NOCTI Welding Practice Test 2026 - Free Welding Certification Practice Questions and Study Guide

When working with Gas Tungsten Arc Welding (GTAW) for welding copper, the generally accepted practice is to use direct current with a negative polarity (DC-). This is because using DC- allows for better control of heat input and creates a stable arc. The negative polarity means that the electrode is connected to the negative terminal of the power source, which results in the bulk of the heat being transferred to the workpiece rather than the electrode. This is especially useful when welding copper, as it facilitates better penetration and fusion of the metal, leading to a stronger joint.

Moreover, copper has high thermal conductivity, which means it can easily dissipate heat. Using DC- helps to focus the heat more effectively on the copper material, allowing for better weld formation. While alternating current (AC) can also be used for certain applications, it is not typically favored for welding copper due to its less effective heat management.

In summary, direct current with a negative polarity is the preferred choice for welding copper with GTAW because it provides better heat control, penetration, and ultimately results in stronger welds.