For large buildings, greater than 250,000sf or buildings
with large footprints and campus situations, more than
one electrical service shall be considered, as well as
medium voltage distribution, up to 15KV, for primary
power distribution to substations.
The routing of site utilities and location of manholes shall
be determined early in the design process in coordination
with the Site Civil Engineer.
Cable Selection. Cable selection shall be based on all
aspects of cable operation and the installation
environment, including corrosion, ambient heat, rodent
attack, pulling tensions, and potential mechanical abuse
and seismic activity.
Direct Buried Conduit. Direct buried PVC, coated
intermediate metallic conduit (IMC) or rigid galvanized
steel (RGS) shall be used only for the distribution of
exterior branch circuits 38 mm (1 1/2'') or smaller. Direct
buried cable shall not be used.
Concrete-Encased Ductbank. Concrete-encased PVC
Schedule 40 ductbanks shall be used where many circuits
follow the same route, for runs under permanent hard
pavements and where service reliability is paramount,
such as service entrances and medium voltage cables.
Concrete encased ducts shall be provided with a cover of
at least 600 mm (24 inches). Ductbanks under railroads
shall be reinforced. Ducts shall slope toward manholes.
Changes in direction shall be by sweeps with a radius
of 7.5 m (25 feet) or more. Stub-ups into electrical
equipment may be installed with manufactured elbows.
Duct line routes shall be selected to avoid foundations
of other buildings and other structures. Electrical and
communication ducts shall be kept clear of all other
underground utilities, especially high temperature water
or steam.
Oakland Federal Building, Oakland, CA.
178 F A C I L I T I E S S T A N D A R D S
FOR THE
PUBLIC
BUILDINGS
SERVICE
6.4 Utility Coordination
Revised March 2005 PBS-P100
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