Section 7.4 of UL 2556 specifies the shrinkback test to measure longitudinal shrinkage of insulation or jacket material. The specimen is immersed in water at 90°C for 24 hours and the shrinkage of the covering relative to the conductor is measured.
Excessive shrinkback can expose conductors at termination points and compromise the insulation system. This test verifies dimensional stability of the extruded covering under thermal stress.