• Todd Engle

Wiring types


Wire types for North American wiring practices are defined by standards issued by Underwriters Laboratories, the Canadian Standards Association, the American Society for Testing and Materials, the National Electrical Manufacturers Association and the Insulated Cable Engineers Association.

Most circuits in the modern North American home and light commercial construction are wired with non-metallic sheathed (NM) cable designated type (often referred to by the brand name "Romex"). This type of cable is the least expensive for a given size and is appropriate for dry indoor applications.

Conductor Materials


As discussed above, we are dealing with:

  • copper: absolutely the best conductor in common use, as it has low electrical impedance, so a relatively small conductor can deliver a lot of power over long distances without too much power loss or heat generation.

  • tinned copper: still sometimes seen on older properties. Copper is tinned for two reasons: to aid soldering; and to stop the copper from reacting with old rubber insulation.

  • aluminum: a good conductor of electricity but has higher impedance to the flow of electrons, which means that larger conductors need to be used for any given amperage. Aluminum was used for residential branch circuit wiring from the mid-1960s to the late 1970s, but was found to be unreliable. (We'll explore this later.)

  • copper-clad aluminum: coating aluminum in copper was an attempt to overcome the issue of oxidization of the aluminum conductors that was leading to failures. It did not have the failures associated with pure aluminum and is considered safe. However, copper-clad should be sized the same as normal aluminum.


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