5 Jan 91
Calculate the length of wire in ft (LB) needed for the
current required from a modification of equation 1-2:
25 amp (Current requirement from
adequate cathodic protection from
item 11 of paragraph 2-6a)
Allowable amp per ft of anode wire
(varies depending on desired anode
life and diameter), found in table
Select 0.0625-in. diameter copper cored anode
wire based on the current requirement of 25 amp,
81 ft of anode wire will be required to provide
an anode life of 15 years.
Length of Anode Ring
For 0.0625 in. LB =
25 ft 9 in.
Calculate the desired diameter of the anode wire ring
(DB). Experience shows that the diameter of the anode
wire ring should be between 40 and 70 percent of the
bowl diameter. For this example, use a hoop diameter
equal to 40 percent of the tank bowl diameter:
DR = 51.5 ft x 40% = 20.5 ft
Select anode wire:
Prior to calculating the circuit resistance of the
anode wire ring, it must first be checked to determine
if the length is adequate for the desired anode life.
For an anode ring diameter of 20.5 ft, the
circumference is 20.5 x B = 64.4 ft. This length is
inadequate for the 0.0625-in. wire (which requires a
minimum of 81 ft to meet the desired anode life).
Therefore, we will increase the hoop diameter by 10
percent to 50 percent of the tank diameter:
DR = 51.5 x 50% = 25.75 ft