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ETL 1110-9-10(FR)
5 Jan 91
0.0052 p 1n [D/(2 AR x DE)]
RN '
LB
Where:
p =
4000 ohm-cm (Water resistivity from
item 3 of paragraph 2-7a)
D
=
56 ft (Tank diameter from item 2 of
paragraph 2-7a)
AR =
22 ft (Radius of main anode circle
from step 7 of paragraph 2-7b)
DE =
0.275 (Equivalent
diameter
factor
from figure 2-17)
LB =
24 ft (Length of each anode from
step 9 of paragraph 2-7b)
RN =
0.0052 x 4000 x ln(56/(44 x 0.275))
24
RN =
1.33 ohms.
If the anode rod length-to-diameter ratio (L/d) is
less than 100, the anode-to-water resistance needs to
be adjusted by the fringe factor. (See step 12 for a
discussion of fringe factor.)
In this case, L = 24 ft and d = 0.0115 ft. L/d,
therefore, is (24/0.0115) = 2086. No fringe factor
correction is required.
11) Calculate the stub anode requirement (NS):
a)
The main anode radius has been calculated to be
22 ft.
The main anodes are spaced to provide
approximately the same distance from the sides
and the bottom of the tank. The main anode will
protect a length inward along the tank bottom
equal to approximately the same spacing that the
anode is spaced away from the tank wall.
b)
The anode suspension arrangement for the tank
being considered is shown in figure 2-20. It can
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