MIL-HDBK-1004/10
Rearranging the equation for n:
n = R /[R - (P p)/S]
v
n
s
n = 4.77/[2-(2,000p)/20]
n = 4.77/(2-100p)
Try n = 4 anodes,
p
=
0.00283 (refer to para. 6.2.1.4b)
4
=
4.77/(2-0283)
4
=
4.77/1.717
4
=
2.78 (not very close)
Try n = 3 anodes,
p
=
0.00289 (refer to para. 6.2.1.4b)
3
=
4.77/(2-0.289)
3
=
4.77/1.711
3
=
2.79
This is the closest possible.
In order to keep total resistance
below 2.0 ohms, use 3 anodes.
(4)
Actual resistance:
R
= (1/n)R
= P p/S
n
v
s
R
= (1/3)4.77 + 2,000 (0.00289)/20
3
R
= 1.59 + 0.29
3
R
= 1.87 ohms which is below 2.0
3
e)
Total weight of anodes for ground bed:
(1)
Weight of anode unit, 60 pounds (size 2 inches x 60
inches)
(2)
Total weight = 3 x 60 = 180 pounds
f)
Theoretical life of anode bed:
W = YSI/E
Rearranging gives
Y = WE/SI
182
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