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ETL 1110-9-10(FR)
5 Jan 91
Where:
I =
8.2 amp (Current requirement from item
10 of paragraph 2-3a)
IA =
1.0 amps/anode (Current
rating
per
anode from table 3-3)
N
=
8.2
=
8.2 anodes; use nine, 2-in.
1.0
by 60-in. packaged rod
anodes
4)
Calculate the resistance of a single anode-to-earth
(RA) from equation 1-6:
RA =
p K
L
Where:
P =
4500 ohm-cm (Soil resistivity
from
item 1 of paragraph 2-3a)
K
=
0.0234 (Shape function from table A-4
[where: L/d = 60 in./2 in. = 30])
L
=
5
ft (60
in.)
(Effective
anode
length).
d
=
2 in. (Anode/backfill diameter)
RA =
4500 x 0.0234
5
RA
=
21.06 ohms
5)
Calculate the number of anodes required to meet
maximum anode groundbed resistance requirement.
A
distributed anode array does not lend itself to an
exact calculation of equation 1-11 because the anodes
are positioned at various locations and are not
located in a straight line. Equation 1-11 assumes a
straight line configuration. However, to approximate
the total anode-to-earth resistance, equation 1-li may
be used.
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