Understanding the Power You Need

If you want to fill your home with a lot of cool digital gadgets, it goes without saying that your house must be connected to an electrical power source. Technology doesn't run on magic beans. Of course, most electricity is generated at power plants. Those plants typically run on coal, natural gas, nuclear power, or hydroelectric generators. The electricity is transmitted to your local power company, which then distributes it to individual customers like yourself.

Alternating stuff

When a power plant generates power, it does so by rotating a magnet so that it passes by a coil. The voltage rises as the magnet nears the coil, then decays as the magnet continues past the coil. As the magnet's opposite pole nears the coil, the voltage builds in the opposite direction. The voltage mimics a sine wave like the one illustrated in Figure 1, and is said to be alternating current because it alternates between positive and negative; first the electrons flow in one direction through the circuit and then in the opposite direction. When the current alternates 60 times per second, it is called 60 cycle. These cycles are also called Hertz, named after the German physicist Heinrich Hertz, who was the first person to artificially produce radio waves.

Current that doesn't alternate between poles is called direct current (DC). DC power flows in one direction. The current from a battery (such as the one in your car or the one in your iPod) is direct current.

Transforming current with transformers

When AC comes from the power company, it's sent in thousands of volts. Devices called transformers step that power down to the 120/240-volt power used in your home. However, most of the digital stuff in your home runs on DC power. This is why you usually plug them into your AC power outlets with AC adapters, which are power cords with small rectangular blocks on them. The block on an AC adapter includes a transformer that steps down the 120-volt AC wall power to a lower voltage, which varies depending on the device. The AC adapter also includes a device called a rectifier, which converts AC voltage to DC voltage.

Amps and volts and other terms

Making the permanent connection to the electricity supplied by your power company happens just once, so getting it done right is important. You should invest some time in getting familiar with the terms and equipment you need to do the job properly. It's good to know this stuff, even if an electrical contractor is doing the work for you, because you want to make sure that you get an installation that will meet your home's needs.

Some of the electrical terms you'll encounter include:

• Amps: Short for amperes, a measurement of electrical current flow. Amps measure the amount of current a conductor can carry. The measurement also specifies the size (electrical capacity) of electrical items, such as a 100-amp panel or a 20-amp breaker.

• Breaker: Common term for a circuit breaker. Circuit breakers close and open circuits. When a breaker trips, the circuit is open and no current flows.

• Conduit or cable: The medium by which you bring power from point to point. Conduits or cables contain conductors (wires) that actually carry the power.

• Current: The flow of electrical energy, as measured in amps.

• Distribution panel: The equipment that parcels out power to different circuits and locations. This panel is also sometimes called a breaker panel or service panel.

• Fuse: Works like a circuit breaker, but is a one-time-use device.

• Ground: Earth or connected to earth; this term also refers to the bare ground conductors or wires with green insulation on the conductors. The ground wires aren't intended for carrying any current unless there's a fault condition.

• Junction: The point where wires or cables are joined together. Junctions are located in junction boxes with the exception of some outdoor cables.

• Meter: Watt-hour meter. The power company uses this device to measure your home's power usage. Test meters also measure volts (voltmeter), amps (ammeter), ohms (ohmmeter), or power factor meter.

• Power: The product of volts multiplied by amps expressed in watts (W) or volt amps (VA). The ungrounded conductors that carry power are also sometimes called the power wires or energized conductors.

• Service: The conductors and equipment bringing power from the utility to the premises' service disconnect.

• Service disconnect: The one to six disconnects that interrupt all power from the power company. This is usually a single main circuit breaker in the service panel.

• VA (volt amps): Measurement of power. VA is the product of volts times amps.

• Volt: The international measurement of electrical potential. One volt is the measurement of the electromotive force necessary to carry one amp of current across a resistance of one ohm.

• Watt: The product of volts times amps in a DC circuit. In an AC circuit, wattage is the product of volts times amps times the power factor.