Electrical wiring

Electrical wiring in general refers to conductors used to carry electricity and their accessories. This article describes general aspects of electrical wiring as used to provide power in or to buildings and structures, commonly referred to as building wiring. Electrical wiring practices vary greatly by locality. This article provides general information that should apply worldwide.

Wiring Safety Codes

In the U.S., U.K, Canada and other industrialized countries installation of wiring is governed by national or local regulations. Often a national technical standards-setting organization will produce a model electrical code, which is then adopted,perhaps with local amendments, by state/provincial or city regulations. The intention of wiring safety codes is to provide technical, performance and material standards that will allow efficient distribution of electrical energy and communication signals, at the same time protecting persons in the building from electric shock and preventing fire or explosion. Electrical codes arose in the 1880's with the early commercial introduction of electrcal power, since many conflicting standards existed for the selection of wire sizes and other design rules for electrical installations.

The first electrical codes in the United States originated in New York in 1881 to regulat installations of electric lighting. The U.S. National Fire Protection Association, a private non-profit association, produced the first draft of the U.S. National Electrical Code in 1885.

Since 1927, the Canadian Standards Association has produced the Canadian Safety Standard for Electrical Installations, which is the basis for provincial electrical codes.

In the United Kingdom wiring installations are regulated by the produced by the IEERequirements for Electrical Installations: IEE Wiring Regulations, BS 7671: 2001 which is now in its 16th edition.

Although these three national standards all deal with the same physical phenomena and broadly similar objectives, they differ significantly in technical detail. As part of the NAFTA program, US and Canadian standards are slowly converging towards each other, in a process known as harmonization. Small countries, with relatively small technical societies, may adopt one of these three standards as their national standard, and concentrate on developing local regulatory amendments instead of redeveloping the basic requirements of a national code.

On or Off The Grid

Template:ActiveDiscuss Electrical wiring may be "on the grid", meaning that it is continuous with common electrical utility supplies. In North America, this means alternating current (AC) at 60 Hz, with 120 volts nominal. In European countries, this means AC at 50 Hz with 230 volts nominal.

"Off the grid" electrical wiring is often configured to carry direct current (DC). DC systems often run at a lower voltage than AC systems and so heavier wiring may be needed. This however is often offset by the fact that off grid systems are usually configured to minimize electricity use.

Wiring Methods

Materials for wiring interior electrical systems in buildings vary depending on:

• Rating of the circuit
• Type of occupancy of the building
• Type of electrical system
• National and local regulations
• Conditions which the wiring must operate.

Wiring systems in a home, for example, are simple, with relatively low power requirements, infrequent changes to the building structure and laayout, usually with dry, moderate temperature, and non-corrosive environmental conditions. In a light commerical environment, more frequent wiring changes can be expected, large apparatus may be installed, and special conditions of heat or moisture may apply. Heavy industries have more demanding wiring requirments, such as very large currents and power ratings, frequent changes of equipment layout, corrosive, wet or explosive atmospheres.

Knob and tube

The eariest method used for wiring in buildings, from about 1880 to the 1940's, was single insulated copper conductors run across interior walls or within ceiling cavities, passing through holes in porecelain insulating tubes, and supported thorughout their length on porcelain insulators. This system is known as "knob-and-tube" from the procelain insulators used. Where conductors entered a wiring device such as a lamp or switch, they were protected by flexible insulating sleeving. Wire splices in such installations were typically soldered and wrapped with cloth tape, or made inside metal junction boxes.

While a knob-and-tube wiring system can be safe and reliable when in good condition, it is not used in modern building construction. The installation is costly due to the high labor content, and originally knob-and-tube installations did not include a safety ground connection.

Older homes may have knob-and-tube wiring for all or part of their electrical system. Such wiring systems may require replacement or upgrade. Wiring in such buildings may be inadequate for modern levels of power use. Wiring may have been damaged by renovations done in the building. Insulation covering the wires may be brittle due to age or may be damaged by rodents or carelessness (for example, hanging objects off wiring running in accessible areas like basements).

Other historic wiring methods

Other methods of securing wiring that are now obsolete include:

• Re-use of existing gas pipes for electric lighting. Insulated conductors could be pulled into the pipes feeding gas lamps.
• Wood moldings with grooves cut for wires. These were eventually prohibited in North American electrical codes by the 1930's.

References

www.insure.com/home/knobtube.html Insuring a home with knob and tube insulation [History of Residential Wiring Methods - U.S.]

• Electric power transmission
• Electricity distribution
• Electrical wiring (U.S.)
• Electrical wiring (UK)