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 e)
The height of the masts is determined by the Equation:
where "M" is the height of the masts, "S" is the height of the assumed salient
plane, "D" is the mast spacing on the diagonal axis as determined by
Equation (1), with C = 40 ft (12 m). "P" is given an empirical value (see
Appendix A, A-1) according to the value of "D" as calculated from Equation
(1).
The height of the masts as determined by the formulae is based on the
condition that the structure to be protected is located between two parallel
rows of masts. To determine the height of the masts, use Equation (1), and
using C = 40 ft (12 m), calculate for D, and then determine M by using the
curves of Appendix A, A-2, Chart No. 1.
f) The protection of a structure by self-standing vertical masts
dictates that the distance from the center line of the structure or complex to
the masts on the normal or the diagonal axis must not be more than 100 ft
(30.5 m). When this condition cannot be met, the protection of the structure
or complex will be by overhead ground wiring. To determine the final
distance, D1, along the diagonal axis, use Equation (1) substituting D1 for D,
with C values between 6 ft (1.8 m) minimum to 25 ft (7.6 m) maximum. D1 shall
not exceed 100 ft (30.5 m).
g) When overhead ground wiring are used for protection, support the
overhead ground wiring on masts located at the vicinity of the protected
structure at distances from the structure established as 6 ft (1.8 m) minimum
to 25 ft (7.6 m) maximum. The lowest point of mid-span sag in the overhead
ground wiring above the salient plane of the protected structure is to be no
less than 10 ft (3.05 m). Increase the distance of cable which is run
parallel to the structure by 1 ft (0.3 m) for each 10 ft (3.05 m) of
horizontal cable greater than 50 ft (15 m). Determine mid-span sag of the
overhead ground wire from the curves of Appendix A, A-2.
4.
Graphic Examples. In Appendix A, A-3, Example 1: L, W, and S are
known, C is given the value of 40, B = 18 ft (explained in Appendix A, A-1,
Definitions of Terms), and N is equal to 6. In Equation (1) substitute these
values and D is found to equal 98.5 ft. In Appendix A, A-1, refer to the
curves at point 98.5 ft (30 m) on the horizontal scale, then extend vertically
to the 50 ft slant line, and carry horizontally to the vertical scale, again
using Equation (1) and substituting actual distance C = 6 ft (1.8 m) minimum
to 25 ft (7.6 m) maximum, this will show a mast height of 95.5 (29 m).
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