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ETL 1110-9-10(FR)
5 Jan 91
Where:
RA =
Backfill column-to-earth resistance
(ohms), calculated in step 5 above
RW
=
Header cable/wire resistance (ohms)
RC
=
Structure-to-earth resistance (ohms).
a)
Backfill column-to-earth resistance (RA)
from step
5:
RA = 0.47 ohm
b)
Wire resistance
A deep anode groundbed is defined as one where the
top of the backfill column is at least 50 ft below
the surface of the earth. Actual depth will vary,
depending on subsurface geology and the distance
over which the current is expected to spread. In
this example, 65 ft was selected as the depth to
the top of the coke breeze column. The anodes can
be supplied through a single or dual feed. Dual
feed is preferred to reduce both the resistance of
the circuit and the chance of a failure due to a
cable break.
No. 4 AWG cable has been chosen.
Cable lengths
have been calculated based on the following
distances,
illustrated in the deep groundbed
example shown in figure 2-7.
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