so wide that it can touch two adjacent switching contacts 31 to 35 at the same time by way of example the end can be configured in the manner of a mushroom or as a wide sliding contact in order to switch over the tap changer 26 from a first of the switching contacts 31 to 35 to a second of the switching contacts 31 to 35 the contact element 28 is pivoted from the first switching contact to the second switching contact in this case the end of the contact element 28 touches the second switching contact during the switchover process here on account of its width before the end disengages from the first switching contact in this way an electrical connection is first established between the contact element 28 and the second switching element during the switchover operation before the electrical connection between the contact element 28 and the first switching contact is interrupted the switching contact 31 is connected to the sensor 16 by a potentiometer p 1 a series resistance which acts in the sensor line can be set by the potentiometer p 1 in order to simulate corrosion in this case a level of the manipulated line can be detected by ascertaining a current intensity of a current i 1 a connecting line 36.