How to Understand Electricity: Volts, Amps and Watts Explained on Appliances > 자유게시판

Most circuits have the metallic components interconnected with a grounding wire connected to the third, round prong of a plug, and to metal boxes and appliance chassis. Portable appliances with metal cases also have a bonding conductor in the flexible cable and plug connecting them to the distribution system. Governments cannot distribute the NEC itself for copyright reasons, though parts that have been adopted into law are not subject to copyright. An older, but still widely used, high-leg delta system uses three phases with 240 volts phase-to-phase for motor loads, and 120 volts for lighting loads by use of a center-tapped transformer; two of the phases are 120 volts to neutral. The common colors are black, red, blue, brown, yellow, and orange (high-leg delta) insulated wire, sometimes other colors. The circuit return conductor (neutral) is also connected to ground at the service entrance panel only; no other connections from neutral to ground are allowed, unlike regulations in some other parts of the world. Ground is a safety conductor with a low impedance path to earth. Neutral wire is the return conductor of a circuit; in building wiring systems, the neutral wire is connected to earth ground at only one point.

Phase wire in a circuit may be any color other than green, gray, or white (whether these are solid colors or stripes). The plug and socket replaced the BS 546 plug and socket, which are still found in old installations or in special applications. This type of cable is the least expensive for a given size and is appropriate for dry indoor applications. In this process, smaller individual wires are twisted or braided together to produce larger wires that are more flexible than solid wires of similar size. Different size wires may be used in the same raceway so long as they are all insulated for the maximum voltage of any of these circuits. Not all wiring methods approved in the NEC are accepted in all areas of the United States. While subtransmission circuits are usually carried on overhead lines, in urban areas buried cable may be used. The Canadian Electrical Code, while developed independently from the NFPA code, is similar in scope and intent to the US NEC, with only minor variations in technical requirement details; harmonization of the CEC and NEC codes is intended to facilitate free trade between the two countries.

An outlet is defined by the NEC as "a point in the wiring system at which current is taken to utilization equipment". Some of these are retained for technical reasons, since the safety of wiring systems depends not only on the wiring code but also on the technical standards for wiring devices, materials, and equipment. Coaxial cable - used for radio frequency signals, for example in cable television distribution systems. Lighting and power receptacle circuits in North American systems are typically radial from a distribution panel containing circuit breakers to protect each branch circuit. Most are equipped with a retaining screw or clip to prevent accidental disconnection. There were previous exceptions for refrigerators because unattended disconnection could cause spoilage of food and for garbage disposals. Specific exceptions apply, such as a cable running to a switch and back (known as a traveler) where the white wire will be the hot wire feeding that switch. Grounding wire of circuit may be bare or identified insulated wire of green or green having yellow stripes. It is either bare or has green insulation. In type NM cable, conductor insulation is color-coded for identification, typically one black, one white, and a bare grounding conductor.

The current produced by a power source can take one of two forms, AC or DC. So it always flows in a loop and two wires are needed to connect the voltage source to the load. Often, 20 ampere circuits are used for general purpose receptacles and lighting. Receptacles protected in this manner or with a GFCI circuit breaker should be labeled "GFCI protected". Most GFCI receptacles allow the connection and provide GFCI protection for down-stream connected receptacles. Ground-fault circuit interrupter (GFCI) protection is required on receptacles in wet locations and locations where there exists an easy path for fault current to travel to earth. This includes all receptacles intended to service kitchen counter surfaces, crawl spaces at or below grade level, basements, garages and accessory buildings, bathrooms, laundry areas, within 6 ft. The smallest branch circuit rating is 15 amperes, used for general purpose receptacles and lighting. Circuits with larger currents (such as for electric furnaces, water heaters, air conditioners, or sub-mains to additional circuit panels) will have larger conductors.

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