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 MIL-HDBK-419A
Personnel protection in permafrost requires an even greater emphasis on the bonding of all metal objects
subject to human contact and to the power system neutral and is described in Volume I, Chapter 2. Because of
the high resistance of permafrost, stray earth currents can be expected to be minimal with consequently
reduced concern with inter-facility power frequency noise problems (see Volume I, Section 2.1.3). In the event
that earth-current related noise problems exist, the common-mode rejection techniques described in Volume I,
Section 6.4 should be applied.
Rock Formations. Are major rock formations near the surface and are they large enough to
influence the design and layout of the earth electrode subsystem? In regions of shallow bedrock, vertical
ground rods may not be usable and horizontal grids, wires, or plates must be used. Large rock outcroppings or
subsurface boulders may force the alternate routing of conductors or the placement of rods. There is no need
to incur the expense of drilling holes in rock to insert rods or lay wires because the resistivity of rock is so high
that generally the rods or wires would be ineffective.
Architectural layout. Design the earth electrode subsystem so that it will not be materially
influenced by the weather shielding effects of parapets and overhangs. Lightning down conductor placement
and routing will frequently be influenced by architectural considerations. Design the earth electrode subsystem
to accommodate such considerations by providing convenient connection points near the down conductors.
Route the interconnecting cable of the earth electrode subsystem near down conductors to avoid long
extensions between the down conductor and the effective grounding point. Configure the earth electrode
subsystem such that convenient connections are possible between the earth electrode subsystem and grounding
conductors of the power and signal ground systems inside the facility.
Landscape features. Preferably locate ground subsystem conductors under sodded areas or those
otherwise covered with vegetation. Locate conductors to take maximum advantage of the wetting effects of
runoff or drainage water from the roof, parking lots, etc. Try to avoid placing major portions of this earth
electrode subsystem under extensive paved areas such as roads and parking lots.
c.
Considering the relative advantages and disadvantages given in Table 1-1, choose a basic type of
electrode most appropriate for meeting the functional requirements of the facility at the site under
construction.
d.
Estimate the relative costs to meet the objectives with the different types of configurations.
Include the cost of materials, installation costs, and relative maintenance and upgrading costs.
1-7
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