Abstract: Welding apparatus (10; 30) having a safety feature comprising: two electrodes (11, 12; 21, 22), whereof at least one of said two electrodes is movably arranged in relation to the other electrode. The electrodes are in non-contact with each other and define a gap (13) in which an object (14) provided with an electrically non-conductive surface to be sealed may be inserted. The welding apparatus comprises an actuator (15; 25) configured to move at least one electrode when activated to squeeze the object, a detector (16; 26) configured to determine a clamping force when the inserted object (14) is squeezed between the electrodes, a distance sensor (17; 23) configured to measure the distance between the electrodes. There is also a conductance sensor (24) configured to measure the conductivity of an object located between the electrodes (11, 12; 21,22) when the object (14) is squeezed, and optionally a position sensor (19b) configured to detect the position of the object (14) inserted between the electrodes.