North American power cord follows the rules and standards for building wiring.
Video Electrical wiring in North America
Terminology
Although many field terminologies of electricians fit the electrical code, their usage may vary: The
- Neutral cable is the back conductor of the circuit; in building a cable system, a neutral cable is connected to the earth's ground at least at one point. The North American standard states that neutral does not switch or merge except in very narrow circumstances. The neutral is connected to the center tap of the power transformer company of the split-phase system, or the wye connection center of the polyphase power system.
- The US electrical code requires that the neutral is connected to the earth only on the "service panel" and there is no other point in the building's cabling system. Formally, the neutral is called a "ground conductor"; in NEC 2008, the terms "neutral conductors" and "neutral points" have been specified in the Code to conform to what is commonly used. Hot are conductors (cables or other) connected to electrical systems that have electrical potential relative to ground or neutral ground.
Maps Electrical wiring in North America
Power codes and standards
The National Electrical Code (NEC) establishes acceptable methods and cabling materials for many states and municipalities in the US. It is sponsored by the National Fire Protection Association (NFPA) and has been periodically revised since 1897. Local jurisdictions typically adopt NEC or other published codes and then distribute documents that explain how local codes vary from published code. The government can not distribute its own NEC for copyright reasons, although the part that has been adopted into law is not subject to copyright.
The purpose of NEC is to protect people and property from the dangers arising from the use of electricity. NEC is not the electrical code of jurisdiction per se; on the contrary, it is standard work that influences that local legislators (eg, city council members, state legislators, etc.) tend to be used as guides when applying local electrical codes. The NFPA states that quotations quoted from the National Electrical Code should have a disclaimer indicating that the quotation is not a complete and authoritative NFPA position and that the original NEC document should be consulted as a definitive reference.
New construction, additions or major modifications must follow the relevant code for that jurisdiction, which is not necessarily the latest version of NEC. The rules in each jurisdiction will show when changes to existing installations are so good that they have to be rebuilt to comply with current electrical codes. Generally the existing installation does not need to be changed to meet the new code.
Other code requirements vary by jurisdiction in the United States. In many areas, a homeowner, for example, may conduct household cabling for a building occupied by the owner; this might even be a complete home. Some cities have more stringent rules and require electrical installation to be performed by a licensed electrician. The work will be checked by the designated authority at several stages before permission is obtained to energize the cable from the local electric utility; the inspector may be a state or municipal employee, or an employee of a utility power supply.
For electrical cables in Canada, the Canadian Electrical Code is a very similar standard published in Canada by the Canadian Standards Association since 1927.
Design and installation of the convention
For residential wiring, some basic rules given in NEC are: The wire
- Phase on the circuit may be black, red, orange (high leg delta) insulated wire, sometimes other colors but never green, gray or white ( whether this is solid color or lines). Special exceptions apply, such as a cable that runs to the switch and returns (known as a traveler) where the white wire will become the hot wire that feeds the switch. Another is for cables that are used to feed an outlet for equipment of 250 VAC 15 or 20 amps that do not require neutral, there is white heat (but must be identified as heat, usually with a black ribbon inside the connecting boxes). li>
- The neutral cable is identified by a gray or white insulated cable, possibly using lines or marks.
- With a striped wire strip cable is neutral, and the fine wire is hot. NEC2008 400.22 (f) enables marking of surfaces with bulges, grooves or white lines on the surface of lamp cables. With transparent cables, copper-colored, silver-colored and silver wires.
- Grounding series wire may be naked or identified in green insulated wire or have green stripes. All metal systems in buildings must be tied to building grounding systems, such as water, natural gas, HVAC pipes, and others.
- Larger cables only have black; this can be correctly identified with the appropriate paint or masking tape.
- All cabling on the circuit except for leads that are part of the device or equipment must be the same measuring instrument. Different cable sizes can be used in the same path as long as all are isolated for the maximum voltage of any of these circuits.
- The code provides rules for calculating the loading of the circuit.
- Ground-fault interference protection (GFCI) protection is required on containers in wet locations. These include all the small circuitry tools in the kitchen, containers in crawl space, basements, bathrooms and containers for laundry rooms, as well as outdoor circuitry within easy reach of the ground. However, they are not required for refrigerators because unattended disconnection can lead to food spoilage, or to waste disposal. In contrast, for refrigerators and other semi-permanent appliances in basements and wet areas, a special non-GFCI outlet is commonly used. Two-wire outlets that do not have a grounding conductor can be protected by upstream gfci and should be labeled "no grounding". Most GFCI containers allow connections and have GFCI protection for downstream plugs. Containers protected in this way should be labeled "GFCI protected". (Outside North America this is referred to as "Current-current devices" or RCD.)
- Most circuits have interconnected metal components with a third ground-connected ground wire, rotary plug cap, and to metal box and tool chassis.
- Furnaces, water heaters, heat pumps, central air conditioning units, and stoves should be on special circuits
- The code provides rules for measuring the power box for the number of cables and wired devices in the box.
- In the fittings, the brass screw is hot, and the silver screw is neutral. The ground screw is usually painted green.
The above is just a brief overview and should not be used instead of the actual National Electrical Code.
Comparison of US practices with other countries
The practice of electrical wiring was developed in parallel in many countries in the late 19th and early 20th centuries. As a result, national and regional variations are growing and prevailing. (see National Electrical Code, power cord, power cord in UK). Some of these are stored for technical reasons, because the security of cabling systems depends not only on wiring codes but also on technical standards for devices, materials, and cable equipment.
Grounding of the distribution circuit is an important difference in practice between the US cable system and people from other regions. Since the early 1960s, cables in new construction have required a separate ground conductor that is used to bind (electrically connected) all the electric drive components that normally do not work. Portable devices with metal boxes also have bonding conductors on flexible cables and connectors that connect them to the distribution system. Returning circuit conductor ( neutral ) is also connected to ground in the service entrance panel only; no other connection from neutral to the permitted ground, unlike the rules in some other parts of the world.
The circuit of resuscitation and power in a North American system is usually radial from a distribution panel that contains circuit breakers to protect every branch circuit. The smallest branch circuit rating is 15 amperes, used for containers and general purpose lighting. Often, 20 amperes of circuits are used for containers and general purpose lighting. In residential construction, branch circuits for higher ratings are usually dedicated to one device, for example, fixed cooking utensils, electric clothes dryers, and air conditioners. Lighting and general purpose containers are at 120 volts AC, with larger devices fed by three single phase wire circuits at 240 volts.
In commercial construction, a three-phase circuit is used. Generally, the container is fed by 120 V or 208 V (at 240 V at home), and can include current special outlets for industrial equipment. Lighting is typically fed by 277 V (with the exception of special use lights that use 120 V). The equipment can be programmed into the building using 120/208 V or 277/480 V.
Countries such as Mexico can adopt the NFPA standard as their national electrical code, with local amendments similar to those in US jurisdictions. The Canadian Electrical Code, while developed independently of the NFPA code, is similar in scope and intent to NEC AS, with only minor variations in details of technical requirements; the harmonization of CEC and NEC codes is intended to facilitate free trade between the two countries.
Wiring method
Most of the circuits in modern North American homes and light commercial construction are fitted with a kind of sheathed non-metal cable (NM). This type of cable is the cheapest for a certain size and is suitable for indoor dry applications. The designation of NM XX-Y shows, respectively, the type of envelope (in this case, non-metallic), the size of the main conductor, and the total number of circuit conductors (exclusive of the grounding conductors). For example, NM 14-2 cable contains three conductors (two plus one ground) at 14 gauge, the size normally used for protected circuits at 15 amperes. Circuits with larger currents (such as for electric furnaces, water heaters, air conditioners, or sub-mains to additional circuit boards) will have larger conductors. Not all US jurisdictions permit the use of non-metallic sheathed cables. NEC does not allow the use of NM cables in large, fireproof, or high-rise structures.
In NM type cables, the conductor insulation is color-coded for identification, usually one black, one white, and a bare grounding conductor. The National Electrical Code (NEC) specifies that the black conductor represents a hot conductor , with a significant voltage to the ground earth; a white conductor representing an identified or neutral conductor, close to the ground potential; and bare/green conductors, safety grounding conductors that are not normally used to carry circuit currents. The cable can be re-colored, so this rule is usually excluded. In 240-volt applications that do not require a neutral conductor, a white cable may be used as a second heat conductor, but must be repainted with tape or by other methods. Four-wire flexible cable connection cable is red as the fourth color; unlike older European practices, color codes in flexible cables are the same as fixed cables.
In commercial and industrial, non-enclosed NM cables are often prohibited in certain areas or all (depending on what building is used for and local/state building codes). Therefore, it is hardly ever used by commercial electricity contractors. Most cables are inserted into inflexible channels, usually EMT due to their cost and durability. Stiff may be required for certain areas and additions, steam-lock fittings may be needed in areas where fire or explosion hazard is present (such as gas stations, chemical plants, grain silos, etc.) PVC can be used if the wire is run underground or where the concrete will be poured. A channel bank is usually made of multiple PVC channels encased in concrete. FMC or Flex is used where EMT or other non-flexible channels are impractical or for short term, known as "whips", to lights or other devices. For electrical circuits, color codes use the same color as home construction, and add additional cables used for the three-phase system. Black, Red and Blue are used for hot wire and White is used as a neutral wire in the 120/208 V circuit. Chocolate, Orange and Yellow are used as heat and gray wires used as neutral wires in 277/480 V. For grounding, regardless voltage, Green is used.
Several other types of cabling systems are used to build cable networks in the United States; these include corrugated metal armor cables, mineral insulated cables, other types of power cords, and various types of power lines. In industrial application cables can be placed on the cable tray. TC type cables are primarily intended for use in tray systems. Special cable rules apply to wet or corrosive locations, and to locations that present an explosion hazard. Wiring materials for use in the United States should generally be manufactured and tested for product standards established by NEMA and Underwriters Laboratories (UL) and must be marked as approved by UL.
The types of approved cables may vary by jurisdiction. Not all approved wiring methods at NEC are accepted in all areas of the United States.
Wire type
The cable type for wiring practices in North America is determined by standards issued by Underwriters Laboratories, the Canadian Standards Association, the American Society for Testing and Materials, the National Association of Electrical Manufacturers, and the Insulated Cable Engineers Association.
XHHW is short for " X LPE (cross linked polyethylene) H igh H anti-eat W resistant to attack. "XHHW is the designation for special insulation materials, temperature ratings, and conditions of use (suitable for wet locations) for power lines and cables.
Cables with XHHW insulation are commonly used in alternating current (AC) electrical distribution systems of commercial, institutional, and industrial buildings and installations, usually at voltage levels (potential difference or electromotive force) ranging from 110-600 volts. This type of insulation is used for solid or stranded copper and aluminum conductors, depending on size.
According to Underwriters Laboratories (UL) Standard 44, XHHW insulation is suitable for use in dry locations up to 90 ° C (194 ° F), or wet locations up to 75 ° C (167 ° F).
Isolation XHHW-2, which is similar to XHHW, is suitable for use in dry or wet locations up to 90 ° C (194 ° F).
THWN stands for " T hermoplastic H fed and W resistant-resistant N ylon-coated. " THWN is the designation for certain insulation materials, temperature rating, and conditions of use (wet location) for power lines and cables.
THHN is short for " T hermoplastic H igh H anti-eating N ylon - coated. " THHN is the designation for certain insulation materials, temperature rating, and conditions of use (suitable for dry and wet locations) for power lines and cables.
Wire with THWN or THHN insulation is commonly used in AC power distribution systems throughout North America, typically at a voltage level of 110 to 600 volts. This type of insulation is used for solid or stranded copper and aluminum conductors, depending on size. Many cables are rated THWN and THHN, and are suitable for use in dry locations up to 90 Â ° C (194 Â ° F), or wet locations up to 75 Â ° C (167 Â ° F).
See also
- America wire gauge
- Swivel cable connector
References
External links
- The Cable and Cable Technical Manual
- NEC at NFPA.org
- NEC Color Code Summary
Source of the article : Wikipedia
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