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 MIL-HDBR-419A
(8) Are transient suppressors or transient suppression circuits installed line-to-ground on each end
of all exterior lines not enclosed in ferrous metal conduit (except rf lines carrying signals above 3 MHz) at first
termination after building penetration?
Inspection. A survey form in Section 2.2.2.4, Part II, is provided for guidance in accomplishing a
b.
thorough visual inspection. Detailed written notes fully describing all noted deficiencies should be made.
c.
Corrective action. Specific corrective action to accomplish in response to each noted deficiency is
difficult to detail. For instance, cable runs less than 90 meters (300 feet) in length are not normally enclosed
end-to-end in electrically continuous, watertight, ferrous metal conduit. Intensity and incidence of lightning in
the immediate area, together with economic feasibility and operational requirements, are normally the
overriding factors in determining whether the installation of metal conduit is justified and feasible. In most
cases, for the example cited, installation of transient suppression circuits on each end of externally exposed
equipment lines is the most feasible solution. However, installation of transient suppression directly at the
line-equipment interface may also be warranted, depending on equipment susceptibility and lightning incidence.
Consider each deficiency individually. Refer to Sections 1.3.3.5 and 1.3.3.7 as required, and correct
deficiencies in the most feasible manner. Some typical and required corrective actions are listed below:
(1) If a secondary ac surge arrester is not installed at the facility, and there is any history of
lightning incidence in the area, install a surge arrester on the line or load side of the main service disconnect
means. Refer to Section 1.3.3.5 to determine that the surge arrester selected will be adequate and effective.
(2) If the surge arrester and transient suppressor does not have a low-impedance, effective path to
earth ground, take whatever action is necessary to provide effective grounding. Neither the arrester nor
suppressor will provide effective transient protection if an effective ground is not available.
(3) If no transient suppressors are installed on externally exposed equipment lines not enclosed
end-to-end in metal conduit, and the lines interface susceptible equipment, as a minimum install transient
suppressors on each end of each line that interfaces susceptible equipment. Refer to Sections 1.3.3.5 and
1.3.3.7 as required.
1.3.3.7 Transient Protection.
1.3.3.7.1 Protection Requirement. Individual items of electrical and electronic equipment that directly
interface any externally exposed equipment lines, including commercial ac, may require transient protection
that is designed as an integral part of the equipment. Whether or not protection is required is dependent on the
damage susceptibility of the equipment of interest, the level of transient suppression provided on externally
exposed lines at building penetration or external equipment termination and the level of transient energy that is
projected to be conducted to the equipment. For use herein, externally exposed lines are defined as lines
exposed to outside weather elements and environmental conditions. The lines may run overhead, run along
grade surface, or be buried in earth. Included are ac power input lines and signal, control, status, and
intrafacility powerlines. The lines are commonly referred to as landlines. Transient protection is not required
in equipment when an interfaced landline is fiber optic in lieu of a metallic line. In order to provide effective
transient protection, the damage (withstand) level for the equipment must be determined, and the amplitude
and number of transients that will be conducted to the equipment must be known. This information is provided
in this section. Three areas of equipment circuitry normally require transient protection, and are listed below:
1-80
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