3.1.1.2
Roof Conductors
Roof conductors shall be connected directly to the roof or ridge roll.
Sharp bends or turns in conductors shall be avoided. Necessary turns shall
have a radius of not less than 200 mm 8 inches. Conductors shall preserve
a downward or horizontal course and shall be rigidly fastened every 900 mm
3 feet along the roof and down the building to ground. Metal ventilators
shall be rigidly connected to the roof conductor at three places. All
connections shall be electrically continuous. Roof conductors shall be
coursed along the contours of flat roofs, ridges, parapets, and edges; and
where necessary, over flat surfaces, in such a way as to join each air
terminal to all the rest. Roof conductors surrounding tank tops, decks,
flat surfaces, and flat roofs shall be connected to form a closed loop.
3.1.1.3
Down Conductors
Down conductors shall be electrically continuous from air terminals and
roof conductors to grounding electrodes. Down conductors shall be coursed
over extreme outer portions of the building, such as corners, with
consideration given to the location of ground connections and air
terminals. Each building or structure shall have not less than two down
conductors located as widely separated as practicable, at diagonally
opposite corners. On rectangular structures having gable, hip, or gambrel
roofs more than 35 m 110 feet long, there shall be at least one additional
down conductor for each additional 15 m 50 feet of length or fraction
thereof. On rectangular structures having French, flat, or sawtooth roofs
exceeding 75 m 250 feet in perimeter, there shall be at least one
additional down conductor for each 30 m 100 feet of perimeter or fraction
thereof. On an L- or T-shaped structure, there shall be at least one
additional down conductor; on an H-shaped structure, at least two
additional down conductors; and on a wing-built structure, at least one
additional down conductor for each wing. On irregularly shaped structures,
the total number of down conductors shall be sufficient to make the average
distance between them along the perimeter not greater than 30 meters 100
feet. On structures exceeding 15 m 50 feet in height, there shall be at
least one additional down conductor for each additional 18 m 60 feet of
height or fraction thereof, except that this application shall not cause
down conductors to be placed about the perimeter of the structure at
intervals of less than 15 meters 50 feet. Additional down conductors shall
be installed when necessary to avoid "dead ends" or branch conductors
ending at air terminals, except where the air terminal is on a roof below
the main protected level and the "dead end" or branch conductor is less
than 5 m 16 feet in length and maintains a horizontal or downward coursing.
Down conductors shall be equally and symmetrically spaced about the
perimeter of the structure. [Down conductors shall be protected by placing
in [pvc] [rigid steel] conduit for a minimum distance of 1800 mm 72 inches
above finished grade level.] [If the conduit is metal, the down conductor
shall be bonded at the top and bottom of the conduit.].
3.1.1.4
Interconnection of Metallic Parts
Metal doors, windows, and gutters shall be connected directly to the
grounds or down conductors using not smaller than No. 6 copper conductor,
or equivalent. Conductors placed where there is probability of unusual
wear, mechanical injury, or corrosion shall be of greater electrical
capacity than would normally be used, or shall be protected. The ground
connection to metal doors and windows shall be by means of mechanical ties
under pressure, or equivalent.
SECTION 13100A
Page 9
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