MIL-HDBK-1004/2A
are often used for protection of transmission lines. In areas where annual
lightning storms are few, no protection for lightning-induced surges may be
necessary. Local naval facility or utility company practice should generally
be followed (refer to MIL-HDBK-1004/6, Lightning Protection) for equipment
protection, aerial-to-underground transition points, and other appropriate
locations.
2.6.2
Application. Select the proper arrester in accordance with the
Basic Impulse Insulation Level (BIL) that applies to the voltage level of the
circuit. Follow the criteria in ANSI C62.1, Surge Arrestors for AC Power
Circuits; ANSI C62.2, Guide for Application of Valve-Type Surge Arresters for
Alternating Current Systems and ANSI C62.33, Varistor Surge-Protective
Devices.
Clearances. Provide the necessary horizontal and vertical
2.7
clearances from adjacent physical objects, such as buildings, structures, or
other electric lines, as required by ANSI C2.
2.7.1
Contingency Interferences. Make provision to protect against
contingency interferences, such as broken poles, broken crossarms, or broken
circuit conductors.
2.7.2
Multipurpose Conditions. Provide for clearance conditions arising
from multipurpose joint use of poles.
2.8
Grounding. For information on grounding of overhead distribution
systems, refer to ANSI C2.
2.8.1
Safety. Provide grounding for all equipment and structures
associated with electrical systems to prevent shock from static or dynamic
voltages.
2.8.2
Ground Resistance Path. Provide a low impedance path at the source
of fault currents, if a circuit contains a deliberate ground connection.
2.8.3
Maximum Ground Resistance. Do not exceed maximum ground resistance
values specified in NFGS-16301, Underground Electrical Work and NFGS-16302,
and ANSI C2. Consider the source of electric power, capacity, magnitude of
fault current, and method of system grounding, as they affect this resistance.
2.8.4
Grounding Methods. Grounding provisions shall conform to NFPA 70.
Grounding methods for transformers mounted at grade are covered in Section 5.
2.8.4.1 Ground Rods. Ground rods may be used either singly or in clusters.
Drive the ground rods to ground water level for an effective and permanent
installation. Provide for corrosion prevention by a proper choice of metals
or by cathodic protection. Where ground water cannot be reached, chemicals
such as magnesium sulphate (MgSO4) or copper sulphate (CuSO4) may be used to
improve soil conductivity where necessary. Manufacturers of ground rods can
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