Electrical systems are an essential part of today’s lifestyle. They power most modern home conveniences, such as lights, appliances, furnaces, air conditioners, televisions, entertainment centers, and computers. An electrical system found in a typical home includes incoming power from a utility company, meter box, main disconnect switch, service panel, breakers or fuses, branch circuits and, at times, sub-panels. All of these supply power to light fixtures, ceiling fans, appliances and other equipment.
Electrical needs are continually growing. Houses built prior to 1940 may still have their original service capacity of 30 or 60 amps, while 100-amp service became the norm sometime in the 1970s. Since the 1990s, most new construction includes 200-amp service.
Utility companies provide power through wires to the meter box from either an overhead service drop or underground conduit. Most older houses have service drops. Three wires (two hot and one neutral) run from the utility company’s transformer to the meter box. These wires, in turn, run to a service panel located on an interior wall near the meter box.
Electrical System Disconnect Breakers
Most service panels have an integrated main disconnect breaker, fuse, or lever. A main disconnect that is not in the service panel may be in a separate panel near the service panel or outside at the meter box. The main disconnect controls the electricity to the breakers or fuses. Branch circuits are controlled by the breakers or fuses and are made up of wire, a means to distribute this wire (i.e. knob & tube, non-metallic cable, plastic or metal conduit & junction boxes), outlets, and/or switches. In a 120-volt circuit there are two wires, one hot (usually black or red) and one neutral (white). In a 240-volt circuit there are three wires, two hot (usually black or red) and one neutral (white).
Grounding Systems
Grounding is a separate system within the electrical system. An effective grounding system disposes unwanted electricity to the ground, removing the potential for shock or electrocution. Today’s practice has ground wires running from outlets and various fixtures to the neutral buss bar in the service panel. Electricians also use wires or straps to bond metal components that are not supposed to carry electricity. Ground wires also run from the neutral buss bar to water pipes and/or grounding rods, thus completing the circuit and making an effective ground.
Circuit Breakers
Breakers or fuses are the weak link in the branch circuit. This is deliberate, serving as the fail safe if the circuit draws more current than it is designed to conduct. Otherwise, the wires would heat up with the potential for fire. Breakers trip and can be reset, while fuses have to be replaced. Single pole breakers typically come in 15 and 20 amps, which provide 120 volts. Double pole breakers are designed up to 50 amps and are used for dedicated appliances or equipment such as air conditioners, electric dryers, ranges, stoves and the like. Electricians use two basic types of fuses for home service panels. Cartridge comes in small (15 to 30 amp), medium (35 to 60 amps) and large (100 amp). Appliances and equipment that require 240 volts of electricity usually employ cartridges. The second type, conventional, typically comes in 15 to 30 amps.
What are GFCI and AFCI?
A Ground Fault Circuit Interrupter (GFCI) or an Arch Fault Circuit Interrupter (AFCI) can also provide protection for circuits. There are both GFCI breakers and outlets. The purpose of both is to provide protection (in fractions of a second) from the likelihood of fatal shock in areas such as kitchen countertops, bathrooms, laundry room & tubs, garages, and basements. GFCI breakers protect the entire circuit, while GFCI outlets only protect the outlet on which they are installed and outlets downstream from them.
AFCIs protect from fire. AFCI breakers detect if there is an arch when electricity moves from one conductor across an insulator (either air or solid insulating material) to another conductor. The heat generated in this process can ignite near combustible materials. Damaged electrical cords or outlets not properly installed can create arch faults.