Quantcast Transient Suppression for RF Coaxial Line

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MIL-HDBK-419A
1.3.3.5.28 Transient Suppression for RF Coaxial Lines. At the present time, effective transient suppressors
for connection from line-to-ground at building penetration for externally exposed rf coaxial lines carrying
signals above the 3 MHz range are still in the development stage, primarily because of insertion losses. The
best method for protecting the lines at present is end-to-end enclosure in ferrous metal conduit, and providing
transient suppression as an integral part of using equipment.
1.3.3.5.29 Equipment-level Transient Suppression.  Equipment-level transient protection is discussed in
paragraph 1.3.3.7 of this chapter. In general, effective protection is provided by low-value resistors in series
with external line inputs, and silicon avalanche diode suppressors connected line-to-ground. Suppressors are
currently available as special order items that are suitable for connection line-to-ground on rf lines carrying
signals up to 500 MHz. The suppressors consist of a spark gap, a silicon avalanche diode suppressor in parallel
with an rf choke, or a combination ZNR and rf choke.
1.3.3.6 Lightning Generated Transient Protection Evaluation. This portion of the procedure is performed to
determine whether effective and adequate transient suppression is provided for protection against damage from
lightning-generated transients. The procedure consists of a detailed review of facility drawings and a detailed
visual inspection.
a.
Facility drawings. Review facility drawings required to determine the following. Sketch items of
interest to aid in subsequent visual examination.
(1)
Are lightning protectors installed on the primary and secondary of commercial ac service
transformer(s)?
(2)  Are buried, incoming ac power service lines enclosed in watertight, ferrous metal conduit
connected to earth ground at the service transformer and to the earth electrode subsystem at the facility end?
Is No. 2 AWG (minimum) bare, stranded copper wire used for earth ground connections?
(3)  Are overhead incoming ac power service lines protected by an overhead guard wire from the
service transformer to the facility service entrance ? Is the guard wire connected to earth ground at each end?
Does the guard wire provide a 1:1 cone of protection for the incoming service lines?
(4)  Is an ac surge arrester installed at the facility main service disconnect means (each main
disconnect if more than one)? Note manufacturer and part number on sketch.
(5)  Are the external landlines and lines which terminate at exterior equipment (including rf
coaxial lines that connect to facility equipment) enclosed in watertight, ferrous metal conduit if the cable runs
are 90 meters (300 feet) or less in length? Is the conduit connected to the applicable earth electrode subsystem
at each end?
(6)  Do buried landlines (more than 90 meters (300 feet) in length and not enclosed in ferrous
conduit) have a guard wire installed end-to-end in the cable trench ? Is the guard wire connected to the earth
electrode subsystem at each end?
(7) Are all rf coaxial cables grounded to the metal bulkhead connector plate at building
penetration?
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