This part of IEC 60793 establishes uniform requirements for measuring the macrobending loss of single-mode fibres (category B) at 1 550 nm or 1 625 nm, category A1 multimode fibres at 850 nm or 1 300 nm, and category A3 and A4 multimode fibres at 650 nm, 850 nm or 1 300 nm, thereby assisting in the inspection of fibres and cables for commercial purposes. The standard gives two methods for measuring macrobending sensitivity:
- Method A - Fibre winding, pertains to category B single-mode fibres and category A1 multimode fibres.
- Method B - Quarter circle bends, pertains to category A3 and A4 multimode fibres. For both of these methods, the optical power is measured using either the power monitoring or the cut-back technique. Methods A and B are expected to produce different results if they are applied to the same fibre. This is because the key difference between the two methods is the deployment, including the bend radius and amount of fibre that is bent. The reason for the difference is that A3 and A4 multimode fibres are expected to be deployed in short lengths with relatively fewer bends compared to single-mode and category A1 multimode fibres. In the following text, the "curvature radius" is defined as the radius of the suitable circular shaped support (e.g. mandrel or guiding groove on a flat surface) on which the fibre can be bent. In addition, informative Annex E has been added to approximate bend loss for category B single-mode fibres across a broad wavelength range at various effective bends.