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 MIL-HDBK-419A
where
duration of the transient, in seconds,
temperature rise,
soil resistivity, ohm-cm, and
transient current density.
Letting
=
60C, one has
The current density, i, at the surface of a short ground rod is approximately constant over the length of the rod
and is given by
where
=
d
rod diameter (cm),
=
rod length (cm), and
=
I
input current (amperes),
For a 10-foot by 1-inch rod (3.05 m x 2.54 cm), the peak transient current which can be handled without causing
greater than
temperature rise is:
(2-71)
2-58
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