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had the most damage in the pairs, and the PVC/glass/nylon, PI, and PTFE/glass wires (codes 1,
2, and 9, respectively) always had the least damage. It should be noted, however, that the
PVC/glass/nylon and PTFE/glass were only tested in two mixed combinations each. The glass
fiber braid has an extremely high modulus and provides protection against this type of force.
The glass fiber braid even provides protection when a blade is used in the standard dynamic cutthrough
test method.
In certain pairings, the XPI, MF-PTFE, PI/PTFE, and PI/PTFE alloy wires (codes 3, 7, 10, and
11, respectively) each showed damage through the insulation, exposing the conductor, when
using the 80-pound load (see figures 50 and 51 and figures D-12 and D-13 in appendix D).
When the load was increased to 120 pounds, the XLETFE wire (code 4) also exhibited damage
through the insulation to the conductor (see figure 52). The most severe damage was seen in the
pairing of PI/PTFE alloy wire with itself (see figure 53). The alloy conductor is harder than the
annealed copper conductor, and does not deform as easily, causing an increase in damage to the
insulation.
The crush test was not performed at elevated temperature or after a heat aging test. Two
scenarios where an elevated temperature may be a problem are (1) when a substitute wire has a
lower or higher temperature rating and (2) blocking to a lower temperature-rated wire would
decrease flexibility.
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FIGURE 50. MF-PTFE WIRE
DAMAGED FROM PI WIRE IN THE
80-POUND CRUSH TEST
FIGURE 51. PI/PTFE ALLOY WIRE
DAMAGED FROM PI/PTFE WIRE IN
THE 80-POUND CRUSH TEST
FIGURE 52. XLETFE WIRE
DAMAGED BY PI WIRE IN THE
120-POUND CRUSH TEST
FIGURE 53. PI/PTFE ALLOY WIRE
DAMAGED BY SAME WIRE TYPE IN
THE 120-POUND CRUSH TEST
5.5 COMPARISON TO PREVIOUS DATA.
Whereas the NAC TR-2333 program used reduction in voltage capability as a parameter for
evaluating the wires, this program selected a DWV pass/fail threshold, so electrical testing
results could not be directly compared. This program also used visual examinations as the
primary tool for determining the severity of wear to the wires or support components.
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6. SUMMARY AND RECOMMENDATIONS.
6.1 SUMMARY.
None of the documents reviewed specifically addressed or restricted mixing of dissimilar wire
types in bundles, but regulations stipulated that the wires selected must meet the environmental,
application, interface, and design requirements. The results indicated that there is not
significantly more insulation wear in mixed wire bundles than in nonmixed wire bundles. The
results of this program did not corroborate the general finding of the Naval Avionics Center TR-
2333. Since the two test programs did evaluate different insulation types, a direct comparison
could not be made.
None of the electrical failures were attributed to the mixing of wire types in the bundles. All
failures were due to damage caused by rubbing against the plate or movement in the clamps
during vibration. The fluids and metal shavings appeared to have some impact on the wire-towire
wear. For most wire types, hydraulic fluid and particulate contamination promoted wear of
the wires. No significant difference was noted when comparing results from annealed copper
conductor and copper alloy conductor wires with the same insulation type.
Softer insulation types suffered more damage in the crush test; however, wire with harder copper
alloy conductors exhibited greater damage than wire with softer annealed copper conductor wires
of the same insulation type. Cross-linked aliphatic polyimide wire exhibited significant levels of
wire-to-wire wear in mixed and nonmixed bundles and in contaminated and uncontaminated
bundles. Polyimide and polytetrafluoroethylene glass wires exhibited significant wire-to-wire
wear in nonmixed, fluid-contaminated bundles. Polyimide wires were the only types that
exhibited some wire-to-wire damage in all uncontaminated combinations.
More damage was caused by straps than by lacing string in the contaminated bundles. There was
little damage from straps or clamps on uncontaminated bundles. No significant differences in
wire-to-wire wear or from clamp wear was noted when comparing the curved end of the bundle
to the straight end configuration. More damage to adjacent wires was caused by twisted pairs of
wires than by single-end wires.
6.2 RECOMMENDATIONS.
Special precautions need to be considered when using many wire types (XPI, soft exterior types
such as PTFE, MF-PTFE, and PI/PTFE, and glass braid covered types such as PTFE/glass) to
prevent wear from clamps or from the structure. Frequent maintenance inspection schedules
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