Lightning Protection Marking and Application Guide
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3. Heavy-Duty Stacks
Stacks above 75ft in height require some special consideration in both design and material used
for the system. All components shall be Class II and class II modified. The components in the
upper 25 feet shall be copper, copper alloy, bronze or stainless steel. The top 25 feet can be a
high corrosion zone and extra protection of a min of 1/16 in coating of lead is required for
terminals, mounting brackets and conductors. Aluminum components are prohibited in this
Class II air terminals on stacks shall be solid copper, copper alloy, stainless steel, titanium or
monel metal. The installation shall be evenly distributed around the top of a round stack at
intervals not to exceed 8 feet. If the stack is square, the location shall be not more than 2 feet from
corners and spaced not more than 8 feet apart.
Each Class II air terminal shall be not less than 18 inches in height and not more than 30 inches in
height. The diameter shall be not less than 5/8 inch in diameter. All terminals shall be connected
together and there shall be at least 2 down conductors on opposite sides of the stack. Reinforcing
steel in concrete stacks shall be electrically continuous and shall be bonded to the lightning
protection system at its upper and lower ends at down-lead locations.
4. Components Selection
A protection system and its components are really simplistic when you step back and look at the
overall system. What is required is a means to catch a lightning strike at some point on the
structure, and then conduct it to an electrode buried in the earth so it can be dissipated.
Along the route to earth, terminals, conductors and grounding electrodes minimize damage to the
structure and contents within it. However simple as it may appear, there are some complexities
along the way. In accordance with NFPA 780 if an LPS component product is listed, labeled per
UL 96 than that product shall be selected and installed. The use of listed products gives greater
assurance that when correctly installed in accordance with 96A or NFPA 780 that the entire
lightning protection system can be “Site inspected” and receive the UL Master Label Certificate.
All components used in an LPS shall be of the following: copper, copper alloy, or electrical grade
aluminum unless otherwise specified in the UL 96A Standard. Copper components shall not be
installed on or in contact with surfaces of aluminum or external galvanized steel surfaces.
Any aluminum or aluminum alloy product shall not come into direct contact with earth, and any
bimetallic fitting shall not be installed within 18 inches above earth level. Aluminum products shall
not be embedded in concrete or masonry, in direct contact with a surface coated with alkaline
paint, installed in wet locations such as inside of eaves or downspouts.
Air Terminals: shall be not less than 10 inches long, less than 3/8-inch in diameter and may be
manufactured in separate parts if longer than 10 inches. The terminal shall be provided with an
integral base support, or shall have not less than five full threads of engagement with a separate
attachment base mounted to the structure. If the terminal has internal threads the wall thickness
shall be not less than 1/16 inch at the base of the threads. Ornaments or decorations are
permitted on air terminals, but shall not exceed 20 square inches in any plane. Air Terminals
longer than 24 inches shall have bracing at half its height and listed for the purpose
Base Supports: The air terminal bases are permitted to be stamped or cast construction. If
stamped, the thickness shall be 0.097 for aluminum and 0.061 for copper material. If cast either
copper or aluminum shall be at least 3/32 inches thick. A base support must incorporate a