Comparison of US Practices With Other Countries
Electrical wiring practices developed in parallel in many countries in the late 19th and early 20th centuries. As a result, national and regional variations developed and remain in effect. (see National Electrical Code, electrical wiring, electrical wiring in the United Kingdom). 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.
Grounding (earthing) of distribution circuits is a notable difference in practice between wiring systems of the United States and those of other regions. Since the early 1960s, wiring in new construction has required a separate grounding conductor used to bond (electrically connect) all normally non-current carrying parts of an electrical installation. Portable appliances with metal cases also have a bonding conductor in the flexible cable and plug connecting them to the distribution system. 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 other parts of the world.
Lighting and power receptacle circuits in North American systems are typically radial from a distribution panel containing circuit breakers to protect each branch circuit. The smallest branch circuit rating is 15 amperes, used for general purpose receptacles and lighting. Often 20 ampere circuits are used for general purpose receptacles and lighting. In residential construction, branch circuits for higher ratings are usually dedicated to one appliance, for example, fixed cooking appliances, electric clothes dryers, and air conditioners. Lighting and general purpose receptacles are at 120 volts AC, with larger devices fed by three wire single-phase circuits at 240 volts. In commercial construction, three-phase circuits are used. Generally, receptacles are fed by 120 V or 208 V (in place of 240 V in a house), and can include special current rated outlets for industrial equipment. Lighting is usually fed by 277 V (with exception for special-use lights that use 120 V). Equipment can be hard-wired into the building using either 120/208 V or 277/480 V.
Countries such as Mexico may adopt the NFPA standard as their national electrical code, with local amendments similar to those in United States jurisdictions. 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 CSA and NEC codes is intended to facilitate free trade between the two countries.
Read more about this topic: Electrical Wiring In North America
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