Electrical wiring in North America
Electrical wiring in North America follows the regulations and standards applicable at the installation location.
New construction, additions or major modifications must follow the relevant code for that jurisdiction, which is not necessarily the latest version of the NEC.
Regulations in each jurisdiction will indicate when a change to an existing installation is so great that it must then be rebuilt to comply with the current electrical code.
[citation needed] For residential wiring, some basic rules given in the NEC are: The foregoing is just a brief overview and must not be used as a substitute for the actual National Electrical Code.
Grounding (earthing) of distribution circuits is a notable difference in practice between wiring systems of the United States and those of other regions.
Portable appliances with metal cases also have a bonding conductor in the flexible cable and plug connecting them to the distribution system.
Countries such as Mexico may adopt the NFPA standard as their national electrical code, with local amendments similar to those in United States jurisdictions.
Most circuits in the modern North American home and light commercial construction are wired with non-metallic sheathed (NM) cable designated type.
FMC or Flex is used where EMT or other non-flexible conduit is impractical or for short runs, known as "whips", to lights or other devices.
For power circuits, the color-coding uses the same colors as residential construction, and adds the additional wires used for three-phase systems.
When running through conduit, such as in commercial applications, it is typical to pull individual wires rather than a preassembled cable.
This, in combination with the ambient temperature and ability of the environment to absorb heat, determines the amount of tolerable copper loss in the wire, and therefore its size in relation to the load current.
[16] The most commonly used insulation type in AC electrical distribution systems throughout North America is THHN ("Thermoplastic High Heat-resistant Nylon-coated"[17]).
This is a specification for PVC insulation (other thermoplastics are permitted, but rarely used) with a nylon jacket for abrasion resistance.
This is similar to the preceding, but rated for dry or wet environments and conductor temperatures up to 75 °C (167 °F),[18] and is commonly used in subsurface conduits which may fill with water.
[18] There are additional restrictions on such wire's use not mentioned here (for example, neither THHN nor THWN may be exposed to sunlight, or directly buried in the ground[20]); see the NEC for details.
[22] The low dielectric constant of the insulation is also beneficial when high-frequency AC is present on the wire, such as the output of variable-frequency drives.
