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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