The electrical systems in building construction can be grouped under four major headings: Power, Lighting, Motor Control Centers, and Special Systems. Like mechanical systems, electrical systems have three distinct portions: Source, Conductor/Connection, and Terminal Unit. For example,take lighting: the source is a wall switch, the conductor/connector is wiring in conduit, and the terminal unit is the fixture. The first two components, the source and the conductor/connector, represent the rough-in phase of the project, and the terminal unit represents the finish portion of the electrical work.
Each of the major categories of electrical systems share common components: conduit or raceways, conductors, devices, switches, panelboards, and fixtures. Raceways and conduits are channels that carry and protect conductors from the source to the terminal unit. Raceways consist of conduit, ducts, cable trays, and surface raceways.
A conductor is a wire or metal bar with a low level of resistance to the flow of electric current. Conductors are generally made of copper or aluminum, and are enclosed in an insulating jacket. Cables are conductors made up of heavy or multiple wires contained in a common jacket. Cable contained in a metallic sheathing (armored) is used where physical protection of the cable is necessary, but the use of conduit is not practical. Other types of conductors include high voltage shielded cable, flat wire or cable for undercarpet installations, low voltage wiring for telephones, and coaxial cable for data transmission.
Boxes are used in electrical wiring at each junction point or at each electrical device to provide easy and safe access for connections. Simply stated, devices control or conduct the flow of electricity without consuming any. Devices include wall switches, outlets, and light dimmers.
Switches are devices that are used to open, close, or change the condition of an electric circuit. Boards serve as a means of grouping and mounting electric components, switches, safety devices, or controls. A load center or panelboard is a specialized type of board used principally for containing circuit breakers.
Fixtures are by far the most elemental portion of the electrical work. Lighting, in building construction, is still the largest single electrical cost center.
The following topics are covered by the estimating charts in this section:
- Cable trays
- Wiring devices
- Starters and controls
- Special systems