The arrangement includes a lighting arrangement which illuminates an over-head wire (1), and at least one photoelectric sensor (21, 22) mounted on a vehicle, underneath the over-head wire. The lighting arrangement includes a first lighting device (23, 24), arranged adjacent to the sensor, and a second lighting device (25, 26) arranged opposite the sensor. The sensor detects a light reflected by the over-head wire, and a light reflected by a slider mirror (4) of the over-head wire, so that an image of the over-head wire and the slider mirror is produced on detector elements (33) of the sensor. ADVANTAGE - Enables supervision both of dimensions and condition of over-head wire at higher speed.