Abstract: An arc welding power supply of the type which employs a saturable reactor circuit to control the supply power from an alternating current source to the welding electrode. A control circuit varies the current through the control winding of the saturable reactor to provide the desired welding current. An additional circuit monitors the welding current and disables the saturable reactor control circuit when the welding current drops below a low threshold value, thus reducing the open circuit voltage between the welding electrode and workpiece and minimizing the danger of electric shock to the welder while changing electrodes. The saturable reactor is connected in series with the primary winding of a transformer which also serves as the output winding of the saturable reactor.