Abstract: A pneumatic jack for electric welding comprises a cylinder which houses a piston the connecting rod of which is connectable with an electrode. The piston rod is movable between a retracted and an extended position and at the closed end of the cylinder an electric switch is located in a recess and is embedded in electrically insulating material. The switch is provided with an operating rod which extends into a passage effecting communication between the bottom of the recess and the interior of the cylinder and which operates the switch when the piston in the cylinder is in the retracted position thereof.