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 MIL-HDBK-419A
3.7.2 Higher Frequency Equipments.
a.
Verify that higher frequency reference points and planes are directly grounded to the chassis and the
equipment case to the extent permitted by circuit design requirements (and unless specified otherwise). If
necessary, review Section 3.2.1.2 before inspecting the higher frequency grounds in the equipment.
b.
Check to see that properly matched constant impedance cables are used for interfacing purposes.
Verify that all connectors are of a type and design that provides a low impedance path from the signal line
shield to the equipment case. Do not permit the use of pigtails for the termination of higher frequency line
shields outside the equipment case.
c.
Check connectors for tightness, cleanliness, and for proper mounting (see Sections 3.2.1.2.2 and 3.3).
Measure the resistance between the connector shell or body and its mounting surface with a double balanced dc
bridge as illustrated in Figure 3-35 (see Section 2.2.2.3.1 for the measurement procedure). The resistance
should not exceed one milliohm. If the resistance exceeds one milliohm, the mounting surfaces should be
recleaned to remove all paint, nonconductive coatings, or dirt and all screws or fasteners should be retightened
to achieve a close mechanical fit.
d.
Measure the point-to-point resistance between selected points on the case or cabinet with the
double balanced bridge. The maximum resistance between any two points on the case or cabinet should be one
milliohm or as specified. If the resistance is greater than one milliohm, check to see that all bonding surfaces
are properly cleaned and that all connections are securely fastened. (Larger sized grounding cables may have to
be added to reduce the resistance to one milliohm or less.)
e.
Record the results of the inspection under Part I of the Inspection Form.
3.7.3 Hybrid Equipments. Before inspecting equipments utilizing both lower and higher frequency interfacing
signals, review Section 3.2.1.3. If the lower and higher frequency signal networks are separate, inspect each in
accordance with the preceding respective instructions. If the networks involve both lower and higher frequency
signals, inspect for conformance with the higher frequency requirements. Record the results of the inspection
under Part I of the Inspection Form.
3.7.4 Installed Equipments. Check to see that installed equipments, in addition, have their cases or cabinets
grounded to the facility ground system of the facility with a cable providing at least 2000 cmil per running foot
(or as specified) as described in Section 3.2.3. Also obtain and record the other information requested in Part II
of the form.
3.7.5 Fault Protection Subsystem. Verify that all exposed metal parts of the equipment are properly grounded
with the green safety wire as prescribed by MIL-STD-138-124A. The size of this wire must conform to Table
l-28 or Table 250-95 of the NEC. Convenience outlets should be grounded in the manner described in Section
3.2.2. Record all information obtained under Part III of the form.
3-47
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