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 MIL-HDBK-419A
Table 1-1
Relative Advantages and Disadvantages of the Principal Types
of Earth Electrodes
Disadvantages
Advantages
Type
Not useful where large rock
Straightforward design. Easy to install
Ring Ground
formations are near surface.
(particularly around an existing facility).
Hardware readily available. Can be
extended to reach water table.
Subject to resistance fluctuations
Can achieve low resistance where rock
Horizontal Bare
with soil drying.
formations prevent use of vertical rods.
Wires (Radials)
Low impulse impedance. Good rf
counterpoise when laid in star pattern.
Subject to resistance fluctuations
Minimum surface potential gradient.
Horizontal Grid
with soil drying if vertical rods not
Straightforward installation if done
(Bare Wire)
used.
before construction. Can achieve low
resistance contact in areas where rock
formations prevent use of vertical rods.
Can be combined with vertical rods to
stabilize resistance fluctuations.
High impulse impedance. Not useful
Straightforward design. Easiest to
Vertical Rods
where large rock formations are near
install (particularly around an existing
surface. Step voltage on earth
facility). Hardware readily available.
surface can be excessive under high
Can be extended to reach water table.
fault currents or during direct
lightning strike.
Most difficult to install.
Can achieve low resistance contact in
Plates
limited area.
Little or no control over future
Can exhibit very low resistance.
Incidental
alterations. Must be employed with
Electrodes
other made electrodes.
(Utility pipes,
building
foundations,
buried tanks)
1-8
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