There are different types of building interior wiring systems.  When the primary purpose of the system is to distribute electrical energy, it is referred to as an electric power system; when the purpose is to transmit information; it is referred to as an electric signal or communication system.  Due to the nature of electricity, its distribution within a structure for poses a single problem: how to construct a distribution system that safely provides the energy required at a desired location.  The safety consideration is all-important because even the smallest interior system is connected to the utility’s powerful electric network and the potential for physical damage, injury and fire is always present.  The solution that the designers of MacAlister utilized and most other buildings is to isolated the electrical conductors from the structure, except at specific points, like wall receptacles where contact is rudimentary.  The isolation method of choice is the, that is evident in MacAlister, is accomplished by insulating the conductors and placing them in protective raceways.  The principle types of interior wiring in use in MacAlister and other buildings are exposed insulated cables, insulated cables in open raceways, and insulated conductors in closed raceways.  The designers of MacAlister more than likely used all three of the aforementioned methods. 

 Exposed Insulated Cables, using the National Electric Code (NEC) nomenclature, cable types NM (Romex) and AC (BX).  Among the most common types of exposed wiring is NEC AC armored cable, commonly known in the smaller sizes by the trade name BX.  It is an assembly of insulated wires, bound together and enclosed in protective armor made of a spiral wound interlocking strip of steel tape.  This type of wiring is usually designed for residences, but is the style of choice for re-wiring buildings.  There is also Non-metallic Sheathed Romex (BX) cable, but it’s also limited to residential construction and buildings of three stories or less. 

Insulated Cables in Open Raceways, this system is specifically intended for industrial application and it relies in both the cable and tray for safety.

Insulated Conductors in Closed Raceways, the primary design used in MacAlister, is the most general type and is applicable to all types of facilities.  In general, the raceway is installed first and the wiring is pulled in or laid in later.  The raceways them are typically:

1.      Buried in the structure; i.e. conduit in the floor slab or under-floor duct.

2.      Attached to the structure; i.e. types of surface raceways, like conduit and wire-ways suspended above hung ceiling.

3.      Parts of the structure; i.e. cellular concrete and cellular metal floors  

Wiring Schematic:

 

Conductors

Electrical conductors (wiring) are the means by which the current is conducted through the electrical system.  The standard of American wire and cable industry for round cross section conductors is the American Wire Gage (AWG).  By convention, a single insulated conductor NO. 6 AWG or larger or several conductors of any size assembled into a single unit, are referred to as cable.  Single conductors NO. 8 AWG and smaller are called wire.  The AWG numbers run in reverse order to the size of the wire, that is to say the smaller the AWG number, the larger the size of the wire.  

           

 

 

The maximum safe operating temperature of the insulation determines conductor current-carrying capacity, or ampacity.  Heat generated as a result of the current flowing is dissipated into the environment.  Thus, for the given environment (open air, buried in earth or enclosed), ampacity increases with the increasing conductor size and with maximum permissible insulation temperature.  The following table clearly represents the aforementioned facts: