CABLE COLD BEND TESTING
The Cold Bend Test is conducted according to IEC 60811-504 and is designed to assess the performance of electrical cables at low temperatures. The test must be carried out on samples of insulation and sheathing material no more than 16 hours after the extrusion or cross-linking process has been carried out.
The test methodology requires a low temperature chamber capable of maintaining the specified test temperature and bending apparatus as described in IEC 60811-504. The sample should be of sufficient length to achieve the specified number of rotations around a mandrel that has a nominal diameter of between 4 and 5 times that of the test sample. As such, the cables themselves will generally have an external diameter of no more than 12.5mm. Cables with a larger diameter will be subject to a Cold Elongation Test as described in IEC 60811-505 instead.
The sample is clamped at the top to the mandrel before being wrapped once around it. The sample must then be conditioned inside the test chamber at the appropriate temperature for the particular polymer for a minimum of 16 hours. The conditioning duration can be reduced when specific pre-cooling criteria have been applied.
Once conditioning has been completed, the test sample is wound around the mandrel, following the number of turns as specified in Table 1 IEC 60811-504 (below) whilst the chamber maintains the same test temperature.
Table 1 IEC 60811-504 – Rotations of mandrel
Overall Diameter of test piece (mm) Number of Turns
< D ≤ 2.5 10
2.5 < D ≤ 4.5 6
4.5 < D ≤ 6.5 4
6.5 < D ≤ 8.5 3
8.5 < D 2
Once wound, the chamber door can be opened and the sample removed without disturbance so that it can condition on the mandrel at room temperature for a further 60 minutes.
To be compliant with the Cold Bend Test the cable insulation or sheathing must not show any cracks, flaws or damage when visually inspected after unwinding.