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 MIL-HDBK-419A
1.2.4 Installation Practices.
a.
Schedule the installation of the earth electrode subsystem so that any needed excavation, such as
hole and trench digging, can be performed while other excavating, clearing, and earth moving operations
associated with construction of the facility are in progress. If the subsystem is installed prior to completion of
other earth moving operations, take the precautions necessary to assure that the components are not damaged
or broken.
b.
Take special care to ensure that all metallic lines, such as water lines, sewer lines (if metal),
armored cable, etc., are carefully bonded to the earth electrode subsystem. Bonding jumpers of 1/0 AWG, or
larger, bare copper wire are to be used for this purpose.
Before covering the earth electrode subsystem with backfill dirt or otherwise rendering it
c.
inaccessible, make visual checks of all joints and connections to check mechanical integrity, to verify the
absence of voids or other indications of poor bonding, and to see that all required interconnections are made.
d.
All bonds in concealed locations must be brazed or welded. Any bonds between dissimilar metals,
such as between a copper wire and cast iron or steel pipe, must be thoroughly sealed against moisture to
minimize corrosion. Bolted clamp connections are to be made only in manholes or in grounding wells and are to
be readily accessible for verification of integrity.
Drive rods only into undisturbed earth or into thoroughly tamped or compacted filled areas. Rods
e.
and cables should be placed in the backfill around foundations only after the soil has been compacted or has had
adequate time to settle. Do not drive or lay rods in gravel beds which have been installed for drainage purposes
unless the rods extend through such beds far enough to provide at least 1.8 to 2.4 meters (6 to 8 feet) of contact
with the undisturbed earth underneath. Do not lay horizontal cables in such beds under any circumstances.
Rods may be driven either by hand sledging, slide hammer, or with the use of power drivers. Use
f.
driving nuts to prevent damage to the driven end, particularly, if two or more sections are to be joined. Deep
driven rods or those driven into hard or rocky soil generally require the use of power drivers with special driving
collars to prevent damage to the rod.
Attach the interconnecting cable to the rods by brazing, welding, or clamping. Use bolted, clamped-
g.
type connections only if the tops of the rods are accessible through grounding wells and a periodic maintenance
program is established to verify the integrity of the connection on a regular basis.
h.
As rods are installed, make a one-time resistance check of each rod once it reaches its intended
depth. After fulfilling the requirement of paragraph 5.1.1.1.7 of MIL STD-188-124A, resistance measurements
shall be conducted on the earth electrode subsystem (as a system) at 3-month intervals for 12 months after
installation and every 21 months thereafter. Use the measurement procedure outlined in Section 2.2.2.2.1.f. In
this way a continuous check is made of the electrode design. If the measured resistance of the rods is less than
the calculated resistance, the use of fewer rods may be acceptable as long as the minimum number required for
terminating lightning down conductors is installed. On the other hand, if the measured resistance of the rods is
greater than calculated, additional rods or longer rods should be installed during the construction stage rather
than waiting until the facility is completed to add additional rods.
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