The wrap back examines a wire/cable’s insulation susceptibility to breach when tightly wrapped around itself and exposed to elevated temperatures. This test is usually required in the individual wire specifications as part of the insulation integrity assessment.
After the elevated temperature exposure, the specimen is visually examined for any insulation cracks (or delamination in the case of tape wrapped insulations). The insulation integrity is then examined with a wet dielectric test.
A pass for the wrap back test means that no wire/cable insulation degradation has been detected. Any visible or electrical degradation of the insulation is considered a failure.
In addition to being used as part of the component certification, this test has often been used as a field assessment of wire/cable insulation quality. If insulation cracks are formed when the wire/cable is placed under mechanical stress at ambient temperatures, then the likelihood of insulation failure in operational conditions if high.
Parameters that can be changed for this test include, but are not limited to:
- Temperature of elevated temperature exposure
- Duration of elevated temperature exposure
- Post-test dielectric voltage