Counter Pro Course Index |
Next
|
Counter Pro
|
| Wire: more to the product than meets the eye! |
 |
Wires seem to be a fairly simple item. They are used to connect an electrical source with an electrical load and carry the electron flow between the two.
You probably sell lots of spark plug wire sets each week as well as spools of ordinary primary wire. You probably are also aware that spark plug wire sets are among the most profitable products your store sells.
But what, exactly, do you know about plug wire or primary wire? Why is one thick and the other thin? Why are different types of coverings used? Are there any real differences between one type of plug wire and another, or are they all the same? Is one type of battery cable pretty much like another? Or are there significant differences which make one type better for a given application than another? And what about booster cables? Are there functional differences between them justifying the large variations in price?
As you are probably realizing, wire is not as simple as you thought. You must have a good understanding of these differences in order to explain these products to your customers intelligently--professionals or do-it-yourselfers (DIYs).
| The Basic Job. |
|
The basic job of any type of wire is to carry a flow of electrons from one end of the wire to the other. In other words, to connect a source with a load.
As we said in the previous sections on ignition systems, electromotive force (EMF) has three basic characteristics which we need to understand: 1) electrical pressure or voltage; 2) electrical volume or amperage; and 3) electrical resistance or ohms. The relationship between these values is explained as follows:
It takes one volt of pressure to force one amp of electron volume through one ohm of electrical resistance.
Because electrons are invisible, these three properties of electricity are sometimes difficult to understand. Fortunately, we can make a very visible comparison between hydraulic flow and electron flow.
Water flowing from an ordinary garden hose is a typical example. The source of the water is the public water utility. The conductor of the water is the hose, while the resistance is the nozzle on the end of the hose. The load is the lawn, which needs watering.
| Demonstrating the relationship between force, volume and resistance. |
|
Resistance to water flow is at a maximum when the nozzle is closed and no water flows. No water can flow since the resistance of the nozzle exceeds pressure value. To reduce the resistance, we can open the nozzle slightly. Now the water squirts out...a long distance. There is some resistance, but less than before. Since the water is at a high pressure, it travels a great distance. (See Fig. 1.)
If we open the nozzle all the way, we reduce the resistance as much as possible. Now the water comes out of the hose under much less pressure, but at a far greater volume. With nearly all resistance eliminated, the pressure is lower and the flow is greater. The water can't travel very far, but you get more of it. (See Fig. 2.)
Electricity works almost the same way as water does in this garden hose illustration. Voltage is pressure. It is what tries to force the movement of electrons against a resistance. Voltage pressure is what forces a spark to jump across the gap at the tip of a spark plug--or across any gap where it can seek a path to ground.
Electrical pressure, "volts" or "voltage," can be measured with a piece of test equipment called a voltmeter, which is a very common shop tool. Two types of voltmeters are frequently used: 1) an analog voltmeter, which uses a swinging needle to show voltage; and 2) a digital voltmeter, which uses LEDs or other graphic readouts to show the voltage measured. (See Fig. 3).
Electrical volume, measured in "amps" or "amperage," increases as resistance decreases. As volume (amperage) grows, the electrical pressure (voltage) tends to drop. Lots of electrons flow, but the pressure drops.
Electrical volume (amperes or amps) can be measured with an ammeter. Because an ammeter is measuring flow, it must be capable of handling the actual volume of electrons flowing without overheating or otherwise destroying itself. For this reason, ammeters generally fall into two categories: 1) "millimeters" which measure fractions of an amp--usually in unit with volt and ohmmeters in a device called a multi-meter; and 2) voltage amperage testers or VATs which are capable of handling the extremely high flows of electrons associated with battery-to-starter circuits and charging circuits.
The third value, ohms of resistance, tries to prevent electron flow. Resistance occurs for a variety of reasons and varies according to the type of material conducting the electricity, the size of the conductor and the temperature of the conductor. All conductors have some level of resistance. Resistance is not a "bad" factor. In fact, resistance is used to control electrical flow and turn it into useful work. For instance, resistance makes a tungsten filament in a light bulk get hot, glow and give off light.
Resistance can be measured with a device called an ohmmeter, another common shop tool.
None of these electrical values should be a mystery to the typical automotive technician. He should be able to understand all of them and use the proper tools to measure their values when needed. Do-it-yourselfers, on the other hand, may not be familiar with these electrical values, and will depend upon you to gain an understanding of how they affect wire and electrical system performance, and which products they should buy.
| High pressure = Low flow |
| Large flow = Lowered pressure |
