People use electricity every day, at work, at home, and in all other facets of modern life. And yet most people don't really understand basic electrical terms like Volts, amps, Watts, and power factor. This article presents an explanation of these terms that will help take some of the mystery out of electricity.

Voltage is a measurement of electrical force or potential. This potential is measured in volts, and is represented in electrical calculations by the symbol V. To paint a simple picture, a voltage source presents a certain amount of electrical pressure in the same way that a faucet provides a certain amount of water pressure. A standard "D" cell used in a flashlight has an electrical potential of 1.5 volts. The electrical outlets in most homes, which provide electricity to a variety of appliances, have a potential of roughly 120 volts. An electric stove, clothes dryer, or central air conditioner usually requires 240 volts to operate. Large pumps and fans used in industrial facilities often operate at 480 volts. And overhead electrical distribution lines may carry electricity at a potential of many hundred or even thousands of volts.

The current of an electrical signal refers to the rate of electrons flowing through a conductor within a unit of time, similar to the amount of water flow through a garden hose. Current is measured in amperes or amps (A), and is represented in electrical calculations by the symbol I. Different types of electrical appliances require different amounts of current to operate. A radio operates on very little current, while an electric oven or large motor requires a much higher current flow. In the same way that a large fire hose allows greater flow than a garden hose, a conductor or wire must have a large diameter to handle a high current flow.

Power is a unit of energy (the ability to do work). Electrical power is measured in Watts (W), and in simple terms is equal to voltage multiplied by current. One Watt equals one Volt multiplied by one amp. For electrical calculations, this is written as W = VI, where V is volts, I is current in amperes, and W is power in Watts. This simple power equation has many applications, and may also take the form of V = W/I or I = W/V. As an example, consider a flashlight with a 5 Watt bulb that runs on two "D" cells. Since I = W/V, the current flow (I) in the circuit is equal to the power (5 Watts) divided by the total voltage (2 x 1.5 Volts = 3 Volts). In this case, I = W/V = 5/3 = 1.66 amps.

An electrical signal can take one of two forms: direct current (DC) or alternating current (AC). Flashlight batteries are a common example of a DC electrical source, which provide a constant, positive electrical potential (in this case, 1.5 volts DC). The signal from an AC electrical source, however, is shaped like a sine wave (see Figure 1), alternating from a positive to a negative value many times a second. The frequency of this change is measured in cycles per second, or Hertz (Hz). The standard AC frequency used in the U.S. is 60 Hz.

Figure 1: AC Sine Wave

Alternating current has become the standard form of electricity supplied to homes, offices, and industries, primarily because an AC signal can easily be transformed from one voltage level to another. A DC signal, on the other hand, is not easily transformed to a different voltage level. As AC electricity is transmitted through the distribution system, its voltage level usually changes several times between the generator and the end user. This change in voltage level is accomplished though the use of transformers, and is necessary to make long-distance transportation of the electricity more economical. In general, the higher the voltage of an electrical source, the more force it has to push the electrons through the resistance of the transmission lines.

The power equation (W = V x I) presented earlier can be applied directly to DC electricity. But to properly understand AC electricity, a variable known as power factor must be included in the equation, such that W = V x I x pf. With AC, the voltage and current waveforms do not necessary alternate together. The two can potentially be out of phase, with one wave leading or lagging behind the other. The power factor variable represents how "in phase" or "out of phase" the voltage and current waves are with respect to each other. Power is only delivered when the voltage and current are fairly well lined up. If voltage and current are completely in phase (as with DC signals), then the power factor is 1. If the voltage and current signals are 90° out of phase, then the power factor is 0, and no real power is generated.

The power factor can vary depending on the type of load present in the circuit. Figure 2 shows voltage and current waveforms that are completely in phase, yielding a power factor of 1. A typical example of this is an incandescent electric light bulb, which operates with voltage and current completely in phase and has a power factor of 1.

On the other hand, Figure 3 shows the voltage and current waveforms for a motor running with no load (shaft disconnected from the load). In this example, the power factor is very close to 0, with voltage and current almost completely out of phase. Very little true power is delivered in this instance.

Figure 2: Voltage and Current Signals In Phase

The electricity supplied to homes consists of a single phase, or voltage signal. But the electricity used by industries is generally three-phase power. This means that three independent voltage signals are delivered through three independent conductors, with each signal being 120° out of phase with the other two (see Figure 4). For a variety of reasons, three-phase power provides a more efficient means of supplying large electrical loads like motors. For three-phase electricity the power equation includes an additional constant:

W = 1.732 x V x I x PF

As with single-phase power, the power factor for three-phase power can vary between 0 and 1.

Figure 3: 3-Phase Power

These explanations of the fundamental electrical terms - voltage, current, power, and power factor - should help consumers better understand the basic principles of electricity. While other aspects of electricity use and transmission can be much more complicated, the symbols W, V, I, and pf hopefully aren't as mysterious as they once seemed.