Unformatted text preview: = 3.2 × 10 m
(i.e., a radius of about 1000 m)
But what the ground lacks in ρ , it makes up for in A!
25 ! Calculation of grounding resistance
! ! ! Because of its large cross sectional area the earth is
actually a pretty good conductor.
Devices are physically grounded by having a
conductor in physical contact with the ground;
having a fairly large area of contact is important.
Most of the resistance associated with establishing
an earth ground comes within a short distance of the
Typical substation grounding resistance is between
0.1 and 1 ohm; fence is also grounded, usually by
connecting it to the substation ground grid.
26 ! Calculation of grounding R, cont’d
! Example: Calculate the resistance from a grounding
rod out to a radial distance x from the rod, assuming
the rod has a...
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- Fall '13
- Orders of magnitude, Voltage source, Voltage drop, Mains electricity, ComEd