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Electrical protection and safety
• This location has coaxial cables that come directly in the building
without going through a bulkhead panel/waveguide hatch.
• The associated antenna tower at this location does not have a
grounding systemmade up of at least 60 m/ 200 ft/ of buried bare
ground conducting wire with multiple paths (minimum of 5, each
40 ft /12 m in length) away from tower base.
• This location has coaxial cables that enter at ceiling height (15 to
20 ft /4 - 6 m above ground level), and all equipment grounding
is done at floor level or below.
The number of bullets that apply indicate your equipment and per-
sonnel risk:
• 2 or less - Low
• 3 to 5 - Moderate
• 6 to 8 - Severe
• 9 or more - Critical
Equipment and structures to be considered
for lightning protection
• The first class needs very little or no additional protection. The
only real requirements for these are that they be effectively con-
nected to a suitable grounding electrode. This class includes:
–
All metal structures except tanks or other enclosures of
flammable materials
–
Water tanks, silos, and similar structures, constructed
largely of metal
–
Flagpoles made of conductive material
• The second class consists of buildings with conducting surfaces
and non-conducting framework, such as metal-roofed and metal-
clad buildings. This type requires the addition of down conductors
to connect the exterior roof and cladding to suitable grounding
electrodes.
• The third class consists of metal-framed buildings with non-
conducting facings. These need the addition of conducting air
terminals suitably located, connected to the frame, and project-
ing beyond and above the facing to act as the lightning terminal
points, eliminating puncture of the facing.
• The fourth class consists of nonmetallic structures, either framing
or facing. These require extensive protection treatment. Included
are:
–
Buildings of wood, stone, brick, tile, or other non-conducting
materials, without metal reinforcing members.
–
High stacks and chimneys. Even with reinforcing members,
these should have full lightning-protection treatment of air
terminals, down conductors, and grounding electrodes.
• A fifth class consists of items of high risk or loss consequences,
which normally receive full lightning protection treatment, includ-
ing air terminals or diverters, down conductors, and grounding
electrodes. These include:
–
Buildings of great aesthetic, historical, or intrinsic value
–
Buildings with readily combustible or explosive materials
–
Structures containing substances that would be dangerous
if released by the effects of a lightning stroke
–
Tanks and tank farms
–
Power plants and water pumping stations
–
Transmission lines
–
Power stations and substations
Installation standard [1]
• The Standard for the Installation of Lightning Protection Systems
[1] document covers traditional lightning protection system instal-
lation requirements for the following:
–
Ordinary structures
–
Miscellaneous structures and special occupancies
–
Heavy-duty stacks
–
Watercraft
–
Structures containing flammable vapors, flammable gases,
or liquids that gives off flammable vapors.
• NFPA 780 gives detailed instructions for the placement and spac-
ing of air terminals on roofs of buildings of various configurations
and on structures other than roofed buildings.
T
ake note
• You cannot eliminate the risk associated with lightning.
• The risk of damage or injury, due to lightning, can be managed.
• Various standards and guidelines exist and these must be studied care-
fully in order to make the best design decisions.
Electricity+Control
September ‘12
26