MIL-HDBK-1004/10

b) Paralleling of Anodes. Common practice to reduce anode bed

resistance is to connect several anodes in parallel in a group. The

resistance of a group of anodes is less than the resistance for a single anode

but is greater than that calculated from the usual parallel resistance formula

due to interactions between the fields surrounding each anode. If the anodes

are arranged in a parallel row, the resistance of a group of anodes can be

approximated by the following formula:

EQUATION:

R

=

(1/n)R

+ P F/S

(12)

n

v

s

where

Rn

=

total anode-to-electrolyte resistance for a group of

vertical anodes, equally spaced and in a single row, to

remote reference (ohms)

n

=

number of anodes

R

=

electrolyte-to-anode resistance for a single vertical

v

anode to remote reference (ohms)

P

=

electrolyte resistivity (ohms-cm) with pin spacing equal

s

to S

S

=

anode spacing (feet)

F

=

paralleling factor from table below:

F

n

F

n

2

0.00261

12

0.00182

3

0.00289

14

0.00168

4

0.00283

16

0.00155

5

0.00268

18

0.00145

6

0.00252

20

0.00135

7

0.00237

22

0.00128

8

0.00224

24

0.00121

9

0.00212

26

0.00114

10

0.00201

28

0.00109

30

0.00104

If multiple rows of anodes are used where the spacing between rows is more

than 4 times the spacing between the anodes in each row, the usual parallel

resistance formula:

1/R

=

1/R

+ 1/R

+ 1/R

+ 1/R

+ ...

may be used.

1

2

3

4

c) Special Formula for Water Tanks. For water tanks where

circular arrays of anodes are commonly used and where the structure surrounds

the anodes and electrolyte, special formulae have been developed to calculate

the anode-to-electrolyte resistance. For a single cylindrical anode, the

formula developed by E. R. Shepard may be used. The formula is as follows:

56

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