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ETL 1110-9-10(FR)
5 Jan 91
8)
Determine the center-to-center spacing (Cc) for the
main anode strings.
a)
To find circumference spacing (CC), use equation
2-5:
2 A AR
CC '
(eq 2-5)
N
Where:
AR =
22 ft (Radius of main anode circle
from previous calculation.
N
=
10 anode strings ([Assumed] Used in
previous calculation)
CC =
2 x 3.1416 x 22 ft
10
CC =
13.8 ft; use 14 ft for center-to-
center
spacing
between
anode
strings.
b)
The cord spacing is approximately the same as
circumferential spacing;
14 ft will be used
(figure 2-19).
9)
Select main anode system
Number of 4-ft long rod segments needed for the
current requirement (from step 5) = 19.
Number of
anode strings utilized (from step 7) = 10. Using two
rod segments per string will provide twenty anodes,
which is sufficient for the current requirement.
However, for rod type anode designs, the main anode
rods should extend from a distance of 4 ft above the
tank bottom to within 4 ft of the HWL. Due to the
curvature of the tank bottom, the total water depth at
the location of the main anodes is approximately 30
ft. Therefore, the minimum rod length should be 22 ft
(30 ft - 4 ft - 4 ft = 22 ft). Since these rods come
in 4 ft lengths, we will use six segments per anode
with a total length of 24 ft.
10) Calculate the resistance of the main anodes to water
(RN) using equation 1-13:
88
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