ETL 1110-9-10(FR)

5 Jan 91

1)

Calculate the length of wire in ft (LB) needed for the

current required from a modification of equation 1-2:

LB =

I

IA

where:

I=

25 amp (Current requirement from

adequate cathodic protection from

item 11 of paragraph 2-6a)

IA =

Allowable amp per ft of anode wire

(varies depending on desired anode

life and diameter), found in table

A-3.

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

Wire

Diameter (DR)

For 0.0625 in. LB =

25

=

81 ft

25 ft 9 in.

0.31

2)

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

3)

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

71

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