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4.7.11* Chimneys, Vents, and Other Objects on Roofs Not in a Zone of Protection. Strike termination devices shall be required on all objects not located within a zone of protection, including metal objects having a metal thickness of less than 3/16 in. (4.8 mm) except as permitted in 4.7.11.1 through 4.7.11.4.
4.7.11.1 Metal objects with a metal thickness of 3/16 in. (4.8 mm) or more and not located in a zone of protection shall require connection to the lightning protection system using a main-size lightning conductor and a main-size connector in accordance with the following:
(1)
It has a surface contact area of not less than 3 in.2 (1940 mm2) or a minimum of 1 1/2 in. (38 mm) of contact along the axis of a round surface.
(2)
Two or more paths to ground are provided, located as is required for strike termination devices.
4.7.11.2* Required strike termination devices shall be installed on objects, as shown in Figure 4.7.11.2, so that the distance from a strike termination device to an outside corner or the distance perpendicular to an outside edge is not greater than 2 ft (0.6 m).
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FIGURE 4.7.11.2
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Air Terminals on a Chimney.
4.7.11.3 Where only one strike termination device is required on an object, at least one main-size conductor shall connect the strike termination device to a main conductor at the location where the object meets the roof surface and provides two or more paths to ground from that location in accordance with Section 4.9 and 4.9.2.
4.7.11.4 Objects on roofs that are less than 10 in. (254 mm) above the surface of the roof shall not require strike termination devices unless they are located within 3 ft (0.9 m) of the ridge or roof edge.
4.7.12 Metal Roof Top Units. Strike termination devices shall be required in accordance with 4.7.12.1 through 4.7.12.3.2 on all roof top mechanical units with continuous metal housings less than 3/16 in. (4.8 mm) thick, such as air-conditioning/heating units, metal air intake/exhaust housings, and cooling towers, that are not located in a zone of protection.
4.7.12.1 Air terminals shall be installed in accordance with 4.7.2 through 4.7.5.
4.7.12.2 The air terminals shall be mounted on bases having a minimum contact area of 3 in.2 (1940 mm2), each secured to bare metal of the housing or mounted by drilling and tapping to the unit's frame in accordance with 4.19.3.2 and 4.19.3.3.
4.7.12.3 At least two main-size conductors shall be installed to connect the unit to the lightning protection system.
4.7.12.3.1 The connection shall be made to bare metal at the base or lower edges of the unit using main-size lightning conductors and bonding devices that have a surface contact area of not less than 3 in.2 (1940 mm2) and shall provide two or more paths to ground, as is required for strike termination devices.
4.7.12.3.2 The two main bonding plates shall be located as far apart as practicable at the base or lower edges of the unit's electrically continuous metal housing and connected to the lightning protection system.
