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2025-05-22 14:57本頁(yè)面
【正文】 be awarded to electrical contractors. Among items with which the designer will be concerned are: preliminary cost estimates, final cost estimates, plans or drawings, technical specifications (which are the written presentation of the work), materials, manuals, factory inspections, laboratory tests, and temporary power. The designer may also be involved in providing information on electrical considerations that affect financial justification of the project in terms of owning and operating costs, amortization, return on investment, and related items. Many electrical designs follow the concept of petitiveness in the mercial sense. Here, cost is a primary consideration, and such designs tend toward minimum code requirements. There is great pressure on the designer to consider cost above maintainability and long life. However, the experienced designer can usually adopt effective promises. Flexibility Flexibility of the electric system means the adaptability to development and expansion as well as to changes to meet varied requirements during the life of the building. Often a designer is faced 4 with providing utilities where the loads may be unknown. For example, many office buildings are constructed with the tenant space designs inplete. In some cases, the designer will provide only the core utilities available for connection by others to serve the working areas. In other cases, the designer may lay out only the basic systems and, as tenant requirements are developed, fill in the details. Often the tenant provides all of his or her own working space designs. Because it is usually difficult and costly to increase the capacity of risers and feeders, it is important that provisions for sufficient capacity be provided initially. Extra conductors or raceway space should be included in the design stage if additional loads may be added later. This consideration is particularly important for mercial buildings with the increasing use of electronic equipment and air conditioning. The cost and difficulties in obtaining space for new feeders and larger switchgear, which would be required when modernizing or expanding a building, may well be considered in the initial design. A load growth margin of 50% applied to the installed capacity of the major feeders is often justified where expansion is anticipated. Each project deserves careful consideration of the proper load growth margin to be allowed. Flexibility in an electric wiring system is enhanced by the use of oversize or spare raceways, cables, busways, and equipment. The cost of making such provisions is usually relatively small in the initial installation. Empty riser shafts and holes through floors may be provided at relatively low cost for future work. Consideration should be given to the provision of satellite electric closets initially for future expansion. Openings through floors should be filled in with fireproof, easily removed materials to prevent the spread of fire and smoke between floors. For puter rooms and the like, flexibility is frequently provided by raised floors made of removable panels, providing
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