Junction box

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An electrical junction box (also known as a ‘jbox’) is an enclosure housing electrical connections. [1] Junction boxes protect the electrical connections from the weather, as well as prevent people from accidental electric shocks.

Contents

Construction

A small metal or plastic junction box may form part of an electrical conduit or thermoplastic-sheathed cable (TPS) wiring system in a building. If designed for surface mounting, it is used mostly in ceilings, under floors or concealed behind an access panel—particularly in domestic or commercial buildings. An appropriate type (such as that shown in the gallery) may be buried in the plaster of a wall (although full concealment is no longer allowed by modern codes and standards) or cast into concrete—with only the cover visible.

It sometimes includes built-in terminals for the joining of wires.

A similar, usually wall mounted, container used mainly to accommodate switches, sockets and the associated connecting wiring is called a pattress.

The term junction box may also be used for a larger item, such as a piece of street furniture. In the UK, such items are often called a cabinet. See Enclosure (electrical).

Junction boxes form an integral part of a circuit protection system where circuit integrity has to be provided, as for emergency lighting or emergency power lines, or the wiring between a nuclear reactor and a control room. In such an installation, the fireproofing around the incoming or outgoing cables must also be extended to cover the junction box to prevent short circuits inside the box during an accidental fire.

Solar panel

A PV junction box is attached to the back of the solar panel and it is its output interface.

See also

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Electrical wiring in North America follows regulations and standards for installation of building wiring which ultimately provides mains electricity.

National Electrical Code

The National Electrical Code (NEC), or NFPA 70, is a regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. It is part of the National Fire Code series published by the National Fire Protection Association (NFPA), a private trade association. Despite the use of the term "national", it is not a federal law. It is typically adopted by states and municipalities in an effort to standardize their enforcement of safe electrical practices. In some cases, the NEC is amended, altered and may even be rejected in lieu of regional regulations as voted on by local governing bodies.

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Electrical wiring

Electrical wiring is an electrical installation of cabling and associated devices such as switches, distribution boards, sockets, and light fittings in a structure.

Electrical wiring in the United Kingdom is commonly understood to be an electrical installation for operation by end users within domestic, commercial, industrial, and other buildings, and also in special installations and locations, such as marinas or caravan parks. It does not normally cover the transmission or distribution of electricity to them.

Structured cabling

In telecommunications, structured cabling is building or campus cabling infrastructure that consists of a number of standardized smaller elements called subsystems. Structured cabling components include twisted pair and optical cabling, patch panels and patch cables.

An earthing system (UK) or grounding system (US) connects specific parts of an electric power system with the ground, typically the Earth's conductive surface, for safety and functional purposes. The choice of earthing system can affect the safety and electromagnetic compatibility of the installation. Regulations for earthing systems vary considerably among countries, though most follow the recommendations of the International Electrotechnical Commission. Regulations may identify special cases for earthing in mines, in patient care areas, or in hazardous areas of industrial plants.

Electrical enclosure

An electrical enclosure is a cabinet for electrical or electronic equipment to mount switches, knobs and displays and to prevent electrical shock to equipment users and protect the contents from the environment. The enclosure is the only part of the equipment which is seen by users. It may be designed not only for its utilitarian requirements, but also to be pleasing to the eye. Regulations may dictate the features and performance of enclosures for electrical equipment in hazardous areas, such as petrochemical plants or coal mines. Electronic packaging may place many demands on an enclosure for heat dissipation, radio frequency interference and electrostatic discharge protection, as well as functional, esthetic and commercial constraints.

A pattress or pattress box or fitting box is the container for the space behind electrical fittings such as power outlet sockets, light switches, or fixed light fixtures. Pattresses may be designed for either surface mounting or for embedding in the wall or skirting board. Some electricians use the term "pattress box" to describe a surface-mounted box, although simply the term "pattress" suffices. The term "flush box" is used for a mounting box that goes inside the wall, although some use the term "wall box". Boxes for installation within timber/plasterboard walls are usually called "cavity boxes" or "plasterboard boxes". A ceiling-mounted pattress is referred to as a "ceiling pattress" or "ceiling box". British English speakers also tend to say "pattress box" instead of just "pattress". Pattress is alternatively spelt "patress" and Wiktionary lists both spellings. The word "pattress", despite being attested from the late 19th century, is still rarely found in dictionaries. It is etymologically derived from pateras.

Knob-and-tube wiring Type of electrical wiring

Knob-and-tube wiring is an early standardized method of electrical wiring in buildings, in common use in North America from about 1880 to the 1930s. It consisted of single-insulated copper conductors run within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nailed-down porcelain knob insulators. Where conductors entered a wiring device such as a lamp or switch, or were pulled into a wall, they were protected by flexible cloth insulating sleeving called loom. The first insulation was asphalt-saturated cotton cloth, then rubber became common. Wire splices in such installations were twisted together for good mechanical strength, then soldered and wrapped with rubber insulating tape and friction tape, or made inside metal junction boxes.

Cable tray

In the electrical wiring of buildings, a cable tray system is used to support insulated electrical cables used for power distribution, control, and communication. Cable trays are used as an alternative to open wiring or electrical conduit systems, and are commonly used for cable management in commercial and industrial construction. They are especially useful in situations where changes to a wiring system are anticipated, since new cables can be installed by laying them in the tray, instead of pulling them through a pipe.

Circuit integrity

Circuit integrity refers to the operability of electrical circuits during a fire. It is a form of fire-resistance rating. Circuit integrity is achieved via passive fire protection means, which are subject to stringent listing and approval use and compliance.

Electrical room

An electrical room is a room or space in a building dedicated to electrical equipment. Its size is usually proportional to the size of the building; large buildings may have a main electrical room and subsidiary electrical rooms. Electrical equipment may be for power distribution equipment, or for communications equipment.

Cable management

Cable management refers to management of electrical or optical cable in a cabinet or an installation. The term is used for products, workmanship or planning. Cables can easily become tangled, making them difficult to work with, sometimes resulting in devices accidentally becoming unplugged as one attempts to move a cable. Such cases are known as "cable spaghetti", any kind of problem diagnosis and future updates to such enclosures could be very difficult.

Copper conductor

Copper has been used in electrical wiring since the invention of the electromagnet and the telegraph in the 1820s. The invention of the telephone in 1876 created further demand for copper wire as an electrical conductor.

A high-resistance connection (HRC) is a hazard that results from loose or poor connections in traditional electrical accessories and switchgear which can cause heat to develop, capable of starting a fire.

Electrical conduit

An electrical conduit is a tube used to protect and route electrical wiring in a building or structure. Electrical conduit may be made of metal, plastic, fiber, or fired clay. Most conduit is rigid, but flexible conduit is used for some purposes.

Electrical busbar system

Electrical busbar systems are a modular approach to electrical wiring, where instead of a standard cable wiring to every single electrical device, the electrical devices are mounted onto an adapter which is directly fitted to a current carrying busbar. This modular approach is used in distribution boards, automation panels and other kinds of installation in an electrical enclosure.

References

  1. "What is a Junction Box (Electrical Box)?". Electrical Knowledge.