Wires and Cables

What you are expected to learn

At the end of this module, you should be able to:

• identify a conducting wire
• identify a wire gauge and give a brief discourse on how to use the wire gauge
• differentiate between wires and cables

How to learn from this module

Going through this module can be both a fun and a meaningful learning experience. All you need to do is make use of your time and resources efficiently. To do this, here are some tips for you:

1. Take time in reading and understanding each lesson. It is better to be slow but sure than to hurry finishing the module only to find out that you missed the concepts you are supposed to learn.

2. Do not jump from one chapter to another. Usually, the lessons are arranged such that one is built upon another, hence an understanding of the first is essential in comprehending the succeeding lessons.

3. Be honest. When answering the test items, do not turn to the key to correction page unless you are done. Likewise, when performing experiments, record only what you have really observed.

4. Safety first. Perform the experiments with extra precaution. Wear safety gears whenever necessary.

5. Don’t hesitate to ask. If you need to clarify something, approach your teacher or any knowledgeable person.

What to do before (Pretest)

1. The ampacity ratings for aluminum and copper-clad aluminum are identical for all guages and temperatures (True or False)

2. Which of the following metals is the best conductor of electricity?

a. steel b. aluminum c. silver d. gold

3. Which of the following conductors will have reddish brown color:

a. copper-clad aluminum wire b. Aluminum c. Copper d. gold

4. Copper is preferred for electrical conductors because it has following features, EXCEPT:

a. Poor Ductility b. High Conductivity c. Resistance to Corrosion d. Low Resistance

5. The Term AWG stands for:

a. Aluminum WIre Gauge b. American Wire Gauge c. African Wire Gauge d. Asian Wire Gauge

Lesson 8: Wires and Cables

• Electricity from voltage supplies are generally conducted through conducting wires made of copper and aluminum although there are some wires made up of silver or gold. Copper is generally used because it is a very good conductor and low in cost. Coppers used are round in cross-section through some applications would require square or rectangular shaped wires.
• A wire may be solid or stranded and may be insulated or non-insulated. Insulation is provided to avoid short circuits and to prevent accident electrocutions. Stranded wires are more flexible than a comparable-sized solid wire.
• Solid wire is made of only one conductor. If bent or flexed repeatedly, solid wire may break. Therefore solid wire is used in places where bending and flexing is not encountered. House wiring is a good example of the use of solid wire. Stranded wire is made up of several individual strands put together in a braid. Some uses for stranded wire include telephone cords, extension cords, and speaker wire, to name a few.
• Stranded wire is flexible, easier to handle, and less likely to develop an open break. Sizes for stranded wire are equivalent to the sum of the areas for the individual strands. For instance, two strands of No. 30 wire correspond to solid No. 27 wire.
• A cable is made up of more than one conducting wire. Each wire inside the cable is individually insulated. Cables are usually used where the voltage value of one wire may differ from those of other wires inside the cable and the insulation prevents the individual wires from being short-circuited to the other wires.
• Manufacturers of copper conductor generally subscribe to a standard of measure propounded by the American Wire Gauge Standard that is the same as Brown and Sharpe (B&S) gauge used by machinists.
• The size of a wire is specified by its gauge number. The higher the gauge number, the smaller the size of the wire. The American Wire Table in the succeeding animation shows the different size copper wires and other properties and characteristics pertaining to that size of wire.
• The cross-sectional areas of circular wires are usually specified in circular-mils (cmil or CM). The cross-sectional areas of square or rectangular wires are given in square mils (smil or SM). A circular mil is the area of a circle with a diameter of 1 mil, the mil being 1/1000th of an inch. A square mil is the area of a square with an edge of 1 mil.
• The diameter of a conducting wire can be measured by using a wire gauge. The wire gauge is a metal disk with different-sized slots around the disk. The slots are numbered. The numbers correspond to the gauge number of the wire that can barely slide into the slot with very little force applied. The animation shows how a wire gauge is used to measure wire diameter.
• Wires are usually manufactured with insulation. Insulation may be made up of different materials although most common are those made from vinyl plastics. Other insulators are neoprene, rubber, nylon, polyethylene, polypropylene, polyurethane, varnished cambric, paper, silicone rubber and others.
• Common circuit troubles are an open in wire conductors; dirty contacts in switches; and dirt, oxides, and corrosion on connectors and terminals.

Virtual Laboratory

Important Terms

• Circular mil (cmil) a unit that specifies the cross-sectional area of round wire. 1 cmil is the cross-sectional area of a wire with a diameter, d, of 1 mil, where 1 mil = 0.001 in. For round wire the cmil area is equal to the square of the diameter, d, in mils.
• Dielectric material another name used in conjunction with insulating materials. An insulator is commonly referred to as a dielectric because it can hold or store an electric charge.
• Ionization current a current from the movement of ion charges in a liquid or gas.
• Specific resistance the resistance of a metal conductor whose cross-sectional area is 1 cmil and whose length is 1 ft. The specific resistance, designated , is specified in cmil/ft.
• Temperature coefficient a factor that indicates how much the resistance of a material changes with temperature. A positive temperature coefficient means that the resistance increases with temperature, whereas a negative temperature coefficient means that the resistance decreases with temperature.
• Wire gage a number assigned to a specific size of round wire in terms of its diameter and cross-sectional area. The American Wire Gage (AWG) system provides a table of all wire sizes that includes the gage size, the diameter, d, in mils and the area, A, in circular mils (cmils).

Self Check

1. A _______________________ may be solid or stranded and may be insulated or non-insulated.

2. ________________________ is generally used because it is a very good conductor and low in cost.

3. ________________________ wire is flexible, easier to handle, and less likely to develop an open break.

4. A ______________________ is made up of more than one conducting wire.

5. Manufacturers of copper conductor generally subscribe to a standard of measure propounded by the _________________________________ Standard that is the same as Brown and Sharpe (B&S) gauge used by machinists.