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Building Design and Construction Handbook - Merritt - Ventech!

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FIGURE 15.6 Cellular steel decking serves as<br />

underfloor electric ducts. Wires in headers distribute<br />

power to wires in the cells.<br />

ELECTRICAL SYSTEMS 15.19<br />

FIGURE 15.5 Raceways incorporated in a concrete<br />

floor, with outlet cover at the top of the floor.<br />

Underfloor raceways are ducts<br />

placed under a new floor in office spaces<br />

where desks <strong>and</strong> other equipment are<br />

frequently moved. Laid in parallel runs<br />

6 to 8 ft apart, with separate ducts for<br />

power, signal, <strong>and</strong> telephone wires,<br />

these raceways may have flat-plate outlet<br />

covers spaced 4 to 6 ft along each<br />

run. Large retail stores also find these<br />

installations a great convenience. The<br />

alternative is feeder runs above the hung<br />

ceiling of the story below, with firerated,<br />

poke-through construction to<br />

reach new outlets above the floor.<br />

Underfloor raceways may be singlelevel<br />

(Fig. 15.5) or two-level (Fig. 15.6).<br />

In steel-frame buildings, with cellular<br />

steel decking, single-level raceways may<br />

be included in the structure of the floor<br />

itself. A concrete header across the cellular<br />

runs provides the means of entering<br />

from the finished floor. A similar arrangement<br />

can be used in cellular<br />

precast-concrete decks, with metal head-<br />

ers for connections. Wireways to carry large numbers of conductors carrying lightcurrent<br />

signal or control circuits are commercially available in fixed lengths.<br />

15.6.8 Access Floor Systems<br />

In large computer rooms <strong>and</strong> in offices with heavy computer or communications<br />

usage, such as a brokerage or a data center, an access floor system may be used.<br />

This offers a false floor above the structural floor. The system consists of 2-ft by<br />

2-ft removable panels, topped with a floor covering, which are supported from 6<br />

to 36 in, or more, above the structural floor by pedestals <strong>and</strong> stringers. The space<br />

below the access floor is used for routing electrical, computer, <strong>and</strong> communication<br />

wiring. It is also used as a plenum for distributing conditioned air to the equipment<br />

<strong>and</strong> the occupied space. Since virtually the entire underfloor space is available <strong>and</strong>

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