MIL-DTL-24640C
a. Conductor to ground (cable, one conductor, unshielded, jacketed). Specimens incorporating a single
insulated, jacketed conductor without shield or armor shall be tested to water. The specimen shall be submerged,
except for its extreme ends (which shall remain exposed to the air), in the water tank for a period of not less than 1
hour. Following this, and while the specimen is still submerged, the specimen shall be tested as follows. The single
conductor shall be electrically connected to one terminal of the megohmmeter. The other megohmmeter terminal
shall be electrically connected to the water surrounding the specimen (as by means of a bare metal wire which is
both connected to the megohmmeter terminal and suspended within the water surrounding the specimen). The
insulation resistance test shall then be performed as specified.
b. Conductor to conductor (cable, unshielded, jacketed). Use for cable types incorporating two or more
insulated conductors (such as, singles, pairs, or triples) with no individual or overall shield: one insulated conductor
shall be selected and electrically connected to one terminal of the megohmmeter. All other conductors within that
transmission line shall be electrically connected to the other megohmmeter terminal. The insulation resistance test
shall then be performed as specified. In a similar manner, the insulation resistance test shall be performed between
each remaining conductor within the selected transmission line and the short circuited combination of all other
conductors within that transmission line. Following this, and in an identical manner, the insulation resistance test
shall be performed on all remaining transmission lines within the specimen.
c. Conductor to conductor with overall shield (cable, overall shielded, and jacketed). Used for cable types
incorporating two or more insulated conductors (such as singles, pairs, or triples) with no individual shields and with
an overall shield: one insulated conductor shall be selected and electrically connected to one terminal of the
megohmmeter. All other unshielded insulated conductors and the overall shield, shall be electrically connected to
the other megohmmeter terminal. The insulation resistance test shall then be performed as specified. In a similar
manner, the insulation resistance test shall be performed between each remaining insulated conductor within the
specimen and the short circuited combination of all other insulated conductors and overall shield.
d. Conductor to conductor with component shield (cable, shielded components, overall unshielded, jacketed).
Used for cable types incorporating one or more individually shielded, insulated conductors: one insulated conductor
shall be selected for measurement, and shall be electrically connected to one terminal of the megohmmeter. All
other insulated conductors within the component and the shield shall be electrically connected to the other
megohmmeter terminal. The insulation resistance test shall then be performed as specified. Following this, and in
an identical manner, the insulation resistance test shall be performed on all remaining insulated conductors within
the component. After the completion of this component, this procedure shall be repeated for all other shielded
components within the specimen. The cable shall then be tested for component shield insulation resistance [see (g)].
e. Conductor to conductor with component shield and one overall shield (or two or more overall shields not
electrically isolated from each other)(cable, shielded components, overall shielded, jacketed). Used for cable types
incorporating one or more individually shielded, insulated conductors. One insulated conductor shall be selected for
measurement, and shall be electrically connected to one terminal of the megohmmeter. All other insulated
conductors within the component and the shield shall be electrically connected to the other megohmmeter terminal.
The insulation resistance test shall then be performed as specified. Following this, and in an identical manner, the
insulation resistance test shall be performed on all remaining insulated conductors within the component. After the
completion of this component, this procedure shall be repeated for all other shielded components within the
specimen. The cable shall then be tested for component shield insulation resistance [see (h)].
f. Conductor to conductor with component shield and two electrically isolated overall shields (cable, shielded
components, overall dual shielded, jacketed). Used for cable types incorporating one or more individually shielded,
insulated conductors. One insulated conductor shall be selected for measurement, and shall be electrically
connected to one terminal of the megohmmeter. All other insulated conductors within the component and the shield
shall be electrically connected to the other megohmmeter terminal. The insulation resistance test shall then be
performed as specified. Following this, and in an identical manner, the insulation resistance test shall be performed
on all remaining insulated conductors within the component. After the completion of this component, this procedure
shall be repeated for all other shielded components within the specimen. The cable shall then be tested for
component shield insulation resistance, see h and overall shield insulation resistance [see (i)].
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