and fire hazard. Since the process is often performed at great heights, the work and equipment must be properly secured, and the operator should wear a safety harness to prevent injury in the event of a fall. Equipment EGW uses a constant voltage, direct current welding power supply, and the electrode has positive polarity. The welding current can range from 100 to 800 A, and the voltage can range between 30 and 50 V. A wire feeder is used to supply the electrode, which is selected based on the material being welded. The electrode can be flux-cored to provide the weld with protection from atmospheric contamination, or a shielding gas—generally carbon dioxide—can be used with a solid wire electrode. The welding head is attached to an apparatus that elevates during the welding process. Also attached to the apparatus are backing shoes which restrain the weld to the width of the workpieces. To prevent them from melting, they are made of copper and are water-cooled. They must be fit tightly against the joint to prevent leaks. References Cary, Howard B. and Scott C. Helzer (2005). Modern Welding Technology. Upper Saddle River, New Jersey: Pearson Education. . Pages 153-56. Arc welding