Electrical wiring
Electrical wiring refers to the placement and configuration of conductive wires for electricity supply in or to some facility. "Building wiring" is a similar term.
Electrical wiring may be "on the grid", meaning that it is continuous with common electrical utility supplies. In most of the Americas, this means alternating current at 60 Hz, with 120 volts nominal. In European countries, this means alternating current at 50 Hz with 230 nominal volts.
"Off the grid" electrical wiring is often configured to carry direct current. This necessitates heavier wiring. For instance, 12 gauge wire is required for a 20 amp AC household circuit in the United States, but the same circuit for DC power should be at least 10 gauge wire (thicker than 12 gauge).
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 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 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 NEC: http://www.nfpa.org/nec/TheNEC/index.asp
