日本在“JISC 9311”标准中规定:交流弧焊机上必须加装自动防止触电装置。这个装置的设计指导思想是,在焊条接触工件以引燃电弧时仍用95伏,但是在电弧引燃后,电弧燃烧,电压立即自动降低到25伏以下。在这样低的电压下,即使焊工误碰焊钳或焊条,也不可能发生触电事故。该装置的原理图如下:引燃电弧时,触点 S_1接通后,触点 S_2脱开,焊钳处电压为95伏。电弧引燃后燃烧时,继电器使触点 S_1脱开,触点 S_2接通后, Japan in the “JISC 9311” standard states: AC arc welding machine must be equipped with automatic devices to prevent electric shock. The design philosophy of this device is that it still uses 95 volts when the electrode contacts the workpiece to ignite the arc, but after the arc has ignited, the arc burns and the voltage drops automatically below 25 volts. Under such a low voltage, even if the welder mistook the welding tongs or welding rods, it is impossible to cause electric shock accident. Schematic diagram of the device is as follows: When the ignition arc, contact S_1 connected, contact S_2 off, the voltage at the welding clamp is 95 volts. When the electric arc ignites and burns, the relay disengages the contact S_1. After the contact S_2 is switched on,