6.15 Lightning
In buildings where a 208/120V service is supplied by the
power company, and there is no intermediate transformer
Protection Systems
isolating the utilization voltages from the various
harmonic generators previously mentioned, the use of
isolated ground panels serving the office power
requirements shall be considered.
safety features in the design of electrical distribution
Raised floors. Access floors shall be grounded. A
systems. Their application on any specific project is a
grounding conductor shall be bonded to every other floor
function of its geographic location, height, proximity of
pedestal and shall be extended to the technology/server
taller adjacent structures and the architectural configuration
room common ground bus.
of the building. The decision to recommend a lightning
protection system shall be made at the earliest stages of
Counterpoise. Where feasible, a grounding conductor
design and shall be supported by a study as prescribed by
(counterpoise) shall be provided in an isosceles triangle
NFPA 780.
configuration with sides greater than or equal to 3
meters(10 feet). The conductor shall be tinned copper not
Master Label. If a decision is made to provide a lightning
less than No. 4/0 AWG and shall be electrically connected
protection system it shall be installed in compliance with
to the incoming domestic water services on either side
UL 96 and NFPA 780. A UL Master Label shall be
of the building as well as the various clusters of three (3)
required.
ground rods spaced at intervals. Ground rods shall be
15mm (5/8'') dia. by 2400mm (96'') long and shall be tin
Alternate Systems. The requirement of a "Master Label"
coated copper. The counterpoise loop will involve direct
imposes certain restrictions or limitations on the
burial in earth 1200mm (24'') min. below grade. The
design of the system which may be in conflict with the
following items shall be connected to the counterpoise
architectural design, particularly if the faade includes
loop:
large curved surfaces which preclude the installation of air
terminals and where the spacing of down conductors are
Lightning protection system "down conductors"
limited. In those instances the design engineer may appeal
Transformers in substations
to the Contracting Officer to waive the "Master Label"
Emergency generator ground
requirement on the basis that the design generally follows
Telecom and data room grounds
the "Faraday Cage" principle of lightning protection.
Separately derived grounds
Grounding. The down conductors shall follow direct
Isolated ground panels
paths from the air terminals to ground connections or
Main switchgears
to the counterpoise loop.
Normal and emergency distribution systems
Flagpoles
207
ELECTRICAL
ENGINEERING
6.15
Lightning Protection Systems
Revised March 2005 PBS-P100
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