, acids, mold and mechanical abuse. It is not affected by water and is quite resistant to fire. It can be used in livestock shelters and other buildings where tough, moistureproof wiring is needed.

Nonmetallic sheathed cable in fiber, type NM, is commonly used in homes. This type of cable should be used only in dry places.

Service entrance cable, type SE, is used to carry electricity into a building. It is connected to the overhead wires at the place where they are attached. The cable is run down the outside and into the service entrance cabinet. Usually it has two insulated conductors and one bare one--with the latter stranded and wrapped around the other two. It also is often used to serve ranges, water heaters and clothes dryers.

Service drop cable, often called triplex, is used by power suppliers from their transformer to a consumer's house or meter pole. It can also be used between buildings and has the advantage of being neater in appearance than three weatherproof wires. Two of the conductors of this cable are insulated with either neoprene or polyethylene. The third conductor is bare and serves as the ground or neutral. The three are twisted together to form a cable, but no outside covering is used.

Armored cable, type ABC, is commonly called BX. It has a metal armor spirally wrapped around the conductors for protection and to serve as a ground. The insulated conductors are wrapped with a special type of paper. It is for use in dry locations only.

Type of Cords

Parallel cord, types SP and SPT, is a flat cord used on lamps, clocks, radios and electric toys. These types replace green-and-yellow twist and other braided cords formerly used on such equipment. A groove down the center of the insulation makes it easy to separate the conductors for making connections. Type SP has rubber insulation, and type SPT has thermoplastic. It is available in sizes 16 and 18 in black, brown, white or ivory.

Junior hard service cord, types SJ, SJT and SJO, has many uses, as on washing machines, drills and trouble lamps. The outer jacket may be rubber (SJ), thermoplastic (SJT) or an oil-resistant rubber compound (SJO). This cord is round and available in sizes 16 or 18 with two to four rubber-insulated conductors.

Hard service cord, types S, ST and SO, is similar to junior hard service. It has a thicker outer insulation for rough use. The S stands for rubber outer jacket; ST for thermoplastic; SO for oil-resistant rubber. It is available in sizes 10, 12, 14, 16 and 18 with two to four conductors.

Heater cords are available as types HPN and HSJ. Type HPN is the most popular heater cord. It has neoprene insulation which will withstand heat. It is waterproof, can be used on any appliance, and comes in sizes 16 and 18.

Type HSJ has asbestos insulation around each conductor with a rubber outer jacket. It is waterproof.

Braided heater cords, while formerly very common, are being replaced by type HPN. Ask for HPN when you need a new cord for a heating appliance.

Special cords for a range or dryer connect these appliances to their special wall outlet. They are usually made with a special plug on one end and attaching lugs on the other.

Christmas tree lighting cords are made for either outdoor or indoor use. Only the outdoor type is waterproof.

Look For The U.L. Label

The Underwriters' Laboratories (U.L.) is a nonprofit organization that examines and tests electrical items. Look for their label on the wire, cable and cords that you buy.

Which Size?

For short distances, do not exceed these loads for commonly used sizes of wire:

For longer distances, use this 115-volt wire size chart based on a 1-percent voltage drop. If you know your load in watts, you can convert it to amperes by dividing by the voltage.

Example: 750 watts divided by 115 volts equals 6.5 amps.

Load,	Length of run, ft.
amps	30	40	50	60	70	80	90	100
5	14	14	12	12	12	10	10	10
6	14	12	12	12	10	10	10	8
7	14	12	12	10	10	10	8	8
8	12	12	10	10	10	8	8	8
9	12	12	10	10	8	8	8	8
10	12	10	10	8	8	8	8	6
12	12	10	8	8	8	6	6	6
14	10	10	8	8	6	6	6	6
16	10	8	8	6	6	6	6	4
18	10	8	8	6	6	6	4	4
20	8	8	6	6	6	4	4	4

Note: For mechanical strength, conductors in overhead spans must be at least No. 10 for spans up to 50 feet and No. 8 for longer spans.

Demonstrations You Can Give

Select two or three different appliances that have worn or defective cords. Show how to replace the cord on each with the right type, explaining why you chose each type.

For More Information

Ask at your library or power supplier office for books or booklets on wiring design. Look up the wire size chart for higher voltage, greater distance and heavier loads than the one given here.