13 Chptr - 307 13 Electrical Systems Key Terms Branch...

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307 13 Electrical Systems Key Terms Branch circuitry Bus bar Cable tray Conduit Devices/loads Disconnect Feeder Load centers Motor control centers Panel boards Raceway Raised floors Surface metal raceways Trench duct Underfloor duct Wire duct Wireways Key Concepts Electrical drawings leave more to the imagination than other kinds of drawings, since they frequently identify a source and a destination but not necessarily a specific path. Objectives Identify the elements of an electrical system. Identify commonly used graphic conventions in electrical drawings. Describe the graphic shortcomings of electrical drawings. 308 Purpose Electrical systems play a critical supporting role in the daily lives of people in thousands of cities and rural areas alike. The most fundamental needs of society—warmth, water, fuel, and light—are met and controlled by electrical systems. One need endure only one power failure to have contemporary society's dependence on electrical power emphasized. The entire power system from electrical generation to distribution to points of consumption is designed by electrical engineers and put into place by industrial, underground
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utility, and electrical specialty constructors, whose work represents a significant portion of the overall costs of construction projects. In building projects, the costs for electrical work ranges from 8 to 12 percent of the hard construction costs, a percentage that is likely to increase in the future as systems, particularly control systems, become more sophisticated. Elements of Electrical Systems There are similarities between mechanical and electrical systems in that both consist of loops of sorts. In HVAC systems, air is conditioned, pumped to remote spaces, partly exhausted, and returned to the air handler for reconditioning. Plumbing systems deliver conditioned water (heated and perhaps purified water) under pressure through conduit (pipes) to remote spaces where it is used; and although it is not returned for reconditioning, the drainage system completes the conceptual loop. Electrical systems move electrons through conductors housed in conduit to remote spaces under a sort of pressure (voltage being the corollary to pressure in plumbing systems, and amperage being the corollary to flow) caused by the imbalance of electrons generated at the utility company. As with mechanical systems, there is the source, a supply and return system, and controls. Power Sources, Distribution, and Controls The electrical power source for most projects is the service provided by the utility company operating in a given region. Overhead or underground lines in easements on private and public property form the power grid, into which an owner taps when construction of a project commences. The power is extended to an owner's parcel of land, and may be further distributed to various locations on the site itself, according to a site plan. The utility company may perform the underground work on a new site, or subcontract the work to a responsible
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13 Chptr - 307 13 Electrical Systems Key Terms Branch...

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