Final answer:
Double-arcing is when an electric arc forms between the electrode and nozzle and also between the nozzle and the workpiece in welding, an undesirable situation that can damage equipment and the quality of the weld.
Step-by-step explanation:
The concept of double-arcing best describes an electric arc that simultaneously forms between the electrode and the nozzle as well as the nozzle and the workpiece. This phenomenon is typically an undesired occurrence in welding because it can damage the welding equipment and affect the quality of the weld. Double-arcing can occur due to several factors such as incorrect setup, a damaged nozzle, or improper distance between the workpiece and the welding tool.
It's important to understand that double-arcing is different from using different types of currents, such as alternating current (AC) or direct current (DC) and is quite unrelated to the pinch effect, which refers to the magnetic attraction between moving parallel electric currents causing a concentration of the arc. This pinch effect can be observed in large electrical systems and is distinct from the more specific incident of double-arcing in welding.