MIL-HDBK-1004/10

(2)

Resistance of a single anode to earth:

P

R

=

K

v

L

where

P

= earth resistivity, ohm-cm

K

= shape function (refer to para. 6.2.1.4a)

L

= backfilled anode length

where

P

=

2,000 ohm-cm

L

=

7.0 feet

K

=

0.0167 (refer to para. 6.2.1.4a)

L/D

=

84 inches/10 inches backfill size

R

=

2,000 x 0.167/7.0 ohms

Rv

=

4.77 ohms

v

(3) Number of anodes required. It was stated in the design

data that the anode bed resistance is not to exceed 2 ohms. Anode size used

is 2-inch diameter x 60 inches long with carbonaceous backfill having overall

dimensions of 10-inch diameter x 84 inches long and spaced 20 feet apart:

R

=

(1/n)R

+

P p/S

n

v

s

where

R

=

anode bed resistance

n

n

=

number of anodes

R

=

single anode resistance

v

P

=

earth resistivity with pin spacing equal to S

s

p

=

paralleling factor (refer to para. 6.2.1.4b)

S

=

spacing between adjacent anodes

where

R

=

2 ohms

n

R

=

4.77 ohms

v

P

=

2,000 ohm-cm

s

S

=

20 feet

NOTE:

p is a function of n as referred in para. 6.2.1.4b) and n

is the number of anodes which are determined by trial and

error.

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