MIL-PRF-29C
3.4.2 Resistance elements.
3.4.2.1 Wirewound. Each resistance element shall be wound on a suitable form with resistance wire. The design
of the winding shall be such as to preclude shorting of turns or arcing between turns under the potential imposed
between any adjacent turns.
3.4.2.1.1 Resistance wire. The resistance wire shall posses a substantially uniform cross section of conductor and
insulation. The wire shall be as free as practicable from particles of impurity and grain growth or other factors
contributing to spot weakness.
3.4.2.2 Film. Films shall be uniformly deposited. The film shall be free of blister, thin spots, areas inadequately
bonded to core, discolored spots, or other blemishes likely to cause flaking or a non-uniform ribbon when spiraled
(helixed). Where used, spiraling shall occupy no less than 70 percent of resistor element actual length. The resistor
element actual length shall be defined as the nominal distance between terminal bands less three sixty-fourths of an
inch. Designers are CAUTIONED on using these resistors in pulse applications (see 6.5)
3.4.3 Engagement of threaded parts. When threaded parts are used, they shall engage by at least four full
threads.
3.4.3.1 Locking of screw-thread assemblies. Screw-thread assemblies shall not loosen as a result of tests
specified herein.
3.5 Terminals. The ends of the resistance element shall be connected to ferrule type terminals, which shall serve
for mechanical mounting and electrical connection. The lead wires from the active resistance element to the ferrules
shall be so arranged and connected that they will be protected from being cut by or placed in contact with the
mounting clips at any angle of rotation of the unit.
3.6 Concentricity and parallelism of ferrules. The ferrules shall be so aligned with respect to each other and the
resistor body that the maximum permissible departure from concentricity shall be as shown on figure 2.
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FIGURE 2. Maximum permissible departure from concentricity.
3.7 Ferrules. Ferrules shall be of one piece construction and of a corrosion resistant nonferrous material or shall
be protected against corrosion by a coating.
3.8 Resistor units. When a resistor unit is constructed by joining a number of individual resistance elements
together, a means shall be provided for locking the segments securely together to prelude separation or disassembly
in the field. There shall be no relative movement among the resistance elements within the housing of the completed
resistor.
3.9 Dielectric withstanding voltage. When resistors are tested as specified in 4.7.2, there shall be no flashover or
evidence of insulation breakdown.
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