Details of Selected NEC Requirements
Article 210 addresses "branch circuits" (as opposed to service or feeder circuits) and receptacles and fixtures on branch circuits. There are requirements for the minimum number of branches, and placement of receptacles, according to the location and purpose of the receptacle outlet. Ten important items in Article 210 have been summarized in a codebook.
Feeder and branch circuit wiring systems are designed primarily for copper conductors. Aluminum wiring is listed by Underwriters Laboratories for interior wiring applications and became increasingly used around 1965 due to its lower cost. Prior to 1972, however, the aluminum wire used was manufactured to conform to the 1350 series aluminum alloy, but this alloy was eventually deemed unsuitable for branch circuitry due to overheating problems and potential fire risk. Today, a new aluminum wire (AA-8000) has been approved for branch circuitry, but it is not readily available and is not manufactured below size #8 AWG. Hence, copper wire is used almost exclusively in branch circuitry.
At this juncture in time a "new technology" of aluminum wire was developed, known as AA-8000 series which is the current aluminum wire used today for branch circuitry, however it is extremely rare to find in branch circuit wiring. Several upgrade options are available for homes with pre-1974 aluminum branch circuit wiring.
A ground fault circuit interrupter (GFCI) is required for all receptacles in wet locations defined in the Code. The NEC also has rules about how many circuits and receptacles should be placed in a given residential dwelling, and how far apart they can be in a given type of room, based upon the typical cord-length of small appliances.
As of 1962 the NEC required that new 120-volt household receptacle outlets, for general purpose use, be both grounded and polarized. NEMA connectors implement these requirements.
The NEC also permits grounding-type receptacles in nongrounded wiring protected by a GFCI.
The 1999 Code required that new 240-volt receptacles be grounded also, which necessitates a fourth slot in their faces. These changes in standards often cause problems for people living in older buildings.
Unlike circuit breakers and fuses, which only open the circuit when the current exceeds a fixed value for a fixed time, a GFCI device will interrupt electrical service when more than 4 to 6 milliamperes of current in either conductor leaks to ground. A GFCI detects an imbalance between the current in the "hot" side and the current in the "neutral" side. One GFCI receptacle can serve as protection for several downstream conventional receptacles. GFCI devices come in many configurations including circuit-breakers, portable devices and receptacles.
Another safety device introduced with the 1999 code is the arc-fault circuit interrupter (AFCI). This device detects arcs from hot to neutral that can develop when insulation between wires becomes frayed or damaged. While arcs from hot to neutral would not trip a GFCI device since current is still balanced, circuitry in an AFCI device detects those arcs and will shut down a circuit. AFCI devices generally replace the circuit breaker in the circuit. They are required in new construction on all 15A and 20A 125V circuits to bedrooms, where most arc fault fires originate.
Read more about this topic: National Electrical Code
Famous quotes containing the words details of, details and/or selected:
“Working women today are trying to achieve in the work world what men have achieved all along—but men have always had the help of a woman at home who took care of all the other details of living! Today the working woman is also that woman at home, and without support services in the workplace and a respect for the work women do within and outside the home, the attempt to do both is taking its toll—on women, on men, and on our children.”
—Jeanne Elium (20th century)
“If my sons are to become the kind of men our daughters would be pleased to live among, attention to domestic details is critical. The hostilities that arise over housework...are crushing the daughters of my generation....Change takes time, but men’s continued obliviousness to home responsibilities is causing women everywhere to expire of trivialities.”
—Mary Kay Blakely (20th century)
“The best history is but like the art of Rembrandt; it casts a vivid light on certain selected causes, on those which were best and greatest; it leaves all the rest in shadow and unseen.”
—Walter Bagehot (1826–1877)