Quantcast  Coaxial Cable Shield Connection Through an Entrance Plate

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MIL-HDBK-419A
(5)  Surge current dissipation: Peak pulse current ratings from 139 amperes for 6.8 V dc suppressor
to 5.5 amperes for 200 V suppressor for 10-by-1000 microsecond waveforms.
(6) Lifetime: Not presently defined. Requires current-limiting resistor in series with protected
line to provide required surge current dissipation at facility level.
Characteristics of gas-filled spark gap suppressors.
c.
Response time: 3 to 5 microseconds for 10-by-1000 microsecond waveforms.
(1)
Clamping voltage: Arc voltage is 20 volts typical.
(2)
Breakdown voltage: 300 to 500 volts typical.
(3)
Standoff voltage: 75 V dc to 1000 V dc.
(4)
(5)
Surge current dissipation: 5,000 amperes for 10-by-50 microsecond waveform.
(6)  Lifetime: Varies depending on surge current amplitude, 50 surges of 500 amperes peak current
with 10-by-1000 microsecond waveform typical.
1.3.3.5.25  Transient Suppressor Packaging Design. Packaging of transient suppressors for standard wires and
twisted shielded pairs is not critical. Leads should be as short as feasible to enable short, direct connections
without bends. Transient suppressors for coaxial and twinaxial lines should be contained in a metal and epoxy
package with appropriate connectors on each end, one male, and one female, to permit inline installation at the
connector panel in the demarcation junction box. Two suppressors must be included in all twinaxial protector
packages.
1.3.3.5.26  Coaxial Cable Shield Connection Through an Entrance Plate. Effective transient protection can be
provided by peripherally bonding each rf coaxial cable to a metal bulkhead connector which in turn is
peripherally bonded to the building entry plate and grounded to the earth electrode subsystem. This scheme will
route transient currents from cable shields to earth ground instead of through terminating equipment to ground.
Also, transient surge currents will be shunted to ground before transient energy is cross-coupled to other
equipment lines in the facility.  The entry plate should be a minimum of 0.64 cm (1/4-inch) thick, and
constructed of steel. The entry plate must contain the required number of appropriate coaxial feedthrough
connectors to terminate all applicable incoming lines. The connectors must also provide a path to ground for
connected cable shields. If external and internal coaxial cables are of a different physical size, the changeover
in connector size should be accomplished by the feedthrough connectors of the entry plate. The entry plate
should be connected to the earth electrode subsystem with a 1/0 AWG (minimum) insulated copper cable. The
cable should be bonded to the entry plate and the earth electrode subsystem with exothermic welds.
1.3.3.5.27 Grounding of Unused Wires.  All unused wires/pairs of communication cable runs should be
connected to ground at each end. This action will reduce transients on the unused lines which otherwise could be
coupled to in-service lines of the cable.
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