National Electrical Code (U.S.)
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The National Electrical Code is a book which contains rules on how to safely install electrical equipment, appliances, and other electrical-supply related infrastructure.
In most cities in the United States, the book is adopted as part of the municipal code as the authoritative set of rules for how electrical work must be done. This means the book carries the force of law in many jurisdictions.
The book is updated and published every 3 years. Recent publication dates were 1993, 1996, 1999, 2002, etc. Most municipalities adopt the most recent book within a couple of years of its publication.
The reason for this book to exist is to codify the best practices of electrical work into a single volume.
In the U.S., any city can be handed a civil liability lawsuit (sued) for creating a situation that results in loss of life. This means that the city should adopt and enforce building codes that specify standards and practices for electrical systems (as well as other departments such as water systems). This creates a system whereby a city can best avoid lawsuits by adopting a single, standard set of building code laws. This has led to the NEC becoming the de facto standard set of electrical code laws.
FS-1037C
A National Electric Code (NEC) is a standard that governs the use of electrical wire, cable, and fixtures, and electrical and optical communications cable installed in buildings in the USA.
Details of NEC requirements
Placement of wall sockets on a wall is governed in the United States by the National Electrical Code, a book which contains rules on how to safely install electrical equipment, appliances, and other electrical-supply related infrastructure.
According to the National Electrical Code, wall sockets should be positioned at least (see the NEC for exact details) 12 inches from the floor. The NEC also has rules about such things as how many electrical sockets should be placed in a given residential dwelling per square feet of floor area.
As of 1999 the NEC requires that new 120-volt household sockets be both grounded and polarized. This means that:
- There must be a slot for a center-line, rounded pin connected to a common ground.
- The two blade-shaped slots must be of differing widths, to prevent devices which use "neutral" as their only ground from being misconnected.
The 1999 Code requires that new 240-volt outlets be grounded also, which necessitates a fourth slot in their socket faces. U.S. 240 centertapped single phase has two of these slots being 'hot', with the neutral being the center tap. There is only one standard for these circuits, but 240 V sockets come in two incompatible varieties. In one the 'neutral' slot accepts a flat blade-prong. In the other the neutral slot accepts a blade with a right angle bend. These are officially NEMA types 14-50R (commonly used with number 8 wire for electric stoves) and 14-30R (commonly used with number 10 wire for electric clothes dryers), respectively, and differ only in current rating (50 A versus 30 A); previous installations would have used the 10-30 or 10-50 configuration.
These changes in standards often cause problems for people living in older buildings.
Another recent change in the NEC mandates the installation of sockets with an integrated balance-fault interrupt device in areas deemed higher risks for shorts and shocks. This includes, but may not be limited to, kitchen counter tops, wet bars, and bathrooms (again, see the NEC for details).
Unlike traditional circuit breakers and fuses, which only open the circuit when the current exceeds a fixed value, a BFI device will interrupt electrical service when voltage is detected on any other point, including but not limited to ground. A BFI basically detects an imbalance in the electricity (i.e. a different amount of electricity flowing in the "hot" side than what is flowing in the "neutral" side). Socket outlets with BFI have the added advantage of protecting other sockets 'downstream' of them, so that one BFI socket can serve as a breaker for several conventional outlets.
A BFI socket typically has a pair of small push buttons between its two receptacles: one labeled 'test' and the other 'reset' (or T and R). Pressing 'test' will short the hot and ground point, which will trip the device, resulting in an audible "snap". Pressing 'reset' will allow the socket to function normally after a test, or after a faulty appliance has been removed from the circuit.
Like fuses and circuit breakers, a BFI socket has a finite number of uses. It must be replaced when a test fails to trip the device.
The NEC was developed by the NEC Committee of the American National Standards Institute (ANSI), was sponsored by the National Fire Protection Association (NFPA), and is identified by the description ANSI/NFPA 70-XXXX, the last four digits representing the year of the NEC revision.
