The contact wire wear measurement is performed with non-contact optical systems, adopting two methods:

• Direct method, by profile measurement using a laser triangulation system.
• Indirect method, by measuring the flat width of the bottom face of the wire, by means of linear cameras.

The direct method is used when the contact wire position is relatively stable with minor vertical and horizontal displacements: it occurs typically in a rigid catenary. The laser-camera triangulation technology adopted is pointed vertically to the wire.

The indirect method is widely used for standard catenary with suspended wire, where the wire position can vary widely in height and stagger. The technology adopts linear cameras that create the image of the wire flat bottom face illuminated by highly intense, narrow LEDs, to allow very short exposure time and a high sampling rate. The overhead wire wear defect is detected via image analysis scanning the bottom face wire width.