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 MIL-HDBK-419A
1.11.1.3.2 Multiple Electrode System. The resistance of a single vertically driven ground rod may also be
reduced if additional ground rods are connected in parallel with the given ground rod using a 1/0 AWG bare
copper cable to interconnect the rods. It is however important to note that total system resistance is sensitive
to electrode spacing. Electromagnetic interaction between multiple (M) ground rods that are spaced too closely
prevents the resistance of the total earth electrode subsystem connected in parallel from being l/M times the
resistance of a single rod. If the electrodes in a multiple electrode system are spaced at 1.5 to 2 times the
length of a rod, the interactive influence is minimized and total resistance of the system will approach the
ideal.
1.11.1.3.3 Earth Electrode Subsystem. The earth electrode subsystem should, soil and tactical conditions
permitting, consist of properly spaced ground rods interconnected in parallel by a bare 1/0 AWG copper cable.
The interconnecting cable for tactical situations should be clamped to the ground rods to facilitate installation
and transportability. Earth electrode subsystems shown in Figures l-9 and l-100 may be installed around the
perimeter of temporary enclosures housing several stand-alone equipments such as portable single subscriber
terminals, telephones, or small switchboards. These earth electrode subsystems should extend 0.6 to 1.8 meters
(2 to 6 feet) beyond the dripline of the enclosure to ensure that any form of precipitation wets the soil around
the system. Earth electrode subsystems in radial or star configurations may be employed but are less suitable
for (a) grounding equipments operating at rf such as radar or microwave systems, or (b) providing low impedance
grounds between interfacing shelters required to lessen interference or voltage surges caused by lightning
discharges. Means of calculating ground resistance of the entire earth electrode subsystem are described in
Section 2.6 of Volume I while measurements of these systems are described in Section 2.7.
1.11.1.3.4 Chemical Treatment. The resistance of driven ground rods may be reduced by chemically treating
the soil around the rod and the interconnecting cable/wire. Addition of ion-producing chemicals such as
magnesium sulphate (epsom salts), sodium chloride (table salt), and potassium nitrate (saltpeter) as well as
bentonite to the soil adjacent to an electrode has the net effect of increasing the apparent cross-sectional area
of the electrode and minimizing the current density of the soil. Use of magnesium sulphate or bentonite is
recommended because of their low corrosive effect on metal and high electrical conductivity. A circular
trench approximately 0.3 meters (1 foot) deep and 0.9 meters (3 feet) in diameter should be dug around the
electrode at a radius of 0.45 meters (1.5 feet) from the center of the electrode. The trench is filled with the
saline solution and covered with earth. In order to provide the best distribution of the treating material with
the least corrosive effect the solution should not actually touch the electrode. Additional information is
provided in Section 2.9 of Volume I.
1.11.2
Detailed Tactical Grounding Requirements.
1.11.2.1 Introduction. It is important that serious consideration be given to grounding implementation. Proper
grounding can have a significant impact on the ability to maintain communications under adverse conditions.
This section contains grounding requirements for tactical deployments of mobile equipment. Grounding
methods set forth are based not only on implementation considerations but also on complying with specific
measured resistance requirements. The tactical deployments of mobile equipments are considered to be of four
types; i.e., stand-alone equipment, stand-alone shelter, collocated equipments and collocated shelters.
1-185
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