Building Design and Construction Handbook - Merritt - Ventech!

15.20 SECTION FIFTEEN
accessible, this system, though relatively expensive, offers flexibility for making
changes in space use, such as adding equipment or rearranging room layouts.
15.6.9 System Furniture
Most modern offices undergo frequent relocation of staff due to workload, project
teaming, or organizational changes. This high ‘‘churn rate’’ is made less of a burden
to building managers by the use of system furniture. System furniture is a coordinated
system of components including partitions, work surfaces, and storage elements
that can be assembled into a variety of workstation configurations. Although,
design of system furniture is not an electrical item of work, the task
lighting, power, and voice/data elements are integral to the system. Individually
controlled task lighting is provided for each workstation, as are power and voice/
data outlets. To accommodate the required services, the specifications must include
clear definition of the types and configuration of the electrical components. Furniture
specifications will include wiring harness, power, lighting, and voice/data
distribution as integral parts of the system. Particular attention should be paid to
the method for feeding the system furniture from building services, capacity and
bending restrictions of voice/data raceways (network cables) (see Fig. 15.7), and
increased neutral currents caused by harmonic loads. Often, a wiring harness will
have eight conductors; three phases, three neutrals (one per phase), an equipment
ground conductor, and an isolated ground conductor.
15.6.10 Flat Conductor Cables (FCC)
These offer similar flexibility to that of an access floor system in that such cables
permit outlets to be located anywhere in a room and allow easy relocation of an
outlet. Flat conductor cables are available not only as power circuits but also in
multiconductor, twisted pair, coaxial, and fiber-optic cables for use in communication
and data systems. Manufacturers offer complete lines of power, data, and
communication floor fittings for FCC system use. Use of FCC is limited to installation
under carpet squares and is most commonly used in renovation work.
15.7 POWER SYSTEM APPARATUS
Most buildings, commercial, industrial, institutional, and residential, receive their
power from a public utility. Usually, the customer is given a choice of voltages.
For example, 240/120-V single-phase, three-wire service is, very common in suburban
and rural areas. This service comes from a single-phase, 240-V transformer,
with one wire from each end of the secondary coil and with the neutral from the
midpoint of its secondary coil. The voltage between the end terminal connections
is 240 V and between each end wire and the neutral, 120 V (Fig. 15.3b).
In large cities, the service to large buildings can be 208/120 V, three-phase,
four-wire, with 208 V available between phase wires and 120 V between a phase
wire and the neutral (Fig. 15.3c). Another choice is 480/277 V, three-phase, fourwire,
with 277 V available between a phase leg and the neutral. It is more economical
to use the higher voltage, 480/277 V, for motors and industrial lighting.