Wiring
Sizes are standardized using American Wire Gage (AWG)
No size smaller than 14 gage should be used for building wiring.
Aluminum wiring is not used in most areas due to question of oxidation, connection deterioration and metal fatigue over long periods of time.
Several major fires have been blamed on the use of Aluminum.
Copper wire is the standard for branch circuits.
Some circuits must be over sized:
Circuit capacity should be 20% more than any motor that is connected to it.
Multiply rated load by 1.25 (1/0.80) to determine wire size.
Same factor should be applied to any circuit expected to poerate continuously for three hours or more.
Conduit
Physically protects wiring.
Size is designated by its interior diameter.
The number of wires of any given size which can fit into a given conduit is specified by code.
Several types or classes of conduit :
Rigid conduit = safest, same wall thickness as sched 40 plumbing pipe. Connections are rigid and threaded. It's installed first, then wire is pulled through it.
Exterior applications, the conduit must be galvanized ; Interior may just be enamel coated.
Intermediate metallic conduit (IMC) = Steel conduit with thinner walls than plumbing pipe, slightly less expensive, generally as acceptable as rigid
Electrical metallic tubing (EMT) = thinnest of the simple metal conduits, galvanized, connections by clamping system instead of threading, sometimes called "thin wall".
Flexible metal conduit = available with or without a flexible waterproof jacket, commonly called "flex" or product name "Greenfield"
Usable everywhere except underground.
Interlocked armored cable = similar to "flex", consists of pre-wrapped set of wires encased in interlocking metal spiral armor.
Factory assembled, no wires can be added in the field. Designated BX cable. May NOT be used underground or embedded in concrete.
No wires pulled through in the field or after installed.
Romex = A sheathed wire consisting of two insulated live wires and one ground wire encased in a single plastic sheath.
alternative to conduit in residential construction, officially designates as type NM or NMC cable.
Can be strung inside walls or exposed in areas such as garages.
No other covering required, Cannot be used in commercial garages
Cannot be embedded in concrete
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