Basic Theory of Electricity
Understanding electricity can sometimes be difficult. The main reason for this is that we cannot see electricity and consequently it is hard to understand something, which is intangible. We just know that when we turn the switch on, the light will turn on, or the fan will start turning. To understand electricity, one must have a basic understanding of three simple electrical terms: volts, amps, and resistance. To assist in imparting a basic understanding of these terms, a simple household water hose example is presented.
Consider a water faucet on the side of your home. If you take a pressure, gauge, screw it onto a faucet at your home and then turn on the water, the pressure gauge will indicate how much water pressure you have at that faucet. It most probably would read between 25 to 40 PSI, which is a typical water pressure for most city-supplied household systems. In this example, you will note that there is no water flowing and what was measured was a static water pressure. Now consider an electrical outlet in your home. With nothing plugged into the outlet, there is no electrical current flowing. One could take a standard voltmeter and insert the test probes of the voltmeter´s leads into the outlet´s socket. By doing this, one can measure the supply voltage at the electrical outlet. The measurement would be somewhere between 117 to 126 volts, which is typical for most household electrical systems. Remember, no current is flowing and what has been measured, is simply the static voltage at that outlet. Remembering the water faucet example, you could equate water pressure to electrical voltage. Consequently, electrical voltage is the driving force behind the electrical current flowing in a conductor (cable or wire); just as water-pressure is the driving force behind water flowing through a hose. The word “voltage” is the same as the word “potential” when talking about electricity, and they are often used interchangeably.
Now consider the water flowing through the hose. You could place a one-gallon bucket at the end of the hose and time how long it takes to fill the bucket. For our example, let us say that it takes 30 seconds. This would equate to a water flow rate of two gallons per minute. In electrical circuits, the amount of electricity flowing through a conductor is measured in amps. Getting more technical than this at this time is not necessary for this discussion. When you think of electrical current flow, think of water flowing through a hose (gallons per minute), which is measured in amps.
Finally, consider electrical resistance. Using our water hose example, if one installed a pressure gauge at a water faucet to which a water hose was attached, and which had water flowing at two gallons per minute, it most probably would read something approximating 25 PSI. In this example, another pressure gauge was installed half way down the length of the hose. With this setup, it may well read something around 15 PSI while the water was flowing unimpeded through the hose at two gallons per minute. Consequently, it would be correct to say that in this example there was a 10-PSI pressure drop over that distance between the two pressure gauges. Why did this pressure drop occur? It did so due to frictional loses of the water flowing through the hose. In other words, the hose has a certain resistance characteristics to the water flowing through it. The higher the flow rate of water through the hose the higher will be the pressure drop due to friction. In electrical circuits, resistance to current flow is the same as pressure drop in our water hose example, and is measured in ohms. Most conductors of electricity are rated for a certain voltage and amperage. This rating in non-technical language means that as long as you do not exceed either value, the conductor will not be damaged by current flowing through it. If the voltage and current are exceeded, then the resistance developed by the elevated values will result in greater resistance being encountered. The resistance will go directly into heat. The conductor will continue to heat, until it reaches it melting point and melts.
Each substance known to man has an electrical resistance characteristic. Whether one is considering water, soil, metal, wood, air, etc., there is an electrical resistance to current flow, measured in “ohms”, that describes that particular condition. Everyone knows that the metal copper is conductive and offers a very low resistance to electrical current flow. Now consider air. It is highly resistive to current flow. However, if you supply an automobile´s spark plug with enough voltage, a spark can be made to jump through the air gap between the sparkplug´s two metal electrodes, resulting in a short burst of electrical current flow through air. In this example of forcing electricity to flow through a non-conductive substance, an extremely high voltage was applied, which exceeded the dielectric strength of the substance, resulting in electrical current flowing. The dielectric strength of a substance is similar to or equates to resistance. In electrical circuit terminology, the word “resistance” and the word “impedance” are often use interchangeably.
There are two kinds of electricity. AC is Alternating Current electricity, and DC is Direct Current electricity. In the vast majority of cases, all cathodic protection systems incorporate direct current electricity technology, whether galvanic or impressed current systems are employed.
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