Science Fair Project Encyclopedia
Electrical wiring (U.S.)
Electrical wiring in general refers to conductors used to carry electricity and their accessories. General aspects of electrical wiring as used to provide power in or to buildings and structures, commonly referred to as building wiring, are described in Electrical wiring.
This article provides information specific to electrical systems in common use in the U.S..
Design and installation conventions
The National Electrical Code specifies acceptable wiring methods and materials in the United States. Local jurisdictions usually adopt the NEC or another published code which they cannot distribute for copyright reasons and then distribute documents describing how local codes vary from the published codes. A new NEC is published every three years.
In addition to new construction, additions or major modifications must follow the latest code. With a few exceptions existing wiring does not have to be changed to meet new codes however it is recommended that older wiring be inspected periodically for safety.
Note: What is commonly called an outlet is called a receptacle in the NEC. In the NEC an outlet is any place where the electricity is used and includes both receptacles and places where permanent light fixtures or other equipment are connected.
For residential wiring, some basic rules based on the 2002 NEC are: (This is just a brief overview and should not be used as a replacement for the actual code.)
- hot circuit to use black or red insulated wire, sometimes other colors, but never green, gray, or white
- neutral circuit to use gray or white insulated wire
- ground circuit to use green insulated wire or bare wire
- minimum 12 gauge solid wire for 20 amp circuits (stranded may also be used, and is of greater ampacity, but is more expensive and requires slightly different techniques)
- minimum 14 gauge wire, solid for 15 amp circuits (some local codes require a minimum of 12 gauge for 15 amp circuits, except for switch legs - that is, circuit portions that are strictly between a light switch and the light that it serves; stranded may also be used, and is of greater ampacity, but is more expensive and requires slightly different techniques)
- all wiring in a circuit except for the leads that are part of a device or fixture must be the same gauge.
- a maximum of 8 duplex receptacles on a normal wiring circuit; a better recommendation is a maximum of 4. Refer to the code for specific formulas.
- ground-fault circuit interruptor protection is required on receptacles near water and outdoor circuits. This includes all small appliance circuits in the kitchen, all receptacles in the bathroom and a receptacle for the laundry, as well as outdoor circuits within easy reach of the ground. However they are not required for refrigerators because unattended disconnection could cause spoilage of food.
- all bedroom circuits with receptacles must have arc fault circuit interuptor protection. Note: the requirement for GFCI applies to the receptacle and the requirement may be met with the use of a GFCI receptacle or a GFCI breaker while the arc fault requirement applies to the entire circuit and is met with an AFCI breaker.
- all parts of the system must be continuously grounded with a ground wire separate from any grounded conduit.
- recommended to put light fixtures on separate circuits than outlets
- minimum of two 20 amp countertop circuits for kitchen use
- furnaces, water heaters, heat pumps, central air conditioning units, stoves on dedicated circuits
- recommended to put ALL major appliances on dedicated circuits (including refrigerator and dishwasher)
- use of exterior components for exterior lighting and outlets
- electrical boxes must be properly sized. (Incorrect box size is a very common mistake. Many sizing guides are incorrect or out of date. Refer to the electrical code.)
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details