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ETL 1110-9-10(FR)
5 Jan 91
to be protected to assure uniform distribution of the
protective current to all structure components. The
higher the soil or water resistivity, the further away
the ground must be located. For this example, previous
experience has shown that the nearest anode should be
located a minimum of 100 ft from the structure to
assure good current distribution. Since there are no
other underground utilities in the area, the groundbed
may be installed either perpendicular or parallel to
the pipe (figures 2-IA and 2-lB).
8)
Determine the
total
circuit
resistance
(RT)
from
equation 1-3:
RT = RN + RW + RC
Where:
RN =
Groundbed resistance-to-earth (ohms)
RW =
Header cable and resistance (ohms)
RC =
Pipe-to-earth resistance (ohms)
a)
RN
=
1.67 ohms
Specify anodes with individual lead wires of
sufficient length so that each anode wire can be
run directly to the rectifier without splices.
(This is virtually always true for anode bed
designs where the individual lead wire lengths
required do not exceed an average of 400 ft.)
b)
Anode lead wire resistance from equation 1-15:
c
LW RMFT
RW '
1000 ft
Where:
LAVG =
Total of each actual lead wire
lengths/number of anodes
=
(140 ft + 120 ft + 100 ft + 80
ft + 60 ft + 40 ft)/6 anodes
=
90 ft per anode
LW
=
LAVG/N
=
90/6
=
15 ft
28
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